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1
Stratoudakis, Yorgos. "A study of fish discarded by Scottish demersal fishing vessels." Thesis, University of Aberdeen, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.339907.
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This study focuses on fish discards generated by demersal vessels fishing in Scottish waters (North Sea and West of Scotland). The analysis is based on data collected by scientific observers onboard commercial vessels during the past two decades (1975 - 1993). Chapter 1 introduces the problem of discarding, describes its implications for fisheries and the marine environment, and gives a brief overview of the sampling scheme. Chapter 2 uses generalised additive models (GAMs) and regression trees to investigate the main reasons that lead Scottish fishers to discard commercially important species (haddock - Melanogrammus aeglefinus, whiting - Merlangius merlangus and cod - Gadus morhua). Different discarding patterns are observed in inshore and offshore areas, with vessels fishing offshore discarding larger fish, irrespective of gear type. In inshore areas, discarding decisions are mainly driven by legal landing size, whereas offshore, high grading decisions due to market pressures and, possibly, quota limitations prevail. Chapter 3 explores the performance of several estimators of total discards and their variances in a simulated population of fishing trips. The simulated population is generated from the residuals of temporal models fitted to the catch and discards observations from the trips sampled under the Scottish discards monitoring scheme. The estimator currently applied to obtain annual estimates of total discards in Scotland is shown to be biased and imprecise, whereas several other estimators perform better under limited sampling coverage. The best estimators from chapter 3 are used in chapter 4 to estimate the total discards and their variances for species that were regularly discarded by Scottish vessels in the period 1988 - 1993. Overall, it is estimated that Scottish vessels generate annually around 100,000 tonnes of demersal fish discards in the North Sea and 30,000 tonnes in the West of Scotland. This suggests that close to 40% of the total demersal catch of Scottish vessels is annually wasted through discarding.
2
Ok, Meltem. "Evaluation Of The Demersal Fish Assemblages Of The Northeastern Levant Sea." Phd thesis, METU, 2012. http://etd.lib.metu.edu.tr/upload/12615068/index.pdf.
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Ecosystem-level changes have taken place in the Mediterranean Sea over the last decades due to both anthropogenic interferences and natural perturbations. Compared to the western Mediterranean Sea, influences of these factors especially on flora and fauna characteristics are much more dramatic and intense in the eastern part, particularly in the northeastern Levant Sea where the study area is located. In this study, life history traits of some core species (both native and immigrant) occupying the continental shelf of the northeastern Levant Sea were studied in this changing ecosystem to improve limited ecological understanding of the demersal fish assemblages of the northeastern Levant Sea. For this purpose, the annual patterns in allocation and utilization of energy in demersal fish species, temporal and bathymetrical trends in fish distribution with respect to biological requirements of the species and strategies adapted by the species in growth, reproduction and energy storage were investigated by examining growth parameters, biological indices and abundance and biomass variations. Influences of environmental variables on spatiotemporal distribution and biological characteristic of Mullus barbatus were also explored by generalized additive models. Biological data were collected at monthly intervals between May 2007 and May 2010 by trawl sampling while sample collection of environmental variables (temperature and salinity) was performed from December 2008 to May 2010. Results of this study reveal that the components of the demersal fish assemblage in the region fulfill their biological activities within a short period of time when the highest productivity is reached in the area. Moreover, results indicate that within this short period of time, some native components of the demersal fish assemblages studied (Mullus barbatus and Pagellus erythrinus) exhibit strategies such as fast growth, early maturation, short reproduction season, secondary spawners to cope with the environmental peculiarities. On the other hand, the successful exotic colonizers develop strategies as well but these successful immigrants also use time (Lagocephalus suezensis) and space (depth) (Upeneus pori) slot that the native species avoid. In some of the species examined (Mullus barbatus and Lagocephalus suezensis), growth is fast, sexual maturity is early, reproduction period is short, and reproduction potential is high. With the peculiar environmental condition, these life history traits are attributed to the &ldquor-strategy&rdquo
of the species. In this study, generalized additive models of Mullus barbatus explain 81.5 % variations in Gonadosomatic Index (GSI), 55.2 % in Hepatosomatic Index (HSI) and 43.9 % in Condition Factor (K). The time component in the GAM model captures the same cyclic pattern observed in GSI of Mullus barbatus. Besides, The GAM results suggest that the highest GSI values associated with the bottom water temperature are between 18 &ndash
19 °
C while the partial effect of bottom salinity is at 38.7 psu. A positive effect of depth on GSI of the species starts after 60 meters depth and increasing trend continues until 125 meters depth and then decreases. The HSI results are almost identical to GSI outputs indicating that the effects of the parameters concerned act in a similar manner. The results of the GAM models failed to explain influence of environmental parameters on vertical and seasonal distribution of adult Mullus barbatus. However 83.5 % variances were explained in distribution of juveniles. The salinity and temperature have the highest impact on the distribution of juveniles among the parameters evaluated. The results indicate that the occurrence of Atlantic Water in the area has a positive influence on M. barbatus, particularly on the recruits through either by its low salinity or by another factor associated with this water mass. The vertical distribution range are set by the high temperatures (>
27 °
C) at the shallow depths during summer and the low temperatures on the shelf break zone (<
16 °
C). A comparison of vertical abundance distribution of Mullus barbatus and the vertical temperature variations indicate that the species may tolerate up to 27 °
C and then individuals move to the deeper depths so that to the cooler waters when the temperature exceeds their tolerance limit. As well as the life history traits adopted by the species, there are some other factors providing advantages to the species. The fisheries regulations, particularly the time limits applied in the area are in favor of the species especially of pre-recruits. In the study area the pre-recruitment phase and summer YOY aggregations in shallow waters of most species studied in this thesis take place during a time when the fishing season is closed.
3
O'Sullivan, Martha. "Population structure of demersal fish species in the north eastern Atlantic." Thesis, Available from the University of Aberdeen Library and Historic Collections Digital Resources. Restricted: no access until Dec. 31, 2010. Online version available for University members only until June 2, 2011, 2009. http://digitool.abdn.ac.uk:80/webclient/DeliveryManager?application=DIGITOOL-3&owner=resourcediscovery&custom_att_2=simple_viewer&pid=26063.
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Coutin, Patrick C. "The effects of long term exploitation on tropical demersal fish stocks." Thesis, Coventry University, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.329574.
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Newton, Paul William. "The trophic ecology of offshore demersal teleosts in the North Irish Sea." Thesis, University of Liverpool, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.250301.
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Kuta, Kevin G. "The Effect of Demersal Reef Fish on Two Species of Gorgonian Coral." NSUWorks, 1992. http://nsuworks.nova.edu/occ_stuetd/356.
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The effect of demersal reef fish on the gorgonians Pterogorgia anceps and Plexaurella grisea was determined under controlled conditions. Demersal reef fish cause significant changes in Pterogorgia anceps zooxanthellae concentration (cells cm-3), bulk density (g cm-3), and spicule concentration (g cm-3). Growth rates as measured by changes in planar area (cm2) are not significantly affected. No significant differences were found among any of the parameters measured for Plexaurella grisea; however, trends in the data were similar to those of P. anceps.
7
Isidro, Eduardo Jose Louca Florencio. "Biology and population dynamics of selected demersal fish species of the Azores Archipelago." Thesis, University of Liverpool, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.307638.
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Buchheister, Andre. "Structure, Drivers, and Trophic Interactions of the Demersal Fish Community in Chesapeake Bay." W&M ScholarWorks, 2014. https://scholarworks.wm.edu/etd/1539616586.
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Management of fisheries resources is increasingly broadening its scope from single-species approaches to more holistic, ecosystem-based approaches that account for interactions of fish with a variety of ecological factors, such as predators, prey, and habitat. This ecosystem based fisheries management (EBFM) approach requires thorough biological and ecological understanding of systems pertaining to community structure, habitat suitability, and food web interactions. to strengthen the ecological underpinnings of EBFM efforts in Chesapeake Bay, the largest estuary in the USA, I conducted synoptic analyses examining the structure, function, and patterns of the bay's demersal fish community. This research relied on I0 years of data from a multi-species, bimonthly bottom trawl survey of the Chesapeake Bay mainstem. The unifying objectives of this work were to 1) synthesize basic biological and ecological information of many Chesapeake Bay fishes, and 2) examine the environmental drivers of community structure and trophic interactions in the Bay. One major hypothesis underlying the more detailed research objectives for each component was that bay-wide patterns in biomass and feeding habits of Chesapeake Bay fishes were mostly driven through bottom-up processes governed by a blend of small- and large-scale environmental factors. as food web structure and trophic interactions are governed by the presence, distribution, abundance, and behavior of species, Chapter 1 focused on evaluating patterns for these basic biological characteristics for a large suite of 50 species and investigating environmental factors that influence the community trends. Univariate and multivariate statistical modeling revealed that the demersal fish community (dominated by five species) was strongly structured along a salinity gradient, and other factors (e.g. dissolved oxygen, temperature, month, and year) helped regulate biomass and diversity trends. Chapter 2 synthesized diet information for 47 fish species, demonstrated the role of five prey groups (mysids, fishes, bivalves, polychaete worms, and crustaceans) in differentiating feeding guilds, and highlighted the importance of non-pelagic prey groups (especially the hyper-benthic mysids) in supporting the nutritional needs of fishes. Diets of 12 predator species were investigated in more detail in Chapter 3 to infer the dynamics of four important prey groups (mysids, bay anchovy, polychaetes, and bivalves) using advanced statistical modeling techniques. Results revealed generally coherent consumption trends across predators for a given prey, suggestive of prey availability driving consumptive patterns. Synchronous annual peaks in prey consumption were indicative of pulses in prey production (particularly mysids and bivalves) that were exploited by predator populations. to evaluate the population-scale effects of these bottom-up alterations in prey productivity, Chapter 4 relied on a simulation model to examine the potential effects that these annual changes in prey availability could have on consumption and production of one representative predator species. The model indicated that enhanced individual growth resulting from pulses in prey production could generate substantial gains in predator spawning stock biomass, recruitment, and fishery yield. However, the bottom-up effects on predator production had only modest effects on rebuilding times of a depleted population relative to controls on fishing mortality. This research represents one of the largest studies on community structure and trophic interactions for demersal fishes in an estuarine environment, contributing to a broader understanding of fish ecology within a complex and dynamic system. By filling research gaps identified for EBFM in Chesapeake Bay, this body of work also supports a more holistic management approach for the sustainable use of resources from the Chesapeake Bay and coastal waters of the Northwest Atlantic Ocean.
9
Greig, Antonio Bernardo. "The potential application of acoustic methods in North Sea demersal fish stock surveys." Thesis, University of Aberdeen, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.485677.
