Climate-driven shift of Sardinella aurita stock in Northwest Africa ecosystem as evidenced by robust spatial indicators [résumé]

ICAWA : International Conference AWA, Dakar, SEN, 13-/12/2016 - 15/12/2016In Northwest Africa, the small pelagic fish are in abundance and play a crucial role for the food safety of populations. The pelagic resources are exploited both by small-scale artisanal and industrial fleets. The landing structure of the countries in the region has been in perpetual change during the last years. The sardinella has been more and more landed by fishermen in Morocco, while the sardine has become a target by fishing vessels in Mauritania and Senegal. This indicates a modification in the distribution areas of pelagic resources. To verify this hypothesis, an outstanding database consisting in 14 acoustic surveys with a consistent and high sampling intensity (2263 trawl hauls) conducted by the RV Fridtjof Nansen from 1995 to 2015 was investigated in this study to identify trends in distribution shifts in pelagic fishes. A focus was made on sardinellas and the main species in the southern part of the region. Two strong spatial indicators are used in this study: the latitudinal extreme location and the barycentre of biomasses. Two clear trends can be observed from the data analysed. Firstly, in the southern and tropical part of this system the typical trend is that pelagic species show an increasing northward distribution. This applies to S. aurita, Trachurus trecae, Chloroscombrus chrysurus, Sphyraena guachancho and Brachydeuterus auritu. A second group is observed, those that do not show any clear trend in distributional shift, but where the distribution is stable over the period. The typical species observed here are S. maderensis and Decapterus rhonchus. Despite some variations in the upwelling intensity, we show that the sea surface temperature is by far the main parameter to explain this northern shift. We also discuss the likely - and largely unknown - influence of the under-estimation of the detections because of the absence of sampling in the shallow coastal zone. The impact of such displacements is also discussed in term of regional management of these shared stocks

Climate-driven shift of Sardinella aurita stock in Northwest Africa ecosystem as evidenced by robust spatial indicators [résumé]

ICAWA : International Conference AWA, Dakar, SEN, 13-/12/2016 - 15/12/2016In Northwest Africa, the small pelagic fish are in abundance and play a crucial role for the food safety of populations. The pelagic resources are exploited both by small-scale artisanal and industrial fleets. The landing structure of the countries in the region has been in perpetual change during the last years. The sardinella has been more and more landed by fishermen in Morocco, while the sardine has become a target by fishing vessels in Mauritania and Senegal. This indicates a modification in the distribution areas of pelagic resources. To verify this hypothesis, an outstanding database consisting in 14 acoustic surveys with a consistent and high sampling intensity (2263 trawl hauls) conducted by the RV Fridtjof Nansen from 1995 to 2015 was investigated in this study to identify trends in distribution shifts in pelagic fishes. A focus was made on sardinellas and the main species in the southern part of the region. Two strong spatial indicators are used in this study: the latitudinal extreme location and the barycentre of biomasses. Two clear trends can be observed from the data analysed. Firstly, in the southern and tropical part of this system the typical trend is that pelagic species show an increasing northward distribution. This applies to S. aurita, Trachurus trecae, Chloroscombrus chrysurus, Sphyraena guachancho and Brachydeuterus auritu. A second group is observed, those that do not show any clear trend in distributional shift, but where the distribution is stable over the period. The typical species observed here are S. maderensis and Decapterus rhonchus. Despite some variations in the upwelling intensity, we show that the sea surface temperature is by far the main parameter to explain this northern shift. We also discuss the likely - and largely unknown - influence of the under-estimation of the detections because of the absence of sampling in the shallow coastal zone. The impact of such displacements is also discussed in term of regional management of these shared stocks

International conference ICAWA 2016 : extended book of abstract : the AWA project : ecosystem approach to the management of fisheries and the marine environment in West African waters

In Northwest Africa, the small pelagic fish are in abundance and play a crucial role for the food safety of populations. The pelagic resources are exploited both by small-scale artisanal and industrial fleets. The landing structure of the countries in the region has been in perpetual change during the last years. The sardinella has been more and more landed by fishermen in Morocco, while the sardine has become a target by fishing vessels in Mauritania and Senegal. This indicates a modification in the distribution areas of pelagic resources. To verify this hypothesis, an outstanding database consisting in 14 acoustic surveys with a consistent and high sampling intensity (2263 trawl hauls) conducted by the RV Fridtjof Nansen from 1995 to 2015 was investigated in this study to identify trends in distribution shifts in pelagic fishes. A focus was made on sardinellas and the main species in the southern part of the region. Two strong spatial indicators are used in this study: the latitudinal extreme location and the barycentre of biomasses. Two clear trends can be observed from the data analysed. Firstly, in the southern and tropical part of this system the typical trend is that pelagic species show an increasing northward distribution. This applies to S. aurita, Trachurus trecae, Chloroscombrus chrysurus, Sphyraena guachancho and Brachydeuterus auritu. A second group is observed, those that do not show any clear trend in distributional shift, but where the distribution is stable over the period. The typical species observed here are S. maderensis and Decapterus rhonchus. Despite some variations in the upwelling intensity, we show that the sea surface temperature is by far the main parameter to explain this northern shift. We also discuss the likely - and largely unknown - influence of the under-estimation of the detections because of the absence of sampling in the shallow coastal zone. The impact of such displacements is also discussed in term of regional management of these shared stocks

