Remote sensing techniques are used to study the large scale patterns related to the seasonal mode... more Remote sensing techniques are used to study the large scale patterns related to the seasonal modes of variability of the marine phytoplankton. Ten years of monthly composite maps of sea surface chlorophyll-a concentration and the PHYSAT database of four Phytoplanktonic Functional Types (PFTs), both from SeaWiFS, are used to investigate characteristics of phytoplankton seasonality in the trades and westerlies wind oceanic biomes, where data density is adequate. We use a combination of wavelet transform and statistical techniques that allow us to quantify both intensity and duration of the seasonal oscillation of chlorophyll-a concentration and PFTs relative occurrence, and to map these relationships. Next, the seasonal oscillations detected are related to four PFTs revealing six major global phytoplanktonic associations. Our results elucidate the intensity and duration of the seasonal dynamic of the chlorophyll-a concentration and of the relative occurrence of four PFTs at a global scale. Thus, the typology of the different types of seasonality is investigated. Finally, an overall agreement between the results and the biogeochemical provinces partition proposed by Longhurst is found, revealing a strong environmental control on the seasonal oscillation of primary producers and a clear latitudinal organization in the succession of the phytoplankton types. Results provided in this study quantify the seasonal oscillation of key structural parameters of the global ocean, and their potential implications for our understanding of ecosystem dynamics.
Le plateau continental sénégalais est soumis à un upwelling côtier saisonnier, sous l'étroite dép... more Le plateau continental sénégalais est soumis à un upwelling côtier saisonnier, sous l'étroite dépendance du régime des vents alizés. La température de surface, mesurée par télédétection, permet de caractériser l'intensité relative et) 'extension géographique superficielle de l'upwelling. L'eau résurgente en zone euphotique, riche en sels nutritifs, commande en partie l'intensité de la production primaire puis secondaire et ses effets possibles sur l'abondance et la distribution des poissons pélagiques, mesurées par écho-intégration, sont estimés. La liaison entre les événements thermiques observés et les mesures de densités établies par méthode acoustique permet de constater que si sur la côte Nord, les bancs de poissons sont localisés dans le périmètre côtier froid, sur la côte Sud, les fortes concentrations sont observées en dehors de la zoneactivede l'upwelling. Par ailleurs, l'analyse dynamique des upwellings successifs de 1984 à 1988 permet d'interpréter en partie, d'une part l'abondance moyenne élevée des espèces pélagiques constatée en 1985 et d'autre part les valeurs élevées observées localement en face du fleuve Casamance.
Tableau !.3 Formules de correction de dérive F(>.) utilisées par les auteurs cités plus haut pour... more Tableau !.3 Formules de correction de dérive F(>.) utilisées par les auteurs cités plus haut pour la calibration de CZCS (N est le numéro d•orbite).
For the first time, a recent bed of Crassostrea gasar is described into the present mangroves env... more For the first time, a recent bed of Crassostrea gasar is described into the present mangroves environment in the marine estuary of the Sine-Saloum (Senegal). The bivalves shells position, in situ in the clayed sediment, indicates a biostrome and not a kjôkkenmôding. It's compared with the beds of Crassostrea gryphoides, in the upper Burdigalian of the rhodanian basin, in a similar environment of tropical estuaries. This observation adds to other data (ostra-coda, palynology) and confirms the tropical climate at this time in our areas.
