Herve Demarcq

• PhD in biological oceanography
• Dr at Institute of Research for Development

Since 2000, Ifremer has conducted yearly aerial surveys during late summer-early fall on juvenile Atlantic bluefin tuna (ABFT) in the Northwestern Mediterranean in order to calculate a fishery-independent index of abundance. This scientific survey provides crucial information for stock assessment, in particular because juvenile ABFT are no longer t...

Satellite products are widely used to understand and monitor the dynamics of the Peruvian coastal upwelling system (PCUS), one of the four major eastern boundary upwelling systems. They complement in situ observations obtained through surveys and oceanographic stations periodically operated by the Peruvian Marine Research Institute (IMARPE). Theref...

Small pelagic fishes play important ecological roles in marine ecosystems, constitute some of the most economically valuable fisheries resources, and play a vital role in West African food security. Often living in upwelling regions, these species appear to have developed mechanisms to cope with environmental variability, such as opportunistic repr...

Climate change is recognised to lead to spatial shifts in the distribution of small pelagic fish, likely by altering their environmental optima. Fish supply along the Northwest African coast is significant at both socio-economic and cultural levels. Evaluating the impacts of climatic change on small pelagic fish is a challenge and of serious concer...

The southern Alboran Sea is a dynamic ecosystem and is highly influenced by Atlantic waters. Unfortunately, despite the importance of the mesozooplankton in this ecosystem, the number of studies on this ecosystem is low. The composition and abundance of mesozooplankton communities were studied during the summer season (July 2017) along the Moroccan...

Fishers have intensively used drifting fish aggregating devices (DFADs) over the last three decades to facilitate their catch of tropical tunas. DFADs increase purse‐seine efficiency, potentially increasing tuna fishing mortality. They could also have impacts on tuna natural mortality and reproductive potential, and assessing the consequences of th...

Along the coast of North-West Africa, fish supply is important at both socio-economic and cultural levels while threatened by climatic changes. To assess the impact of climate change on the distribution of small pelagic fish, a comprehensive trend analysis was conducted using data from 2,363 trawl samplings and 170,000 km of acoustics sea surveys s...

The spatiotemporal variability of the major phytoplankton groups, such as dinoflagellates and diatoms, provides crucial information about the ecosystem’s status, especially when it comes to coastal regions that are influenced by permanent anthropogenic pressure. The purpose of this study was to develop specific models for the retrieval of diatoms a...

The way animals select their breeding habitat may have great impacts on individual fitness. This complex process depends on the integration of information on various environmental factors, over a wide range of spatiotemporal scales. For seabirds, breeding habitat selection integrates both land and sea features over several spatial scales. Seabirds...

The Sahara desert is a major global source of dust that is mostly transported southwest over the ocean off West Africa. The presence of this dust impacts the remote sensing of ocean surface properties. These aerosols have absorbing properties that are poorly accounted for in the standard ocean color data processing algorithm. This can result in an...

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...

NASA (National Aeronautics and Space Administration) has acquired to the present-day data on the temporal and spatial distribution of chlorophyll-a (Chl-a) biomass from the Moderate-Resolution Imaging Spectroradiometer (MODIS) Aqua sensor for ocean color. In our work, the daily Chl-a biomass was estimated from the MODIS product OC3M bio-optical sta...

The competitive exclusion principle predicts that species exhibit segregation mechanisms to coexist. In the Humboldt Current System, South American sea lions Otaria byronia (SASL) coexist with South American fur seals Arctocephalus australis (SAFS); however, the existence of temporal and spatial partitioning in foraging strategies remains unknown....

In Algiers Bay, coccolithophore blooms of Holococcolithophora sphaeroidea species were identified from in situ observations during August 2003, July–August 2013, July 2015, and July 2017. This study determines for the first time in Algiers Bay the episodes of coccolithophore blooms from 2003 to 2018 using satellite and in situ observations. In addi...

El Norte del ecosistema de la Corriente de Humboldt, localizado a lo largo del Sudeste del Océano Pacífico, frente a Perú, es considerado uno de los más productivos sistemas naturales en el mundo, siendo de gran relevancia el estudio del fitoplancton como base de la trama trófica marina. Tomando en cuenta las relaciones entre la superficie celular,...

