Spatial functionnal analysis application on fisheries acoustics data coupled with fine scale environmental data [résumé de poster]

ICES. Working Group of Fisheries Acoustics, Science and Technology (WGFAST), Somone, SEN, 25-/04/2022 - 28/04/2022In this work, we were interested in the application of functional, spatial data analysis (FSDA) on coupling acoustic (Sv) and environmental (water temperature, fluorescence, salinity and turbid-ity) data. To do this we use data from an acoustics fisheries surveys (R/V Thalassa, Ifremer, AWA campaign) carry out in West African waters using multifrequency echosounder (18, 38, 70, 120, 333 kHz) and a scanfish (high performance towed undulator). FSDA were compared to classical statistical methods namely multivariate functional principal component analysis, classical prin-cipal component analysis, classification on principal component scores, classical additive model, spatial functional additive model. The interest to improve such statistical analysis is applied here to the study the effect at fine scale of environmental parameters on the distribution of coastal sound scattered layers. We first considered an aggregated analysis of the environmental data then we considered a more complete analysis of the data via their functional characters

Spatial functionnal analysis application on fisheries acoustics data coupled with fine scale environmental data [résumé de poster]

ICES. Working Group of Fisheries Acoustics, Science and Technology (WGFAST), Somone, SEN, 25-/04/2022 - 28/04/2022In this work, we were interested in the application of functional, spatial data analysis (FSDA) on coupling acoustic (Sv) and environmental (water temperature, fluorescence, salinity and turbid-ity) data. To do this we use data from an acoustics fisheries surveys (R/V Thalassa, Ifremer, AWA campaign) carry out in West African waters using multifrequency echosounder (18, 38, 70, 120, 333 kHz) and a scanfish (high performance towed undulator). FSDA were compared to classical statistical methods namely multivariate functional principal component analysis, classical prin-cipal component analysis, classification on principal component scores, classical additive model, spatial functional additive model. The interest to improve such statistical analysis is applied here to the study the effect at fine scale of environmental parameters on the distribution of coastal sound scattered layers. We first considered an aggregated analysis of the environmental data then we considered a more complete analysis of the data via their functional characters

Acoustic study of water masses over Senegalese continental shelf : effect of environmental variable on the structure of zooplankton layers [résumé]

ICAWA : International Conference AWA, Dakar, SEN, 13-/12/2016 - 15/12/2016The macrozooplankton organisms aggregate at specific depths and occur as scattering layer on echosounder records. They constitute an important component in the marine food web in direct contact with primary producers. We review phytoplankton and zooplankton literature in Senegal, and then characterized the Senegalese water masses of the "Petite côte" on physicochemical and biological criteria using an in situ data set collected during an acoustics survey (ECOAO) led onboard FRV Antea in 2013. Then we described at fine scale spatial and temporal variation of macrozooplankton layers in relation with their environment. Two areas with different characteristics have been discriminated: the upwelling's cell area and the upwelling's offshore area more stratified, warm and sharply separated from the other area by a strong thermal boundary. The spatio-temporal variation of scattering layer's thickness of macrozooplankton is strongly influenced by depth and time of the day. The scattering layer's thickness increases with depth along a coast-high sea gradient, but no variation is reported along longitudinal plane i.e. North-South. In both areas nocturnal layers are thicker and deeper than diurnal ones. The hydrological structure of the water column also influence the macrozooplankton scattering layer. The scattering layer requires "stable" physical conditions which support vertical stratification. In the upwelling's area cell, the parameters correlated to scattering layer thickness during night time are chlorophyll 'a' and dissolved oxygen. In the upwelling's offshore area, temperature, water density and chlorophyll 'a' concentration have a significant effect on the scattering layer's thickness during the daytime. However, during the nighttime, chlorophyll 'a' has no significant effect on the scattering layer's thickness. This absence of correlation between chlorophyll 'a' and scattering layer thickness could be explained by an inverse diel vertical migration of a macrozooplankton group. On this basis we assume that trophic relationship between phytoplankton and macrozooplankton operate during the day at the surface

Acoustic study of water masses over Senegalese continental shelf : effect of environmental variable on the structure of zooplankton layers [résumé]