Post-larval prediction is important, as post-larval supply allows us to understand juvenile fish ... more Post-larval prediction is important, as post-larval supply allows us to understand juvenile fish populations. No previous studies have predicted post-larval fish species richness and abundance combining molecular tools, machine learning, and past-days remotely sensed oceanic conditions (RSOCs) obtained in the days just prior to sampling at different scales. Previous studies aimed at modeling species richness and abundance of marine fishes have mainly used environmental variables recorded locally during sampling and have merely focused on juvenile and adult fishes due to the difficulty of obtaining accurate species richness estimates for post-larvae. The present work predicted post-larval species richness (identified using DNA barcoding) and abundance at 2 coastal sites in SW Madagascar using random forest (RF) models. RFs were fitted using combinations of local variables and RSOCs at a small-scale (8 d prior to fish sampling in a 50 × 120 km2 area), meso-scale (16 d prior; 100 × 200 km2), and large-scale (24 d prior; 200 × 300 km2). RF models combining local and small-scale RSOC variables predicted species richness and abundance best, with accuracy around 70 and 60%, respectively. We observed a small variation of RF model performance in predicting species richness and abundance among all sites, highlighting the consistency of the predictive RF model. Moreover, partial dependence plots showed that high species richness and abundance were predicted for sea surface temperatures <27.0°C and chlorophyll a concentrations <0.22 mg m-3. With respect to temporal changes, these thresholds were solely observed from November to December. Our results suggest that, in SW Madagascar, species richness and abundance of post-larval fish may only be predicted prior to the ecological impacts of tropical storms on larval settlement success.
IV Congress of Marine Sciences, Encuentro de la Oceanografia Fisica Espanola (EOF 2014), 11-13 Ju... more IV Congress of Marine Sciences, Encuentro de la Oceanografia Fisica Espanola (EOF 2014), 11-13 June 2014, Las Palmas de Gran Canaria.-- 1 page
ABS TRACT Casamance river is a sursaline inverse estuary. A precise knowledge of bathymetry of it... more ABS TRACT Casamance river is a sursaline inverse estuary. A precise knowledge of bathymetry of its numerous marshy areas would allow to predict with a model, jts salinity which governs economic activities as fishing and rice-growing. Four campaigns for ground truth measurements have been done with determination of the usual hydrobiological parameterS.The use of a hand-borne radiometer with spectral windows identical to the three Spot channels, used over various type of shallow waters showed that the channel 3/channel 1 ratio correlates highly with chlorophyll content (C3/C1 = K.Ln(Chl.1) and, on other hand with depth in the 0.8-0.02 meters range (C3/Cl=-K.Ln(z) 1. Using a Spot imagery for October 86 (end of rainy season) , we classified 4 water's category: "deep water" (> O. 6m) , shallow water,partly emerged sludge and land. Similarly to ground measurements resultsfwe defined with ttie Spot channel 3/channel 1 ratio a semi-quantitative scale of depths. On test areas bathymetry was determined by relative value. This preliminary results need to be refined, and the depth scale to be improved and extended to larger areas; this will allow to take in account the shallow waters areas in the salinity budget of Casamance river.
The present study deals with the correction of chlorophyll-a (Chl-a) estimated from fluorescence ... more The present study deals with the correction of chlorophyll-a (Chl-a) estimated from fluorescence data, the proposed method test for the first time a ratio between Chl-a from high-performance liquid chromatography (HPLC) measurements and its corresponding fluorescence. Considering the variability of this ratio with depth, the adjustment of fluorescence data was greatly improved. This ratio increase in the oceanic surface layer probably because of the quenching effect, however, it decreases and becomes stable with depth. This approach can be used to correct fluorescence values for future large datasets of biological variables. Finally, this method is designed for a global scale and/or regional applications.
HAL (Le Centre pour la Communication Scientifique Directe), Apr 22, 2022
This study introduces the concept of portfolios of distribution maps, which consist of the reduce... more This study introduces the concept of portfolios of distribution maps, which consist of the reduced set of empirical orthogonal maps that best explain spatial biomass distributions of a given species over time. The approach is demonstrated for the distributions of common octopus (Octupus vulgaris) off Mauritania over the last thirty years. The maps in the portfolio are the subset of empirical orthogonal maps that allowed to recover 60% of the spatiotemporal biomass distribution variance and whose temporal weights were significantly correlated with abundance. For octopus during the hot season, one single map explained half of the overall variance of the distribution data, while during the cold season, the portfolio of octopus distribution maps consisted of four maps, with the temporal weights of the second map being negatively correlated with upwelling intensity six months before. The size of each portfolio represents the number of distinct spatial patterns describing octopus spatial distributions. Assuming that specific but hidden processes * Corresponding author 2 explain each biomass spatial distribution of the portfolio, the size of a map portfolio might be interpreted as a proxy for system resilience. A small portfolio could reflect systems that are more fragile.