Biodiversité et habitats: Données des campagnes océanographiques dans la région du Courant des Canaries (CCLME)

Cette présentation résume les données obtenues au cours des 12 campagnes espagnoles et norvégiennes développées sur le plateau et le talus continental, entre les 20 et 2000 m de profondeur, dans la région CCLME, qui pourront être incorporées au SIG régional, dès la publication des résultats. Les bases de données disponibles incluent des informations faunistiques et paramètres environnementaux pris en 1350 stations de chalutage de fonds, 24 pélagiques et 449 échantillonnages du plancton, 209 dragages du benthos, 1269 stations de CTD et 966 heures (11,398 km) d’observations de mammifères et oiseaux marins. L’incorporation de ces informations au SIG permettra visualiser les cartes de distribution à l’échelle régionale des types de sédiments et variables océanographiques, des espèces demersales, benthiques et pélagiques, cétacés et oiseaux marins, (incluant celles vulnérables, en liste rouge ou endémiques), et leurs densités et biomasses. Comme produit final on aboutira à une vision globale de la biodiversité et des facteurs affectant sa distribution en Afrique noroccidental, ainsi que à la caractérisation et localisation des sites d’intérêt écologique ou biologique, ‘hot-spots’ de la biodiversité, écosystèmes vulnérables et aires marines protégées. Certains écosystèmes ont déjà été localisés dans le talus de la Mauritanie (géant récif corallien, canyons et montagne sous-marins) et du Maroc (canyon d’Agadir, communautés des grandes éponges et gorgonaires), ainsi que dans le plateau des îles de Cap Vert (fonds d’éponges, gorgonies et d’autres suspensivores). Une population de baleines jubartes provenant de l'hémisphère sud a été découverte d'occuper le plateau continental entre Conakry et la péninsule du Cap-Vert. Tandis que les analyses se développent et le processus d’identification taxonomique se finalise, le SIG pourrait inclure des informations déjà disponibles sur la localisation des mangroves, des 20 AMP et des 40 sites côtiers d’intérêt écologique; une révision exhaustive des contenus des projets internationaux développés dans la région (SIAP, BAGIS, ODINAFRICA) et de la bibliographie existante (Maurin, 1968; Bonnet et al., 1971; Domain, 1980; Lelouf, 1993, entre autres) permettrait compléter aussi la cartographie bionomique.FAO, NORA

Micronektonic acoustic density variations along Benguela Current Large Marine Ecosystem continental shelf from 1994 to 2001

ICAWA : International Conference AWA, Lanzarote, ESP, 17-/04/2018 - 20/04/2018The Benguela Current Large Marine Ecosystem (BCLME) is situated along the coast of south-western Africa, stretching from Tombua (Angola) in the north (16°N, 11°W) southwards to the east of the Cape of Good Hope (South Africa) (29°S, 17°E) and includes the study zone, from 17°S, 9°E to 31°S, 17°E. In this work, we focused on the Namibian continental shelf where fishing activities are mostly due to industrial fishing. Acoustic data were recorded with a 38 kHz echosounder, from 10 to 500 m depth over 8 surveys totalling 46 302 nmi from 1994 to 2001. To get homogenous data (i) only off-upwelling season surveys (October to June) were studied and (ii) only continental shelf data were considered (10-150 m). The mean volume backscattering strength (Sv in dB) was used as a micronektonic biomass proxy to assess its spatial inter-annual variability. Diel transition periods were removed from analyses to avoid micronektonic density changes bias due to diel vertical migrations. Data were echointegrated at a spatial resolution of 0,1 nmi*1 m depth using the Matecho tool. (i) On horizontal dimension, the variability in annual micronektonic densities was assessed using the mean Sv value for each 0,1 nmi Elementary Sample Unit (ESU). Then, hot and cold spots were computed from the combined analysis of the spatial correlation and the Moran's I index of these values. (ii) On vertical dimension, the change of micronektonic spatial structure between day and night was assessed using the mean Sv value for each 1 m depth step. The inter-annual variability inside the eastern boundary upwelling ecosystem of the BCLME was analysed. (i) No significant change in micronektonic density was observed over the study period. Mean micronektonic acoustic density values observed were lower than in other African Atlantic large marine ecosystems. (ii) Hot and cold spots were spatially stable over time. Further analysis of physico-chemical parameters should improve the understanding of this pattern. (iii) A different vertical structure was reported between day and night, suggesting a migration from bottom to surface at dusk, as in the well-known diel vertical migrations. In perspective, physical processes occurring in the water column from turbulence to mesoscale activities should be considered in future studies

International conference ICAWA 2017 and 2018 : extended book of abstract : the AWA project : ecosystem approach to the management of fisheries and the marine environment in West African waters

