Search

Precipitation regime shifts in the Sahel have dramatic humanitarian and economic consequences such as during the 1970's and 1980's severe droughts. Though Sahel precipitation changes during the late 20th century have been extensively studied, little is known about the decadal variability prior to the 20th century. Some evidences suggest that during the second half of the 19th century the Sahel was as much or even more rainy than during the 1950's and 1960's. Here, we reproduce such anomalous Sahel humid period in the late-19th century by means of climate simulations. We show that this increase of rainfall was associated with an anomalous supply of humidity and higher-than-normal deep convection in the middle and high troposphere. We present evidence suggesting that Sea Surface Temperatures (SSTs) in the Atlantic basin played the dominant role in driving decadal Sahel rainfall variability in this early period.

In fisheries acoustics the analysis of data usually often concern biomass assessment mainly for small pelagic fish stocks using the well-known echointergration approach. Other can concern the analysis of single fish using their target strength (TS in dB) and more seldom analysis can also be done with the fish school descriptors using e.g. shoal extraction method (Movies+, Ifremer Software). In the framework of the Preface project we have focused on the micronektonic layers observed by scientific echosounder. Matecho, a friendly automatized processing method to extract information and perform echo-integration, fish shoal extraction and also performs a segmentation, on each zone of a cruise with a constant twilight, of the echointegrated echogram from an echo level threshold fixed by user to extract micronektonic layers in the water column. Here we describe this methodology which allows an accurate description of the spatial organisation and structuration of the marine ecosystem. The process is based on three main steps which consist in : (i) adjust the echo level threshold in dB, (ii) the extraction of the echoes inside each contours and the calculation of the layer descriptors, (iii) and then the correction of the extraction. Finally the echo segmentation, setup to extract micronektonic sound scattered layer, allows to get 34 layers descriptors, e.g., minimum/maximum depth (m), geographical position in 3D, maximum depth width (m), duration of the layer, surface covered by the layer, mean volume backscattering strength 'Sv' (dB re 1 m-1)': mean nautical area scattered coefficient 'Sa' (or NASC m2 nmi-2), to characterise their spatial position in the water column and acoustics properties. Moreover, a second class of descriptors, classified by elementary sampling unit (ESU), are estimated e.g. number of layer per ESU, layer depth per ESU. An innovative descriptor is also computed using this methodological approach: the water column fulling rate per layer and per ESU. Both classes of descriptors are then available for ecological studies.

Small pelagic fish (SPF) species are heavily exploited in eastern boundary upwelling systems (EBUS) as their transformation products are increasingly used in the world food chain. Management relies on regular monitoring, but there is a lack of robust theories for the emergence of the populations’ traits and their evolution in highly variable environments. This work aims to address existing knowledge gaps by combining physical and biogeochemical modelling with an individual life-cycle based model applied to round sardinella (Sardinella aurita) off northwest Africa, a key species for regional food security. Our approach focused on the processes responsible for seasonal migrations, spatio-temporal size-structure, and interannual biomass fluctuations. Emergence of preferred habitat resulted from interactions between natal homing behaviour and environmental variability that impacts early life stages. Exploration of the environment by the fishes was determined by swimming capabilities, mesoscale to regional habitat structure, and horizontal currents. Fish spatio-temporal abundance variability emerged from a complex combination of distinct life-history traits. An alongshore gradient in fish size distributions is reported and validated by in situ measurements. New insights into population structure are provided, within an area where the species is abundant year-round (Mauritania) and with latitudinal migrations of variable (300 to 1200 km) amplitude. Interannual biomass fluctuations were linked to modulations of fish recruitment over the Sahara Bank driven by variability in alongshore current intensity. The identified processes constitute an analytical framework that can be implemented in other EBUS and used to explore impacts of regional climate change on SPF.

The bonga shad (Ethmalosa fimbriata) is the third exploited of the small pelagics (after Sardinella aurita and S. maderensis) in the Senegalese waters and is commonly consumed locally. This fishery is mainly practiced by artisanal fishermen and is of great importance for the Senegalese economy as for food security in the region. Our investigations are aimed to inform the selection of management tools based on the dynamics of bonga shad exploitation to increase the likelihood of fishermen. The current rate of exploitation (E) was estimated (0.8), updating current statute (fully exploited) and indicating that the bonga shad in Senegal is over-fished. Moreover, we report a seasonal variability in recruitment and biomass of the Senegalese bonga shad, and a downward trend over the study period as well as a maximum size decrease of -8.8 cm (18 %) in 63 years. Such changes are attributed to increase in fishing capacity. To reverse the overexploitation status of the bonga shad stock, it is necessary to put the mesh of encircling nets from 40mm to 60 mm, to reduce the fishing effort drastically, apply regulations on the capture, sale and processing of juveniles and exclusion of seiners and monofilaments on the Senegalese Southern Coast.

The micronectonic 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 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. Then we described at fine scale spatial and temporal variation of micronektonic 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 micronectonic is strongly influenced by depth and the time of the day. The continental shelf scattering layer's thickness increases with depth, but no variation is reported in longitudinal plane. In both areas nocturnal layers are thicker and deeper than diurnal ones. The hydrological structure of the water column also influence the micronectonic scattering layer. The scattering layer requires "stable" physical conditions which support vertical stratification. In the upwelling's area cell, the chlorophyll-a (CHL) concentration is correlated to scattering layer thickness during night time. In the upwelling's offshore area, sea temperature, water density and oxygen have a significant effect on the scattering layer's thickness during the nightime. However, during the daytime, CHL has a significant effect on the scattering layer's thickness. This correlation between CHL and scattering layer thickness in the upwelling's offshore area during day could be explained by an inverse diel vertical migration of a micronectonic group. On this basis we assume that trophic relationship between phytoplankton and micronecton operate during the day at the surface in this area.