This study introduces the concept of map portfolio as the set of principal maps that best explain the spatial distributions of a given species over time. An application is developed on octopus’s distribution off Mauritania over the past thirty years. The maps that make up the portfolio are the subset of the empirical orthogonal maps that allow to r...

Note Politique, projet AWA (Pollution marine, dégradation des habitats marins et effets du changement climatique en Afrique de l'ouest). AWAtox un projet de démonstration AWA Dossier Noctiluca-mai 2022 "Etat des connaissances sur le premier bloom algal massif de Noctiluca scintillans observé sur la Petite Côte du Sénégal". 1. Observation de la pre...

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 fluoresce...

The southern Alboran Sea is a highly dynamic region in the Mediterranean. However, there is few data on microphytoplankton which is, an important component of the marine ecosystem. We therefore collected microphytoplankton samples and related the biomass and diversity patterns to ambient variability, considering cross-shore and longitudinal gradien...

This study investigates the spatial distribution and temporal variability of chlorophyll-a (Chl-a) biomass in the Algerian Basin (AB) along its meridional and cross-shore dimensions, focusing on coastal enrichments. After correcting most atmospheric disturbances in the daily MODIS Level-2 data series between 2003 and 2018, a fortnightly climatology...

In the Canary Current System (CCS), coherent structures and concurrent movements of surface waters such as meanders, filaments and eddies strongly control the ocean bio-optical proprieties response to the coastal upwelling process. One of the outstanding problems is to understand the mechanisms of the bio-optical proprieties transfer and the connec...

Upwelling ecosystems exhibit strong spatio-temporal variations of environmental conditions that drive the dynamics of marine diversity and ressources. Yet little is known in these ecosystems concerning the diversity of groundfishes. We studied the effects of environment (sea surface temperature, chlorophyll a concentration and bathymetric strata) a...

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

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 regime...

Fisheries observer programs represent the most reliable way to collect data on fisheries bycatch. However, their limited coverage leads to important data gaps that preclude bycatch mitigation at the basin scale. Habitat models developed from available fisheries observer programs offer a potential solution to fill these gaps. We focus on tropical tu...

The Oualidia Lagoon is a semi enclosed marine ecosystem connected to the Atlantic Ocean of Morocco and exposed to human activities, mainly agriculture and oyster farming. The present study aims to characterize the spatio-temporal variation of the phytoplankton assemblage and to highlight the effect of the main environmental parameters on this impor...

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 differen...

Understanding the interannual effect of various environmental factors on biodiversity distribution is fundamental for developing biological monitoring tools. The interannual variability of environmental factors on presettlement fish assemblages (PFAs) has been so far under investigated, especially in Madagascar. Numerous explanatory variables inclu...

An important decrease in small pelagic fish condition and size has been observed in the most productive ecosystem of the Mediterranean Sea, the Gulf of Lions, since 2008, leading to an important fishery crisis. Previous studies suggested bottom-up control to be the most probable cause for these changes. Here, we investigate whether an environmental...

Based on satellite and in situ data, the dynamic characteristics and vertical structure of a surface intensified mesoscale dipole recently expelled from the South East Madagascar Current (SEMC) is described for the first time. The dipole was surveyed 250 nautical miles south of Madagascar between 14 and 23 November 2016, during west-east and south-...

This work is part of the MADRidge Project special issue which aims to describe pelagic ecosystems in the vicinity of three prominent shallow seamounts in the South West Indian Ocean: one here named MAD-Ridge (240 m below the surface) plus Walters Shoal (18 m) on the Madagascar Ridge, and La Pérouse (60 m) on the abyssal plain east of Madagascar. Th...

Spatial anomalies associated with seamounts and islands have been detected in the South West Indian Ocean using a new surface chlorophyll-a based enrichment index (EI). Calculated from daily L3 4-km MODIS chl-a data from 2003 to 2018, the EI was used to quantify recurrent (seasonal) surface enrichment associated with these features. Most notable we...

The La Pérouse seamount (60 m depth) has so far been poorly studied despite it being a short distance (160 km) from Réunion Island. As part of the MADRidge project, a multidisciplinary cruise was conducted to evaluate the effect of this shallow seamount on the local hydrology and ecology. Current measurements, temperature and chlorophyll-a profiles...

There is a growing interest in the management of seamounts of the Southwestern Indian Ocean (SWIO) both in waters under national jurisdictions and in the Areas Beyond National Jurisdiction (ABNJ). New scientific knowledge has been gathered through various oceanographic cruises during the past decade, and new agreements are under consideration globa...

