Dissertations / Theses on the topic 'Demersal Fisheries'

A problem commonly encountered in stock assessments of tropical marine resources in developing countries is data paucity, which invariably results from the lack of both human and economic capacity within the government to implement and maintain programmes for data collection and analysis. With special reference to the demersal fishery of Brunei Darussalam, this thesis examines approaches for extracting useful information from data-poor fisheries to assess the state of resources and inform fishery management actions. By using official fishery statistics, augmented by local ecological knowledge (LEK) obtained from fishers engaged in either the large-scale (LS) or small-scale (SS) fisheries in Brunei, changes in demersal fishery resources over the years were assessed. The sustainability of Brunei’s demersal capture fishery was evaluated in the face of its ongoing development and climate change. Using trophodynamic indicators such as mean trophic level (MTL), Fishing-in- Balance (FiB), trophic spectra (TS) and community structure analyses, LS fishery catches of Brunei between 2000 and 2009 revealed a deteriorating state of the coastal demersal ecosystem. Closer examination of the abundance of overall demersal finfish stocks, using the Catch-Per-Unit-Effort (CPUE) index – standardised for other factors not related to abundance – indicated a declining trend, even when total catches remained stationary, although trends in abundance of the different demersal fish families varied. This rapid significant change in recent years is further supported by fishers’ LEK on relative abundance of Brunei marine resources. The study on LEK has also revealed the ‘shifting baseline syndrome’ (SBS) among currently active fishers and their exploited populations, a phenomenon not previously reported for Brunei fisheries. Findings from the study are synthesised with other information, where a number of key issues and policy options are discussed, and recommendations for the management of the fishery are made. This thesis demonstrates that researchers in data-poor fisheries can utilise different assessment tools, given the resources at their disposal, to assist in the management of marine resources.

Includes bibliographical references.
Seabird bycatch in commercial fisheries is one of the major factors causing decreases in many seabird populations. In trawl fisheries, high mortalities have been recorded as a result of seabirds being struck by trawl warps (the cables used to tow the trawl net). Tori (bird-scaring) lines have been used to decrease seabird mortality in some trawl fisheries by up to 90%. However, tori lines are not effective at reducing the number of birds that drift towards the trawl warps while feeding on factory discards alongside the vessel. The Albatross Task Force (ATF) helped to develop and test a new device, the Rory Line (RL), to be used in conjunction with tori lines, and designed to reduce warp strikes by placing a physical barrier between the scupper (where factory discards are released) and the danger zone (where the trawl warps enter the water) at the stern of the vessel. This study tests the efficacy of the RL at reducing the number of birds drifting into the danger zone and the number of birds being struck by the trawl warps.

The dynamics of demersal fish species assemblages and stocks on the continental shelf of Ghana, West Africa were investigated using data from trawl surveys conducted between 1963 and 1990, and in relation to marine environmental and nearshore forcing factors. Time series analysis was used to examine the dynamics of the marine environment. Classification and ordination methods were used to identify fish assemblages and to identify factors that determine assemblage formation and dynamics. The response of the identified assemblages to changes in the Ghanaian shelf ecosystem were assessed. Between 1964 and 1992, three distinct environmental time blocks (ETBs) in the continental shelf ecosystem off Ghana were recognised. In the first ETB (i. e. before 1972) sea surface and bottom temperatures were relatively high and salinity was low. The second ETB (1972 - 1982) was characterised by low temperatures, high but stable salinity, reduced rainfall and freshwater input into the sea. In the third ETB (1982 - 1992), the system bore a resemblance to the first block with rising temperatures and decreasing salinity. Six fish species assemblages were identified, namely the supra-thermocline sciaenid and lutjanid assemblages, two sparid assemblages (shallow and deep elements), the deep shelf assemblage and the upper slope assemblage. During ETB I and ETB3, the assemblages were easier to identify using ordination techniques, than during ETB2. Species diversity also decreased during ETB2 especially in waters between 10 and 50 m deep. This behaviour of the assemblagesis attributed to the increase in abundance of Balistes capriscus, a species that dominated the ecosystem for nearly 20 years from about 1971, and the observed environmental changes. The estimated density of demersal fish was higher in the upwelling season than in the thermocline season and decreased from 50 kg ha-1 in 1963-64 to 32.4 kg ha-1 in 1990. The density reached its lowest value of 22.5 kg ha-1 in the period between 1973 and 1977. The potential yield of the total demersal biomass (excluding triggerfish) is estimated to be 36,000 - 55,000 mt per annum. With landed catches exceeding 60,000 mt in some years, it is apparent that the resource is over-exploited. A number of policy options are discussed and recommendations for the management of the fishery are made.