The coastal location of the Senegal induces specific heat wave (HW) events. HWs are defined as daily temperature (daily maximum or minimum temperature, or mean apparent temperature) higher than the 95th moving percentile during at least three consecutive days over the boreal spring period (Mars-April-May, 1979-2014). A hierarchical classification enables to define three homogeneous regions in terms of HW occurrences over Senegal (Zone #1, #2 and #3, from West to East). In order to study how atmospheric circulation is linked to these HW occurrences, composites of anomaly fields of ERA-Interim reanalysis have been computed using as reference date the starting day of each HW detected in GSOD (Global Summary of the Day) observations database. Results show that two patterns control the occurrence of HWs: regional-scale positive pressure anomalies centred around 35°N-10°W, and more local negative anomalies around 20°N-15°W. This structure leads to enhanced north-easterly winds advecting higher temperatures and moister air over the three zones of Senegal, and lower temperatures and drier air over the central Sahel. The intensity of this relationship is the largest for Zone #1, intermediate for #2 and the weakest for #3. The increased moisture signal over Senegal is highest for the composites associated with minimum and apparent temperature. Indices linked to this structure can be used to evaluate the predictability of such HW events.

In Atlantic Africa there is a crucial need to better assess the effect of climate change on marine ecosystems, particularly over the continental shelf and inside the national exclusive economic zones. Nevertheless there is a lack of observation carried out in the African ecosystems and the times series are often short or disrupted. Space-based observations allow precise synoptic observation of marine ecosystem and is often use to monitor, e.g., Eastern boundary upwelling ecosystems, from 36 years of constant monitoring from some major parameters as Sea Surface Temperature and more than twenty years for Ocean-Colour related parameters as surface primary productivity. The spatially heterogeneous trends observed show that these systems are highly variable, at temporal scales decades) that potentially impact some of their marine resources at rates that compete with the decline of human activities, beyond over-fishing. In this work we will present the effect of global warming at regional level for the three large marine ecosystems of Atlantic Africa on the sea surface temperature, wind stress and chlorophyll concentration as a proxy of primary production. The Canary and the Benguela systems are particularly impacted by the global warming, especially in their tropical parts, while Pacific systems show a more stable trend, due to their constantly high activity that partly counteracts some effects of the global warming.

Using the segmentation algorithm within Matecho (Perrot et al., 2018) we are able to deliver 15 descriptors to characterize the acoustic micronektonic layers in the water column. Even if the species composition is not known, these descriptors which are obtained using the same methodology allow for comparison between ecosystems and to study inter-annual variability. Some of these descriptors are new and others are based on the ones usually used to characterize pelagic fish schools using echointegration per shoal (Weill et al., 1993). In this work we will focus on the new ones and show some application cases in the three Atlantic African Large Marine Ecosystems, to monitor potential perturbations due to global change. All layer descriptors are estimated per layer and per elementary sampling unit of 0.1 nautical miles (ESU) with an accuracy of 1 meter depth. In this study we present four classes of descriptors: spatial (e.g. altitude, mean depth, minimal depth); morphological (e.g. width, ESU number, filling rate of water column); acoustic (e.g. mean volume backscattering strength Sv (dB)) and the layer number per ESU. In this study we focus on the original descriptors: (i) Filling rate of the water column (%): this indicator is based on the calculation of the width of the micronektonic layer vs. the local bottom depth. (ii) Filling rate contribution of first layer (%): this indicator shows the contribution of the first layer (the closest layer of surface) in the global filling rate. It is computed by dividing the filling rate of first layer by the filling rate of all layers. (iii) Number of layers: this indicator is calculated for each ESU, giving the number of layers in this water column. The descriptors have been computed over more than 1 million of ESUs, 992 737 in the CCLME, 166 183 in the GCLME and 462 807 in the BCLME. Such descriptors allow classification of micronekton layers and appear relevant to monitor changes in the ecosystem. Next step will be to use multifrequency or even wide-band data to improve the quality of descriptors. They were efficiently applied to study diel vertical behaviour as well as the effect of water mass characteristics on the spatial structure of the layers. In future applications it should help in the classification of the layers per functional group as well as to improve our knowledge on ecosystem organization and functioning.

A consistent Sea Surface Salinity (SSS) signature of the tropical Atlantic meridional and equatorial interannual modes is extracted from in situ observations and a regional numerical simulation, by a statistical analysis on the 1980-2012 period. Oceanic and/or atmospheric processes responsible for the signature of each mode are identified through a mixed-layer salt budget in the validated model. The meridional mode is associated in spring with a meridional SSS dipole in the equatorial band, due to changes in fresh water flux related to a meridional shift of the Inter-Tropical Convergence Zone (ITCZ). It is also associated with large SSS anomalies in the north and south west tropical Atlantic, due to advection of relatively fresh equatorial waters by strengthened western boundary currents, and off the Congo River where both meridional and vertical advection are involved. The equatorial mode is associated in summer with 3 zonal bands of alternating SSS anomalies between 5°S and 10°N. The southernmost band is due to vertical advection and diffusion at the mixed layer base, the two others to a shift of the ITCZ-related rainfall maximum, with additional contribution of meridional advection in the northernmost band. The equatorial mode also leads to large SSS anomalies in the North Brazil Current retroflection region, mainly due to horizontal advection of equatorial SSS anomalies. The SSS signatures of the meridional and equatorial modes are well captured by the SMOS satellite during particular events.

