Second Workshop on Atlantic chub mackerel (Scomber colias) (WKCOLIAS2)

The Atlantic chub mackerel Scomber colias has become an increasingly important commercial species in the European Atlantic waters in the last 10–15 years, probably through an expansion process from NW African waters and due to market needs. However, at present there are no assessment or advice requirements. In the WK framework, available information of the species in the West Atlantic waters has been compiled in order to evaluate possible geographical differences and trends, and the feasibility to describe its population structure. Though the Atlantic chub mackerel is not routinely included among the target species in the acoustic surveys performed in the Atlantic Iberian waters and the Mediterranean Sea, a synoptic overview of the species is possible over all its West Atlantic distribution. Moreover, the data available have indicated latitudinal trends, mainly in the landings’ length composition, L50 and the spawning periods. Nevertheless, even if some degree of connectivity likely exists and migrations are occurring between adjacent areas, some subunits could be considered for management purposes. From the assessment models’ trials carried out, the results or reference points obtained for the European fisheries cannot be retained at present. Therefore, continuing collating information from fisheries and biological sampling of the species, obtaining reliable biomass estimations from scientific surveys and identifying management units seem the main priorities to address in future research work and in case of assessment requirements

Pelagic fisheries in the Mauritanian EEZ : New methods for new insights

Les contextes national et international sont marqués par une prise de conscience de plus en plus grande de l’importance du poisson pour la sécurité alimentaire des populations des pays sous-développés. En Mauritanie, les petits pélagiques constituent une source de protéines animales accessibles aux faibles pouvoirs d’achat et contribuent à garantir la sécurité alimentaire de nombreuses populations. Malgré la présence d’une variabilité naturelle importante des espèces pélagiques, ce travail de thèse montre qu’il existe des éléments de stabilité dans l’écosystème pélagique dans la zone nord-ouest africaine. L’hypothèse de la présence des stocks sédentaires au niveau des zones de nourriceries en Mauritanie et au Sénégal est démontrée. La répartition spatio-temporelle des sardinelles en relation avec la dynamique de l’océan (upwelling, température de surface et chlorophylle) a été examinée. L’analyse des statistiques de la pêche sur une série de plus de trente (30) ans ne soutiennent pas l’immigration en provenance du Sénégal vers la Mauritanie d'Avril à Septembre selon l’hypothèse de Boëly (1978). Ce travail de thèse examine des hypothèses de migrations possibles des sardinelles dans la zone nord-ouest africaine et d’importantes implications en matière de gestion sont discutées. Pour finir, ce travail est replacé dans son contexte plus global de l’aménagement de la pêcherie des petits pélagiques. De nouvelles perspectives pour l’application des techniques géostatistiques (indicatrices et co-krigeage) et modélisation statistique sont envisagées pour l’étude de la dynamique des stocks des sardinelles et chinchards.National and international context marked by an awareness of growing importance of pelagic fish for food security of people in underdeveloped countries . The depletion of demersal species also makes this extremely important resource for the future pelagic fisheries in Mauritania. Mauritanian EEZ is characterized by the existence of a favorable development of several species hydro-climatic and morphological phenomena , small pelagic species that represent more than 90% of the fisheries potential is about one million tones. The major problems facing the management of these species is understanding the roles played by them in their biogeography intrinsic spatio- temporal dynamics ( short-lived , aggregation , etc. ..) and the evaluation of their abundances . Assessment of exploited fish stocks is a priority. However, the recurring difficulty of evaluations of these fisheries, naturally very unstable, often reflected a lack of precision in the methods used , the incompleteness of the data ( which is also a problem of sampling) or sampling uncontrolled .The Mauritanian small pelagic fisheries are multi-species (sardines , horse mackerel , sardinella ) . In addition to the data provided by the logbooks including the holding is mandatory for industrial units, survey data for the landing craft and coastal segment often used to calculate the abundance, acoustic surveys , are an important means for quantify the abundance and study the distribution of these resources. The data collected by observers on board fishing industrial units are also a source of important information.Based on these data , this work aims at the reconstruction of the main series of abundances of small pelagic stocks in the northern part of West Africa , to be used in the adjustment of stock assessments models. Given the importance of the environmental component in very large fluctuations observed, the integration of this dimension in the analysis of this series catches the role of each of these factors (fisheries and environment) in the variability of abundance seasonal and amplitude of their migration.In addition to these conventional data Mauritania introduced on board commercial fishing vessels with VMS . This system allows the transmission by satellite to the body control the ship's position every hour is an important technological advance. This new type of data could therefore be a new source for estimating abundance and fishing effort of small pelagic species through appropriate statistical methods. A method for the interpretation in terms of paths abundance index was applied. The coupling of VMS and logbook will help to improve the definition of nominal fishing effort and catch location at fine spatial and temporal.The general problem is how to improve the estimation of the abundance of small pelagic stocks , understand fluctuations in the abundance and migration strategy of the species as well as tactics and strategies implemented by fleets to fish resources whose behavior is often erratic . It is therefore to adresse several issues in particular:What is the trend of the evolution of the abundance of pelagic species in the North West African area? The interpretation of the trajectories in terms of VMS fishing can it be used to map the abundance of key species? What are the seasons abundances? Environmental parameters they play an important role on the distribution of species? Will there a difference between tactics and strategies of the different fleets fishing for small pelagic? Data logs and data collected by observers on board can be used as a priori knowledge? To address these issues , we proceed to the mobilization of all relevant time series and implement innovative statistical and geostatistical methods , some of which applied for the first time in the sub -region for these stocks