The Benguela Current Large Marine Ecosystem (BCLME) is situated along the coast of south-western Africa, stretching from Tombua (Angola) in the north (16°N, 11°W) southwards to the east of the Cape of Good Hope (South Africa) (29°S, 17°E) and includes the study zone, from 17°S, 9°E to 31°S, 17°E. In this work, we focused on the Namibian continental shelf where fishing activities are mostly due to industrial fishing. Acoustic data were recorded with a 38 kHz echosounder, from 10 to 500 m depth over 8 surveys totalling 46 302 nmi from 1994 to 2001. To get homogenous data (i) only off-upwelling season surveys (October to June) were studied and (ii) only continental shelf data were considered (10-150 m). The mean volume backscattering strength (Sv in dB) was used as a micronektonic biomass proxy to assess its spatial inter-annual variability. Diel transition periods were removed from analyses to avoid micronektonic density changes bias due to diel vertical migrations. Data were echointegrated at a spatial resolution of 0,1 nmi*1 m depth using the Matecho tool. (i) On horizontal dimension, the variability in annual micronektonic densities was assessed using the mean Sv value for each 0,1 nmi Elementary Sample Unit (ESU). Then, hot and cold spots were computed from the combined analysis of the spatial correlation and the Moran's I index of these values. (ii) On vertical dimension, the change of micronektonic spatial structure between day and night was assessed using the mean Sv value for each 1 m depth step. The inter-annual variability inside the eastern boundary upwelling ecosystem of the BCLME was analysed. (i) No significant change in micronektonic density was observed over the study period. Mean micronektonic acoustic density values observed were lower than in other African Atlantic large marine ecosystems. (ii) Hot and cold spots were spatially stable over time. Further analysis of physico-chemical parameters should improve the understanding of this pattern. (iii) A different vertical structure was reported between day and night, suggesting a migration from bottom to surface at dusk, as in the well-known diel vertical migrations. In perspective, physical processes occurring in the water column from turbulence to mesoscale activities should be considered in future studies

Acoustics surveys in North-West Africa reveal a spatial shift of small pelagic fish related to intense warming [résumé]

ICES. Working Group of Fisheries Acoustics, Science and Technology (WGFAST)., Somone, SEN, 25-/04/2022 - 28/04/2022In the southern part of the CCLME, northward shifts in the distribution of sardinella and other species have been attributed to an intense warming trend in sea surface temperature. Such warming is higher than 0.5 °C per decade in the southern part of the CCLME, the greatest in-crease in SST observed in the tropical Atlantic. The acoustics abundance of Sardinella aurita, the most abundant species along the coast, has increased in the subtropics and fallen in the inter-tropical region. Small pelagic acoustics assessment surveys confirm a robust northward shift of around 180 km per decade in S. aurita habitat, while S. maderensis did not move significantly. Spatial shifts in biomass from 70 to 230 kilometres were observed for six others exploited small pelagic species during the last 20 years, at similar ranges to those recorded for surface isotherms in their habitat. The change occurs more quickly in the central part of the CCLME. This shift widely overlaps national boundaries and combined to overexploitation adds a new threat on the pelagic fish resources. Such results are an advocacy to continue to lead acoustics survey on small pelagic in the West Africa

Intense warming causes a spatial shift of small pelagic fish : early warning for food security in North-West Africa [résumé]

ICAWA : International Conference AWA, Lanzarote, ESP, 17-/04/2018 - 20/04/2018Along the coast of North-West Africa, fish supply is important at both socio-economic and cultural levels. Reports by fishermen emphasise changes in the distribution of fish species important for food security. Northward shifts in the distribution of sardinella and other species have been attributed to a warming trend and the redistribution of upwelling intensity and productivity. As a result, the abundance of sardinella along the coast has increased in the subtropics and fallen in the intertropical region. Independent observational time series confirm a robust northward shift in Sardinella aurita since 1995, which we attribute to the intense warming of this region, where the greatest increase in sea surface temperature of all tropical regions is found. The spatial shifts in biomass of several hundred kilometres observed during the last 20 years are of the same order of magnitude as those recorded for surface isotherms in the sub-regional pelagic habitat of sardinella. Such changes are an important policy consideration for food security management in several West African countries

International conference ICAWA 2017 and 2018 : extended book of abstract : the AWA project : ecosystem approach to the management of fisheries and the marine environment in West African waters

Along the coast of North-West Africa, fish supply is important at both socio-economic and cultural levels. Reports by fishermen emphasise changes in the distribution of fish species important for food security. Northward shifts in the distribution of sardinella and other species have been attributed to a warming trend and the redistribution of upwelling intensity and productivity. As a result, the abundance of sardinella along the coast has increased in the subtropics and fallen in the intertropical region. Independent observational time series confirm a robust northward shift in Sardinella aurita since 1995, which we attribute to the intense warming of this region, where the greatest increase in sea surface temperature of all tropical regions is found. The spatial shifts in biomass of several hundred kilometres observed during the last 20 years are of the same order of magnitude as those recorded for surface isotherms in the sub-regional pelagic habitat of sardinella. Such changes are an important policy consideration for food security management in several West African countries