This data set is the result of the calculation of an original "enrichment index" (EI) f... more This data set is the result of the calculation of an original "enrichment index" (EI) from chlorophyll-a (chl-a) remote sensing data (MODIS-Aqua sensor) and initially dedicated to highlight localized chl-a enrichments associated to isolated seamounts and islands in the South West Indian Ocean, in order to estimate their contribution in increasing the local primary productivity. Details and results are described in the DSR-II paper entitled "Satellite observations of phytoplankton enrichments around seamounts in the South West Indian Ocean with a special focus on the Walters Shoal" from Demarcq et al. 2020.<br> 1. Initial data used<br> We used daily L3 data chl-a and sea surface temperature (SST) collected by the MODIS (Moderate-resolution Imaging Spectroradiometer) sensor on board the Aqua platform (downloaded from https://oceancolor.gsfc.nasa.gov/) from January 2003 to December 2018. This has a spatial resolution of 1/24° (ca. 4.5–5 km). The data covers the region (45°S – 10°S / 25°W – 80°W).<br> 2. The calculation method<br> The calculations were done at the pixel level. The EI is the difference (expressed in %) between the value of each 'candidate pixel' and its medium range surrounding, defined as the average value of all chl-a values around the candidate pixel between a fix range of distance between 30 and 90 km, the R1 and R2 terms of the equation enclosed.<br> 3. Data sets<br> The data set contains two files:<br> - the monthly climatology (12 frames) of the EI from January to December (2003 to 2018 average), in an internally compressed netCDF-4 format (NC-compliant or almost)<br> - the yearly average of the EI (period 01/2003 - 12/2018)<br> <br> Two images are joined with this data set:<br> - a "technical view" of the yearly average of the index for the full region sub-region (45°S – 10°S / 25°W – 80°W)<br> (file: indsw4_modis_p100_4km_16y_20030101_20181231.R2018.0.enrichment-index.dist-30-90km.png). - a slightly improved view of the yearly average of the index for the sub-region (40°S – 10°S / 30°W – 70°W [...]
Knowledge of ocean surface dynamics is crucial for oceanographic and climate research. The satell... more Knowledge of ocean surface dynamics is crucial for oceanographic and climate research. The satellite-tracked movements of hundreds of drifters deployed by research and voluntary observing vessels provide high-frequency and high-resolution information on near-surface currents around the globe. Consequently, they constitute a major component of the Global Ocean Observing System (GOOS). However, maintaining this array is costly and in some oceanic regions such as the tropics, spatio-temporal coverage is limited. Here, we demonstrate that the GPS-buoy equipped fish aggregating devices (FADs) used in tropical tuna fisheries to increase fishing success are also capable of providing comparable near-surface current information. We analyzed millions of position data collected between 2008 and 2014 from more than 15,000 FADs and 2,000 drifters, and combined this information with remotely-sensed near-surface current data to demonstrate that the surface velocity components of FADs and drifters are highly correlated in the Atlantic and Indian Oceans. While it was noted that the subsurface structures of FADs did slow them down relative to the drifters, particularly in the Atlantic Ocean, this bias was measurable and could be accounted for
... African Journal of Marine Science is co-published by NISC (Pty) Ltd and Taylor &amp;amp;a... more ... African Journal of Marine Science is co-published by NISC (Pty) Ltd and Taylor &amp;amp;amp;amp;amp; Francis ... 1 IRD, UMR 212 EME, CRHMT, avenue Jean Monnet, 34209, Sète, France 2 Branch Fisheries, Department of Agriculture, Forestry and Fisheries, Private Bag X2, Rogge Bay 8012, South ...