The chronology of overfishing in a remote West-African coastal ecosystem

Classic studies of marine overexploitation traditionally analyze cases of “fishing down the food web”: turning to smaller species at lower trophic levels after depleting the larger top predators. Much less documented, however, is the preceding phase in which higher trophic level species, previously not exploited or consumed locally, are increasingly added to the catch. Worldwide, this phase happened centuries ago due to technological developments and thus passed before scientific scrutiny and conservation awareness arose, leaving it largely unstudied. Here, we combine a historical reconstruction of fishery with a relatively recent fishing monitoring program to document this early phase in the Parc National du Banc d’Arguin in Mauritania, a marine protected area in Mauritania, West Africa. Long-term trends in mean trophic level of exploited species and total catches provide evidence for an increasing fishing pressure toward the top of the food web, and suggest that the state of “fishing down the food web” is now happening in this ecosystem. This involves the recent intensive targeting of rays and sharks. We show that their contribution to the local economy is marginal compared with the traditionally fished species

Toward new scenario on small pelagic fish spatial population dynamics related on both hydrodynamic and biogeochemical simulations [résumé]

International audienceSmall pelagic fish species are keystone species in upwelling ecosystems due to their dominant biomass and role in transferring energy from low trophic levels to top predators. These ecosystems are often termed “wasp-waist” because few small pelagic species dominate and manage this energy transfer. Atmospheric variability leads to fluctuations in upwelling intensity, duration, and extent, creating complex responses from small pelagic fish species. This complexity involves factors like fish migration, larval retention, predation, competition, fishing, food, oxygen, and temperature limitations. Increasing studies demonstrate that spatially explicit biophysical individual-based models, driven by precise hydrodynamic and biogeochemical simulations, can capture much of this complexity. Sensitivity tests on such models provide significant insights into the main drivers of small pelagic fish biomass variability. We present a generic, adaptable model for various small pelagic fish species and regions, capable of full life cycle multi-generational studies. The model explores age truncation effects, homing behavior, and evolutionary impacts. Using Sardinella aurita off North-West Africa as a case study, we simulated the hydrodynamic and biogeochemical environment with coupled regional models (ROMS-PISCES) over 05°-40°N and 05°-30°W at ~8 km resolution from 1980-2009. This approach suits data-poor ecosystems, requiring (1) validated inter-annual hydrodynamic and biogeochemical simulations, (2) specific Dynamic Energy Budget parameters, and (3) basic rules for fish school kinematics. This framework helps analyze fish spatio-temporal distribution and biomass complexities, achieved by comparing modeled and observed fish populations through Pattern Oriented Modelling

Toward new scenario on small pelagic fish spatial population dynamics related on both hydrodynamic and biogeochemical simulations [résumé]

International audienceSmall pelagic fish species are keystone species in upwelling ecosystems due to their dominant biomass and role in transferring energy from low trophic levels to top predators. These ecosystems are often termed “wasp-waist” because few small pelagic species dominate and manage this energy transfer. Atmospheric variability leads to fluctuations in upwelling intensity, duration, and extent, creating complex responses from small pelagic fish species. This complexity involves factors like fish migration, larval retention, predation, competition, fishing, food, oxygen, and temperature limitations. Increasing studies demonstrate that spatially explicit biophysical individual-based models, driven by precise hydrodynamic and biogeochemical simulations, can capture much of this complexity. Sensitivity tests on such models provide significant insights into the main drivers of small pelagic fish biomass variability. We present a generic, adaptable model for various small pelagic fish species and regions, capable of full life cycle multi-generational studies. The model explores age truncation effects, homing behavior, and evolutionary impacts. Using Sardinella aurita off North-West Africa as a case study, we simulated the hydrodynamic and biogeochemical environment with coupled regional models (ROMS-PISCES) over 05°-40°N and 05°-30°W at ~8 km resolution from 1980-2009. This approach suits data-poor ecosystems, requiring (1) validated inter-annual hydrodynamic and biogeochemical simulations, (2) specific Dynamic Energy Budget parameters, and (3) basic rules for fish school kinematics. This framework helps analyze fish spatio-temporal distribution and biomass complexities, achieved by comparing modeled and observed fish populations through Pattern Oriented Modelling