Over the past few decades it has become recognised that an ecosystem approach is required to manage world fisheries. Management strategies must ensure that non-target (bycatch) as well as target catches are sustainable. To achieve this, detailed commercial catch and biological information is required. The composition of catches made by trawlers operating off the south and west coasts of South Africa was investigated. Distinct fishing areas were identified on each coast, based on target species and fishing depth. Catch composition differed markedly among the areas defined. Although hake Merluccius sp. dominated South Coast catches, a large proportion of the catch was composed of bycatch. On the West Coast, hake dominated catches and this domination increased with increasing depth. On both coasts approximately 90% of the observed nominal catch was processed and landed. Estimates of annual discards suggested that the fishery discarded 38 thousand tons of fish per annum (16% of the nominal trawl catch). The data also indicated that hake discarding, the capture of linefish and the increased targeting of high value species might be cause for concern. Spatial analysis indicated that a variety of factors such as trawling position, catch size and catch composition affects bycatch dynamics. The monkfish Lophius vomerinus is a common bycatch species that has been increasingly targeted by demersal trawlers. This study showed that L. vomerinus is a slow-growing, long-lived species (West Coast males L∞ = 68.50cm TL, t₀ = -1.69yr, K = 0.10yr⁻¹; West Coast females L∞ = 110.23cm TL, t₀ = -1.54yr, K = 0.05yr⁻¹; South Coast sexes combined L∞ = 70.12cm TL, t₀ = - 0.80yr, K = 0.11yr⁻¹), that matures at approximately 6 years of age. These traits could have serious management implications for the species. Per-recruit analysis suggested that the stock might be overexploited, although further investigation is required to confirm this. Solutions were suggested for each of the concerns raised, taking cognisance of the differences observed between the South and West Coasts and the economic dependence of South Coast companies on bycatch. The needs of future research were considered.

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.

Fishing gears, and especially those that are towed across the seabed, can impose a number of impacts on the marine environment. The long term implications of many of these impacts are poorly understood and often hard to quantify from both the ecological and economic perspective (L0kkeborg, 2004). At a global level the general trend towards ecosystem based management (FAO, 2003; Pikitch et al .. 2004) and adopting the precautionary principal (FAO, 1995b, 1996) implies these impacts should be reduced. Within Europe, the focus of management has primarily been on reducing the level of commercially important species being caught incidentally ("bycatch") and subsequently discarded. These reductions have mainly been pursued through the application of restrictions on the type of fishing gear that can be used (generally termed "technical measures"). However, hard management constraints such as technical measures tend to impose increased costs on fishers, primarily through reduced productivity. These create incentives to mitigate the effectiveness of the measures, and may ultimately result in a failure to achieve the management objective. Despite ongoing attempts to reduce these impacts, bycatch and discarding rates are estimated to be in the range of 20% to 60% of catch weight for European fisheries (European Commission, 2007b). This study investigates the importance of individual environmental impacts within the context of European demersal trawl fisheries and then assesses the effects of attempting to reduce one of these impacts, that of bycatch and discarding, through the application of gear based technical measures. Priorities for the reduction of impacts are quantified at the stakeholder group level using the Analytic Hierarchy Process (AHP). The results indicate that Europe's historical focus on reducing primarily commercial discards with technical measures needs to be broadened to account for other non-commercial impacts. The effects of attempting to reduce bycatch and discarding through the application of gear based technical measures are then considered using two case studies. Ex post assessments are undertaken on two fisheries; the UK East coast Crangon crangon (Brown shrimp) fishery and the Belgian large beam trawl fishery. In both instances vessel level productivity was observed to have fallen as a result of taking up bycatch reduction measures with productivity effects estimated to range between -14% and -23%. On the basis of these findings, a review was undertaken of alternative measures that may better account for the set of incentives fishers face. Whilst not yet widely applied in the context of fisheries, their potential tb simultaneously improve both economic performance and resource sustainability means they have been receiving increasing attention (Grafton et al., 2006a). Such measures appear to provide a potential solution to the main issues surrounding command and control type measures and are likely to have application when attempting to reduce discards in fisheries.

