Anthony Acou

PatriNat (OFB-MNHN-CNRS-IRD)

With the loss of biodiversity worldwide, understanding species distribution is essential for species management, but modelling the distribution of rare and poorly detectable species can be challenging because of data gaps and observer biases. Over‐ or under‐predictions are frequent, leading to uncertainty in spatial management measures, particularl...

Report available at : https://mnhn.hal.science/mnhn-04475562v2 Abstract : Currently, 106 species of chondrichthyans (40 rays, 59 sharks, and 7 chimaeras) can be found in the marine waters of metropolitan France. 14 chondrichthyans are listed on French IUCN red list and/or national and international legislations and most of them (63 species) are D...

Despite the popularity of stable isotope analysis (Carbon and Nitrogen), the drivers of species isotopic niches and their consequences on food web functioning remained poorly described, especially in estuaries. Here, we hypothesised that species niche characteristics are influenced by ecosystem hydro-morphological features and the functional struct...

The temporal asynchronies in larvae production from different spawning areas are fundamental components for ensuring stability and resilience of marine metapopulations. Such a concept, named portfolio effect, supposes that diversifying larval dispersal histories should minimize the risk of recruitment failure by increasing the probability that at l...

L’impact des barrages sur la continuité écologique est connu et largement documenté. Chez les espèces catadromes, en empêchant l’accès à l’amont, les obstacles créent des surdensités en aval induisant une forte compétition intraspécifique, ce qui peut donner lieu à une réduction de la croissance, une dégradation des conditions sanitaires et, in fin...

Competition arises when species share a limited resource, but this can be avoided through niche partitioning. Despite the large body of literature on diadromous fishes, very few studies have focused on niche partitioning when competing for resources. Diadromous fishes are suffering a global decline throughout their range in part due to their peculi...

L’anguille est une espèce emblématique, classée en danger critique d’extinction par l’UICN. Elle est caractérisée par un cycle biologique complexe, partagé entre le milieu marin, où se déroulent la reproduction et la phase larvaire, et les milieux aquatiques continentaux, où se déroulent la croissance et la maturation sexuelle. Les vallées estuarie...

Species identification remains crucial for interpreting acoustic backscatter delivered by active acoustic methodologies. The study took place in a Marine Protected Area where highly restricted areas were present such as no take zones. We used an innovative methodology coupling split-beam and multibeam echosounders to detect and classify monospecifi...

A database of 168 904 hauls covering the period from 1965 to 2019, from 46 surveys containing both fisheries-dependent (fishing vessels) and -independent data (scientific surveys) were collated from across the eastern Atlantic (Greater North Sea, Celtic Sea, Bay of Biscay and Iberian coast) and Metropolitan French Mediterranean waters. Data on diad...

La protection des populations d'élasmobranches est identifiée comme un enjeu fort dans l'ensemble des façades métropolitaines bien que le statut de conservation d'une majorité d'espèces présentes dans ces eaux ne soit pas connu faute de données. Les programmes de mesures au titre du deuxième cycle de la Directive Cadre Stratégie Milieu Marin (DCSMM...

Life-history traits of eels display a high level of phenotypic plasticity in response to large-scale biogeographical drivers, as well as local conditions encountered during the continental phase. Here, we provided a biogeographical snapshot of the variability of life-history traits of eels (Anguilla anguilla), across a large proportion of their nat...

Despite the importance of estuarine nurseries in the regulation of many fish stocks, temporal and spatial movements and habitat use patterns of juvenile fish remain poorly understood. Overall, combining several movement metrics allowed us to characterize dispersal patterns of juvenile flounder, Platichthys flesus, along an estuarine seascape. Speci...

Anthropogenic pressures have resulted in declines in diadromous fish. Many diadromous fish which were commercially important are now threatened and protected. Little is known about their marine life history phases, and no observation-based Species Distribution Model exists for this group of species at sea. Yet, fisheries dependent and independent d...