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In the North Sea, groundfish stock assessment relies on independent bottom trawl surveys to tune the annual indices that are estimated from commercial landings. These surveys have been carried out by several European fishery institutions since the mid 19605 under standardized protocols which have allowed a long time series to be built for the main commercial stocks. An echo-integration survey is an independent metliod with a high ' sampling rate that can be carried out underway. Although it is successfully used on some stocks in the Barents Sea and off the North American Pacific coast, this method is not commonly used for demersal fish quantification. This study investigates the use of echointegration data, gathered during regular bottom trawl surveys in the North Sea~ in providing tuning indices for commercial stocks. To do this, density values extracted from bottom following layers in the acoustic dat{and partitioned by the corresponding catch proportions were compared to the density values obtained from the bottom trawl catches. Univariate and multivariate linear models including depth, position and time of day were fitted and showed very low correlation for demersal species, while resulting in reasonable to good correlation for aggregating pelagic species. As the acoustic method has a dead zone next to the seabed, an analysis of the dead zone dimensions in the study area as well as its mitigation was performed and a software routine was developed to optimize the data USge close to the seabed. A different approach, which allocated acoustic backscatter to targets according to visual interpretation of the echograms and scrutiny protocols, was performed on the optimized data and the density values compared to those of the catches. Correlation results did. not show significant improvement; however the scrutiny process revealed that demersal species were not evident on the echograms, irrespective ofthe catch in the bottom trawl. It is concluded that this discrepancy is due to the aggregation patterns in groundfish, and not necessarily the dead zone alone. Quantification of pelagic species can benefit from the use of echo-integration during bottom trawl surveys, however modifications to the survey design to allow targeted trawls and a systematic survey track are suggested to improve future studies.
10
Moore, Cordelia Holly. "Defining and predicting species-environment relationships : understanding the spatial ecology of demersal fish communities." University of Western Australia. Faculty of Natural and Agricultural Sciences, 2009. http://theses.library.uwa.edu.au/adt-WU2010.0002.
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[Truncated abstract] The aim of this research was to define key species-environment relationships to better understand the spatial ecology of demersal fish. To help understand these relationships a combination of multivariate analyses, landscape analysis and species distribution models were employed. Of particular interest was to establish the scale at which these species respond to their environment. With recent high resolution surveying and mapping of the benthos in five of Victoria's Marine National Parks (MNPs), full coverage bathymetry, terrain data and accurate predicted benthic habitat maps were available for each of these parks. This information proved invaluable to this research, providing detailed (1:25,000) benthic environmental data, which facilitated the development and implementation of a very targeted and robust sampling strategy for the demersal fish at Cape Howe MNP. The sampling strategy was designed to provide good spatial coverage of the park and to represent the park's dominant substrate types and benthic communities, whilst also satisfying the assumptions of the statistical and spatial analyses applied. The fish assemblage data was collected using baited remote underwater stereo-video systems (stereo- BRUVS), with a total of 237 one-hour drops collected. Analysis of the video footage identified 77 species belonging to 40 families with a total of 14,449 individual fish recorded. ... This research revealed that the statistical modelling techniques employed provided an accurate means for predicting species distributions. These predicted distributions will allow for more effective management of these species by providing a robust and spatially explicit map of their current distribution enabling the identification and prediction of future changes in these species distributions. This research demonstrated the importance of the benthic environment on the spatial distribution of demersal fish. The results revealed that different species responded to different scales of investigation and that all scales must be ix considered to establish the factors fish are responding to and the strength and nature of this response. Having individual, continuous and spatially explicit environmental measures provided a significant advantage over traditional measures that group environmental and biological factors into 'habitat type'. It enabled better identification of individual factors, or correlates, driving the distribution of demersal fish. The environmental and biological measures were found to be of ecological relevance to the species and the scale of investigation and offered a more informative description of the distributions of the species examined. The use of species distribution modelling provided a robust means for the characterisation of the nature and strength of these relationships. In addition, it enabled species distributions to be predicted accurately across unsampled locations. Outcomes of the project include a greater understanding of how the benthic environment influences the distribution of demersal fish and demonstrates a suite of robust and useful marine species distribution tools that may be used by researcher and managers to understand, monitor, manage and predict marine species distributions.
11
Johnson, Andrew Frederick. "Determining the habitat requirements of demersal fish for the design of marine protected areas." Thesis, Bangor University, 2012. https://research.bangor.ac.uk/portal/en/theses/determining-the-habitat-requirements-of-demersal-fish-for-the-design-of-marine-protected-areas(af07034d-cf7d-4839-9c55-59fdbaf5534d).html.
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Understanding the relationship between habitat and fish distribution is a central component in the recent shift towards ecosystem based fisheries management (EBFM). Determining the habitat requirements of commercially and ecologically important species will be essential if spatial management strategies such as marine protected areas (MP As) are to be used successfully to conserve marine resources. A review of demersal fish habitat research highlighted numerous areas lacking in this field of habitat science. These included the propensity for studies to focus on abiotic habitat variables such as depth and sediment over large spatial scales (≥ 100s km²) and the low number of studies analysing biotic habitat variables in general. I conclude that development of sound predictive science in this field is reliant on a change in research focus toward reductions in study scale, or increases in resolution for abiotic habitat variables and more integration of biotic variables into studies. The three field studies included in this thesis analyse the importance of prey resource for the distribution of demersal fishes over spatial scales ranging from hundreds of metres to tens of kilometres. The first study investigates the relationship between prey and predator abundance and prey size and predator mouth gape size for nine demersal fish species around the Balearic Islands in the Mediterranean. The results demonstrate that prey abundance and size are of significance for some demersal fish species feeding primarily on benthos and will help in defining habitat requirements of demersal fish species. Demersal fish feeding ecology is studied in more depth when I investigate the effects of a bottom trawl fishery on an invertebrate benthic community and the subsequent effects this has on two commercially important flatfishes (P. platessa and L. limanda). This chapter closes the gap between the effects of bottom fishing on benthic communities and the reduced condition of some fishes found within these areas. The results of this study suggest that alterations in prey abundances, sizes and availabilities caused by chronic bottom trawling may lead to reduced feeding efficiencies, particularly for species with narrow prey spectrums. This in turn could result in reduced conditions of affected fishes living in chronically disturbed areas. The final data chapter uses detailed habitat maps, based on differences in sediment characteristics between three sites to take a small spatial scale, high resolution approach to describing demersal fish habitat. This investigates changes in the feeding ecology of a demersal fish species, Callionymus lyra, with body length. Although significant differences in prey size and prey taxa selectivity were found, no significant relationships between prey resource and predator distribution were apparent for any of the year classes analysed. The potential ecological and methodological reasons for these findings are discussed in-depth. Finally, a general discussion examines the main findings and suggests areas for future development.
12
Smith, Alastair. "On brain, behaviour and biochemistry of the deep-sea demersal grenadier fish, Coryphaenoides (Nematonurus) armatus." Thesis, University of Aberdeen, 1996. http://digitool.abdn.ac.uk/R?func=search-advanced-go&find_code1=WSN&request1=AAIU089956.
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In surface-dwelling vertebrates, pineal melatonin is secreted in a manner directly related to photoperiod. Despite an absence of solar light, several deep-water fishes show some seasonality. The presence of central melatonin receptors was investigated using in vitro autoradiography in the deep-sea fish Coryphaenoides (Nematonurus ) armatus. No specific 2-[125I]iodomelatonin (IMEL) binding was found in optic tectum, cerebellum or hypothalamus. Specific binding was however found over mid-brain tegmentum and hindbrain. Two possible cues in the deep-sea are seasonal depositions of phytodetritus and diurnal/semidiurnal currents. Both gustatory and acousticolateralis systems are well developed and capable of detecting such cues. The principle sites of specific IMEL binding are regions which integrate inputs from these non-optic senses. The behaviour of deep-sea scavenging fishes was investigated using a baited free-fall photographic and fish tracking system - AUDOS (Aberdeen University Deep Ocean System). Data collected during spring (April, 1994) at 4800m depth, NE Atlantic were compared with previous studies at the same location during summer, 1989. The time and species of first arrivals and mean staying time showed no differences between years or season. However, radial swimming speed (0.009 m.s-1) of C.(N) armatus was significantly slower than in previous studies. A change in size distribution to smaller individuals in spring 1994, might also suggest C.(N) armatus may undertake major episodic or seasonal migrations. The white muscle protein content of deep-water fishes is about 40% lower than in shallow-water species. This appears to be accompanied by lower numbers of ribosomes. Any increase in RNA content to compensate for low efficiency at low temperatures is not apparent and may be due to reductions caused by other factors.
13
Darwall, William Robert Thomas. "Spatial patterns and trophic modelling within the Lake Malawi demersal fish community : conservation and fisheries applications." Thesis, University of Hull, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.402706.
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Knuth, Friedrich Alexander. "Exploring the geospatial relationships between demersal fish and seafloor morphometrics along the southeast Atlantic continental shelf." Thesis, College of Charleston, 2015. http://pqdtopen.proquest.com/#viewpdf?dispub=1585544.
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Marine Protected Areas (MPAs) are successful place-based management tools in protecting Essential Fish Habitat (EFH) from commercial and recreational fishing pressures. In the southeast Atlantic, the morphometric environment of the seafloor has been found to be a control on Essential Fish Habitat (EFH) (Sedberry and Van Dolah 1984). To this end, modern methods of acoustic data acquisition and morphometric analysis of the seascape are promising oceanographic techniques for identifying and delineating EFH. In July, 2013, the NOAA Ship Pisces collected bathymetric, backscatter and water column data for potential habitat sites along the U.S. Southeast Atlantic continental shelf. A total of 205 km2 of seafloor were mapped between Mayport, FL and Wilmington, NC, using the SIMRAD ME70 multibeam echosounder system. In addition, a total of n = 7410 fish presences were recorded within the water column, using the SIMRAD EK 60 split-beam echosounder system. These data were processed in CARIS HIPS, QPS Fledermaus, MATLAB and Echoview. This study provides a morphometric characterization and quantitative assessment of fish present within each survey site and identifies features of the bathymetry that help explain the presence of demersal fish. A total of 106 unique maps were created, illustrating seafloor morphometrics and fish distributions across the seascape. In ArcGIS, 14 morphometrics were generated as candidate explanatory variables for fish abundances in small (5-12 cm), medium (12-29 cm) and large (>29 cm) size classes. We explored fish-seascape interactions at two spatial scales in the GIS using a site-wide and 50 x 50 m grid scale. At the site- wide scale, X¯ Slope (R2 = 0.97), X¯ Slope of Slope (R2 = 0.90) and σ Depth (R2 = 0.87) provided the strongest explanatory power in a bivariate analysis and may be used to help identify EFH at a coarse scale. At a 50 x 50 m grid scale, X¯ Slope, X¯ Slope of Slope and X¯ Backscatter emerged as the strongest contributing variables, when combined in a multivariate analysis. Overall, multivariate model R2 values were low and not predictive, but allow for the identification of variables contributing to the characterization of fish-seascape interactions at a finer scale.
15
Al-Habsi, Saoud. "Trophic relationships of a demersal fish assemblage in the Arabian Sea elucidated by stable isotope approaches." Thesis, University of Newcastle Upon Tyne, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.432492.