Case study for Western (Brazil) and Eastern (Cape Verde, Senegal) tropical Atlantic countries, information on marine and coastal natural resources and their use and exploitation status

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 G...

The Peruvian Upwelling Ecosystem (PUE) is one of the most productive ecosystem in the world in terms of productivity and fish catches, partly because its geographical location is affected by remote physical processes, such as the interannual climate variability of the Equatorial Pacific Ocean (EPO), whose dominant signal is El Niño Southern Oscilla...

ln Atlantic Africa there is a crucial need to better assess the effect of cllrnate 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 ln the African ecosystems and the times series are often short or disrupted. Space-based obs...

In the Peruvian eastern boundary upwelling system hydrogen sulfide outbreaks and their coastal surface sulfur plumes influence the coastal ecosystem, local fisheries, aquaculture, and the tourism due to their toxic properties. Hydrogen sulfide is produced by organic matter degradation in oxygen-limited conditions and may cause mass mortality of mar...

In the Peruvian eastern boundary upwelling system hydrogen sulfide outbreaks and their coastal sulfur plumes influence the marine ecosystem, the local fisheries and the tourism due to their toxic properties. They may cause mass mortalities of marine organisms and represent a major limitation for coastal aquaculture. In the past, the local inhabitan...

In the Peruvian eastern boundary upwelling system hydrogen sulfide outbreaks and their coastal sulfur plumes influence the marine ecosystem, the local fisheries and the tourism due to their toxic properties. They may cause mass mortalities of marine organisms and represent a major limitation for coastal aquaculture. In the past, the local inhabitan...

Abstract 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 effect...

In marine ecosystems top predator populations are shaped by environmental factors affecting their prey abundance. Coupling top predators’ population studies with independent records of prey abundance suggests that prey fluctuations affect fecundity parameters and abundance of their predators. However, prey may be abundant but inaccessible to their...

This study investigated variations of landings of two key species, Sardinella aurita and Sardinella maderensis, in Senegalese waters over a ten-year period (2004–2013). Using generalized additive models, it was found that fishing gear played a major role in explaining differences in monthly landings for both species (51–71% deviance explained). Its...

We analyzed the temporal variability of the fishing fleet of Dosidicus gigas, located outside the exclusive economic zone of Peru (EEZ), with a spatial luminosity index. The nighttime satellite images were provided by the Operational Linescan System (DMSP-OLS) from 2004 to 2015. 2995 images were processed, selecting pixels in the range of 30–63 Dig...

We investigated the habitat utilization, vertical and horizontal behaviour of Atlantic bluefin tuna Thunnus thynnus (ABFT) in relation to oceanographic conditions in the northwestern Mediterranean Sea, based on 36 pop-up archival tags and different environmental data sets. Tags were deployed on early mature ABFT (127–255 cm) between July and Novemb...

In Northwest Africa, the small pelagic fish are in abundance and play a crucial role for the food safety of populations. The pelagic resources are exploited both by small-scale artisanal and industrial fleets. The landing structure of the countries in the region has been in perpetual change during the last years. The sardinella has been more and mo...

Remote sensing techniques based on the measurement of the "Ocean color" allow to estimate a proxy of the phytoplanktonic biomass through the estimation of "chlorophyll a" concentrations in surface waters with generic algorithms, now from almost two decades, in a near operational way. Although it incompletely describes the water column structure, th...

Tropical tuna purse-seine fisheries spatially co-occur with various megafauna species, such as whale sharks, dolphins and baleen whales in all oceans of the world. Here, we analyzed a 10-year (2002–2011) dataset from logbooks of European tropical tuna purse-seine vessels operating in the tropical Eastern Atlantic and Western Indian Oceans, with the...

South Pacific jack mackerel, Trachurus murphyi, has an ocean-scale distribution, from the South American coastline to New Zealand and Tasmania. This fish, captured by Humans since the Holocene, is nowadays heavily exploited and its population has decreased substantially since the mid-1990s. The uncertainty associated to jack mackerel population str...

El Ecosistema de Afloramiento Peruano (EAP) es una de las zonas marinas con mayor productividad pesquera en el mundo y por su ubicación geográfca, es afectada por procesos físicos remotos, principalmente por la variabilidad climática interanual proveniente del océano Pacifco Ecuatorial, cuya señal dominante es El Niño y la Oscilación Sur (ENOS). Con...

