Dissertations / Theses on the topic 'Demersal specie'
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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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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.
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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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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.
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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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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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Guerra, Alessandro. "Estimates of length-at-50% maturity of two South African demersal species: Monkfish, Lophius vomerinus, and Kingklip, Genypterus capensis." Master's thesis, Faculty of Science, 2019. http://hdl.handle.net/11427/31570.
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Long-lived and slow-growing fish species are especially vulnerable to overfishing. Deep-sea species are elusive and difficult to study, making their management challenging. South African monkfish, Lophius vomerinus, and kingklip, Genypterus capensis, are two demersal species living off the west and south coast of South Africa. These species are exploited as bycatch in the Hake fisheries, and represent an important resource for the fishery. However, reproductive information is scarce, and key life-history parameters have not been updated in recent years. Length-at-50% maturity (L50) is a fundamental biological parameter to monitor stock-health, spawning potential and improve fishery management. This research was focused on computing L50 estimates for both species, separated by sex and coast. As the stock structure for both species is still under debate, reproductive information and L50 estimates were compared between west and south coast. In addition, L50 was compared with previous studies to detect significant differences or changes over time. Demersal survey samples were used. Individuals were classed a 5 stage maturity scale and consequently referred to as mature or immature. For L. vomerinus, a significant difference in L50 between sexes was found, in contrast with previous findings in literature. However, no significant difference between the two areas was reported, corroborating the one-stock hypothesis. Furthermore, I speculate that L. vomerinus aggregate for spawning activities. The analysis of G. capensis revealed differences between coasts, reinforcing the theory of multiple South African stocks. Most importantly, the results showed a critical reduction in females L50 from previous studies. This reduction is believed to be a consequence of excessive fishing pressure exerted particularly during the latter half of the 20th century, which overexploited immature females on the west coast and main female spawners on the south coast. Further research needs to be done to verify these findings and the stock structure of the populations.
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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.
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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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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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Mafunda, Patrick Siyambulela. "Aspects of the reproduction of male and female African penguins (Spheniscus demersus) with special reference to sperm biology and cryopreservation." University of the Western Cape, 2018. http://hdl.handle.net/11394/6551.
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Philosophiae Doctor - PhDIn the marine environment, penguins have been described as curators and serve a critical role in ecological balance. The African penguin (Spheniscus demersus) has undergone a rapid population decline, mainly due to disturbances in their natural habitat. The African penguin was up-listed from vulnerable to endangered on the IUCN Red List for Threatened Species in 2010 and thus urgent conservation action is required. Integral to long-term conservation action of any species is a basic knowledge of its reproductive biology, which is currently lacking for African penguins. The main aim of this investigation was to evaluate techniques for the collection of semen in African penguin and to determine sperm quality in order to cryopreserve sperm for in vitro fertilization (IVF) purposes of captive and wild populations. Semen was collected once a week during two breeding seasons from two captive African penguins. Ejaculates (n=51) were obtained over two breeding seasons (Jan-Feb and Jun-Oct) and evaluated for semen volume, sperm concentration, sperm vitality, sperm motility and sperm morphology. In addition twelve (six females and six males, n=4 were breeding pairs) captive African penguins were monitored for hormone (estradiol, testosterone, progesterone) levels prior to and after the egg-laying period.
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Giliberto, Irene. "Implementazione di un sistema per la classificazione di banchi di pesce da dati di acustica." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2014. http://amslaurea.unibo.it/6484/.
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La tesi è finalizzata ad una preliminare fase di sperimentazione di un algoritmo che, a partire da dati di acustica, sia in grado di classificare le specie di pesce presenti in cale mono e plurispecifiche. I dati sono stati acquisiti nella fascia costiera della Sicilia meridionale, durante alcune campagne di ricerca effettuate tra il 2002 e il 2011, dall’IAMC – CNR di Capo Granitola.
Sono stati registrati i valori delle variabili ambientali e biotiche tramite metodologia acustica e della composizione dei banchi di pesci catturati tramite cale sperimentali: acciughe, sardine, suri, altre specie pelagiche e pesci demersali.