Diel vertical migration (DVM) of micronekton is a behavioural mechanism driven by a trade-off between predator avoidance and access to prey. This trade-off is controlled by environmental forcing that can lead to changes of DVM pattern under changing environmental conditions. Time series of hydro acoustic surveys between 1995 – 2015 of three large Atlantic ecosystems (Canary Current - CCLME, Guinea Current - GCLME, and Benguela Current - BCLME) were analysed to calculate DVM patterns based on volume backscattering strength (Sv). DVM related descriptors (n=15) were calculated for areas according to bathymetric definitions (shelf = 10 – 150 m bottom depth, slope = 150 – 500 m bottom depth, and plain > 500 m bottom depth). Typical DVM I pattern, with micronekton descending during daytime and ascending during night-time, were observed on the slope and plain in all three ecosystems, but not on the shelf with only negative day-night values in the CCLME and BCLME. Lower daytime Sv values during the day compared to night-time suggest either less dense patches of micronekton leading to negative day-night differences in the CCLME and GCLME or insufficient measurements of certain depth strata (e.g., 0 – 10 m surface). Only a few significant and different DVM descriptors suggest a change in the CCLME and the GCLME in the last 20 years. All other insignificant descriptors assume natural variability in large Atlantic ecosystems. Our results provide insight into inter-annual variability in micronekton DVM patterns.

Fronts, eddies, and upwelling shape larval fish habitats in the Canary Current Ecosystem. In the last five years, five sea-going expeditions have been undertaken to investigate the influence of these ocean processes on the life of fishes and their early life stages. The use of different sampling techniques (e.g. midi/maxi multinet, GULF VII, and CTD) allowed us to understand horizontal and vertical larval fish distribution patterns. Frontal zones that function as natural barrier for plankton drift were identified enabling the formation of spatially segregated larval fish assemblages. Mesoscale eddies compensated an offshore drift of water masses during the upwelling process retaining fish larvae at the shelf break. An upwelling intensity driven spatio-temporal niche partitioning was observed between larval round sardinella (Sardinella aurita) and larval European sardine (Sardina pilchardus). While climate models predict a change of the upwelling intensity in upwelling ecosystems, we suggest that dominance relationships of small pelagic fishes will fluctuate according to upwelling intensity variation. The results of our studies improve the understanding of how fishes avail the dominant physical features in upwelling ecosystems and aid to comprehend population dynamics.

Matecho is an automated processing method to extract information and perform echo-integration and fish shoal extraction from various scientific echo-sounder sources providing digital acoustic data on fisheries and aquatic ecosystem. The open-source initiative helps foster collaboration and technological transfer. Matecho supports various formats, such as the international standard format for the exchange of fisheries acoustics raw and edited data. The procedure allows the semiautomatic cleaning of echogram data and the application of automatic data filters, i.e., transient noise, attenuated signal and impulsive noise removal and background noise reduction. Echo-integration processing is executed for each depth layer and integrates their characteristics per elementary sampling unit. Sound scattered layers are automatically detected by segmentation from the echo-integrated echogram, and shoals are extracted according to an iterative process of aggregation of filtered echogram echoes that allows, in both cases, the calculation of the ad hoc parameters describing morphological, spatial location and acoustic characteristics of sound scattered layers and shoals. Matecho is open-source software for researchers and provides end users with a user-friendly, free executable program.

ICAWA : International Conference AWA, Lanzarote, ESP, 17-/04/2018 - 20/04/2018; Factors influencing landed prices and those of processed products (fish and processed) are mainly landed quantities and product quality. The latter are in turn influenced by the seasonality of sardinella conditioned by the temperature of the water. It is usually in cooroon periods (April to June) that sardinella landings are more important and it is at this time also that the prices of fresh fish and processed products are the lowest. On the other hand sardinella is rare in lolli most often (October to December) and it is at this period also that the prices are generally higher. Nevertheless, depending on whether one is on the Petite Côte or on the Grande Côte, fishermen's appreciations of the periods of abundance of sardinellas differ. However, from the analysis of fishermen's knowledge on sardinella migration and bioecological models, it appears that sardinella are present on Senegalese coasts during periods of low temperature. As the cold water periods are later and shorter, the sardinella will be increasingly rare on the coast in Senegal, its higher price, accessibility is more difficult and consequently the animal protein deficit of the populations more accentuated.