ICAWA : International Conference AWA, Dakar, SEN, 13-/12/2016 - 15/12/2016The macrozooplankton organisms aggregate at specific depths and occur as scattering layer on echosounder records. They constitute an important component in the marine food web in direct contact with primary producers. We review phytoplankton and zooplankton literature in Senegal, and then characterized the Senegalese water masses of the "Petite côte" on physicochemical and biological criteria using an in situ data set collected during an acoustics survey (ECOAO) led onboard FRV Antea in 2013. Then we described at fine scale spatial and temporal variation of macrozooplankton layers in relation with their environment. Two areas with different characteristics have been discriminated: the upwelling's cell area and the upwelling's offshore area more stratified, warm and sharply separated from the other area by a strong thermal boundary. The spatio-temporal variation of scattering layer's thickness of macrozooplankton is strongly influenced by depth and time of the day. The scattering layer's thickness increases with depth along a coast-high sea gradient, but no variation is reported along longitudinal plane i.e. North-South. In both areas nocturnal layers are thicker and deeper than diurnal ones. The hydrological structure of the water column also influence the macrozooplankton scattering layer. The scattering layer requires "stable" physical conditions which support vertical stratification. In the upwelling's area cell, the parameters correlated to scattering layer thickness during night time are chlorophyll 'a' and dissolved oxygen. In the upwelling's offshore area, temperature, water density and chlorophyll 'a' concentration have a significant effect on the scattering layer's thickness during the daytime. However, during the nighttime, chlorophyll 'a' has no significant effect on the scattering layer's thickness. This absence of correlation between chlorophyll 'a' and scattering layer thickness could be explained by an inverse diel vertical migration of a macrozooplankton group. On this basis we assume that trophic relationship between phytoplankton and macrozooplankton operate during the day at the surface

Sound-scattering layers related to pelagic habitat characteristics : the case [résumé de poster]

ICES. Working Group of Fisheries Acoustics, Science and Technology (WGFAST), Somone, SEN, 25-/04/2022 - 28/04/2022Understanding the relationship between sound scattering layers (SSLs) and pelagic habitat char-acteristics is a substantial step to apprehend ecosystem dynamics. SSLs are detected on echo sounders representing aggregated marine pelagic organisms. In this study, SSL characteristics of zooplankton and micronekton were identified during an upwelling event in two contrasting areas of the Senegalese continental shelf. Here a cold upwelling-influenced inshore area was sharply separated by a strong thermal boundary from a deeper, warmer, stratified offshore area. Mean SSL thickness and SSL vertical depth increased with the shelf depth. The thickest and deepest SSLs were observed in the offshore part of the shelf. Hence, zooplankton and micronek-ton seem to occur more frequently in stratified water conditions rather than in fresh upwelled water. Diel vertical and horizontal migrations of SSLs were observed in the study area. Diel pe-riod and physicochemical water characteristics influenced SSL depth and SSL thickness. Alt-hough chlorophyll-a concentration insignificantly affected SSL characteristics, the peak of chlo-rophyll a was always located above or in the middle of the SSLs, regularly matching with the peak of SSL biomass. Such observations indicate trophic relationships, suggesting SSLs to be mainly composed of phytoplanktivorous zooplankton and micronekton. Despite local hypoxia, below 30m depth, distribution patterns of SSLs indicate no vertical migration boundary. The results increase the understanding of the spatial organization of mid-trophic species and migra-tion patterns of zooplankton and micronekton, and they will also improve dispersal models for organisms in upwelling regions

Comparative analysis of pelagic compartment organization by bathymetric strata in the Canary Current Large Marine Ecosystem [résumé]

ICES. Working Group of Fisheries Acoustics, Science and Technology (WGFAST), Somone, SEN, 25-/04/2022 - 28/04/2022The Canary Current Large Marine Ecosystem (CCLME) is located along the North West African coast from Morocco to Guinea Bissau. In this work, 14 Nansen fisheries acoustics surveys have been led from the southern border of Senegal (12.15°N) to the Cape Blanc (20.77°N) during the hot wet season, i.e., outside the seasonal upwelling period, from 1995 to 2015. The aim of this study was to scrutinize the water column organization in a bathymetric gradient starting from the coast to the offshore area, discretised in three areas: inshore ( 500m). Here, we worked on acoustic sound scattering layers (SSL) and on the whole water column through echointegrated data (EI). SSL and EI descriptors highlighted sig-nificant difference between the three depth strata. Study of the Diel Vertical Migration (DVM) highlighted that volume backscattering coefficient (proxy of pelagic abundance) vertical profile from transition area has a pattern globally similar to offshore one while inshore presented an inversed pattern. Analyse of annual change using EI descriptors reveal one common trait: the number of SSLs significantly increase whatever the depth strata considered. This study high-lights differences and similarity in water column organization between depth strata

On the resiliency of an eastern boundary upwelling ecosystem exposed to multiple stressors : an acoustic approach [résumé de poster]