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Cotterell, Stephen Paul. "Fish landings, discards and benthic material from demersal trawling in the western English Channel (ICES VIIe)." Thesis, University of Plymouth, 2006. http://hdl.handle.net/10026.1/2751.
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This study examined the impact of inshore single boat otter trawling from Newlyn, Looe, Plymouth and Salcombe and pair boat demersal trawling from Looc and Plymouth on the benthic environment off the SW peninsula of the UK between 1998 and 2000. Fish and shellfish species (54 and 11 species respectively) were measured at sea and the non-fish material (124 species) was analysed later. Overall 79.8 % of the sample was landed fish and shellfish, 15.8 % was discarded fishes and 4.4 % was invertebrates and other material (by weight). Related information about the substrate and tide were generated from British Geological Survey data and a computer simulation of the maximum mean tidal strength. In agreement with the different abiotic regime, the dominant fishes were different in Newlyn and the other ports. According only to port, the Looe and Plymouth samples were not significantly different, either as full samples or for their fish and non-fish components. The Salcombe samples were not significantly different to those from Looc or Plymouth for the non-fish part of the sample. Including the type of trawling meant that the greatest similarity was for the non-fish part of the sample although the relative amounts of the components varied. The pair trawling samples contained more landed, less discarded and less non-fish material than their single boat equivalents. Pair trawl samples also contained fewer examples of large invertebrate species. Several within and between-species relationships were explored to assess the wider interpretation of the fish community data. This examined size of Raja spp., several predator-prey relationships and the utility of Marlhasterias glacialis as an indicator of fishing disturbance. Disturbance as measured by Abundance Biomass Comparison was similar whether according to the non-fish or full sample, and suggested that the whole region was relatively undisturbed (with Newlyn apparently the most impacted area). Analysis of the relative contribution of selected groups to taxonomic diversity showed the derived conservation priorities for 'orders' of fishes were Elasmobranches > Pleuronectiformes > Gadiformes. In general, the fact of 'losing' orders of fishes was more important for single rather than pair trawl samples, which suggests that single boat samples were collected from structurally more complex areas supporting a wider taxonomic diversity. The analysis of groups for conservation priority was also carried into the invertebrates with echinoderms being highly influential for Newlyn. Taxonomic diversity (A+ and A) was also proposed as an addition to the definition of 'Good Environmental Status' according to the proposed EU Marine Strategy Directive. When examining the abiotic and biotic data sets, the fish species bore the closest similarity to the abiotic data suggesting that much of the study area was dominated by similar invertebrate species that tended to be scavengers and in most analyses the positive influence of the voluntary Inshore Potting Agreement management regime was evident. In a novel analysis, there was broad agreement between the data and literature sources for the location of the fishes in relation to the substrates and for eight of the most commonly occurring species it was possible to be more precise in their substrate preferences than suggested from the literature. The landed fish part of the sample was shown to be a statistically good approximation of the landed part of the haul (for which the commercial data was known) in > 95 % of the hauls. Finally, data on the commercial landings for each port show that the boats sampled in this study were representative of these ports.
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Sampson, Mark Robert. "Modelling the distribution and abundance of several demersal fish species on the Agulhas Bank, South Africa." Thesis, Rhodes University, 2002. http://hdl.handle.net/10962/d1006207.
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The Agulhas Bank supports a speciose fish community, many of which are commercially important. Despite substantial research being conducted on aspects of their biology spatial aspects of their distribution and abundance in relation to environment parameters has been ignored. This study, therefore, addressed aspects related to the distribution and abundance of representative species on the Agulhas Bank within a Geographic Information System (GIS). Four candidate species were chosen due to their importance either in numbers or unit mass to the South African demersal trawl fishery. The species also shared morphological and taxonomic similarities. The candidate species chosen were the two Cape hake species, shallow-water hake Meluccius capensis, and deep-water hake Merluccius paradoxus, and the two pleuronectiform species being Agulhas sole Austroglossus pectoralis and redspotted tonguesole Cynoglossus zanzibarensis. The use of a GIS was appropriate and allowed for hidden spatial patterns be exposed and illustrated visually, while also facilitating the quantification of the relationships between distribution/abundance and certain environmental predictors using statistical methods The Department of Marine and Coastal Management, Cape Town, supplied biological data in the form of length frequency and biomass information from spring (AprillMay) and autumn (September/October) cruises conducted between 1986 and 1993 on the R. V. Africana. The Council for National Geoscience, Cape Town, supplied sediment data for the entire southern African coastline. Initial exploratory data analysis highlighted potential relationships between environmental variables and abundance for each specie's life-history stanzas. Variations in spatial distribution were found to be significantly different between each life-history stanzas within species. Fish density as a function of the additive effects of the various environmental parameters, including temperature, depth and sediment type, was assessed using a Poisson Generalized Additive Model (GAM), while distribution was analysed with a logistic GAM. A predictive logistic model was then created, taking into consideration the importance of the predictor variables for each species, allowing for predictive estimates to be made for each species by inputting environmental information within the study area. The importance of certain environmental variables influencing distribution and abundance were noted. General patterns indicated that sediment was the most important to both the distribution and abundance of the two pleuronectiform species and juvenile life-history stanzas, while the adult gadoids' distribution and abundance appeared to be depth dependent.
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Fraser, Helen M. "Do fish predators in the North Sea live beyond their means is prey production sufficient to meet consumption? /." Thesis, Available from the University of Aberdeen Library and Historic Collections Digital Resources, 2008. http://digitool.abdn.ac.uk:80/webclient/DeliveryManager?application=DIGITOOL-3&owner=resourcediscovery&custom_att_2=simple_viewer&pid=24693.
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Currie, Jock. "Historical baselines and a century of change in the demersal fish assemblages on South Africa's Agulhas Bank." Doctoral thesis, University of Cape Town, 2017. http://hdl.handle.net/11427/27385.
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Accurate interpretation of recent variability observed in fish populations, species compositions, distribution ranges or ecological indicators, depends on knowledge of their past dynamics and historical states. The onset of systematic fisheries data collection typically lagged decades or even centuries behind modern fishing exploits. As a consequence, pre-disturbed reference points and descriptions of subsequent change are rarely available. A remarkably detailed set of historical trawl survey data from South Africa provided such a rare opportunity. Government-funded exploration of the Agulhas Bank fishery potential resulted in meticulously-documented trawl survey data from 1897-1904, when prior human impacts on those resources were negligible. Although they used less effective technology, the information recorded and methods used were similar to modern surveys. This thesis investigated change in demersal fish fauna of the Agulhas Bank and documents comparisons between historical trawl surveys and modern re-enactments at the same locations. In comparing trawl survey catches over multiple decades or among different periods, unquantified changes in fishing power pose a key challenge. The shape, size, materials, mesh sizes and speed at which trawl nets are dragged, interact with the behaviour, size and shape of fish, influencing fishing performance. To accurately compare current catch rates with those of historical trawl surveys, the same trawl gear and methods were carefully replicated in repeat surveys at three sites. An investigation of literature and photographs of the original vessel and equipment were conducted to support the construction of a replica 'Granton' otter trawl net. The net was composed of Manila hemp with a headline length of 27 m (90 ft) and was attached to flat wooden trawl boards. The historical towing speed was estimated as 1.34 m s⁻¹ (2.6 knots). Three parts of the shallow Agulhas Bank that were surveyed 111 years prior, were re-surveyed in 2015. Species composition was contrasted between the historical and re-survey periods by way of unconstrained ordination, permutational multivariate analysis of variance and tests of the homogeneity of multivariate group dispersions. Taxa discerning between periods were identified with similarity percentage analyses. Changes of standardised catch between periods were tested for 27 taxa, using a non-parametric bootstrap approach. Proportions among size-classes, recorded for three taxa, were tested using Fisher's exact test. Results revealed a substantially transformed demersal catch assemblage, where the period effect explained almost half of the measured variance among samples. These changes included the disappearance or heavy depletion of kob (Argyrosomus spp., absent in re-surveys), panga (Pterogymnus laniarius; 2.4% of historical catch abundance) and east coast sole (Austroglossus pectoralis; 4.6% of historical catch abundance), which had jointly contributed 70-84% of historical catch composition. Average re-survey catches were largely made up of gurnards (Chelidonichthys spp.; 3 792% of historical abundance), horse mackerel (Trachurus trachurus; 4 738% of historical abundance), spiny dogfish (Squalus spp.; 3 121% of historical abundance), hake (Merluccius capensis; 558% of historical abundance) and white sea catfish (Galeichthys feliceps; 13 863% of historical abundance). Analysis of available length information confirmed the expectation that fish sizes (specifically M. capensis and A. pectoralis) had declined. This implies that comparisons by weight would be more severe for declined abundances and less severe for those that increased, relative to contrasts of numerical abundance. Habitat preferences as well as geographic and depth distribution appeared to separate the taxa that increased from those that declined. These factors, together with reproductive and growth characteristics, as well as indirect trophic impacts, likely shaped the responses of demersal fauna to fishing and other human impacts during the 111 years between trawl surveys. An assessment of distribution changes of 44 common demersal taxa was undertaken. These analyses were restricted to the last 30 years of trawl survey data as the units and spatio-temporal resolution of prior data were incompatible. Standardised catches were used from annual spring and autumn south coast trawl surveys conducted by the government fisheries department. Geostatistical delta-generalised linear mixed models were used to predict species distribution functions, which were used to calculate annual estimates of latitude/longitude centres of gravity and effective areas occupied by each population. Average trends over the study period (1986-2016) were assessed using a Bayesian state-space model. Of nine species found to have a trend in average location, six moved westward or south-westward, while three moved eastward or north-eastward. Two species showed a trend of contracting spatial extent and one showed an expansion. Across the entire assemblage combined, there was a significant contraction in extent and a westward shift in average location. These assemblage-wide average trends are interpreted to be driven by climate forcing. Fishing impacts are expected to have contributed to the eastward movement in centre of gravity for kob, lesser sandshark (Rhinobatos annulatus) and white stumpnose (Rhabdosargus globiceps). Interpretation of these distribution shifts is hampered by a lack of knowledge on subsurface hydrographic trends on the Agulhas Bank, which is identified as a research priority. My research revealed substantial change in demersal fish communities on South Africa's Agulhas Bank and adds novel insight to the history underlying current states of demersal ecosystems. Valuable additions include a) documentation of the extent to which demersal assemblages have transformed during the last century at three representative inshore sites; b) estimates of current abundances relative to pre-disturbed baselines at those sites, which c) highlights drastic local depletion for certain taxa and d) reveals substantial abundance increases of certain species during the post-industrial fishing period; e) novel evidence of distribution trends in south coast demersal species; and f) identification of trends in the average distribution of the demersal fish assemblage, suspected to be climate-forced. Long-term comparisons, using minimally-disturbed baselines, revealed drastic transformation of the fish assemblage during a century of industrialisation, which points to trawling-induced alteration of benthic habitats and substantial changes in ecosystem structure. Besides the provision of novel historical context for current and future studies and decision-making, this work counters the erosive nature of shifting baselines in South Africa's marine environment.