Climatological mixed layer heat/salt budget terms derived from a NEMO 1/4° forced model simulation and from a PREFACE observation-based product are compared in the eastern tropical Atlantic. Mean spatial patterns of mixed layer depth, SST and SSS are in good agreement despite some local biases. For the annual mean heat balance, atmospheric fluxes are quite different along the coasts, while horizontal advection mostly differs around the equator, maybe due to the low resolution of the observations (2.5°) that cannot resolve small meridional scales. The seasonal heat balance is compared in boxes off Angola, in the northeast Gulf of Guinea and in the Atlantic cold tongue. Seasonal variations of heat fluxes are correlated except in the last box, while advection is everywhere poorly correlated. For the annual mean salt balance, model and observations show similar freshwater fluxes, with larger spatial contrasts in the model, while advection mostly differs around the ITCZ. In the Benguela region, model and observations roughly agree on freshwater fluxes and advection seasonal variations. Off Angola, SSS variations are uncorrelated. The observed product does not explicitly resolve vertical diffusion, an important process for the heat/salt balance in the Gulf of Guinea. The seasonal characteristics of the simulated EUC transport are compared to observations based on cruises and moorings at 23°W. In the model, the EUC transport is slightly larger than observed on average, while its seasonal cycle is of comparable amplitude and shows a maximum around September and minimum in November, leading the observations by one month. The maximum velocity is also biased high but seasonal cycles are consistent and roughly phased with the transport seasonal cycle. The EUC core in the model is shallower than observed but with a similar seasonal cycle and coinciding maxima in depth and transport. Its latitudinal position is more south of the equator, with a seasonal cycle opposite in phase and larger than observed. A test simulation with interannual wind forcing but climatological fluxes forcing is compared to the reference simulation to identify the respective role of dynamic and thermodynamic forcing on the EUC characteristics, in particular its salinity maximum.

Fluctuations in abiotic factors, e.g., temperature, salinity, food availability, will result in specific spawning tactics. This drives some populations to create reproductive strategies to ensure the survival of their offspring. The analysis of comparative functional responses can be used in different contexts to improve the understanding and prediction of the environmental impact on small pelagic population fecundity (PF). Successful recruitment into a population is subject to variations in fecundity. Significant seasonal and inter-annual differences in PF of Ethmalosa fimbriata in southern Senegalese coastal waters could be observed. Here we show that the population is able to fit its spawning tactic to variable conditions in an upwelling environment. It appears that E. fimbriata aims at spawning in water temperatures of around 24°C and at an upwelling intensity of 3 m3 s-1 m-1. Understanding the spawning tactics of an highly exploited fish species is important in the context of climate change to get efficient forecast in countries where fisheries is crucial at socio-economical level, in order that decision maker can provide ad hoc adaptation plan for the fisheries sector.

ICAWA : International Conference AWA, Mindelo, CPV, 13-/11/2017 - 17/11/2017; Several activities have been conducted on the thematic of « ecosystem indicators, sensu lato» during the AWA project (www.awa-project.org). This communication reports those related to the Tasks 3 of the WP4. Its first part introduces the indiAWA network which has emerged as a result of the AWA project. IndiAWA is a research and expertise network focussing on indicators and ecosystem approaches for fisheries and global change in West Africa. Started in the AWA context, IndiAWA has the ambition to continue on the long term, after AWA phase 1 funding period, as well as to be an open network, with the addition of extra AWA contributors, and to constitute a growing task force for West Africa. With AWA's consortium and extended collaborations, the general and long-term objective of indiAWA is to develop ecosystem indicators and to promote regional solutions for an Ecosystem Approach to the management of fisheries and the marine environment in West Africa waters. In line with AWA's philosophy, this long-term objective of indiAWA comes in three main components, including scientific research, capacity building and communication objectives. These components are presented and their sub-components or particular objectives are specified in the first part of the communication. The second part brings then an illustration of the indiAWA's approach applied to the Guinean shelf case study. In this study, the ecosystem indicators calculated on the basis on three decades of national scientific trawling surveys, coupled with others indicators from commercial fishing activities on the same period, allows now to detect some of the fisheries ecosystem effects that were not perceptibles in former studies, based on both shorter data series and period of exploitation. The third and last part of the communication concludes with some perpectives and work to be continued and developped on this thematic on the future by the AWA/indiAWA consortium.

ICAWA : International Conference AWA, Mindelo, CPV, 13-/11/2017 - 17/11/2017; Artisanal fisheries still play a large role in many economics, especially in developing countries. These fishers and the coastal communities in general, face various risks in their everyday life including uncertainty about the success of fishing, uncertain prices for fish and uncertain costs for inputs such as fuel, and many more. In addition, foreign fleets, changing world markets and other global factors including climate change in particular can put additional pressures on top of this. We have used field surveys and economic experiments among fishing communities to assess how fisher perceive these risks and how they cope with them. The surveys were carried out in Senegal and Cape Verde, with 691 and 671 valid interviews, respectively. In this presentation, we will provide insights into some parts of our results including the general situation of the fisheries and fishers, climate change perceptions, and on coping mechanisms.

The interest of modelling the effect of oceanographic factors on micronektonic acoustic densities and its variability is relevant in the context of climate change to better understand the environmental processes controlling ecosystem productivity. Ultimately for the stakeholders, we plan to forecast changes induced by climate change effects and study inter annual variability. Satellite data have been processed using the same time steps as the time series of fisheries acoustic surveys carried out by the R/V Dr. Fridtjof Nansen along the Atlantic African coasts, overlapping three Large Marine Ecosystems. The observed split at Cape Blanc (21°N) separates the coastal upwelling into a strong and stable dynamic upwelling, and a highly seasonal one. Because of the highly non-linear nature of the relationships the BRT modelling accounts for a considerably higher part of the environmental variability, compared to classic multivariate approaches. Environmental data are extracted from daily series of AVHRR (SST), MODIS (SST and Chl-a) and others at spatial resolution between 4 and 25 km. Boosted Regression Tree classification is well suited to show the importance of the large scale environmental variability, despite a limited set of variables. It is interesting to note that the inter-annual variability is not significant in the model, showing that the underlying environmental forcing is associated with relatively stable processes. The structural variables, i.e., bathymetry and distance to the coast, consistently explain a large part of the variability. SST has a minor influence in the north (consistently cold and windy) and a pronounced effect in the south where seasonality is high and variable. Especially in Senegal and Guinea, the detrimental effects of the coastal upwelling (mostly offshore drifts due to strong winds) are strongly attenuated by the wider continental shelf which favour retention processes. The next step will be to couple our results with climate projections to forecast major changes in African coastal systems as the micronektonic compartment is essential at mid-trophic level in all marine ecosystems. Considering the oceanographic factors relative influence, and under the assumption of similar warming in the three Atlantic African LMEs, a stronger ecosystem perturbation is expected in BBCLME, then in the CCLME and particularly when comparing the southern part of the CCLME vs North part. In all LME i.e. including GCLME, the oceanographic factors relative influence get a significant role confirming the important changes expected due to climate change on the ecosystems and thus in the fisheries.