ICES. Working Group of Fisheries Acoustics, Science and Technology (WGFAST), Somone, SEN, 25-/04/2022 - 28/04/2022The resistance of an east border upwelling system was investigated using relative index of ma-rine pelagic biomass estimates under a changing environment spanning 20-years in the strongly exploited southern Canary Current Large marine Ecosystem (sCCLME). We divided the sCCLME in two parts (north and south of Cap Blanc), based on oceanographic regimes. We de-lineated two size-based groups ('plankton' and 'pelagic fish') corresponding to lower and higher trophic levels, respectively. Over the 20-year period, all spatial remote sensing environ-mental variables increased significantly, except in the area south of Cap Blanc where sea surface Chlorophyll-a concentrations declined and the upwelling favorable wind was stable. Relative index of marine pelagic abundance was higher in the south area compared to the north area of Cap Blanc. No significant latitudinal shift to the mass center was detected, regardless of trophic level. Relative pelagic abundance did not change, suggesting sCCLME pelagic organisms were able to adapt to changing environmental conditions. Despite strong annual variability and the presence of major stressors (overfishing, climate change), the marine pelagic ressources, mainly fish and plankton remained relatively stable over the two decades, advancing our understanding on the resistance of this east border upwelling system

On the resiliency of an eastern boundary upwelling ecosystem exposed to multiple stressors : an acoustic approach [résumé de poster]

ICES. Working Group of Fisheries Acoustics, Science and Technology (WGFAST), Somone, SEN, 25-/04/2022 - 28/04/2022The resistance of an east border upwelling system was investigated using relative index of ma-rine pelagic biomass estimates under a changing environment spanning 20-years in the strongly exploited southern Canary Current Large marine Ecosystem (sCCLME). We divided the sCCLME in two parts (north and south of Cap Blanc), based on oceanographic regimes. We de-lineated two size-based groups ('plankton' and 'pelagic fish') corresponding to lower and higher trophic levels, respectively. Over the 20-year period, all spatial remote sensing environ-mental variables increased significantly, except in the area south of Cap Blanc where sea surface Chlorophyll-a concentrations declined and the upwelling favorable wind was stable. Relative index of marine pelagic abundance was higher in the south area compared to the north area of Cap Blanc. No significant latitudinal shift to the mass center was detected, regardless of trophic level. Relative pelagic abundance did not change, suggesting sCCLME pelagic organisms were able to adapt to changing environmental conditions. Despite strong annual variability and the presence of major stressors (overfishing, climate change), the marine pelagic ressources, mainly fish and plankton remained relatively stable over the two decades, advancing our understanding on the resistance of this east border upwelling system

Comparative analysis of pelagic compartment organization by bathymetric strata in the Canary Current Large Marine Ecosystem [résumé]

ICES. Working Group of Fisheries Acoustics, Science and Technology (WGFAST), Somone, SEN, 25-/04/2022 - 28/04/2022The Canary Current Large Marine Ecosystem (CCLME) is located along the North West African coast from Morocco to Guinea Bissau. In this work, 14 Nansen fisheries acoustics surveys have been led from the southern border of Senegal (12.15°N) to the Cape Blanc (20.77°N) during the hot wet season, i.e., outside the seasonal upwelling period, from 1995 to 2015. The aim of this study was to scrutinize the water column organization in a bathymetric gradient starting from the coast to the offshore area, discretised in three areas: inshore ( 500m). Here, we worked on acoustic sound scattering layers (SSL) and on the whole water column through echointegrated data (EI). SSL and EI descriptors highlighted sig-nificant difference between the three depth strata. Study of the Diel Vertical Migration (DVM) highlighted that volume backscattering coefficient (proxy of pelagic abundance) vertical profile from transition area has a pattern globally similar to offshore one while inshore presented an inversed pattern. Analyse of annual change using EI descriptors reveal one common trait: the number of SSLs significantly increase whatever the depth strata considered. This study high-lights differences and similarity in water column organization between depth strata

On the robustness of an eastern boundary upwelling ecosystem exposed to multiple stressors

The resistance of an east border upwelling system was investigated using relative index of marine pelagic biomass estimates under a changing environment spanning 20-years in the strongly exploited southern Canary Current Large marine Ecosystem (sCCLME). We divided the sCCLME in two parts (north and south of Cap Blanc), based on oceanographic regimes. We delineated two size-based groups ("plankton" and "pelagic fish") corresponding to lower and higher trophic levels, respectively. Over the 20-year period, all spatial remote sensing environmental variables increased significantly, except in the area south of Cap Blanc where sea surface Chlorophyll-a concentrations declined and the upwelling favorable wind was stable. Relative index of marine pelagic abundance was higher in the south area compared to the north area of Cap Blanc. No significant latitudinal shift to the mass center was detected, regardless of trophic level. Relative pelagic abundance did not change, suggesting sCCLME pelagic organisms were able to adapt to changing environmental conditions. Despite strong annual variability and the presence of major stressors (overfishing, climate change), the marine pelagic ressources, mainly fish and plankton remained relatively stable over the two decades, advancing our understanding on the resistance of this east border upwelling system