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.

Anthropogenically-induced climate change has resulted in increases in water temperature and the frequency and severity of hypoxic events in coastal areas worldwide. Temperature and hypoxia affect fishes' energetics which can, in turn, be reflected in changes in reproductive success and shifts in spatial distributions. in an effort to quantify these changes in Atlantic croaker (Micropogonias undulatus) and spot (Leiostomus xanthurus) in Chesapeake Bay. I: (1) estimated standard and maximum metabolic rates and hypoxia tolerances at five temperatures (10, 15, 20, 25 and 30°C) using intermittent-flow respirometry, (2) examined the effects of hypoxia exposure on metrics of reproductive potential and, (3) developed an individual-based, dynamic-seascape model of Atlantic croaker and spot based on data from the respirometry trials, The first set of experiments showed that metabolic scope (i.e., the difference between standard and maximum metabolic rates, and within which all aerobic metabolic processes must operate) increased with increasing temperature in both species between 10 and 20°C, but plateaued above 25°C in Atlantic croaker and above 20°C in spot. Except at 10°C, the metabolic scope of Atlantic croaker was less than that of spot at all temperatures. in contrast to previous studies with Atlantic croaker from the Gulf of Mexico, the relative expression of hypoxia-inducible factors and metrics of reproduction (gonadosomatic index, most-advanced oocyte stage, and proportion of atretic oocytes) did not differ between Atlantic croaker captured under normoxic and hypoxic conditions in Chesapeake Bay. Simulations of the movements and distribution of Atlantic croaker and spot using individual-based models suggested that these species would occupy areas with warmer and better-oxygenated water than indicated by trawl survey observations from 1988-2014. Additionally, simulations indicated that a greater proportion of Atlantic croaker and spot in the Virginia waters of Chesapeake Bay would occupy the lower portion of Chesapeake Bay than indicated by capture rates from the trawl survey. My research suggests Atlantic croaker and spot are well-adapted to the environmental conditions of Chesapeake Bay during summer and are likely not affected by the frequent hypoxic episodes occurring in the subestuaries of the lower Chesapeake Bay. The apparent larger effect of elevated temperature on the metabolic scope of spot may provide them a greater capacity for movement, growth, and reproduction in warmer conditions and thus, a competitive advantage over Atlantic croaker as water temperatures continue to rise due to anthropogenically-induced climate change. My results indicate that intermittent exposure to hypoxic conditions is unlikely to negatively affect the reproductive potential of Atlantic croaker. Additional research, however, is necessary to better understand how this intermittent hypoxia exposure affects the endocrine pathways controlling reproduction. Finally, although climate-change science frequently focuses on the effects of rising coastal water temperature, and fisheries science and management on the effects on fish distributions, the results of my individual-based models suggest that predicting the effects of anthropogenically-induced climate change should not focus on temperature alone, as this may not be the most important driver of changes in fish distribution. More specifically, other factors such as time-area specific hypoxic events, prey availability, and predator avoidance likely contribute to the spatial distributions of these species in Chesapeake Bay.