HAL (Le Centre pour la Communication Scientifique Directe), Apr 17, 2018
ICAWA : International Conference AWA, Lanzarote, ESP, 17-/04/2018 - 20/04/2018Along the coast of ... more 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
Remote sensing techniques are used to study the large scale patterns related to the seasonal mode... more Remote sensing techniques are used to study the large scale patterns related to the seasonal modes of variability of the marine phytoplankton. Ten years of monthly composite maps of sea surface chlorophyll-a concentration and the PHYSAT database of four Phytoplanktonic Functional Types (PFTs), both from SeaWiFS, are used to investigate characteristics of phytoplankton seasonality in the trades and westerlies wind oceanic biomes, where data density is adequate. We use a combination of wavelet transform and statistical techniques that allow us to quantify both intensity and duration of the seasonal oscillation of chlorophyll-a concentration and PFTs relative occurrence, and to map these relationships. Next, the seasonal oscillations detected are related to four PFTs revealing six major global phytoplanktonic associations. Our results elucidate the intensity and duration of the seasonal dynamic of the chlorophyll-a concentration and of the relative occurrence of four PFTs at a global scale. Thus, the typology of the different types of seasonality is investigated. Finally, an overall agreement between the results and the biogeochemical provinces partition proposed by Longhurst is found, revealing a strong environmental control on the seasonal oscillation of primary producers and a clear latitudinal organization in the succession of the phytoplankton types. Results provided in this study quantify the seasonal oscillation of key structural parameters of the global ocean, and their potential implications for our understanding of ecosystem dynamics.
Le plateau continental sénégalais est soumis à un upwelling côtier saisonnier, sous l'étroite dép... more Le plateau continental sénégalais est soumis à un upwelling côtier saisonnier, sous l'étroite dépendance du régime des vents alizés. La température de surface, mesurée par télédétection, permet de caractériser l'intensité relative et) 'extension géographique superficielle de l'upwelling. L'eau résurgente en zone euphotique, riche en sels nutritifs, commande en partie l'intensité de la production primaire puis secondaire et ses effets possibles sur l'abondance et la distribution des poissons pélagiques, mesurées par écho-intégration, sont estimés. La liaison entre les événements thermiques observés et les mesures de densités établies par méthode acoustique permet de constater que si sur la côte Nord, les bancs de poissons sont localisés dans le périmètre côtier froid, sur la côte Sud, les fortes concentrations sont observées en dehors de la zoneactivede l'upwelling. Par ailleurs, l'analyse dynamique des upwellings successifs de 1984 à 1988 permet d'interpréter en partie, d'une part l'abondance moyenne élevée des espèces pélagiques constatée en 1985 et d'autre part les valeurs élevées observées localement en face du fleuve Casamance.
Tableau !.3 Formules de correction de dérive F(>.) utilisées par les auteurs cités plus haut pour... more Tableau !.3 Formules de correction de dérive F(>.) utilisées par les auteurs cités plus haut pour la calibration de CZCS (N est le numéro d•orbite).
For the first time, a recent bed of Crassostrea gasar is described into the present mangroves env... more For the first time, a recent bed of Crassostrea gasar is described into the present mangroves environment in the marine estuary of the Sine-Saloum (Senegal). The bivalves shells position, in situ in the clayed sediment, indicates a biostrome and not a kjôkkenmôding. It's compared with the beds of Crassostrea gryphoides, in the upper Burdigalian of the rhodanian basin, in a similar environment of tropical estuaries. This observation adds to other data (ostra-coda, palynology) and confirms the tropical climate at this time in our areas.