In fluctuating environments, matching breeding timing to periods of high resource availability is crucial for the fitness of many vertebrate species, and may have major consequences on population health. Yet, our understanding of the proximate environmental cues driving seasonal breeding is limited. This is particularly the case in marine ecosystem...

International conference ICAWA 2015 : extended book of abstract : the AWA project : ecosystem approach to the management of fisheries and the marine environment in West African waters

Environmental changes and human activities can have strong impacts on biodiversity and ecosystem functioning. This study investigates how, from a quantitative point of view, simultaneously both environmental and anthropogenic factors affect species composition and abundance of exploited groundfish assemblages (i.e. target and non-target species) at...

Different dolphin and tuna species have frequently been reported to aggregate in areas of high frontal activity, sometimes developing close multi-species associations to increase feeding success. Aerial surveys are a common tool to monitor the density and abundance of marine mammals, and have recently become a focus in the search for methods to pro...

In order to optimize frontal detection in sea surface temperature fields at 4 km resolution, a combined statistical and expert-based approach is applied to test different spatial smoothing of the data prior to the detection process. Fronts are usually detected at 1 km resolution using the histogram-based, single image edge detection (SIED) algorith...

The lack of reliable fishery-dependent data and fundamental understanding of the biology of most shark species causes concern for the sustainable management of shark populations in the Mediterranean Sea. The blue shark (Prionace glauca), a wide-ranging shark occurring in all tropical and temperate seas, is also one of the most heavily fished sharks...

The Mediterranean and Black Seas are semi-enclosed basins characterized by high environmental variability and growing anthropogenic pressure. This has led to an increasing need for a bioregionalization of the oceanic environment at local and regional scales that can be used for managerial applications as a geographical reference. We aim to identify...

Kaplan, D. M., Chassot, E., Amandé, J. M., Dueri, S., Demarcq, H., Dagorn, L., and Fonteneau, A. Spatial management of Indian Ocean tropical tuna fisheries: potential and perspectives. – ICES Journal of Marine Science, doi.10.1093/icesjms/fst233. Effective use of spatial management in the pelagic realm presents special challenges due to high fish a...

We use a combination of satellite, in situ and numerical data to provide a comprehensive view of the seasonal coastal upwelling cycle off NW Africa in terms of both wind forcing and sea surface temperature (SST) response. Wind forcing is expressed in terms of both instantaneous (local) and time-integrated (non-local) indices, and the ocean response...

Sardinella spp. are the main species fished in Mauritanian waters. Logbook data (1991–2009) were used to standardise CPUE. This clearly revealed that the abundance of sardinella peaked in the warm season(July–September) which is the main, if not the only significant spawning season for round sardinella.This study does not directly confirm or falsif...

In the Humboldt Current system, large colonies of boobies and cormorants breed in sympatryand feed on anchovy. Their breeding success depends largely on prey availability around the colonies, which may be compensated to some extent through variation in their foraging effort. Anchovy availabilityin this ecosystem may depend on natural shifts in its...

A new methodology to derive an SST-based upwelling index was based on a rigorous spatial analysis of satellite SST fields and their variability, by referring to previous works, from Wooster et al. (1976), Santos et al. (2011). The data was precautiously processed by considering data quality aspects (including cloud cover) and the best way to derive...

Ce document présente une méthode objective visant à identifier et à évaluer les regroupements des bancs de thons autour des monts sous-marins. La méthode associe la sélection statistique des monts sous-marins actifs sur la base d'une analyse du temps de pêche de la flottille et du schéma de points spatiaux. Le document analyse brièvement les caract...

An improved automatic detection of mesoscale frontal activity is proposed, based on the edge detection algo-rithm initially presented by Cayula and Cornillon (1992). The performance and the sensitivity of their original method have been extensively tested on a very large MODIS SST data set at 1 km resolution, over the Canary Upwelling System, and c...

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 characterist...

An improved automatic detection of mesoscale frontal activity is proposed, based on the edge detection algo-rithm initially presented by Cayula and Cornillon (1992). The performance and the sensitivity of their original method have been extensively tested on a very large MODIS SST data set at 1 km resolution, over the Canary Upwelling System, and c...