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Chatfield, Brenton Sean. "How to find the one that got away : predicting the distribution of temperate demersal fish from environmental variables." University of Western Australia. School of Earth and Geographical Sciences, 2008. http://theses.library.uwa.edu.au/adt-WU2009.0009.
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Knowing where species are and understanding why is paramount for developing relevant and sustainable conservation and resource management strategies. The need for this information is becoming urgent as fishing activity, resource extraction and the impacts of coastal developments continue to put marine resources under increasing pressure. As logistical and financial constraints can restrict our ability to collect data in the marine environment, the ability to predict distributions based on known associations with different environmental variables would enhance our capacity to manage these resources. Before attempting to predict the distribution of species and groups of species, the underlying species-environment relationships must be examined to determine whether associations between species and the environment can: (i) be identified, (ii) be used to develop models that can accurately predict distributions, and (iii) are general enough to allow accurate predictions beyond the sampled area. Most studies to date have compared the composition of fish assemblages between sites to determine how different environmental variables influence distribution. While widely applied, these methods do not consider how individual species respond to multiple environmental gradients and they lack the ability to predict distributions across different combinations of variables along those gradients. This lack of prediction also limits our capacity to assess what marine biodiversity is presently threatened by global, regional, and local human pressures on marine ecosystems. '...' Thus, summarising and modelling species data at higher levels would result in models with poorer predictive accuracy and a loss of ecological information. The generality of the species-environment relationships defined by the models were assessed by evaluating the transferability of models between different areas. Models developed from data collected over a wider geographic extent could more accurately predict the distribution of species across a smaller spatial extent than vice versa. This indicated that while general theories of the ecology of temperate demersal fish can be defined, the actual patterns of distribution may vary from site to site, suggesting caution when using predictions beyond the sampled area for management purposes. Overall, species distribution modelling identified how different species and groups of species responded to the combined influence of multiple environmental gradients and was able to accurately predict distributions based on the defined associations. Their application has led to a greater understanding of the species environment relationships and will help to identify those areas that may be important for conservation. Their predictive ability will allow general predictions of distribution of fish species across unsurveyed areas and provides the ability to assess the potential impact from implementing different policy and management strategies.
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Atkinson, Lara Jane. "Effects of demersal trawling on marine infaunal, epifaunal and fish assemblages: studies in the southern Benguela and Oslofjord." Doctoral thesis, University of Cape Town, 2009. http://hdl.handle.net/11427/6224.
Full textAbstract:
This thesis investigates the impacts of the demersal trawl fishery on infaunal, epifaunal and fish assemblages in the southern Benguela upwelling system for the first time. In the absence of representative areas of similar habitat protected from trawling in the southern Benguela region, infaunal and epifaunal assemblages were compared between heavily and lightly trawled areas to assess the impacts of the otter-trawl fishery. Infauna were sampled at four sites, from southern Namibia to near Cape Town by means of five replicate grab samples at each paired heavily and lightly trawled area. Invertebrate epifauna were sampled at two sites in heavily and lightly trawled areas using a finemeshed otter trawl. Sites ranged in depth from 350-450 m in unconsolidated sediment habitat. Epifaunal assemblages showed greater differences at heavily trawled areas with significantly reduced species diversity, average number of species and individuals. Several epifaunal species were absent from heavily trawled areas highlighting their vulnerability to impacts of trawling. Multivariate analyses show significant differences in composition of both infaunal and epifaunal assemblages among the sites and between trawling treatments at all sites. The results of this study suggest that intense trawling activities are at least partially responsible for significantly altering benthic community composition, affecting epifauna to a greater measurable extent than infauna. Biological Traits Analysis (BTA) was used to explore potential changes in ecological functioning of benthic assemblages, comparing areas exposed to heavy and light trawl intensities in the Benguela system. BTA incorporates biological traits (life-history, morphology and behaviour) of infaunal and epifaunal species with biomass, capturing a broad range of information of marine benthic assemblages. Seventeen percent of the infaunal traits analysed showed a significant difference between heavily and lightly trawled areas. Twenty-four percent of epifaunal biological traits investigated were significantly different between areas of heavy and light trawling. This study suggests that more intense trawling modifies some trait constituents of the benthic assemblage in the southern Benguela region, confirming the sensitivity of functional traits analysis in detecting changes induced by trawling disturbance. Biological traits analysis of benthic invertebrates shows promise as a practical technique for incorporation into monitoring programmes and for developing indicators of benthic ecosystem health, needed for implementation of an ecosystem approach to fisheries management in South Africa. A lack of representative untrawled areas in the trawl grounds of southern Africa precluded investigations comparing trawl impacts with unfished reference sites. A bilateral agreement between South Africa and Norway (NORSA) provided the opportunity to conduct experiments in an untrawled area of Oslofjord, Norway, where a shrimp trawl fishery for Pandalus borealis operates nearby. Infauna Abstract 2 were sampled at four untrawled sites in Oslofjord with five replicate grabs after which an Agassiz beam sled was dragged across two of the sites (impact sites) four times, simulating a trawl disturbance. Infauna were re-sampled at all four sites immediately after trawling (post-impact), 14 days and 64 days after the impact to monitor recovery of infaunal populations. Multivariate analyses comparing the impact sites with paired control sites for each sampling occasion showed no significant differences in infaunal assemblages at any stage of the experiment. Whilst it is considered possible that the trawl simulation was not a sufficient impact to represent that of a commercial trawl effect, it is considered more likely that trawl activities in Oslofjord do not inflict measurable impacts on infaunal assemblages. However, the impact of trawling on epifaunal assemblages in Oslofjord was not investigated in this study. Annual research survey data collected over the past 24 years (1986-2009) provide an opportunity to explore long-term demersal fish assemblage composition changes on the west coast of South Africa. Differences in spatial (latitude and depth) and temporal (seasonal and annual) factors were examined using multivariate analyses. Possible long-term changes were investigated using the Sequential T-test Algorithm to detect Regime Shifts (STARS). Results indicate geographic differences in fish assemblage composition from the northern to the southern region on the west coast of South Africa. The fish community composition is also clearly influenced by depth with a distinct change in fish assemblages in the shelf break region between 300 m and 400 m. Multivariate analyses also show two clear temporal changes in assemblage composition, firstly, in the early 1990s and secondly, in the mid- 2000s. STARS analyses detect long-term shifts in 27% of demersal species with the majority of speciesâ shifts detected either in the early- to mid-1990s or in the past decade (2002 to 2009). Multivariate analyses among year groups reveal an increase in three fast-growing, early maturing species and decreases in two slow-growing, long-lived species. STARS analysis detected increases in two of the same fast-growing species, decreases in an additional four slow-growing, long-lived species, but four other slow-growing, long-lived species showed the opposite trend (i.e. increases). The hypothesis of an increase in fast-growing, early maturing species and a decline in slow-growing, longlived species in fished systems is therefore only partially supported by these findings. Shifts in demersal fish assemblages coincide temporally with spatial shifts observed in small pelagic species and west coast rock lobster. The shifts in the demersal fish assemblage composition detected in this study are probably a reflection of long-term indirect effects of fishing in combination with environmental changes. Abstract 3 The response of benthic invertebrate assemblages to two levels of fishing intensity in the southern Benguela region justifies regular monitoring of epifauna during existing annual demersal research surveys and infaunal monitoring through dedicated, periodic sampling initiatives. Demersal fish assemblage data should be regularly assessed for changes in community composition. Representative protected areas can serve as reference areas against which fishing impacts could be assessed and improve our understanding of ecosystem effects of demersal fishing.
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Klaer, Neil L., and n/a. "Changes in the structure of demersal fish communities of the South Eastern Australian Ccontinental Shelf from 1915 to 1961." University of Canberra. Resource, Environmental & Heritage Sciences, 2006. http://erl.canberra.edu.au./public/adt-AUC20060804.154133.
Full textAbstract:
Haul-by-haul steam trawler catch and effort data for 1918�23, 1937�43 and 1952�57,
which covers a large portion of the history of steam trawling in the Australian South
East Fishery, were examined in detail for the first time. There were 64,371 haul records
in total. The catch-rate for all retained catch combined shows a strong decline overall,
with a brief recovery during World War II, probably due to increased retention of
previously discarded species. The fishing fleet moved to more distant fishing grounds
and deeper waters as the catch-rate declined. The catch-rates of the main commercial
species followed a similar pattern in a number of regions within the fishery. The catchrate
of the primary target species � tiger flathead (Neoplatycephalus richardsoni) �
dropped considerably from the early, very high, catch-rates. Chinaman leatherjacket
(Nelusetta ayraudi) and latchet (Pterygotrigla polyommata) � species that were
apparently abundant in the early years of the fishery � virtually disappeared from
catches in later years. The appearance of greater catches of jackass morwong
(Nemadactylus macropterus), redfish (Centroberyx affinis), and shark/skate during the
war and afterwards was probably due to increased retention of catches of these species.
The disappearance of certain species from the catch may be due to high fishing pressure
alone, or to a combination of fishing pressure, changes in the shelf habitat possibly
caused by the trawl gear, and environmental fluctuations.
Catch-rates in weight per haul per species were standardised to annual indices of
abundance using a log-linear model. Standardised annual index trends for flathead,
latchet and leatherjacket indicate a strong to severe decline over the period covered by
the data. All species showed seasonal patterns, but the peak season varied depending on
the species. The distribution of standardised catch-rate by area also differed greatly by
species, and no single area showed consistent differences across all species. Day trawls
caught more flathead, redfish and latchet, while night trawls caught more morwong and
leatherjacket. Moon phase had less influence on catch-rates than the other factors
examined. Correlation of annual index trends with a number of annual mean
environmental factors was examined and no strong correlations were found.
Annual catches of the major commercial trawl species on the SE Australian shelf were
estimated from recorded total trawl catches, catch species composition from subsamples
and estimates of the rate of discarding. These annual catches, standardised
indices of abundance and biological population parameters were used in single-species
stock reduction models to estimate absolute biomass trends. Biological population
parameters and the biomass estimates were used to calculate management reference
point fishing mortality rates F0.1, Fspr30 and Fmsy. Results showed that simple plausible
population models can be constructed that account for catches over the long period of
time from 1915 to 1961.
Simple mass-balance ecosystem models were built for the demersal community of the
SE Australian shelf for 1915 and 1961 using the Ecopath software. Model inputs were
consistent with a more comprehensive SE marine ecosystem model in development by
CSIRO. The models demonstrate that biomass estimates produced by the single species
stock reduction models can be consistently integrated into simple plausible massbalance
ecosystem models.
Modern stock assessments for the main commercial species in this fishery today mostly
used data collected since about 1985. Abundance indices and total catch estimates from
this study have been used in the most recent assessments for tiger flathead and
morwong, allowing construction of the exploitation history for these species spanning
almost 100 years. Use of the historical information has increased confidence in the
estimates of the modern stock assessments � particularly management reference points,
and has allowed us to quantify changes in fish abundance that have simply been
documented anecdotally in the past.