ICAWA : International Conference AWA, Mindelo, CPV, 13-/11/2017 - 17/11/2017; Marine environmental law has been emerging in West Africa in 70's. International convention has been ratified and national law progressively developed. This communication will show the development of marine environmental law in West African countries using examples from Senegal, Mauritania and Cabo-Verde. This field of law use to be very sectorial. However, the development of integrative ways of regulations at international level impacts West African national law on marine environment. Lastly, examples of first steps toward an integrative way of regulation are underlined in West African countries.

The understand of the fine scale process occurring in the ocean needs high resolution data and ad hoc analysis approach to improve the knowledge of ecosystem functioning. During an international survey carry out in 2014'AWA’ on-board the research vessel Thalassa (Ifremer, Brest) along the coast of Mauritania and Senegal we have used simultaneously multifrequency scientific echosounder and a Scanfish, both system allow a continuous acquisition of high- quality data at high spatial and temporal resolution over long distance. The functional data analyses have recently raising in serval field of statistics and appear to be well suited for the analysis of this dataset. In fact such data has spatial-functional nature and may be considered as observations of a stochastic process X in space of continuous functions over an interval T. Let X1(t), X2(t),.., Xn(t), t T, be the collection of n observations from X. First, we study an eventual horizontally or vertically variation of the acoustic intensity, we consider for a given frequency (here 200 kHz) and one vessel radial the two cases: vertical and horizontal variations of the acoustic intensity. Unsupervised functional classification used, shows a horizontal and vertical variation of acoustic intensity for a given frequency and a given radial. The approach can led to scrutinized at fine scale the processes occurring in three dimensions in the pelagic environment. The statistical functional classification applied to this case study appears powerful, ad hoc for ecological studies of marine ecosystem and will be extend to model the spatial structuration of the pelagic ecosystem according to the physcio-chemical parameters of the water mass which will allow to improve the forecast of the effect of the environment on marine ecosystem organization.

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.

Senegalese artisanal fishermen, in their fishing activity, cut the year into four fishing seasons (autumn, winter, spring, and summer). Each of these seasons is characterized by a type of regular natural phenomena that they observe for decades that serve as benchmarks for determining their duration (beginning, middle and end). The benchmarks on these four fishing seasons are the presence of stars (types of stars) the presence of certain species (types of fish types of birds), the temperature of the air and water, types of winds, the nature of the sea. It is from these benchmarks that they measure the evolutions (variation and change) observed in each season in order to be able to adapt their activities accordingly. The changes noted by the fishermen concern the disturbances on noted the duration of the periods of cold and periods of heat such as initially recorded according to the seasons, the disturbances on the marks on the movement of the fish according to the seasons. Thus, through the expression 'there are no more seasons as before', the fishermen note the appearance of discrepancies between the current seasonal cycles and the seasonal cycles of the 60s attesting to a loss of benchmarks due to irregularities of certain phenomena that characterized each season. Climate change thus appears through the'ruptures' between what the old fishermen now live compared to what they used to live.

Small pelagic fish are the main fish resource in North West Africa. In Senegal, they are mainly represented by the sardinellas (Sardinella aurita and S. maderensis). The fishery, mostly composed by purse seins and encircling gill nets, is predominantly performed by artisanal fishers and is of great importance for the Senegalese economy and for food security in the region. However this fisheries is totally (engine fuel and fishing gear) subsidized by the state. Because of these effects, sometimes negative, this subsidy is the subject of severe criticism in the world. In such context, the operating conditions for this fishery have changed during the recent years, thus a bioeconomic model is developed to simulate the dynamics of sardinella exploitation and analyze the impact of subsidies on the dynamics of the fishery. This model may also allow managers and decision makers to analyze the responses of the fishery to economic (price, costs), biologic (growth, mortality, recruitment) and management (tax, subsidies, licenses, spatial regulations) parameters.

Since the onset of AWA, a number of studies have focused on the management and ecology in West Africa. Here we provide a short insight of the main highlights on a selection of contrasted modelling case studies. Understanding the functioning of the ecosystem is essential to promote ecosystem approach to fisheries management and the marine environment (EAMME) and path providing advices to decision makers and managers. In the EAMME, the civil society addressed various questions to AWA on which specific models have been developed to provide at least first insight to the answers, e.g., on the effect of artificial reef implementation in marine protected area; the possible equilibriums between national fisheries sharing a same trans-boundary fish stock; the feedback between local exploitation, fish market and fisheries mobility, the responses of a fishery to economic, biologic and management parameters, the spatial variability of primary productivity as well oceanographic circulation at regional level or the fish egg advection over the continental shelf. More complex modelling exercise have also been conducted taking advantage of previous research led on sardinella aurita. In this way a coupled model taking into account environmental variability, fish growth and spatial behaviour was developed. We present as example new hypothesis on adult mediated connectivity between EEZ, inter-annual variability and interest to work on climate change with such model. We propose a prospective of what further research could be conducted to continue to bring up relevant information for a sub-regional EAMME in North West Africa fostering exchanges between modellers and marine scientists and all stakeholders.