La metodologia proposta per la classificazione dei segnali acustici nasce dalla fusione di logica fuzzy e teorema di Bayes, per dar luogo ad un approccio modellistico consistente in un compilatore naïve Bayes operante in ambiente fuzzy. Nella fattispecie si è proceduto alla fase di training del classificatore, mediante un learning sample di percentuali delle categorie ittiche sopra menzionate, e ai dati di alcune delle osservazioni acustiche, biotiche e abiotiche, rilevate dall’echosurvey sugli stessi banchi. La validazione del classificatore è stata effettuata sul test set, ossia sui dati che non erano stati scelti per la fase di training. Per ciascuna cala, sono stati infine tracciati dei grafici di dispersione/correlazione dei gruppi ittici e le percentuali simulate. Come misura di corrispondenza dei dati sono stati considerati i valori di regressione R2 tra le percentuali reali e quelle calcolate dal classificatore fuzzy naïve Bayes. Questi, risultando molto alti (0,9134-0,99667), validavano il risultato del classificatore che discriminava con accuratezza le ecotracce provenienti dai banchi.
L’applicabilità del classificatore va comunque testata e verificata oltre i limiti imposti da un lavoro di tesi; in particolare la fase di test va riferita a specie diverse, a condizioni ambientali al contorno differenti da quelle riscontrate e all’utilizzo di learning sample meno estesi.
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King, Nicola Jane. "Deep-sea demersal ichthyofauna of contrasting localities - Mid-Atlantic Ridge, Nazaré Canyon (North Atlantic Ocean) and Crozet Plateau (Southern Indian Ocean) - with special references to the abyssal grenadier, Coryphaenoides (Nematonurus) armatus (Hector, 1875)." Thesis, University of Aberdeen, 2006. http://digitool.abdn.ac.uk/R?func=search-advanced-go&find_code1=WSN&request1=AAIU602325.
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The first observations of deep-demersal scavenging fishes are presented from three regions of the world’s oceans with contrasting overlying productivity: the Mid-Atlantic Ridge (MAR) and Nazaré Canyon, Northeast Atlantic Ocean, and the Crozet Plateau, Southern Indian Ocean. The MAR is the most significant topographic feature of the North Atlantic Ocean and is under the influence of a sub-polar front with increased productivity to the north. Twenty-two taxa were photographed at bait; 14 at 42°N and 17 over two transects at 51 and 53°N respectively. Decreases in biodiversity across the 51°N transect compared to the 42 and 53°N transects, support the hypothesis that 48°N - 52°N is a region of faunal change in demersal fish assemblages in the North Atlantic Ocean. The Nazaré Canyon is a large submarine canyon intersecting the Iberian continental margin which received high levels of organic matter from local upwelling and terrigenous sources. Nine fish species were photographed at the baited ROBIO lander at all depths within the canyon. It is hypothesised that the increased organic input positively influences benthic food supply within the canyon, supporting elevated populations of scavenging fauna. The Crozet Plateau is situated in the southern reaches of the Indian Ocean, where the abyssal seafloor (ca. 4200 m) received differing levels of surface-derived organic enrichment. Demersal ichthyofaunal biodiversity, abundance and biomass were sampled by a trawl at a eutrophic site (M5) and oligotrophic site (M6). Demersal fish species richness, abundance and biomass were greater at M5 compared to M6, and dominated by Macrouridae. However, overall results were not significant, leading to the conclusion that the rattail fishes are transient between sites. Six species new to science were collected and are described herein (one Ophidiid, three Liparidae and two Zoarcidae), as well as several other rare specimens of Ophidiid and Zoarcid.
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Guijarro, González Beatriz. "Population dynamics and assessment of exploited deep water decapods of Balearic Islands (western Mediterranean): from single to multi-species approach." Doctoral thesis, Universitat de les Illes Balears, 2012. http://hdl.handle.net/10803/97300.
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In the western Mediterranean, deep water decapod crustaceans form a considerable fraction of the megafaunal biomass in the upper and middle slope, being a very important component of the catches of the commercial fishery. The main objective of this thesis is to analyse the community and population dynamics of the deep water decapod crustaceans off the Balearic Islands. Data have been obtained from scientific surveys, from the fishing sector and from selectivity pilot studies. Univariate and multivariate techniques have been used to analyse the data. The knowledge derived from this thesis provide relevant information about how the species traits are mainly affected by water masses, sediment characteristic, trophic resources and fishing, since they influence the bathymetric distribution, abundances, biological parameters and condition of decapod crustaceans at a local scale. This knowledge is a key point for a better assessment of the resources and for a better application of the Ecosystem-Based Approach Management in the Mediterranean deep water ecosystems
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Morfin, Marie. "Dynamiques spatio-temporelles d'espèces démersales clés du golfe du Lion : bénéfices potentiels d’aires marines protégées." Thesis, Montpellier 2, 2013. http://www.theses.fr/2013MON20158.