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Polanco, Fernández Andrea [Verfasser]. "Dynamics of the continental slope demersal fish community in the Colombian Caribbean : deep-sea research in the Caribbean / Andrea Polanco Fernández." Gießen : Universitätsbibliothek, 2016. http://d-nb.info/1118289889/34.
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Lundy, Caroline. "Genetic structure of demersal fish populations in oceanic environments : implications for management of European hake (Merluccius merluccius), a commercially important species." Thesis, University of East Anglia, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.323388.
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Snyder, Susan Susan. "Polycyclic Aromatic Hydrocarbon Metabolites as a Biomarker of Exposure to Oil in Demersal Fishes Following the Deepwater Horizon Blowout." Scholar Commons, 2014. https://scholarcommons.usf.edu/etd/5436.
Full textAbstract:
The Deepwater Horizon blowout occurred on April 20th, 2010, releasing 4.9 million barrels of Louisiana crude oil into the Gulf of Mexico (GoM). Subsequent to the Deepwater Horizon blowout, sediment cores revealed oil on the northern GoM seafloor and abnormal skin lesions were seen in GoM fishes. Exposure to polycyclic aromatic hydrocarbons (PAHs), a component of crude oil, in fish has been associated with many sublethal effects, including cancer and population-level effects. Using a biomarker of exposure to PAHs, this thesis evaluates inter-species, temporal and spatial differences in exposure to hydrocarbon contamination between three species of fish with varying levels of association with the sediment, that were potentially exposed to Deepwater Horizon crude oil: golden tilefish (Lopholatilus chamaeleonticeps), king snake eel (Ophichthus rex) and red snapper (Lutjanus campechanus), and examines patterns in these data using life history, behavior and environmental data.
In 2011, 2012 and 2013, bile samples and biometric data were collected from fish via demersal longlining and bile was analyzed for three PAHs, naphthalene, phenanthrene and benzo[a]pyrene and their metabolites, using high performance liquid chromatography with fluorescence detection (HPLC-F). Bile of golden tilefish had significantly higher concentrations of naphthalene and phenanthrene metabolites, compared to red snapper and king snake eel. For biliary naphthalene metabolites, golden tilefish had an average concentration of 240 ug g-1, compared to 61 ug g-1 for red snapper and 38 ug g-1 for king snake eel, for the year 2012. Biliary naphthalene metabolite concentration has decreased 8% in golden tilefish samples, between 2012 and 2013, indicating continuous exposure to petrogenic pollution, while naphthalene metabolites decreased 49% over time for red snapper and 37% for king snake eel, indicating episodic exposure to elevated petrogenic pollution prior to 2011. The concentration of naphthalene metabolites measured in golden tilefish in this study are some of the highest concentrations measured in the GoM and internationally, while naphthalene metabolite concentrations for red snapper and king snake eel are similar to 1990's GoM data. In contrast, concentrations of benzo[a]pyrene metabolites were statistically similar for all three species, suggesting a difference in the disposition of or exposure to benzo[a]pyrene contamination. Concentrations of benzo[a]pyrene metabolites are relatively low when compared to other GoM and international data, for all three species.
This study has identified a species of GoM fish, golden tilefish, that is exposed to a present-day source of petrogenic PAH pollution and certain fish species that were episodically exposed, in the years following the Deepwater Horizon blowout. With residual Deepwater Horizon oil still found in GoM sediments, coastal marshes and beaches, there is a need to identify these chronic exposures to persistent PAH pollution, monitor PAH concentrations in over time and evaluate the resulting sublethal effects to better understand the impacts of the Deepwater Horizon blowout on marine resources such as GoM fisheries.
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Martínez, Iñigo. "Demersal fish assemblages around sea bed features : Buzzard oil & gas field platform in the North Sea and Jones Bank, Celtic Sea." Thesis, University of Aberdeen, 2011. http://digitool.abdn.ac.uk:80/webclient/DeliveryManager?pid=183828.
Full textAbstract:
The maximum number (Nmax) of fish was recorded using baited underwater camera (BUC) techniques to study spatio-temporal changes of the fish community in localize areas. In the central North Sea (~100m depth) abundance models revealed that for both, whiting and flatfish, the Nmax was influenced by light level at the time of deployment. Nmax of hagfish was strongly related to current speed in a non-linear way with a predicted upper threshold (~11 cm.s-1) above which Nmax declined. Current speed and inter-annual variation had an important effect on haddock Nmax. Large predators that prompt avoidance mechanisms (e.g. large conger eel, marine mammals and fishing vessels) and bottom current speed >25 cm.s-1 can modify demersal fish behaviour depending on size and species and therefore have important effects on BUC-derived data. The BUC was applied for the first time to the monitoring of the Buzzard platform, a new oil and gas development in the central North Sea that host 12 demersal and benthic fish species. The benthic taxa, flatfish and hagfish, showed higher numbers closer to the platform whilst the most mobile species showed constant numbers (haddock) or highest numbers outside of the 500m of Exclusion Area (whiting). No significant changes in fish diversity were found between the areas surveyed before the platform construction. After the construction, the species richness and diversity were higher outside the 500m Exclusion Area surrounding the platform. Offshore sand banks, like oil platforms, can modify the composition of the local fish abundance. BUC and commercial trawl observations on the Jones Bank (75-150m depth, Celtic Sea) recorded 23 species, the highest richness, on top of the bank and 18 species on the slope and off-bank areas. Conger eel and Nephrops were both absent from the top of the bank site whereas haddock was only observed in the bank area.
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Federizon, Ricardo. "Using vital statistics and survey catch composition data for tropical multispecies fish stock assessment application to the demersal resources of the Central Philippines /." Online version, 1993. http://bibpurl.oclc.org/web/37178.
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Camara, Mohamed Lamine. "Biodiversité taxonomique et fonctionnelle des assemblages de poissons de Guinée et son évolution sous l’effet de la pêche." Thesis, Montpellier, 2016. http://www.theses.fr/2016MONTT121/document.
Full textAbstract:
En Guinée, le constat a été établi par divers auteurs que l’intensification de l’exploitation des ressources démersales sur ces dernières décennies a induit une baisse générale de leur abondance. Cette intensification est supposée avoir induit également des modifications de la structure multi-spécifique et fonctionnelle des assemblages de poissons de cette zone, mais peu d’études ont permis d’en juger jusqu’ici, la plupart des travaux antérieurs sur ces ressources ayant concerné des approches strictement mono-spécifiques et des approches strictement taxonomiques. Dans ce contexte, l’objectif de cette thèse est de contribuer à un diagnostic écosystémique plus complet de l’état actuel des ressources marines guinéennes et de déterminer en particulier si la diversité taxonomique et fonctionnelle des assemblages de poissons a été affectée par la pêche.Les données de campagnes de chalutages scientifiques collectées sur le plateau continental guinéen entre 1985 et 2012, les statistiques sur les captures de pêche et dix-sept traits fonctionnels liés aux fonctions de locomotion et d’acquisition de nourriture de 50 espèces de poissons démersaux sont étudiés à travers divers indicateurs de diversité pour analyser l’impact de la pêche.Les résultats montrent que l’intensification de la pêche a eu des effets significatifs sur certaines caractéristiques générales du peuplement en question. Depuis 1985, on observe ainsi une baisse de la densité et du niveau trophique moyen des poissons ainsi qu’un turnover des dominances, par lequel les espèces principales, à forte valeur commerciale, caractérisées par des masses corporelles importantes et une croissance lente sont progressivement remplacées par des espèces de plus petites tailles à moindre valeur commerciale et à croissance rapide. On observe également une baisse significative de la richesse fonctionnelle dont l’évolution conforte les résultats obtenus à partir des évaluations taxonomiques et confirme que l’écosystème côtier du plateau continental est perturbé en lien avec la pression de pêcheIn Guinea, was highlighted by various authors that the intensification of the exploitation of demersal resources over recent decades has led to a general decline in abundance. This intensification is supposed to have also induces changes in the specific and multi-functional structure of the fish assemblages of this zone, but few studies have Judging far, most previous work on these resources with relevant strictly mono-specific approaches and strictly taxonomic approaches. In this context, the aim of this thesis is to contribute to a more complete ecosystem diagnosis of the current state of the Guinean marine resources and in particular whether the taxonomic and functional diversity of fish assemblages was affected by fishing. Data from scientific trawl surveys collected on Guinean continental shelf between 1985 and 2012, statistics on catches of fishing and seventeen functional traits related to locomotion functions and food purchase 50 groundfish species are studied diversity through various indicators to analyze the impact of fishing.The results show that the intensification of fishing has had significant effects on certain general characteristics of the population in question. Since 1985, we thus observed a drop in the density and the mean trophic level of fish and a turnover of dominance, whereby major species of high commercial value, characterized by substantial body masses and slow growth are gradually replaced by species of smaller sizes at lower commercial value and rapid growth. There is also a significant decrease in functional richness whose evolution confirms the results obtained from the taxonomic assessments and confirms that the coastal ecosystem of the continental shelf is disrupted in connection with fishing pressure
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Bagley, Phil. "Investigations of the behaviour of demersal grenadier fish, Coryphaenoides (Nematonurus) armatus in the abyssal Pacific and Atlantic oceans using an autonomous acoustic tracking vehicle." Thesis, University of Aberdeen, 1993. http://digitool.abdn.ac.uk/R?func=search-advanced-go&find_code1=WSN&request1=AAIU049186.
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The deep-sea has long been perceived as a food limited environment. The recent discovery of seasonal inputs of organic matter into the deep, in areas of the North Pacific and North Atlantic Oceans, has led to questions about the behaviour of deep-sea demersal animals. This thesis describes an autonomous acoustic tracking system (AUDOS: Aberdeen University Deep Ocean Submersible) developed to address the behaviour question; primarily of the demersal grenadier fish, Coryphaenoides (Nematonurus) armatus, but also other shallower living species. Deep-sea acoustic pinger and Code Activated Transponder (CAT) ingestible fish tags, capable of operating at depths of 600m, are described. Deep-sea pingers operated with an early version of AUDOS, returning directional information on fish which ingested tags. The CAT, which is acoustically interrogated by a scanning sonar mounted on AUDOS, returns precise direction and range of individually tagged fish. AUDOS is an autonomous free-fall vehicle incorporating a microprocessor based logging unit which also controls a camera, current meter and compass, enabling several tagged fish to be individually located within a 500m radius. On-board environmental monitoring allows relationships between fish movements and the localised current to be addressed. Three locations were visited during 5 research cruises, Station M (32o50'N, 122o50'W) in the North Pacific Ocean, station MAP (29o30'N, 21o16'W) in the North Atlantic Ocean and the Porcupine Seabight area (51o20'N, 14o0'W) also in the North Atlantic Ocean. Tracking results indicate that C. (N.) armatus adopt an active foraging strategy at each of these stations. Evidence was found for a faster mean swimming speed, for the grenadier, in October (0.0692 m.s-1) compared to February (0.0262 m.s-1) at station M. Fish activity is elevated in October following a seasonal enrichment of the benthos by downward flux of particulate organic matter from the surface. At the Continental slope region of the Porcupine Seabight, the grenadier was found to be moving up the slope rather than directly using the current to forage for food (Station MAP).