In this study we provide a baseline data on semidemersal fish assemblages and biology in a heterogeneous and yet less studied portion of the shelf of Antalya Gulf. The distribution of fish abundance in three transects subjected to different fisheries regulations (fishery vs non fishery areas), and including depths of 10, 25, 75, 125, 200 m, was studied between May 2014 and February 2015 in representative months of winter, spring, summer and autumn seasons. A total of 76 fish species belonging to 40 families was collected and semidemersal species distribution was analyzed in comparison with the whole community. Spatial distribution of fish was driven mainly by depth and two main assemblages were observed: shallow waters (10-25; 75 m) and deep waters (125-200 m). Significant differences among transects were found for the whole community but not for the semidemersal species. Analysis showed that this was due to a strong relation of these species with local environmental characteristics rather than to a different fishing pressure over transects. Firstly all species distribute according to the bathymetrical gradient and secondly to the bottom type structure. Semidemersal species were then found more related to zooplankton and suspended matter availability. The main morphological characteristics, sex and size distribution of the target semidemersal species Spicara smaris (Linnaeus, 1758), Saurida undosquamis (Richardson, 1848), Pagellus acarne (Risso, 1827) were also investigated.

The demersal fishery off the west coast of South Africa experiences decreased catches per unit effort of hake, Merluccius capensis and M. paradoxus, following the onset of strong south easterly winds. Research has demonstrated that, during daylight hours, Cape hakes migrate vertically in the water column in response to strong south easterly winds, decreasing their availability to the bottom trawl. Hydroacoustic, trawl and environmental data were collected off the West Coast during both calm and wind-swept periods in an attempt to understand the forces that initiate this behaviour, its spatial variability and the implications for demersal trawl estimates of abundance. Near-bottom currents appear to be the primary factor influencing the vertical distribution of the demersal fish community, of which hake constitutes a large proportion, during daylight hours. Correlation between wind and near-bottom currents suggest that the poleward component of the currents increase in velocity within eight hours following the onset of south easterly winds. The fish avoid boundary layers where currents change direction and speed dramatically, and seem to concentrate in waters with relatively stable current regimes. This result questions the assumption of CPUE-based assessment models that hake availability to the bottom trawl is constant or varies randomly. The incorporation of acoustic assessment techniques to demersal surveys has potential, but may be most valuable by supplementing swept-area estimates of abundance, since the sampling efficiency of these methods varies within the water column. The incorporation of wind indices and gear performance data to Cape hake assessment models have been identified as useful considerations for the future.

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.

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 région
The 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

L'aquaculture et la pêche impactent l'environnement, les ressources et le fonctionnement des écosystèmes. L’un des enjeux en écologie est de placer ces activités anthropiques dans un cadre de développement durable. Afin de quantifier et de limiter ces impacts, différentes méthodes d’évaluation environnementale ont vu le jour. L’Analyse de Cycle de Vie (ACV) est une méthode pertinente pour évaluer le bilan environnemental d'un produit en prenant en compte l’ensemble de ses étapes de vie, "du berceau à la tombe", depuis l’extraction des matières premières et leurs transformations pour l'élaboration du produit, jusqu’à la fin de vie. Cette thèse porte sur l’adaptation de l’ACV au domaine de l'aquaculture et de la pêche en Tunisie. Son objectif est d'explorer les perspectives offertes par cette méthodologie afin de mieux caractériser le fonctionnement des systèmes de production de poissons et leur lien avec l’environnement. Cette étude a montré que les pratiques aquacoles et la production d'aliment de poisson sont les contributeurs majeurs aux impacts environnementaux, ceci est expliqué par l'utilisation de farine et d'huile de poisson dans la fabrication de l'aliment. Les résultats ont également montré que les impacts du chalutage de fond sont proportionnels à la quantité de carburant nécessaire pour la production. Ce travail a permis d'étudier et comparer les impacts environnementaux de l'activité aquacole et de la pêche au chalutage de fond en Tunisie. Les résultats de cette thèse ont un intérêt pour les gestionnaires en proposant des voies d'amélioration et des recommandations stratégiques de gestion pour améliorer les deux secteurs afin de les placer dans un contexte de développement durable
The main goal of ecology is to place human activities within a framework of sustainable development by enhancing their economic benefits, their social attractiveness and their environmental performances. Ecosystems that support fisheries and aquaculture are subject to several alterations of significant relevance to their functioning and to their abilities to provide goods and services. Therefore, the long-term sustainability of fishing and aquaculture is a major concern from an environmental and ecological viewpoint. Both activities carry risks of negative environmental impacts because of its close relation with the immediate environment. To better understand environmental impacts and ensure the sustainability of fishing and aquaculture, it is necessary to develop an integrative sciencebased approach to impact assessment. Life Cycle Assessment (LCA) has emerged as a robust method to estimate potential environmental impacts associated with a product. It allows the assessment of environmental impacts “from cradle to grave”, taking into account all stages of a product’s life. This thesis focuses on the adaptation of LCA to demersal trawling and aquaculture in Tunisia. The goal is to explore how LCA improves the environmental evaluation of seafood production systems and how it helps to better understand their links with the environment. Results revealed that rearing practices and fish feed were the greatest contributors to the impacts studied due to the production of fish meal and oil and the low efficiency of feed use. The study also showed that impact intensity of demersal trawling was proportional to the amount of fuel consumed. LCA is a valuable tool for assessing how to improve environmental sustainability of demersal trawling and aquaculture