Post-larval prediction is important, as post-larval supply allows us to understand juvenile fish ... more Post-larval prediction is important, as post-larval supply allows us to understand juvenile fish populations. No previous studies have predicted post-larval fish species richness and abundance combining molecular tools, machine learning, and past-days remotely sensed oceanic conditions (RSOCs) obtained in the days just prior to sampling at different scales. Previous studies aimed at modeling species richness and abundance of marine fishes have mainly used environmental variables recorded locally during sampling and have merely focused on juvenile and adult fishes due to the difficulty of obtaining accurate species richness estimates for post-larvae. The present work predicted post-larval species richness (identified using DNA barcoding) and abundance at 2 coastal sites in SW Madagascar using random forest (RF) models. RFs were fitted using combinations of local variables and RSOCs at a small-scale (8 d prior to fish sampling in a 50 × 120 km2 area), meso-scale (16 d prior; 100 × 200 km2), and large-scale (24 d prior; 200 × 300 km2). RF models combining local and small-scale RSOC variables predicted species richness and abundance best, with accuracy around 70 and 60%, respectively. We observed a small variation of RF model performance in predicting species richness and abundance among all sites, highlighting the consistency of the predictive RF model. Moreover, partial dependence plots showed that high species richness and abundance were predicted for sea surface temperatures &lt;27.0°C and chlorophyll a concentrations &lt;0.22 mg m-3. With respect to temporal changes, these thresholds were solely observed from November to December. Our results suggest that, in SW Madagascar, species richness and abundance of post-larval fish may only be predicted prior to the ecological impacts of tropical storms on larval settlement success.
IV Congress of Marine Sciences, Encuentro de la Oceanografia Fisica Espanola (EOF 2014), 11-13 Ju... more IV Congress of Marine Sciences, Encuentro de la Oceanografia Fisica Espanola (EOF 2014), 11-13 June 2014, Las Palmas de Gran Canaria.-- 1 page
ABS TRACT Casamance river is a sursaline inverse estuary. A precise knowledge of bathymetry of it... more ABS TRACT Casamance river is a sursaline inverse estuary. A precise knowledge of bathymetry of its numerous marshy areas would allow to predict with a model, jts salinity which governs economic activities as fishing and rice-growing. Four campaigns for ground truth measurements have been done with determination of the usual hydrobiological parameterS.The use of a hand-borne radiometer with spectral windows identical to the three Spot channels, used over various type of shallow waters showed that the channel 3/channel 1 ratio correlates highly with chlorophyll content (C3/C1 = K.Ln(Chl.1) and, on other hand with depth in the 0.8-0.02 meters range (C3/Cl=-K.Ln(z) 1. Using a Spot imagery for October 86 (end of rainy season) , we classified 4 water's category: "deep water" (> O. 6m) , shallow water,partly emerged sludge and land. Similarly to ground measurements resultsfwe defined with ttie Spot channel 3/channel 1 ratio a semi-quantitative scale of depths. On test areas bathymetry was determined by relative value. This preliminary results need to be refined, and the depth scale to be improved and extended to larger areas; this will allow to take in account the shallow waters areas in the salinity budget of Casamance river.
The present study deals with the correction of chlorophyll-a (Chl-a) estimated from fluorescence ... more The present study deals with the correction of chlorophyll-a (Chl-a) estimated from fluorescence data, the proposed method test for the first time a ratio between Chl-a from high-performance liquid chromatography (HPLC) measurements and its corresponding fluorescence. Considering the variability of this ratio with depth, the adjustment of fluorescence data was greatly improved. This ratio increase in the oceanic surface layer probably because of the quenching effect, however, it decreases and becomes stable with depth. This approach can be used to correct fluorescence values for future large datasets of biological variables. Finally, this method is designed for a global scale and/or regional applications.
HAL (Le Centre pour la Communication Scientifique Directe), Apr 22, 2022
This study introduces the concept of portfolios of distribution maps, which consist of the reduce... more This study introduces the concept of portfolios of distribution maps, which consist of the reduced set of empirical orthogonal maps that best explain spatial biomass distributions of a given species over time. The approach is demonstrated for the distributions of common octopus (Octupus vulgaris) off Mauritania over the last thirty years. The maps in the portfolio are the subset of empirical orthogonal maps that allowed to recover 60% of the spatiotemporal biomass distribution variance and whose temporal weights were significantly correlated with abundance. For octopus during the hot season, one single map explained half of the overall variance of the distribution data, while during the cold season, the portfolio of octopus distribution maps consisted of four maps, with the temporal weights of the second map being negatively correlated with upwelling intensity six months before. The size of each portfolio represents the number of distinct spatial patterns describing octopus spatial distributions. Assuming that specific but hidden processes * Corresponding author 2 explain each biomass spatial distribution of the portfolio, the size of a map portfolio might be interpreted as a proxy for system resilience. A small portfolio could reflect systems that are more fragile.