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Lelli, Stefano. "Contribution to a better knowledge of biology, distribution and diversity of demersal species along the Lebanese coast, eastern Mediterranean : a focus on Lessepsian fish species." Thesis, Perpignan, 2017. http://www.theses.fr/2017PERP0051.
Full textAbstract:
L’objectif de cette étude était de contribuer à une meilleure connaissance des espèces démersales dans les eaux côtières libanaises en Méditerranée orientale. Différents aspects relatifs à la distribution, la diversité, et la biologie de ces espèces ont été étudiés. Les données ont été collectées à partir de captures expérimentales dans le cadre du projet ‘CIHEAM-PESCA Libano’. Un mélange hautement diversifié d'espèces de poissons (téléostéens et sélaciens), de céphalopodes et de crustacés, ainsi que de organismes macro-benthiques ont été échantillonnés. La distribution spatio-temporelle et la diversité ont été évaluées respectivement à l'aide de la ‘capture par unité d'effort’ qui a été assimilée à un indice d’abondance et du nombre total d'espèces capturées dans les relevés.Des relations longueur-poids ont été établies pour plusieurs espèces présentant un nombre d’individus suffisant. Finalement, l'accent a été porté sur la biologie et l'écologie d'une espèce lesseptienne et exploitée, l’holocentre rouge, Sargocentron rubrum. Cette étude constitue une première étape dans la gestion des pêches et la conservation dans cette régionThe aim of this study was to contribute to a better knowledge of demersal species in the Lebanese coastal waters, Eastern Mediterranean. Various aspect related to the distribution, diversity and biology of these species were studied. The data were collected from a three-year experimental survey in the framework of the ‘CIHEAM-PESCA Libano project’. A highly diversified mix of fish species (teleosteans and selaceans), cephalopods and crustaceans were sampled. Spatio-temporal distribution and diversity was evaluated respectively using the ‘Catch Per Unit Effort’ which was considered as an approximation of an abundance index and the total number of species caught in the surveys
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Watson, Stephen C. L. "The impact of multiple stressors on coastal biodiversity and associated ecosystem services." Thesis, University of St Andrews, 2017. http://hdl.handle.net/10023/16817.
Full textAbstract:
Marine and coastal ecosystems are subject to diverse and increasingly intensive anthropogenic activities, making understanding cumulative effects critically important. However, accurately accounting for the cumulative effects of human impacts can be difficult, with the possibility of multiple stressors interacting and having greater impacts than expected, compounding direct and indirect effects on individuals, populations, communities and ecosystems. Assessment of multiple stressors therefore requires extensive scientific research that directly tests how single or multiple ecological components are affected by stressors, both singly and when combined, and as a consequence, cumulative effects assessments are now increasingly included in environmental assessments. Currently, there is a need to assess these at larger spatial scales, with additional research also urgently needed on the responses of ecological components, processes and functions to single and cumulative stressors. As cumulative environmental impacts could be better addressed by regional stressor effects assessments that combine methods for predicting multiple pressures on ecosystem recovery alongside degradation, this study used several separate approaches that can be used in parallel to give support for local management measures. I tested four completely different methods - a range of multi-metric indices, a food web model (Ecopath), a predictive model (Ecosim) and a Bayesian Belief Network model. Each approach was tested and compared in two shallow water estuarine systems, in Scotland and England, initially concerning the impact of nutrient enrichment and subsequent recovery and was followed by an investigation of how the addition of multiple stressors (nutrient levels, temperature and river-flow rates) would impact the future state of each system. The response to stressors was highly context dependent, varying between and within geographic locations. Overall, each of the four different approaches complemented each other and gave strong support for the need to make big reductions in the pressures and to consider trade-offs between impacting pressures. The models and tools also indicate that in order to reach an improved overall environmental state of each ecosystem, a focus on nutrient reductions are likely to be the most effective of the controls on stressors explored and that cumulative effects of the management of nutrient inputs and increased water temperatures and river-flow are likely to exist.
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Nascimento, Marcela Conceição do [UNESP]. "Alimentação de peixes na plataforma continental externa e talude superior na região sudeste-sul do Brasil." Universidade Estadual Paulista (UNESP), 2006. http://hdl.handle.net/11449/99562.
Full textAbstract:
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Este trabalho tem como propósito indicar a atividade alimentar diária de Antigonia capros, Synagrops spinosus e Urophycis mystacea (Teleostei). Essas espécies apresentam hábitos demersais e são muito freqüentes na plataforma continental externa e talude superior das regiões Sudeste e Sul do Brasil. Para a identificação de padrões de atividade alimentar diária, foram analisados resultados de coletas realizadas em diferentes horários ao longo do dia, agrupados em cinco períodos: amanhecer, manhã, tarde, entardecer e anoitecer. Em cada período foram identificados estômagos em diferentes graus de repleção e de digestão. Após essa análise, foi observado que cada espécie apresentou características específicas na captura de alimento. Nas três espécies foi verificado que houve aumento na atividade alimentar nos períodos do dia com menor intensidade luminosa. Nestes períodos ocorreu maior consumo de animais bentônicos. Constatou-se também que nos horários de maior e menor atividade, houve variação entre o consumo de organismos bentônicos e pelágicos.
The aim of this study was to investigate the daily feeding activity of Antigonia capros, Synagrops spinosus and Urophycis mystacea (Teleostei). These species present demersal behavior and are very frequent in Brazilian South and Southeast outer continental shelf and the continental slope. We carried out collections in different times of the day clustered in five periods: dawn, morning, afternoon, nightfall and night, in order to identify the patterns of daily feeding activity. In each period the different levels of digestion and repletion of the material in the stomachs were identified. Through this analysis we oberved that each species presented specific food capturing characteristics. An increase in the feeding activity was observed in the less lightened periods. In these periods there was higher consumption of benthonic animals. We have also found out a relation between the periods of higher and lower activity and the consumption of benthonic and pelagic organisms.
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Nascimento, Marcela Conceição do 1980. "Alimentação e relações tróficas de peixes demersais marinhos da região Sudeste e Sul do Brasil." [s.n.], 2012. http://repositorio.unicamp.br/jspui/handle/REPOSIP/315788.
Full textAbstract:
Orientadores: Antonia Cecília Zacagnini Amaral, Gonzalo Velasco CanzianiTese (doutorado) - Universidade Estadual de Campinas, Instituto de Biologia
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Resumo: O ambiente marinho apresenta ecossistemas altamente ricos e diversos, entretanto o conhecimento sobre esses ecossistemas e os organismos que neles vivem ainda é muito esparso. Sabe-se que a perda de diversidade nesses sistemas vem crescendo sem ser apropriadamente avaliada. No Brasil, o desnvolvimento de novas fronteiras para a pesca e sua utilização, muitas vezes com pouca regulamentação e/ou fiscalização, tem levado muitos recursos à sobreexplotação. Esta forma de exploração evidencia o uso dos recursos marinhos sem um planejamento adequado. Para que haja tal planejamento, é necessário que se conheçam as vias energéticas e as relações entre os organismos que compõem esse ecossistema. De forma a contribuir para este conhecimento, no presente trabalho foram estudadas a dieta e as relações tróficas de seis espécies de peixes demersais abundantes nas regiões Sudeste e Sul do Brasil: Antigonia capros; Ariomma bondi, Genypterus brasiliensis, Synagrops bellus, Synagrops spinosus e Ventrifossa macropogon. O material provém das coletas do Programa REVIZEE Score-Sul, realizadas entre Cabo Frio (RJ) e Cabo de Santa Marta Grande (SC). Os peixes tiveram a sua dieta analisada por meio do conteúdo estomacal. Além da composição da dieta, foi avaliada a influência da profundidade, do tamanho dos indivíduos, da sazonalidade e do período do dia na obtenção de alimento. Adicionalmente, construiu-se um modelo trófico de balanço de biomassa para avaliar a comunidade demersal da área. Neste estudo foi observado que há um intenso consumo de invertebrados bentônicos, especialmente crustáceos, por todas as espécies, apesar de cada uma apresentar particularidades no comportamento alimentar, como foi constatado nas análises de dieta. Observou-se ainda que as espécies apresentam variações no consumo de alimentos relacionadas à profundidadade, tamanho dos indivíduos e área geográfica onde foram coletadas, e que os fatores que mais causam essas alterações são as variações sazonais. O consumo de invertebrados bentônicos verificado nas análises de dieta e no modelo é maior em espécies de níveis tróficos mais baixos, mas também é significativo em espécies de níveis superiores. Nesta última categoria estão inclusos grandes predadores, como tubarões e atuns, que puderam ser avaliados por meio de dados secundários na construção do modelo. Estes resultados ressaltam a importância da inclusão dos organismos bentônicos nas políticas pesqueiras e planos de manejo, uma vez que se trata de um dos principais pontos de sustentação de todo o ecossistema marinho, sobretudo o demersal
Abstract: The knowledge about marine environments and their rich and diverse ecosystems is improving across the world, but still has gaps, mainly in tropical areas. It is known that the diversity loss is globally increasing without being properly measured. Studies have shown that fisheries are looking for new areas and species aiming to attempt the global fisheries demand. This kind of resource exploitation brings evidence of inadequate fisheries planning. It is necessary the knowledge about the energy pathways and ecosystem relationships to develop appropriate fisheries management for different areas and objectives. Aiming to improve this knowledge and contribute to the appropriate fisheries management, we studied the diet and the trophic relationship of six abundant demersal fishes from Brazilian Southeast and South: Antigonia capros, Ariomma bondi, Genypterus brasiliensis, Synagrops bellus, Synagrops spinosus and Ventrifossa macropogon. The samples were collected during REVIZEE Score-Sul program, between Cabo Frio (RJ) and Cabo de Santa Marta Grande (SC). The fishes were studied based on their gut contents. It was evaluated the diet composition and the influence of depth, season, day time and specimens' size, on food choice. Additionally, we built a trophic model to evaluate the demersal community. We observed intense benthos consumption (especially crustaceans) by all species, despite their specificity. We also observed changes on food consumption according to depth, area and specimen's size, but the main responsible for changes on food consumption are the seasonal variations on the oceanographic dynamics. Benthos consumption is higher in low trophic levels than in high ones, but it is significant in high trophic levels species too, including top predators as sharks and tunas, assessed by secondary data during the model construction. These results show the necessity to include benthos impacts on fisheries management, once they are the main support of the entire marine ecosystem, especially demersal ecosystems
Doutorado
Ecologia
Doutor em Ecologia
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Bosco-Santos, Alice 1987. "Concentrações de elementos químicos em fígado e músculo de peixes demersais do sistema estuarino de Santos-Cubatão (SP) = aspectos temporal e espacial." [s.n.], 2011. http://repositorio.unicamp.br/jspui/handle/REPOSIP/287681.