Analisaram-se as proporções de Rioraja agassizi, Atlantoraja cyclophora, A. platana e A. castelnaui na categoria “raias-emplastros”, nos desmbarques de 11 embarcações da pesca comercial, de arrasto duplo de portas e de parelhas, totalizando 358 lances realizados em 20 viagens. Elas atuaram entre as isóbatas de 10 e 430 m e entre os paralelos 23° S (Estado do Rio de Janeiro) e 31° S (Estado do Rio Grande do Sul), de 1995 a 1997 e de 2001 a 2003. Entre as espécies estudadas, A. cyclophora foi a mais freqüente nos lances realizados entre 60 e 265 m de profundidade, com ampla distribuição entre 23° 30’ S e 27°20’ S. As análises das pescarias sugerem que a profundidade e a latitude, entre outras variáveis, foram importantes apenas na captura de A. cyclophora. As carcaças foram desembarcadas em três tipos de cortes, a partir dos quais o peso corporal foi estimado. Também foram avaliadas as estruturas populacionais das quatro espécies. Os estimadores dos parâmetros de crescimento, largura de disco (LD) de primeira maturação sexual e taxa de mortalidade natural (M) foram calculados para machos e fêmeas, respectivamente: R. agassizi LD = 289 mm e 425 mm; K= 0,142 e 0,078 ano-1; t0= -1,653 e -1,811 anos; LD50 = 270 e 330 mm, M = 0,061 e 0,052 ano-1; A. cyclophora LD = 478 e 518 mm; K= 0,077 e 0,073 ano-1; t0= -4,518 e -4,485 anos; LD50 = 355 e 415 mm, M = 0,085 e 0,085 ano-1; A. platana LD = 733 e 823 mm; K= 0,057 e 0,052 ano-1; t0= -1,267 e -1,225 anos; LD50 = 500 e 550 mm, M = 0,061 e 0,021 ano-1; A. castelnaui LD = 794 e 1004 mm; K= 0,066 e 0,046 ano-1; t0= -1,978 e -2,235 anos; LD50 = 670 e 740 mm, M = 0,069 e 0,047 ano-1. Em alguns anos, o modelo relativo de rendimento-por-recruta resultou em valores próximos ou superiores aos pontos de referência biológica para machos de R. agassizi, e fêmeas de A. platana e de A. castelnaui. As taxas de explotação e mortalidade por pesca de A. cyclophora foram crescentes entre 2001 e 2003.
The proportions of the skates Rioraja agassizi, Atlantoraja cyclophora, A. platana and A. castelnaui landed by commercial fishing boats were analyzed. Data were collected from 358 hauls of 20 trips made by 11 double-otter trawlers and pair-trawlers. Fisheries were carried out between 10 and 430 m deep and from 23° S (State of Rio de Janeiro) to 31° S (State of Rio Grande do Sul) between 1995-1997 and 2001-2003. A. cyclophora was the most frequent in all hauls between 60 and 265 m deep among the studied species, with a wide distribution between 23°30’ S and 27°20’ S. The analyses of the fisheries suggested that depth and latitude, along with other variables, have importance only for A. cyclophora catches. The skates carcasses were landed in three types of cuts from which the body weight was estimated. The population structures of the four species were also evaluated. The growth parameters estimates, the disc width (DW) at first sexual maturation and the instantaneous natural mortality rate (M) for males and females were, respectively: R. agassizi: DW = 289 mm and 425 mm; K= 0,142 and 0,078 year-1; t0 = -1,653 and -1,811 years; DW50 = 270 and 330 mm, M = 0,061 and 0,052 year-1; A. cyclophora: DW = 478 and 518 mm; K= 0,077 and 0,073 year-1; t0= -4,518 and -4,485 years; DW50 = 355 and 415 mm, M = 0,085 and 0,085 year-1; A. platana: DW = 733 and 823 mm; K= 0,057 and 0,052 year-1; t0= -1,267 and -1,225 years; DW50 = 500 and 550 mm, M = 0,061 and 0,021 year-1; A. castelnaui: DW = 794 and 1004 mm; K= 0,066 and 0,046 year-1; t0 = -1,978 and -2,235 years; DW50 = 670 and 740 mm, M = 0,069 and 0,047 year-1. In some years, the relative yield-per-recruit model resulted values similar or higher than the biological reference points estimated for males of R. agassizi and females of A. platana and A. castelnaui. The exploitation ratio and the instantaneous fishery mortality rate for A. cyclophora increased between 2001 and 2003.