Anthropogenic pressures have resulted in declines in diadromous fish. Many diadromous fish which were commercially important are now threatened and protected. Little is known about their marine life history phases, and no observation-based Species Distribution Model exists for this group of species at sea. Yet, fisheries dependent and independent d...

European eel is thought to be a symbol of the effects of global change on aquatic biodiversity. The species has persisted for millions of years and faced drastic environmental fluctuations thanks to its phenotypic plasticity. However, the species has recently declined to historically low levels under synergistic human pressures. Sublethal chemical...

Life-history trait expression not only depends on the current environmental constraints, but also on the past ones that shaped traits expressed earlier in life. Such an effect, named carry-over, can occur in fish nursery grounds when juvenile performances after settlement are influenced by their larval traits in combination with conditions experien...

Very few tidal power plants exist in the world. The first one was built in the Rance estuary (Brittany, France) in 1966 and the second one in South Korea. However, with the increasing demand in renewable energy, other tidal power plant projects are being studied. These power plants are larger than unidirectional fluvial hydropower plants and strong...

92 espèces de raies et requins sont présentes de manière permanente ou occasionnelle dans les eaux de France métropolitaine. En 2013, le comité UICN France et le MNHN ont classé 3 d’entre elles (Squatina squatina, Dipturus intermedius et Rostroraja alba) en danger critique d’extinction (modalité « CR » de l’UICN). Dans le cadre de la Directive Cadr...

Little is still known about the biology and ecology of many elasmobranchs which often inhibits species specific management measures from being implemented. The primary aim of this study was to improve the knowledge on the distribution and habitat use of the threatened and data deficient shagreen ray, Leucoraja fullonica, using fisheries dependent d...

Deciphering the effects of historical and recent demographic processes responsible for the spatial patterns of genetic diversity and structure is a key objective in evolutionary and conservation biology. Using population genetic analyses, we investigated the demographic history, the contemporary genetic diversity and structure, and the occurrence o...

River fragmentation is expected to impact not only movement patterns and distribution of eels within catchment, but also their life-history traits. Here, we used otolith multi-elemental signatures to reconstruct life sequences of European silver eels within an obstructed catchment, just before the removal of hydropower dams. Beyond providing an ini...

As human activities caused a dramatic decline of European eel population since the 1970s, the European Union has set targets to ensure a 40 % escapement to the sea of the silver eel biomass by considerably reducing anthropogenic impact. Thus, human obstacles to fish migration like dams and hydropower plants should enable efficient management measur...

Marine communities are strongly structured by bathymetry and distance from the coast. Shallow coastal areas host diverse and abundant fish communities and are subjected to strong anthropo-genic pressures. However, assessments of good ecological status of pelagic fish populations do not generally take into account the ultra-coastal fringe of the coa...

The European Marine Strategy Framework Directive (MSFD) requires the achievement of good ecological status of the marine environment (Ministère de l’Écologie, du Développement durable et de l’Énergie, 2013) for all members of European Union. This directive concerns all the component of the marine environment, including fish. Up to now, fish are are...

Les espèces amphihalines présentent la particularité d’effectuer des migrations entre environnements marin et dulçaquicole. En France métropolitaine, deux catégories d’amphihalins sont présentes : les anadromes qui effectuent la majorité de leur croissance en mer et se reproduisent en eau douce (e.g., les aloses, l’esturgeon, les lamproies et les s...

Deciphering the effects of historical and recent demographic processes responsible for the spatial patterns of genetic diversity and structure is a key objective in evolutionary and conservation biology. Using genetic analyses, we investigated the demographic history, the contemporary genetic diversity and structure, and the occurrence of hybridiza...

Surveying pelagic fish population dynamics in ultra-shallow waters (<20m) is often limited by research vessel size, which not usually navigate in shallow waters. Here, we use a multibeam echosounder to detect fish shoals and assess their characteristics (acoustic density and 3-D morphology) in ultra-shallow waters to follow European Marine Strategy...