Full textAbstract:
Orientador: Wanilson Luiz SilvaDissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Geociências
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Resumo: A região de Cubatão (SP) abriga o maior polo industrial da América Latina e nos anos de 1980 ficou internacionalmente conhecida como um dos lugares mais seriamente poluídos do planeta por consequência de atividades industriais que ocasionaram grandes perturbações ambientais locais. Desde então, a contaminação da biota do sistema estuarino de Santos-Cubatão vem sendo monitorada e tem apresentado níveis elevados de elementos químicos nos organismos. Entretanto, ainda não foram realizados estudos que levem em consideração amostragens sazonais, que poderiam refletir as consequências das variações físico-químicas do ambiente na transferência de elementos químicos para a biota. No presente estudo, concentrações de As, Se e metais (Cd, Cr, Cu, Fe, Mn, Ni, Pb e Zn) foram determinadas em tecidos hepático e muscular de quatro espécies de peixes demersais do sistema estuarino em foco. No inverno/2010 e verão/2011, exemplares de Diapterus rhombeus, Genidens genidens, Centropomus parallelus e Mugil Liza foram coletados nos rios Morrão, Casqueiro e Cubatão. As amostras foram liofilizadas e os elementos químicos extraídos por digestão ácida com posterior análise por ICP-MS. Os resultados foram comparados ao LMT (limite máximo de tolerância) determinado pelo Ministério da Saúde do Brasil. Concentrações de As, Cr, Cu, Fe, Mn, Pb, Se e Zn foram, em geral, acima do LMT estabelecido pela legislação brasileira, e o tecido hepático apresentou concentrações químicas muito superiores às registradas no tecido muscular. Mugil Liza foi a espécie que acumulou mais elementos químicos em ambos os tecidos e é a melhor bioindicadora da área de estudo. As associações com o substrato e o hábito alimentar mostraram-se fatores decisivos na absorção de elementos químicos pelos organismos. Variabilidades sazonais foram observadas para as concentrações de Cd, Cr, Cu, Fe, Mn e Zn nos tecidos dos organismos analisados. Apesar de o rio Morrão ser considerado um dos cenários mais impactados do sistema estuarino de Santos-Cubatão, a biodisponibilidade de elementos químicos naquele ambiente não parece diferente de ambientes historicamente menos impactados, como os rios Casqueiro e Cubatão
Abstract: The city of Cubatão (SP) holds the largest industrial center in Latin America. During the 1980s, this region became internationally known as one of the most polluted cities in the world. This was a result of local industrial activities that caused large local environmental disturbances. Since then, biota contamination along the Santos-Cubatão estuarine system has been monitored, and high levels of contamination amongst organisms have been found. Environmental monitoring of the biota, taking into account the importance of seasonal variability, has not been considered. Concentrations of As, Se and metals (Cd, Cr, Cu, Fe, Mn, Ni, Pb, and Zn) were determined in liver and muscle tissue of four species of demersal fishes of the Santos-Cubatão estuarine system. Specimens of Diapterus rhombeus, Genidens genidens, Centropomus parallelus and Mugil Liza were collected in summer and winter, in the Morrão, Casqueiro and Cubatão rivers. The samples were freeze-dried, underwent acid digestion and subsequently were analyzed using an ICP-MS. The results were compared to the LMT (maximum allowable) guidelines determined by the Brazilian Ministry of Health. Concentrations of As, Cr, Cu, Fe, Mn, Pb, Se, and Zn were generally above the LMT, as established by Brazilian legislation. Specific organs were analyzed and compared, for instance, liver tissue had contaminant concentrations much higher than those recorded in the muscle tissue. Mugil Liza was the species that accumulated more chemical elements in both tissues. The association with the substrate and eating habits proved to be decisive factors in the absorption of specific contaminants by the organisms. Seasonal variability was observed for concentrations of Cd, Cr, Cu, Fe, Mn, and Zn in the tissues of organisms analyzed. Although the Morrão river is considered one of the scenarios most impacted of the Santos-Cubatão estuarine system, the bioavailability of specific chemical pollutants in this work does not support this scenario, as indicated by the results found in the less impacted environments, such as Cubatão and Casqueiro rivers
Mestrado
Geologia e Recursos Naturais
Mestre em Geociências
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Tableau, Adrien. "Interactions trophiques au sein des communautés bentho-demersales : Influence de la disponibilité alimentaire sur la capacité d’accueil des nourriceries côtières de juvéniles de poissons." Thesis, Rennes, Agrocampus Ouest, 2015. http://www.theses.fr/2015NSARH095/document.
Full textAbstract:
Les habitats côtiers à fonds meubles sont essentiels dans le cycle de vie de nombreuses espèces de poissons. Ces habitats ont pour caractéristique d’être peu étendus mais sont aussi très productifs et jouent à ce titre un rôle de nourricerie pour les juvéniles de poissons bentho-démersaux. Les fortes abondances de proies semblent être l’une des raisons principales de la présence des juvéniles au sein de ces habitats. Bien que déjà étudié, le caractère limitant de la nourriture disponible fait toujours l’objet de débats dans la communauté scientifique. Une des raisons principales est que l’étude des milieux côtiers est rendue complexe par la diversité des facteurs entrant en jeu dans le développement des jeunes stades de poissons. A partir du cas d’étude de la baie de Vilaine, une des nourriceries les plus productives du golfe de Gascogneles recherches menées dans cette thèse visent à définir le rôle du facteur alimentaire dans l’organisation de la nourricerie et dans sa capacité à soutenir le développement des juvéniles de poissons. Le fil conducteur de cette thèse est donc de déterminer si le facteur alimentaire limite la production de juvéniles. Les résultats montrent une forte exploitation de la production alimentaire ainsi qu'une superposition spatiale entre les densités de juvéniles de poissons et de leurs proies. La cohérence de ces résultats tend à soutenir l'hypothèse que la capacité d'accueil de la baie de Vilaine est atteinte et donc que le facteur alimentaire est limitant. Les implications de ce mécanisme de régulation sur la dynamique des populations nourricerSoft sediment coastal habitats are essential in the life cycle of numerous fishes. These habitats are spatially-limited but very productive, and play a key role of nursery for the juveniles of benthic and demersal fishes. High abundance of prey seems to be one of the main reasons of the presence of juvenile fish within these habitats. Although widely studied, the limiting aspect of the feeding factor is still debated in the scientific community. One of the main reasons is that studying coastalhabitats is complex because numerous factors influence the development of the first life stages of fish. From the study case of the Bay of Vilaine, one of the most productive nurseries of the Bay of Biscay, research conducted in this thesis aims to define the role of the feeding factor in the organisation of the nursery and in its capacity to support the development of juvenile fish. The common thread of this thesis is thus to determine if the feeding factor limits the juvenile fish production. The results show a strong exploitation of the food production by the juvenile fish community and a spatial match between the densities of juvenile fish and their prey. The consistency of these results tends to support that the hypothesis that the carrying capacity of the Bay of Vilaine is reached, and that the feeding factor is limiting. The consequences of this regulation process on the dynamics of nursery-dependent fish populations are discussed
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Ambusaidi, Hilal Saud. "Distribution and assemblages of demersal fish in Oman." Thesis, 1994. http://hdl.handle.net/1957/35315.
Full textAbstract:
The Sultanate of Oman has 1700 km of coastline extending from the Arabian Gulf
south to the Arabian Sea. The demersal fish distributions and assemblages have not previously
been well defined. In winter, variations in the oceanography of the area are minimal. In
summer, however, the Arabian Sea is strongly influenced by the southwest monsoon.
For this study the continental shelf off Oman was divided into eight regional areas and
research trawl data on the distribution of demersal fish assemblages was studied using two
forms of multivariate statistical analysis: two-way indicator species analysis and detrended
correspondence analysis. The study was carried out to examine the influence on the species
assemblages of geographical zonation, seasonal variation, and factors such as depth, time of
day, and distance from untrawlable ground. There was seasonal variation in the fish
assemblages and this variation was greatly influenced by the summer monsoon. Within each
regional area depth appeared to be the major factor determining species distribution.
In addition to the multivariate analyses, univariate techniques were applied to the
catch rate data for forty commercial species to study in detail the influence of time of day and
distance from untrawlable ground, factors which could potentially influence stock assessment
estimates of fish biomass. Because the data were highly unbalanced, they were analyzed using
General Linear Model with five factors, two continuous variables, and ten interaction terms
to examine variation in the log-transformed catch rates. The factors time of day and distance
from untrawlable ground, in combination with other factors, had significant effects on the
catch rates for half of the species.Graduation date: 1995
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Martínez, Murillo María de las Nieves. "Size-based dynamics of a demersal fish community : modeling fish-fisheries interactions /." 2003.
Find full text
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Parra, Hugo Alexandre Esteves. "Habitat predictive modelling of demersal fish species in the Azores." Master's thesis, 2013. http://hdl.handle.net/10400.3/3092.
Full textAbstract:
Dissertação de Mestrado, Estudos Integrados dos Oceanos, 25 de Março de 2013, Universidade dos Açores.Species distribution modelling of the marine environment has been extensively used to assess species–environment relationships to predict fish spatial distributions accurately. In this study we explored the application of two distinct modelling techniques, maximum entropy model (MaxEnt) and generalized linear models (GLMs) for predicting the potential distribution in the Azores economic exclusive zone (EEZ) of four economically important demersal fish species: blackbelly rosefish, Helicolenus dactylopterus dactylopterus, forkbeard, Phycis phycis, wreckfish, Polyprion americanus and offshore rockfish, Pontinus kuhlii. Models were constructed based on 13 years of fish presence/absence data derived from bottom longline surveys performed in the study area combined with high resolution (300 m) topographic and biogeochemical habitat seafloor variables. The most important predictors were depth and slope followed by sediment type, oxygen saturation and salinity, with relative contributions being similar among species. GLMs provided ‘outstanding’ model predictions (AUC>0.9) for two of the four fish species while MaxEnt provided ‘excellent’ model predictions (AUC=0.8–0.9) for three of four species. The level of agreement between observed and predicted presence/absence sites for both modelling techniques was ‘moderate’ (K=0.4–0.6) for three of the four species with P. americanus models presenting the lowest level of agreement (K<0.1). For the scope of this study, both modelling approaches presented here were determined to produce viable presence/absence maps which represent a snap–shot of the potential distributions of the investigated species. This information provides a better description of demersal fish spatial ecology and can be of a great deal of interest for future fisheries management and conservation planning.
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Chiu, Yu-Ting, and 邱鈺婷. "Assemblage Composition of Demersal Fish in the East China Sea in summer 2009 to 2011." Thesis, 2013. http://ndltd.ncl.edu.tw/handle/29185396599357138124.