De nombreux prédateurs marins se nourrissent directement des prises des pêcheurs. Ces interactions, définies comme de la déprédation, engendrent des conséquences socio-économiques considérables pour les pêcheurs ainsi que des implications de conservation pour la faune sauvage. D’un côté, la déprédation endommage le matériel et augmente l’effort de pêche pour atteindre les quotas. D’un autre côté, la déprédation augmente le risque de mortalité des prédateurs marins (prise accidentelle ou rétorsion létale par les pécheurs). La pêcherie à la palangre est la plus impactée par la déprédation, principalement par les odontocètes, ce qui incite à trouver des solutions. La majorité des études se concentrant sur la déprédation s’est principalement basée sur des observations en surface, de ce fait la manière dont les prédateurs retirent les poissons sur les lignes reste confuse. Par ailleurs, l’impact de la déprédation sur le comportement des pêcheurs ainsi que les facteurs expliquant leur détectabilité n’ont reçu que peu d’intérêt. L’objectif de cette thèse est donc d’étudier ces problématiques par un suivi acoustique, une utilisation de balises et une approche en écologie comportementale humaine, en se concentrant sur la pêcherie palangrière française ciblant la légine australe (Dissostichus eleginoides) impactée par la déprédation des orques (Orcinus orca) et des cachalots (Physeter macrocephalus). Les capitaines ont été décrits comme recherchant leur ressource selon la théorie de « l’optimal foraging », mais avec des perceptions de la compétition et du succès de pêche qui divergent. Certains capitaines seraient ainsi plus enclins à remonter les palangres au plus proche et à rester sur une zone, même en présence de compétition, augmentant alors le risque d’interaction. L’acoustique des navires a révélé que certaines manoeuvres (marche arrière par exemple) propagent différemment sous l’eau. La manière dont les capitaines manoeuvrent leur palangrier influencerait ainsi leur détectabilité et donc leur risque d’interaction avec les prédateurs. D’autre part, l’utilisation de capteurs sur les palangres et les animaux a révélé que les orques et les cachalots sont capables de déprédater sur les palangres posées sur le fond marin. Ces observations laissent à penser que les odontocètes sont en mesure de localiser l’activité de pêche bien avant la remontée de la ligne, ce qui pourrait être expliqué par une signature acoustique spécifique du déploiement de la ligne. L’ensemble des résultats de cette thèse suggère que la déprédation sur les palangres démersales est très probablement sous-estimée. Cette thèse apporte également des éléments importants pour la lutte contre la déprédation, en montrant la nécessité de protéger les palangres dans l’intégralité du processus de pêche
Many marine predator species feed on fish caught by fishers directly from the fishing gear. Known as depredation this interaction issue has substantial socio-economic consequences for fishermen and conservation implications for the wildlife. Costs for fishers include damages to the fishing gear and increased fishing effort to complete quotas. For marine predators, depredation increases risks of mortality (lethal retaliation from fishers or bycatch on the gear). Longline fisheries are the most impacted worldwide, primarily by odontocetes (toothed whales) depredation, urging the need for mitigation solutions to be developed. Most of studies assessing depredation have primarily relied on surface observation data, thus the way odontocetes interact with longlines underwater remains unclear. Besides, the way fishermen respond to depredation during fishing operations, or can influence their detectability to odontocetes, have been poorly investigated. This thesis therefore aimed at investigating these aspects through a passive acoustic monitoring, bio-logging and human ecology approaches, focusing on the French Patagonian toothfish (Dissostichus eleginoides) longline fisheries impacted by killer whales (Orcinus orca) and sperm whales (Physeter macrocephalus). Firstly, this thesis reveals that captains behave as optimal foragers but with different personal perception of competition and fishing fulfilment. Some captains would thus be more likely to stay within a patch or to haul closest longline even in presence of competition, suggesting these captains would show higher interaction rates. Additionally, the propagation of vessels’ acoustics varied depending on the type of manoeuvre (e.g. going backward vs. forward). The way captains use their vessels to navigate may therefore influence their detectability and so their depredation level. Secondly, loggers deployed on both the longlines (accelerometers) and odontocetes (GPS-TDR) revealed that killer whales and sperm whales are able to depredate on longlines while soaking on the seafloor. These observations suggest, therefore, that odontocetes can localise fishing activity before the hauling, which could be partially explained by specific acoustic signatures recorded during the setting process. Altogether, the results of the thesis suggest that depredation rates on demersal longlines are most likely underestimated. The thesis also brings some important insights for mitigation measures, suggesting that countermeasures should start from setting to hauling