The Guinea Current Large Marine Ecosystem (GCLME) extends from Bissagos Island (Guinea Bissau) in the north (11°N, 16°W) to Cape Lopez (Gabon) in the south (0°S, 8°E) and includes the study zone, from 4°N, 8°W to 6°N, 3°E. Acoustic data were recorded with a 38 kHz echosounder, from 10 to 500 m depth over 7 surveys, 6 were selected here, totalling 16 618 nmi from 1999 to 2006. To get homogenous data, (i) only off-upwelling season surveys (April to September) 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 Matecho tool (Perrot et al., 2018). (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). (ii) On vertical dimension, the water column variation (%) filled by micronektonic acoustic layer (filling rate) across years was estimated using a linear regression and the change of micronektonic spatial structure between day and night was assessed using the mean Sv value for each 1 m depth step. GCLME have a narrow continental shelf vs. other African Atlantic LMEs. No significant change of micronektonic biomass proxy has been observed from 1999 to 2006 in this study (Fig. 1). As expected, a difference is observed in the vertical micronektonic acoustic density between day and night (Fig. 3). However, there is a paradoxical process, indeed there is an increase in Sv during nighttime. Two hypotheses are proposed: (i) the increase in density could be explained by an offshore horizontal diel migration or (ii) a very high contribution of the micronektonic density occurring in surface (0-10 m) is suspected, which corresponds to the blind zone of the research vessel. According to the new descriptor “water column filling rate”, a significant change in the system is reported. Indeed there is an increase in five years. Future investigations should focus on this interesting phenomenon, which could be link to an effect of global change. We have to take care that such increase could also inform on a major change in the trophic web in this part of the GCLME. These findings can be interpreted as an early warning signal and encourage for future study.

Sardinella aurita is an overexploited small pelagic fish and a key species in Senegal at socioeconomics level, nevertheless the growth parameters which is a good indicator of fish stressors, have not been updated since 30 years. In this work, we analysed S. aurita (n = 32 300) age and growth in Senegal taking into account the tropical seasonality. Growth parameters are then compared with those previously obtained in the literature on the same geographical area (since 60 to 34 years) and more widely in different locations in tropical North Atlantic and Mediterranean Sea. The results show a significant difference of growth parameters in Senegal since thirty years, indeed growth of S. aurita became slower and its maximum size has significantly decreased. The comparison of S. aurita variability in growth performance reported in Mauritania-Senegal coast, as well as in Mediterranean Sea and Eastern/Western Atlantic Ocean reveals a significant influence of environmental parameters and/or the level of exploitation. In one hand in tropical Atlantic, S. aurita growth in Eastern Central is similar to the one reported in Western Central, while S. aurita growth is rather slow in Mediterranean Sea where, vs tropical Atlantic, Sea temperature and prey availability are lower. On the other hand, in the Atlantic Western Central, where the fishing pressure on the stock is lower over the last decade vs Atlantic Eastern Central, an increase in asymptotic length is observed, while in the Mediterranean Sea and Atlantic Eastern Central, where the fishing pressure is higher, the asymptotic length has drastically decreased. We assume that the fishing pressure and the climate change, or a combination of both, have an effect on the biological parameters of S. aurita.

All predictions agree that tilapia is destined to become the major aquaculture species of tomorrow. Tilapia is grown in more than 100 countries and production reaches 4.3 million tonnes making this fish group the second largest for global aquaculture, after that of carp. The modern development of its breeding requires energy for production systems e.g. to supply oxygen equipment or automatic food vending machines or the heating of livestock ponds. This work proposes to valorise the waste resulting from the activities in fish farming by the processes of anaerobic digestion to produce energy. For this, faeces of Tilapia Oreochromis niloticus were sampled periodically and their methanogenic potential (BMP test) determined and compared to a reference substrate (poultry droppings); with or without inoculum. The μCG analysis made it possible to determine the relative proportions of methane (CH4) in the biogas as a function of the duration of production. Biochemical methane potential (BMP) tests showed rapid kinetics of biogas production of fish faeces in the presence of inoculum (+ inoculum) compared with the production of biogas in faeces alone. This kinetics of biogas production is reversed between the third and fourth week. In both cases, the proportion of methane is generally greater than 60% from the second week of incubation, which shows the quality of the biogas produced. The composition of CH4 and CO2 does not change with or without inoculum. However, there is a significant difference in total CH4 volume which is twice as large with inoculated fish faeces than uninoculated fish or poultry droppings. Our results show that fish droppings are good methanogenic substrates and the use of the inoculum allows for a quick start of biogas production and avoids MO losses. Realized on a large scale, the valorisation of aquaculture fish faeces could constitute a source of green energy for the development of fish farming in Africa. And thus a smart initiative to fight against climate impact on small pelagic fish stock displacement in tropical areas.