Full textAbstract:
碩士國立臺灣大學
海洋研究所
101
The East China Sea (ECS) possess extensive continental shelf and fishing grounds in eastern Asia. The seasonal monsoon caused some variations of water currents succession and complicated climatic condition. Input of fresh water from Changjiang (CJ) attribute to nutrient-rich condition at the adjacent areas of the estuary. In this research, oceanographic survey was conducted across the inshore-offshore transects to collect all of the environmental factor and demersal fish samples. The increasing of fresh water input, due to the Changjiang flood in 2010, which may affect the marine ecosystem was evaluated in this study. Totally, 7992 demersal fish including 126 species were collected in Cr. 905, Cr. 932 and Cr. 966. The demersal fish species composition of each station was examined. The highest similarities for CLUSTER and nMDS similarity were found in the same station among the years. Dissolved oxygen at the bottom is positively correlated to the surface salinity, but negatively correlated to nitrate and chlorophyll a concentration. Fish species composition varied greatly between each station, especially inshore and offshore sites. This result implied that the fish communities were influenced by ecosystem heterogeneity and the environmental conditions. Higher diversity appeared at offshore sites that have higher dissolved oxygen and diverse habitats. The effects of anthropogenic activities to the ECS ecosystem needed a long-term observation.
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N'Singi, Kumbi Kilongo. "Some aspects of the biology and fishery of two deep-water demersal fish off Angola." Doctoral thesis, 2012. http://hdl.handle.net/10400.1/11062.
Full textAbstract:
O sistema marinho de Angola é caracterizado pela presença de dois sistemas oceanográficos
bem distintos, o sistema da corrente quente de Angola a norte e o da corrente fria de Benguela
a sul. As espécies Dentex macrophtalmus e Merluccius polli são duas das principais espécies
de peixes na pescaria demersal industrial de Angola. No entanto, estas espécies são parte de
uma pescaria multi-específica, pelo que é importante conhecer, para a sua gestão, a sua
associação com outras espécies, comerciais e não-comerciais, e os padrões da sua distribuição.
Neste estudo investigaram-se os padrões na distribuição e dieta destas duas espécies, a partir
de informação recolhida durante os cruzeiros de investigação anuais realizados em Angola desde 1994.
A distribuição de M. polli é em geral mais profunda que a de D. macrophtalmus, mas ambas as espécies são mais abundantes na plataforma inferior e talude superior, e ambas realizam migrações ontogenéticas, sendo que os indivíduos de maior tamanho são em geral encontrados em zonas mais profundas que os juvenis. Além disso, ambas as espécies são mais abundantes na zona entre Benguela e o Namibe, e observam-se concentrações elevadas de juvenis na zona da Frente Angola-Benguela.
No que se refere à dieta, observou-se que ambas as espécies mudam a sua dieta com o crescimento, e que tanto uma como a outra são preferencialmente piscívoras, sendo que as espécies da família Myctophidae são as mais representadas nos conteúdos estomacais analisados. Observaram-se ainda diferenças apreciáveis na dieta com a área de captura, indicando uma estratégia de alimentação oportunista.
Em geral, os resultados deste estudo deverão contribuir para melhorar a gestão das pescarias de Angola, sobretudo no sector industrial, permitindo uma gestão mais integrada dos diferentes mananciais explorados.
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Sargent, Philip S. "The effects of increasing habitat complexity with artificial reefs on demersal fish density in coastal Newfoundland Waters /." 2002.
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Fang, Pin-Ren, and 方品仁. "Spatial and temporal variations of demersal fish assemblages in the East China Sea in 2010 to 2012." Thesis, 2015. http://ndltd.ncl.edu.tw/handle/87772625336075996366.
Full textAbstract:
碩士國立臺灣大學
漁業科學研究所
103
In order to understand the demersal fish assemblages and its link to the environments, beam trawl surveys and hydrographic measurements were conducted across the East China Sea continental shelf in 2010 - 2012. The results suggested that the fish assemblages varied with the depth and salinity gradients with significant difference in composition between inshore and offshore areas. Water temperature might be an important factor in shaping the spatial pattern during spring and autumn periods. Bio-indices (e.g. diversity, richness and evenness) showed negative correlations with Chl. a concentrations and nutrients levels and positively correlated with dissolved oxygen. The eutrophication and subsequent hypoxia in the inshore area during summer periods favored the high dominance of opportunistic species (Amblychaeturichthys hexanema). These results suggested the negative impacts of eutrophication and hypoxia on the demersal fish assemblages. Seasonal changes of fish compositions were only found in the inshore area, which may attribute to the succession of dominant species. In addition, we found moderate recovery of fish communities after summer hypoxia but the short-periods of alleviation from stressful condition might not be adequate to compensate the simplified assemblages during hypoxia. Despite the variation of primary productions in different seasons, d13C value of fish muscle suggested that in situ primary production was the main food sources to the demersal fish rather than the terrestrial POM. d15N of demersal fish were higher in autumn than in summer, which might attribute to the preferential uptake of isotopic lighter N source or the shift in baseline rather than elongation of food chain. Our results provided further insights into the demersal fish assemblages in the ECS, and the influences of environmental parameters on fish compositions.
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Chang, Ni-Na, and 張妮娜. "Relationship between environmental conditions and assemblage structures of demersal fish in the East China Sea: impacts of eutrophication." Thesis, 2013. http://ndltd.ncl.edu.tw/handle/38933739666629107208.
Full textAbstract:
博士國立臺灣大學
海洋研究所
101
The East China Sea (ECS) received large quantities of freshwater, nutrients, and organic matters from the adjacent Changjiang and experienced severe eutrophication and hypoxia in recent decades. Frequent flood events related to climate change may further magnify the impacts of land-based materials on the ECS. Nevertheless, the basic knowledge about response of ECS benthic organisms to these disturbances remain poorly understood. Risk and benefit assessments of flood-induced high primary production and riverborne POM are also scarce. The present study aimed to recognize the links between demersal fish assemblage structures and environmental characteristics across the ECS. Also, we assess the balance between food source contribution and hypoxia risk caused by the increased primary production by analyzing fish community structures and stable isotope compositions for zooplankton, crustaceans and demersal fish. The inshore area of ECS, corresponding to the trawling-prohibited zone, was prone to low DO condition and hypoxia. Biological indices, including species richness and diversity exhibited significantly negative correlations with nutrient concentrations and positive correlations with bottom-water dissolved oxygen, indicating the negative impacts of eutrophication and accompanied hypoxia on the inshore fish assemblages. This area was also heavily dominated by the opportunistic fish Gobiids— Amblychaeturichthys hexanema, reflecting low survival rate of most fishes over there. Thus, the efficacy of inshore trawling-prohibition practice, which intended to restore the ECS fish stocks, was probably very limited. The stable isotope analyses indicated great reliance of benthic organisms on the marine productions regardless of distance from shore. Relatively higher δ13C of demersal fish and crustaceans in the inner shelf implied their uptake of marine blooming materials. Conversely, terrestrial POM plays minor role in nourishing the benthic consumers in the ECS. The Changjiang flood event in 2010 further enhanced the hypoxia formation and resulted in the lowest fish diversity in the inner shelf. Yet fish assemblages inhabited the normoxic mid to outer shelf demonstrated positive response to the Changjiang flood event. Therefore, the Changjiang River discharge only benefits the ECS benthic ecosystem on condition that the bottom waters maintain higher levels of DO.
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陳怡伶. "Exploitation and management of demersal fish resources in waters off Guei-Shan Island, northeastern Taiwan: a biological perspective." Thesis, 2009. http://ndltd.ncl.edu.tw/handle/88952627233843915931.
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Chang, Ni-Na, and 張妮娜. "Biodiversity and Biological-Environmental Relationships of the Demersal Fish Assemblage in the East China Sea in 2008 Summer." Thesis, 2009. http://ndltd.ncl.edu.tw/handle/72556078137095833182.
Full textAbstract:
碩士國立臺灣大學
海洋研究所
97
The East China Sea (ECS) was characterized by nutrient-rich condition, high primary productivity and high fishery yield, due to the massive input of nutrient from Changjiang (CJ). However, the anthropogenic nutrient load from CJ has increased over 10-fold since 1960’s, and caused frequent eutrophication and hypoxia events. In addition, construction of Three Gorges Dam has been proved to reduce the nutrients discharge. The effects of present nutrient status on the benthos assemblage were still obscure. Nevertheless, we presume that the nutrient status in the ECS is still excessive, and may injure the benthos communities in the ECS. To verify our assumption, oceanographic survey was conducted across the inshore-offshore transects. Totally 3935 dermal fish including 71 species were collected by the beam trawl. Fish species composition varied greatly between northern and southern sites as well as between inshore and offshore sites. Higher diversity appeared at offshore sites and lowest diversity occurred at the inshore site close to Changjiang Estuary. The fish community structure among each site was related to depth, latitude, dissolved oxygen, PO4 and NO2. Besides, the fish species diversity is significantly positive correlated to dissolved oxygen and negative to concentrations of various nutrients and chlorophyll a. This result implied that the fish communities were not only determined by specific biogeographic distribution, but also by the nutrients and hypoxia conditions. In conclusion, the nutrient status in the ECS is still redundant, and its follow up consequences, including organic matters accumulation and benthic hypoxia have negatively impacted the community of demersal fish.
46
Jamir, Tomas Vergel C. "Distribution, seasonal variation and community structure of the demersal trawl fauna of Ragay Gulf, Philippines." Thesis, 1998. http://hdl.handle.net/1957/27783.
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47
Chen, Yu-Sheng, and 陳育生. "The diversity and assemblage of demersal fish, and reproductive, condition and feeding cycles of the dominant species in surrounding waters of theThree Northern Isles, Taiwan." Thesis, 2016. http://ndltd.ncl.edu.tw/handle/f7nm6t.
Full textAbstract:
碩士國立臺灣海洋大學
海洋事務與資源管理研究所
104
The diversity and assemblage of demersal fish, as well as spawning, condition and feeding cycles of the dominant fish species were examined using bi-weekly or monthly samplings and daily catch records from small bottom trawlers operate in surroundings waters of the Three Northern Isles, Taiwan between Nov. 2012 and Dec. 2015. Results indicated that bycatch (both in number and weight) from these vessels was on average, about 50% of the total. These bycatches included ~20-30% (in number), and more than 50% (in weight) of economical important fish species. The species richness, evenness and diversity were higher both for economically important and bycatch species from end of summer to fall or early winter period (i.e., Sept.-Dec or Sept.-Jan.), while they were lower between end of spring to summer period. The percentage of juvenile bycatch also was higher between end of summer to winter, and lower during the spring, which was opposite with that seen in adult fish. Two fish assemblages been identified were roughly corresponding to cooler (i.e., Sept.-Mar.), and warmer (i.e., Jun.-Aug.) seasons for both economic and bycatch species, and these assemblages were not structured by habitat types or water depths. The spawning season of most fish species occurred in the spring and summer. Most fishes also showed high feeding activity during summer-fall period, and reached highest condition factor in the fall, with a second in summer. The optimum exploitation and management strategies including implementation of close season during the spring and summer to protect spawner, and explore the resources with additional mesh size limitations during the fall when most fishes were plump, and juvenile fishes were abundant, are then suggested accordingly to ensure the sustainable use of the demersal fishery resources of the region.