Toward new scenario on small pelagic fish spatial population dynamics related on both hydrodynamic and biogeochemical simulations [résumé]

International audienceSmall pelagic fish species are keystone species in upwelling ecosystems due to their dominant biomass and role in transferring energy from low trophic levels to top predators. These ecosystems are often termed “wasp-waist” because few small pelagic species dominate and manage this energy transfer. Atmospheric variability leads to fluctuations in upwelling intensity, duration, and extent, creating complex responses from small pelagic fish species. This complexity involves factors like fish migration, larval retention, predation, competition, fishing, food, oxygen, and temperature limitations. Increasing studies demonstrate that spatially explicit biophysical individual-based models, driven by precise hydrodynamic and biogeochemical simulations, can capture much of this complexity. Sensitivity tests on such models provide significant insights into the main drivers of small pelagic fish biomass variability. We present a generic, adaptable model for various small pelagic fish species and regions, capable of full life cycle multi-generational studies. The model explores age truncation effects, homing behavior, and evolutionary impacts. Using Sardinella aurita off North-West Africa as a case study, we simulated the hydrodynamic and biogeochemical environment with coupled regional models (ROMS-PISCES) over 05°-40°N and 05°-30°W at ~8 km resolution from 1980-2009. This approach suits data-poor ecosystems, requiring (1) validated inter-annual hydrodynamic and biogeochemical simulations, (2) specific Dynamic Energy Budget parameters, and (3) basic rules for fish school kinematics. This framework helps analyze fish spatio-temporal distribution and biomass complexities, achieved by comparing modeled and observed fish populations through Pattern Oriented Modelling

Toward new scenario on small pelagic fish spatial population dynamics related on both hydrodynamic and biogeochemical simulations [résumé]

International audienceSmall pelagic fish species are keystone species in upwelling ecosystems due to their dominant biomass and role in transferring energy from low trophic levels to top predators. These ecosystems are often termed “wasp-waist” because few small pelagic species dominate and manage this energy transfer. Atmospheric variability leads to fluctuations in upwelling intensity, duration, and extent, creating complex responses from small pelagic fish species. This complexity involves factors like fish migration, larval retention, predation, competition, fishing, food, oxygen, and temperature limitations. Increasing studies demonstrate that spatially explicit biophysical individual-based models, driven by precise hydrodynamic and biogeochemical simulations, can capture much of this complexity. Sensitivity tests on such models provide significant insights into the main drivers of small pelagic fish biomass variability. We present a generic, adaptable model for various small pelagic fish species and regions, capable of full life cycle multi-generational studies. The model explores age truncation effects, homing behavior, and evolutionary impacts. Using Sardinella aurita off North-West Africa as a case study, we simulated the hydrodynamic and biogeochemical environment with coupled regional models (ROMS-PISCES) over 05°-40°N and 05°-30°W at ~8 km resolution from 1980-2009. This approach suits data-poor ecosystems, requiring (1) validated inter-annual hydrodynamic and biogeochemical simulations, (2) specific Dynamic Energy Budget parameters, and (3) basic rules for fish school kinematics. This framework helps analyze fish spatio-temporal distribution and biomass complexities, achieved by comparing modeled and observed fish populations through Pattern Oriented Modelling

Toward new scenario on small pelagic fish spatial population dynamics related on both hydrodynamic and biogeochemical simulations [résumé]

International audienceSmall pelagic fish species are keystone species in upwelling ecosystems due to their dominant biomass and role in transferring energy from low trophic levels to top predators. These ecosystems are often termed “wasp-waist” because few small pelagic species dominate and manage this energy transfer. Atmospheric variability leads to fluctuations in upwelling intensity, duration, and extent, creating complex responses from small pelagic fish species. This complexity involves factors like fish migration, larval retention, predation, competition, fishing, food, oxygen, and temperature limitations. Increasing studies demonstrate that spatially explicit biophysical individual-based models, driven by precise hydrodynamic and biogeochemical simulations, can capture much of this complexity. Sensitivity tests on such models provide significant insights into the main drivers of small pelagic fish biomass variability. We present a generic, adaptable model for various small pelagic fish species and regions, capable of full life cycle multi-generational studies. The model explores age truncation effects, homing behavior, and evolutionary impacts. Using Sardinella aurita off North-West Africa as a case study, we simulated the hydrodynamic and biogeochemical environment with coupled regional models (ROMS-PISCES) over 05°-40°N and 05°-30°W at ~8 km resolution from 1980-2009. This approach suits data-poor ecosystems, requiring (1) validated inter-annual hydrodynamic and biogeochemical simulations, (2) specific Dynamic Energy Budget parameters, and (3) basic rules for fish school kinematics. This framework helps analyze fish spatio-temporal distribution and biomass complexities, achieved by comparing modeled and observed fish populations through Pattern Oriented Modelling