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Les espèces démersales représentent 50% des captures des pêcheries françaises du golfe du Lion, dont la plupart sont pleinement exploitées, voir surexploitées depuis plusieurs décennies. Cette thèse évalue la pertinence d'aires marines protégées (AMPs) comme outil de gestion et de conservation de ces populations. Jusqu'à présent de telles zones ont été uniquement mises en place le long des côtes pour protéger des espèces très peu mobiles. Le problème est plus complexe pour les espèces vivant en haute mer car leur habitat est plus large et plus diffus. Pour ce faire, la distribution spatiale de 12 espèces démersales exploitées clés ont été étudiées de 1994 à 2010, à l'aide d'observations scientifiques et d'outils statistiques ad hoc. Une approche géostatistique a permis de détecter des structures d'auto-corrélation spatiale pour l'ensemble des espèces, et de produire des cartes de distributions annuelles de chaque espèce. Ces distributions sont apparues très stables sur les dix-sept années, mis à part un phénomène d'expansion/ rétraction avec le niveau d'abondance totale sur la région. Par ailleurs une approche par modèle linéaire généralisé a révélé des associations importantes de ces espèces à un habitat stable dans le temps. Ces résultats sont en accord avec la théorie du bassin de MacCall selon laquelle l'association d'une espèce à un habitat est densité-dépendant, et l'augmentation de la densité d'individus dans une zone serait à l'origine de la colonisation d'habitats sub-optimaux. Protéger l'habitat optimal d'une espèce permettrait alors de constituer un habitat «source», si la zone est judicieusement choisie ; en effet le report de l'effort de pêche à l'extérieur de l'AMP peut au contraire rendre cette mesure inefficace voir délétère. Par ailleurs les populations adultes occupaient généralement des zones plus concentrées et incluses dans l'aire de répartition des juvéniles. Ces zones communes d'habitats essentiels (reproduction et nourriceries) peuvent être potentiellement intéressantes à protéger dans un cadre monospécifique. L'hétérogénéité observée des répartitions d'une espèce à l'autre implique l'instauration de zones très clairsemées, et rend la gestion difficile dans une cadre pluri-spécifique. Une zone de taille raisonnable a tout de même été identifiée, représentant 20% de la population de chaque espèce et représentative de la diversité des habitats de cette régionDemersal species represent 50% of French fisheries catches in theGulf of Lions, most of which are fully exploited, or overfished for decades. This thesis evaluates the relevance of marine protected areas (MPAs) as a tool for conservation and management of these populations. So far these areas have been implemented only along the coast to protect the very few mobile species. The problem is more complex for deep sea species because their habitat is broader and more diffuse. To do this, the spatial distribution of 12 key demersal species exploited were studied from 1994 to 2010, with scientific observations and ad hoc statistical tools. A geostatistical approach allowed to detect spatial autocorrelation structures for all species, and produce maps of annual distributions of each species. These distributions appeared very stable over 17 years, apart from a phenomenon of expansion/ contraction with the level of total abundance in the region. In addition, a generalized linear model approach revealed significant associations of these species to a temporally stable habitat. These results are consistent with MacCall basin theory, according which habitat suitability is a density-dependent thus the increase of individuals in an area make them colonize sub-optimal habitats. An optimal habitat under protection could thus be "source" habitat, if the area is carefully chosen. Indeed reporting the fishing effort outside the MPA can instead make this measure ineffective or deleterious. The adult population were generally in more concentrated areas and included in the spatial range of juveniles. These common areas of essential habitat (breeding and nursery) may be potentially interesting to protect a single species . However, the heterogeneity of distributions of a species to another involves the introduction of very sparse areas, making the management difficult. However an area of reasonable size has been identified, covering 20% of the population of each species and representative of the diversity of bottom habitats in the region
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Kide, Saïkou Oumar. "Analyse de la diversité et de la structuration spatio-temporelle des assemblages démersaux dans la zone économique exclusive mauritanienne." Thesis, Aix-Marseille, 2018. http://www.theses.fr/2018AIXM0085/document.