A pesca de fauna acompanhante, o âbycatchâ, pode ser considerada uma das maiores ameaÃas à vida nos oceanos. A influÃncia das capturas de fauna acompanhante nos ecossistemas marinhos faz com que esta seja uma das questÃes de conservaÃÃo da natureza mais importantes atualmente. Por vÃrias dÃcadas existiu na costa de Fortaleza uma intensa atividade da pesca de arrasto de camarÃo, que acidentalmente capturava raias, com o uso de embarcaÃÃes motorizadas. Tal atividade foi proibida a partir de 2003, pela Portaria no 35 do MinistÃrio do Meio Ambiente (Instituto do Meio Ambiente e dos Recursos Naturais RenovÃveis). O objetivo do presente estudo foi avaliar se a proibiÃÃo da pesca de arrasto de camarÃo utilizando-se embarcaÃÃes motorizadas em Ãreas costeiras (1) afeta a abundÃncia de raias demersais; (2) que parcela das populaÃÃes dessas raias està sujeita ao efeito da proibiÃÃo da referida atividade pesqueira; (3) se espÃcies consideradas pela LegislaÃÃo Brasileira atual como sob algum grau de ameaÃa tambÃm sÃo afetadas por esta proibiÃÃo. No presente estudo, foram realizadas 14 amostragens cientÃficas na enseada do Mucuripe, Fortaleza/CE, entre setembro de 2004 e novembro de 2010, cada uma com 10 arrastos de fundo a cerca de 14 m de profundidade, utilizando rede de arrasto-de-portas. Foram ainda, compilados dados nÃo publicados de abundÃncia de raias capturadas como fauna acompanhante da pesca de arrasto de camarÃo, utilizando-se embarcaÃÃo motorizada, na enseada do Mucuripe, entre 1997 e 1998. A proibiÃÃo da pesca de arrasto de camarÃo utilizando-se embarcaÃÃes motorizadas, em Ãreas costeiras, afeta positivamente a abundÃncia de raias demersais previamente impactadas por essa atividade. AlÃm disso, Ãrea costeira investigada abriga todas as classes de tamanho das raias Dasyatis guttata e Gymnura micrura e portanto pode ser considerada uma Ãrea importante para a reproduÃÃo destas espÃcies. Por fim, essa mesma Ãrea abriga, ainda, diversas espÃcies consideradas pela LegislaÃÃo Brasileira atual como ameaÃadas (n=4) ou sobreexplotadas ou ameaÃadas de sobreexplotaÃÃo (n=7).
Bycatch fisheries may be considered one of the greatest threats to marine life. The influence of these captures in marine ecosystems makes it one of the most pressing issues on nature conservation today. For decades, there was in Fortaleza, CE, a shrimp otter trawl fisheries activity conducted by motorized boats that accidently captured batoids. This activity has been prohibited by the Brazilian Ministry of Environment since 2003. The goal of the present study was to evaluate if the prohibition of shrimp otter trawl fisheries activity conducted by motorized boats on coastal areas (1) affects the abundance of demersal batoids; (2) which portion of these batoidsâ populations is under the effect of the prohibition of this fishery activity; and (3) if species considered by the current Brazilian legislation as under any level of threat also are effected by this prohibition. In the present study, fourteen scientific sampling were carried out on Mucuripe Bay, Fortaleza, CE, between September 2004 and November 2010. During each survey, 10 stations were sampled with otter trawl net, circa 14 m depth. In addition, unpublished data on the abundance of batoids captured as bycatch by shrimp fisheries in this same bay, between 1997 and 1998, were compiled. The prohibition of the shrimp fisheries using motorized boats, in coastal areas, affects positively the abundance of demersal batoids previously impacted by this activity. Furthermore, the coastal area studied is used by all size classes of the batoids Dasyatis guttata and Gymnura micrura and, therefore, it may be considered important for reproduction of these species. Lastly, this same Bay is also home for several species that currently are considered by the Brazilian legislation as endangered (n=4) or overexploited or threatened of overexploitation (n=7).