This data set is the result of the calculation of an original "enrichment index" (EI) f... more This data set is the result of the calculation of an original "enrichment index" (EI) from chlorophyll-a (chl-a) remote sensing data (MODIS-Aqua sensor) and initially dedicated to highlight localized chl-a enrichments associated to isolated seamounts and islands in the South West Indian Ocean, in order to estimate their contribution in increasing the local primary productivity. Details and results are described in the DSR-II paper entitled "Satellite observations of phytoplankton enrichments around seamounts in the South West Indian Ocean with a special focus on the Walters Shoal" from Demarcq et al. 2020.<br> 1. Initial data used<br> We used daily L3 data chl-a and sea surface temperature (SST) collected by the MODIS (Moderate-resolution Imaging Spectroradiometer) sensor on board the Aqua platform (downloaded from https://oceancolor.gsfc.nasa.gov/) from January 2003 to December 2018. This has a spatial resolution of 1/24° (ca. 4.5–5 km). The data covers the region (45°S – 10°S / 25°W – 80°W).<br> 2. The calculation method<br> The calculations were done at the pixel level. The EI is the difference (expressed in %) between the value of each 'candidate pixel' and its medium range surrounding, defined as the average value of all chl-a values around the candidate pixel between a fix range of distance between 30 and 90 km, the R1 and R2 terms of the equation enclosed.<br> 3. Data sets<br> The data set contains two files:<br> - the monthly climatology (12 frames) of the EI from January to December (2003 to 2018 average), in an internally compressed netCDF-4 format (NC-compliant or almost)<br> - the yearly average of the EI (period 01/2003 - 12/2018)<br> <br> Two images are joined with this data set:<br> - a "technical view" of the yearly average of the index for the full region sub-region (45°S – 10°S / 25°W – 80°W)<br> (file: indsw4_modis_p100_4km_16y_20030101_20181231.R2018.0.enrichment-index.dist-30-90km.png). - a slightly improved view of the yearly average of the index for the sub-region (40°S – 10°S / 30°W – 70°W [...]
Knowledge of ocean surface dynamics is crucial for oceanographic and climate research. The satell... more Knowledge of ocean surface dynamics is crucial for oceanographic and climate research. The satellite-tracked movements of hundreds of drifters deployed by research and voluntary observing vessels provide high-frequency and high-resolution information on near-surface currents around the globe. Consequently, they constitute a major component of the Global Ocean Observing System (GOOS). However, maintaining this array is costly and in some oceanic regions such as the tropics, spatio-temporal coverage is limited. Here, we demonstrate that the GPS-buoy equipped fish aggregating devices (FADs) used in tropical tuna fisheries to increase fishing success are also capable of providing comparable near-surface current information. We analyzed millions of position data collected between 2008 and 2014 from more than 15,000 FADs and 2,000 drifters, and combined this information with remotely-sensed near-surface current data to demonstrate that the surface velocity components of FADs and drifters are highly correlated in the Atlantic and Indian Oceans. While it was noted that the subsurface structures of FADs did slow them down relative to the drifters, particularly in the Atlantic Ocean, this bias was measurable and could be accounted for
... African Journal of Marine Science is co-published by NISC (Pty) Ltd and Taylor &amp;amp;a... more ... African Journal of Marine Science is co-published by NISC (Pty) Ltd and Taylor &amp;amp;amp;amp;amp; Francis ... 1 IRD, UMR 212 EME, CRHMT, avenue Jean Monnet, 34209, Sète, France 2 Branch Fisheries, Department of Agriculture, Forestry and Fisheries, Private Bag X2, Rogge Bay 8012, South ...
HAL (Le Centre pour la Communication Scientifique Directe), Apr 17, 2018
ICAWA : International Conference AWA, Lanzarote, ESP, 17-/04/2018 - 20/04/2018Along the coast of ... more 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
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