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La zone économique exclusive Mauritanienne est le siège d’upwelling et constitue une zone de transition où cohabitent des espèces d’affinités tempérée et tropicale. Pour comprendre le comportement spatio-temporel des assemblages démersaux du point de vue de leur composition, structuration, distribution de probabilité et diversité face aux préoccupations écologiques. Les facteurs abiotiques contribuent à la structuration des assemblages démersaux persistants au cours du temps. Les effets de la pêche étaient relativement faibles. Les trajectoires temporelles entre les assemblages et les conditions environnementales ont été mises en évidence pour certaines années et des zones. Dans les types d’habitats, un groupe minoritaire d’espèces très agrégatives obéissant au modèle de distribution en log-séries de Fisher et un autre majoritaire peu ou pas du tout agrégatives obéissant au modèle de distribution binomiale négative tronquée ont été identifiés. La diversité spécifique peut être divisé en deux groupes distincts et complémentaires : la richesse spécifique et l'autre associé à l’équitabilité. Un seul composant de la diversité ne peut donc pas représenter la diversité des poissons démersaux de la zone étudiée. Les GLM des indices complémentaires ont montré essentiellement un effet temporel et l’interaction Année-Strates bathymétriques. Aucun effet de l’effort de pêche n’a été observé sur la richesse spécifique, ni de la concentration en chlorophylle sur l’équitabilité. Ce travail pourrait fournir aux gestionnaires et aux scientifiques des connaissances complémentaires sur la dynamique spatio-temporelle des assemblages démersaux exploités dans des écosystèmes d’upwellingThe Mauritanian exclusive economic zone is the seat of an upwelling phenomenon and constitutes a transition zone where species of temperate and tropical affinities coexist. To understand the spatio-temporal behavior of demersal assemblages from the point of view of their composition, structure, distribution of probability and diversity faced to ecological concerns. Abiotic factors contribute in the structuring of persistent groundfish assemblages over time. The fishing effects were relatively low, although significant in some years and in some specific geographic areas. Temporal trajectories between groundfish assemblages and environmental conditions have been highlighted for some years and in some specific areas. In each type habitats, two species groups were identified: a minority group of species very aggregative well fitted by Fisher’s log-series distribution and another majority of species little or not aggregative well fitted by the truncated negative binomial distribution. Diversity indices analyzed reveal that this set can be split into two distinct and complementary groups: a group associated with the species richness and another group associated with evenness. One component of diversity may not represent the diversity of the groundfish in the study area. GLMs of complementary indices showed essentially a temporal effect and Bathymetric strata-Year interaction. No effect of fishing effort was observed on the species richness and neither was the concentration of chlorophyll a on the evenness. This work could provide managers and scientists to further knowledge on the spatio-temporal dynamics of groundfish species assemblages exploited in upwelling ecosystems
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CRISCOLI, ALESSANDRO. "Distribuzione spaziale di giovanili di specie ittiche di interesse commerciale." Doctoral thesis, 2008. http://hdl.handle.net/11573/392174.
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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.
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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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Novaglio, C. "Evaluating baseline conditions and resulting changes in demersal fish communities of South East Australia." Thesis, 2016. https://eprints.utas.edu.au/23119/1/Novaglio_whole_thesis.pdf.
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Knowledge of the full extent and severity of ecological changes in human-influenced
ecological systems is needed to identify today’s management priorities and to set
realistic restoration objectives for the future. However, reconstructing ecosystem
baselines and understanding the causes and rates of ecological changes is often
hampered by the scarcity of data about population and community status before
exploitation, and by the challenges of fitting these (historical) data into modern
analytical methods.
This study aimed to identify the main sources of fishing impacts on marine
communities of South East Australia and to gather and examine historical data
available for the region that can provide information on baseline (pre-fishing)
conditions to compare changes in fish communities as the fishing industry developed.
South East Australia provides an ideal case study as its history of exploitation is
relatively recent and there were surveys undertaken prior to exploitation.
While a range of commercial fisheries have evolved in South East Australia since
European colonization, during the last century bottom trawling has been the major
fishing activity in the region. Bottom trawl surveys that included information on
demersal species abundance and community structure were carried out both before
and at different stages since trawling exploitation begun, and thus provide insights
into the full extent of fishing impacts on South East Australian demersal fish
communities.
These surveys, covering the period 1898-1997, were performed by various research
agencies, which collected and organized catch and effort data in different formats Additionally, the detail of the information reported changes across surveys and over
the years. Hence, the initial need was to collect, digitalize and standardize all the
information available. The bottom trawl survey dataset resulting from this step
contained a total of 3,083 tows sampling 574 species among chondrichthyes and
osteichthyes. It spans the entire history of trawling exploitation and is analyzed in this
study as an entire dataset for the first time.
A comparison of pre- with post-trawling exploitation data (1898-1910 and 1980s-
2010s, respectively) revealed marked changes in the structure of demersal fish
communities of South East Australia. These included shifts in the catch composition
of the main families, as well as sharp declines in the total and individual family catch
rate, most likely related to the effect of fishing. Among the steepest declines were
those of key commercial families, such as flatheads and morwongs, on the continental
shelf of Tasmania.