ICAWA : International Conference AWA, Lanzarote, ESP, 17-/04/2018 - 20/04/2018; In the early 2000s, Senegal set up several Marine Protected Areas (MPAs) along its coastal zone for the purpose of biodiversity conservation and the sustainably of fisheries. However, the impact of MPAs may vary depending on the types of fishing. In Senegal, the sardinella fishing accounts for 70% of total catches. This fishery is of crucial for food security and employment. Given this importance, it is necessary to evaluate the impact of the MPAs often considered as a tool for fisheries management. An analytical, dynamic and spatial bio-economic model of sardinella fishery has been developed and simulations over 40 years were carried out. The model takes into account the migration of the resource and that of fishermen. The main results show that the fishery is economically overexploited and that the society loses about 15 billion CFA over 40 years of exploitation, i.e. 375 million CFA per year. To reach an optimal level of exploitation, it would be necessary to halve the current fishing capacity. The closure rates of 10, 20 and 30% lead to increases in biomass (8 to 28%) and rent (5 to 11%). Spatio-temporal closure measures lead inevitably to overcapacity in unclosed areas. The objective 11 of the Aichi Convention will have a reserve effect on the resource but also weak improvements in economic indicators for this fishery. Lastly we show that if we expect that the MPAs provide a significant impact on sardinella fishery in Senegal, they should be accompanied by a limitation of fishing capacity.

ICAWA : International Conference AWA, Lanzarote, ESP, 17-/04/2018 - 20/04/2018; An analysis based on a multi-decadal physical–biogeochemical hindcast simulation (1980-2009) was conducted to characterize the drivers of the spatial distribution of phytoplankton biomass and production in the north-west (NW) African upwelling system. To that end, a comparative box analysis representing homogeneous sub-regions in the NW African upwelling system has been conducted. The sub-regions have been defined using the near-surface horizontal circulation patterns. In each box, we analysed the dynamics of primary productivity and nutrients with regard to advective and diffusive matter fluxes at the boundaries and local biological production and/or uptake. The nature and variability of the matter exported from the coastal margin to the adjacent open ocean were also subsequently depicted. This variability of the primary production may impact the distribution and abundance of fish populations, and their associated fisheries, on a large range of timescales.

ICAWA : International Conference AWA, Lanzarote, ESP, 17-/04/2018 - 20/04/2018; Many questions remain open concerning the effect of environmental variability on abundance and distribution dynamics of round sardinella (Sardinella aurita) over the Canary upwelling system. This issue is of special relevance due to the great role that sardinella plays in northwest African fisheries and marine ecosystems. Here, the possible climate drivers of sardinella population migration along the northwest Africa are addressed. To this aim, we have used data provided by the coupled model compounded by the Regional Oceanic Modelling System ROMS, configured for the northwest African upwelling system, and by the biogeochemical model PISCES, which simulates plankton productivity and carbon biomass based upon the main nutrients. This coupled model has been run over the period 1980-2009 using an atmospheric reanalysis and consistent oceanic boundary conditions. Finally, an evolutionary individual-based Lagrangian model has been used to simulate the spatio-temporal behaviour of sardinella according to the environmental constraints obtained from ROMS-PISCES. Strikingly, a robust anomalous increase (decrease) of sardinella biomass has been identified from early to late winter off Cape Blanc (Saharan coast) in response to the Pacific El Niño conditions. This dipolar pattern reflects an alteration of the normal migration of sardinella between the Saharan and the Mauritanian waters and seems to be primarily mediated by the effect that El Niño-related anomalous winds has on the meridional currents along the northwest African coast. This sardinella response to El Niño is reinforced in late winter through an anomalous warming of the Mauritanian waters due to an anomalous weakening of coastal upwelling also forced by the aforementioned El Niño-related anomalous winds. According to our results this anomalous response of sardinella biomass might be predicted, for El Niño years, few months in advance from the El Niño-related SST patterns. This fact opens the possibility to the development of predictive tools, which should be necessarily assessed in further works.

ICAWA : International Conference AWA, Lanzarote, ESP, 17-/04/2018 - 20/04/2018; The link between the boreal spring sea surface salinity (SSS) and the May-June-July (MJJ) sea surface temperature (SST) in the equatorial Atlantic Cold Tongue (ACT) region is investigated at interannual time scales from 1990-2012 using observations and model. Results reveal a significant correlation between April-May-June (AMJ) interannual SSS anomalies (SSSA) and the MJJ SST anomalies (SSTA). Most of extreme interannual SSSA appear the years of extreme interannual SSTA in the ACT region. Thus, major salty and desalted ACT events are followed by 1-month major warm and cold ACT events and confirms the idea that boreal spring SSSA could be used as a predictor of ACT events. Based on the model mixed-layer salinity budget and sensitivity experiments, we found that the interannual variability of the SSS is mainly controlled by horizontal advection during salty and desalted ACT events and changes in the horizontal advection are largely due to changes in winds.

Benguela Niños and Niñas are intermittent, extreme warm and cold events that develop near the border between Angola and Namibia. These extreme events have been intensively studied these past years because of their significant impacts on the regional rainfall and the local marine ecosystem. Recently, Imbol Koungue et al. [2017], evidenced the role played by the Interannual Equatorial Kelvin waves during the onset of Benguela Niños and Niñas over 15 years (1997-2012). The present study is an update of the recent paper by Imbol Koungue et al. [2017]. We aim to revisit most of the Benguela Niños and Niñas developing before 1998 along the Angolan and Namibian coastlines using monthly averaged from an Ocean General Circulation Model (OGCM) for the period 1958 - 2015 which has been validated using available observation datasets. Preliminary results show the occurrences of 55 anomalous coastal events (29 warm and 26 cold) over the period 1958 - 2015. In agreement with recent studies, most of these anomalous coastal events are remotely forced via Interannual Equatorial Kelvin Wave (IEKW) propagations at interannual timescales with equatorial variability leading coastal SST variability by 1 month. Meridional transport anomalies across the ABF seem to contribute to the development of these anomalous coastal warm events. We show that October to April appears to be the favourable season in which anomalously warm or cold coastal events in the South-east Atlantic Ocean peak and are also linked to the remote oceanic forcing (IEKW).