The fish belonging to the Family lactariidae commonly called whitefish/false trevally/big-jawed jumper is represented by a single species Lactarius lactarius (Bloch and Schneider, 1801 ) and is widely distributed in Indian waters. Though, L. lactarius has high demand in coastal markets, there is no concerted study on the stocks and population structure from any of the Indian coasts. Hence, the present investigation was undertaken to study its biology, stock and population characteristics from Karnataka waters. The findings would help to evolve suitable management measures for the rational exploitation of the white fish resources olong the Kornataka coast. Data for the present study were collected from three major fish landing centres of Karnataka state viz., Mangalore, Malpe and Karwar during September 1997 -August 1999. Besides the key characters of the family lactariidae and the genus Lactarius, the species has been described in detail for easy identification based on the morphological, morphmetric and meristic characters.

Fishes constitute slightly more than one half of the total number of approximately 54,711 recognized living vertebrate species of the world. Flatfishes represent an interesting and diverse order of marine, estuarine and to a lesser extent, freshwater euteleostean fishes. They are common species in most marine fish assemblages right from the poles to the tropics. Flatfishes captured in tropical fisheries are often not identified even to genus or family level rather, much of the catch is merely identified as “Pleuronectiformes”; 54-80% of the total landings of tropical flatfishes consist of unidentified species. For flatfishes inhabiting tropical seas, despite recent progress, considerable diversity is still being discovered and the taxonomy of many tropical flatfishes remains especially problematic. Failure to identify species, and erroneous species identifications, still represent serious impediments to collection of meaningful data for many of these smaller species. Work on Indian flatfishes has been scattered over the time period and ample scope exists for a study on the diversity of the group. Based on the present collections from different parts of South India and Andaman Islands during the period 2004 - 2010, 63 species of flatfishes belonging to 8 families and 26 genera have been collected. The most speciose family was Soleidae with 9 genera and 17 species, followed by Bothidae with 9 genera and 14 species and Cynoglossidae with 2 genera and 13 species. Family Bothidae had representations from deep sea. New distributional records were Aserraggodes kobensis and Brachirus annularis for the Indian waters. Psettodes erumei a major resource in the flatfish fishery has virtually been absent in the landings except for stray numbers in large trawlers off Mangalore. The study points out the decline of the resource off South India. This calls for immediate steps to device steps to protect and preserve this species. New emerging resources in the fishery are Synaptura commersoniana in the estuarine landings off Kochi. Occurrence of Pardachirus pavoninus, Heteromycteris oculus and Paraplagusia bilineata in the ‘rollermadi’ landings at Pamban point to the existence of these ornamental varieties in the Gulf of Mannar.

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