The effect of trawling on demersal fish communities of South East Australia was also
revealed by the application of species accumulation curves to the survey dataset.
Specifically, the rate of species accumulation with area decreased as trawling
intensity increased, suggesting that trawling modified community structure through
the removal of particular species and through changes in the abundance and spatial
distribution of the remaining species.
This study’s findings have direct application to management and monitoring of the
natural resources in South East Australia, and important implications for sustainable
use and conservation prioritization. The study also provides a framework and
approach that can be of guidance for the collection, standardization and analysis of
analogous, patchy, unbalanced and overlooked historical datasets around the world.
19
Canha, Ângela Maria Lourenço. "Caracterização das rejeições na pescaria de demersais nos Açores." Master's thesis, 2014. http://hdl.handle.net/10400.3/3102.
Full textAbstract:
Dissertação de Mestrado, Estudos Integrados dos Oceanos, 26 de Fevereiro de 2014, Universidade dos Açores.Desde 2004 que o Departamento de Oceanografia e Pescas da Universidade dos Açores é a instituição responsável pela implementação na Região Autónoma dos Açores de um programa de observação das rejeições da pesca comercial nas pescarias de palangre de fundo. Foram amostradas as rejeições de todas as espécies demersais de acordo com um esquema de amostragem aleatório estratificado baseado na arte de pesca e segmento de frota. O objectivo deste trabalho é caracterizar as rejeições em termos de composição específica, quantificar em número e em peso as taxas de rejeição observadas e estimar a rejeição para o total da frota de pesca de demersais com palangre de fundo. As rejeições observadas foram ampliadas por viagem para cada segmento de frota e para cada ano através de dois métodos diferentes: pela teoria da amostragem e considerando que o volume de rejeições é proporcional a uma variável auxiliar. No total, 275 viagens e 993 lances foram amostrados totalizando 1209 dias de mar. A amostra representa entre 0,5% em 2006 e 1,3% em 2007 de cobertura das viagens. Foram rejeitados em média, 117 ± 8.8 kg de pescado por viagem enquanto por lance foram rejeitados em média 32.4 ± 1.3 kg de pescado. Neste estudo foram identificadas 107 espécies diferentes das quais 94 espécies rejeitadas. As espécies que mais contribuíram para as rejeições em número foram o Helicolenus dactylopterus, Etmopterus spinax e o Beryx splendens. A variável auxiliar viagens estimou rejeições anuais que variaram entre 363 t em 2006 (CV = 38.3%) e 665 t em 2010 (CV = 21.8%). A utilização das descargas nas estimativas produziu valores de rejeição que oscilaram entre as 163 t em 2009 (CV = 40.7%) e 249 t em 2007 (CV = 26.7%). Se a variável auxiliar for o esforço (número de anzóis), os resultados variaram entre as 750 t em 2009 (CV = 7.1%) e as 1345 t em 2011 (CV = 3.8%) de pescado rejeitado. Este trabalho contribui com as primeiras estimativas de rejeições para a pescaria de demersais com palangre de fundo.
ABSTRACT: Since 2004, the Department of Oceanography and Fisheries from the University of the Azores began to implement a fisheries observer monitoring program for discards in set longline. Discards from all demersal species were analysed using a stratified sampling scheme based on fishing gear and fleet segmentation. The main goal of this study is to characterize the species composition of discards, quantify in number and weight discards rates and estimate discards for the all set logline fleet. Monitored discards were raised by trip for each fleet segment and year using two methods: sample mean ratio and ratio estimator through two different auxiliary variables. Overall, 275 fishing trips and 993 sets were sampled totaling 1209 days at sea. Sampling coverage represented between 0.5% in 2006 and 1.3% in 2007 of fishing trips. On average 117 ± 8.8 kg of fish by trip were discarded while 32.4 ± 1.3 kg of fish were discarded by set. In this study, 107 species were identified of which 94 were discarded. Helicolenus dactylopterus, Etmopterus spinax and Beryx splendens were the species that contributed the most to discards. Estimates of annual discards based on trips ranged from 363 t in 2006 (CV = 38.3%) and 665 t in 2010 (CV = 21.8%), while estimates based on landings varied from 163 t in 2009 (CV = 40.7%) and 249 t in 2007 (CV = 26.7%). Estimates of discards based on effort (number of hooks) ranged between 750 t in 2009 (CV = 7.1%) and 1345 t in 2011 (CV = 3.8%). This work contributed with the first estimates of discards for the demersal set longline fishery in Azores.
20
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
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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.