ICAWA : International Conference AWA, Lanzarote, ESP, 17-/04/2018 - 20/04/2018; The objective of this study is to describe the low-frequency modulation of the Equatorial Kelvin Wave (EKW) activity in the tropical Atlantic as well as the low-frequency modulation of the local stratification and coastal winds along the coast of south-western Africa. We aim at investigating the control of these forcings in modulating the oceanic interannual variability off the coasts of Angola/Namibia and the phenomenology of Benguela Niño/Niña events. The methodology is based on the development of a high resolution (1/12°) long-term (1958 - 2008) numerical simulation of the South-Atlantic Ocean using the Regional Ocean Modeling System (ROMS). The evaluation of the model performances show that the model is skilful in reproducing the mean state and the interannual variability. The evaluation of the equatorial forcing reveals a low-frequency modulation of the EKW activity with a significant reduction of the EKW energy from 1958 to 1990, then re-energized up to 2008. Variations are associated with change in EKW baroclinic mode contribution to interannual sea level anomalies: from 1958 the second baroclinic mode dominate, and is then balance by the third baroclinic mode after the late 1990's. Concomitantly, further analyses show a decrease of the wind stress forcing and a modulation of the magnitude of wind projection coefficients according to the oceanic baroclinic modes in the Guinea gulf with in particular a strong increase of the third EKW mode. Changes are associated with the increase (decrease) of the intensity (maximum depth) of the equatorial stratification. Our results suggest that the change in the remote equatorial forcing may play an important role in the modulation of the variability off the coasts of South-West Africa. These results will be confronted to the low frequency modulation of local wind variations and Coastal Trapped Waves (CTW) signature due to different stratification state along the south-eastern coast of Africa. Indeed, modulation of the coastal stratification will most likely impact the characteristics of CTW propagation and their efficiency to imprint the coastal interannual variability in the Benguela Upwelling System.

ICAWA : International Conference AWA, Lanzarote, ESP, 17-/04/2018 - 20/04/2018; The PREFACE program allowed the deployment and annual maintenance of an ATLAS mooring at 6° S, 8° E during PREFACE cruises. A first mooring was bought by South Africa in 2006 and was deployed successfully for a year during a pilot project. PREFACE allowed to buy a second mooring needed to establish a permanent location as one replaced a mooring by a complete calibrated one. This is an extension of the PIRATA array of moorings in the tropical South-East Atlantic and an African contribution to the global observing system. PREFACE acquired an ATLAS mooring which is equipped with an extra currentmeter at 10 m depth and an extra short wave radiation sensor which allows calculation of the radiative flux and the net heat budget at a 10 minute temporal resolution. Turbulent sensible and latent heat fluxes can also be calculated at a 10 minute resolution. Sensible and Daily average is available in real time. A CO2 sensor is also deployed on the mooring. The strategic location of the mooring in the stratocumulus deck which is a problem to coupled models, offshore of the Congo River plume and upstream of the Angola Current make this mooring a unique measuring platform which has continuously worked in real time since May 2013. Mooring data and satellite remote sensing estimates of salinity indicates numerous intrusions of low salinity water from the Congo River since 2013. While the air and sea surface temperature (SST) distribution is unimodal, the upper ocean subsurface temperature and dynamic height is bi-modal and seems to be a seasonal Rossby wave triggered by a seasonal kelvin waves along the equator. PIRATA mooring, altimetry and SST allow monitoring the passage of Rossby waves all the way to Brazil modifying the SST in a region that is known to impact the regional Brazilian climate.

ICAWA : International Conference AWA, Mindelo, CPV, 13-/11/2017 - 17/11/2017; The project 'Enhancing Prediction of Tropical Atlantic Climate and its Impacts – PREFACE' (www.preface-project.eu) is a 4.5 year research project funded by the European Union under FP7- Environment. The project gathers 28 partners from 18 countries across Africa and Europe, with expertise in oceanography, climate modelling and prediction, and fisheries science, targeting climate prediction and marine-ecosystem changes in the eastern boundary and equatorial upwelling regions of the tropical Atlantic. Since 2013 and in a spirit of strong international cooperation, PREFACE has made important contributions towards improving the Atlantic observational network and climate prediction models – whilst enhancing local capacity and harvesting the synergy from inter-projects collaboration – such that we can now usefully forecast climate from a season to a decade in advance over large regions of the tropical Atlantic Ocean, and over parts of continental South America and Africa. A particular example is the skill in predictions of ocean surface temperature and Sahel rainfall a season to several years ahead. There is also a potential to predict stock biomass from a season to years in advance. We showed that the upwelling intensity in North West Africa and consequent marine productivity are redistributed due to warming trends, and we report a northern spatial shift of round sardinella. In the southeast Atlantic, a similar shift is reported on the same species. Such potentially predictable changes impact food security management and demand adequate policy measures. However, more work is required to make the most use of these predictions. Climate model errors and modelling of biophysical relations continue to be a major challenge. These introduce uncertainties in future projections of climate change and its impacts in this region. They also limit shorter-term climate prediction. Thus much more work is needed to improve models. Collaborative climate research on the Atlantic remains a key priority.