A l’occasion d’un audit de la Commission européenne sur l’évaluation coordonnée des espèces et habitats marins dans le cadre des Directives Oiseaux (DO), Habitats-Faune-Flore (DHFF) et de la Directive-Cadre Stratégie pour le Milieu Marin (DCSMM), une étude approfondie a été réalisée sur le niveau d’intégration de la surveillance et de l’évaluation...

Lampreys are ancestral jawless vertebrates with particularly complex life histories. Due to increased anthropogenic pressures, population declines have been observed. For semelparous diadromous lampreys, the marine phase remains largely a black box, making targeted management and conservation measures difficult to implement. Here, we collated a dat...

The European eel Anguilla anguilla is listed as critically endangered by the IUCN. Among many threats, the introduced parasitic nematode Anguillicola crassus is suspected to alter the eels' swim bladder and jeopardize their reproductive oceanic migration. To date, gaining knowledge about the distribution and prevalence of A. crassus requires indivi...

Since the 20th century, fishing effort has increased considerably, leading to the decline of many chondrichthyan species. Their life history characteristics (late maturity, slow growth and low fertility) increase their vulnerability to fishing pressure. Little is known about the biology and ecology of chondrichthyan, notably due to a lack of data,...

The European eel is critically endangered. Although the quality of silver eels is essential for their reproduction, little is known about the effects of multiple contaminants on the spawning migration and the European eel management plan does not take this into account. To address this knowledge gap, we sampled 482 silver eels from 12 catchments ac...

In the global context of river fragmentation, predicting fish migration is urgent to implement management actions aimed at protecting and promoting the free movement of diadromous fish. However, large-scale applicability of conservation measures requires transferable models that enable prediction of migration even in data-poor regions. Here, we sur...

Hydropower plants are commonly reported as a major cause of the worldwide decline of freshwater eels (Anguillidae), so that management solutions are urgently needed to mitigate their impacts. Where downstream passage solutions are complex to develop, turbine shutdown appears as an effective management solution to protect silver eels during their ri...

The ecology of leptocephali remains poorly known but they appear to feed on marine snow that can vary spatially and temporally according to the food web dynamics. This study provided new information about the position of leptocephali within the functional structure of microbial plankton and other food web components of the western South Pacific (WS...

1. The drastic decline in European eel Anguilla anguilla stock is now widely recognized. However, while various causes for this decline have been identified, the relative importance of each cause remains unclear. 2. During the catadromous migration of silver eels, the negative impact of dams is frequently highlighted, but mainly for powered dams (w...

Seven South Pacific anguillid eel species live from New Guinea to French Polynesia, but their spawning areas and life histories are mostly unknown despite previous sampling surveys. A July–October 2016 research cruise was conducted to study the spawning areas and times, and larval distributions of South Pacific anguillid eels, which included a shor...

River infrastructures such as weirs, hydropower stations or water reservoirs represent obstructions to migration for diadromous fish. Knowledge of accurate behaviour of fish in front of such structures is required to protect migrants from hazardous areas, guide them towards safe passage or adapt structure to improve the escapement. We developed and...

Several routes are available for the downstream migration of silver eels in the river Rhine system. Very different effects on migration success can result from this choice, such as speed and migration duration or escapement rate. We studied the downstream migration of silver eels in a river section with two different routes. The first route is the init...

Understanding the population structure of tropical anguillids residing in the Pacific is vital for their conservation management. Here, the population genetic structure of five sympatric freshwater eels (Anguilla marmorata Quoy & Gaimard, A. megastoma Kaup, A. obscura Steindachner, A. reinhardtii Günther and A. australis Richardson) across 11 weste...

Metazoan parasites were studied in 96 Alosa alosa and 78 Alosa fallax from North-East Atlantic coastal waters and connected rivers (among them three sympatric sites) in order to increase knowledge on these anadromous endangered fish and measure the parasitic impact on host condition. All shads were infected by one to six metazoan parasite taxa amon...

Current knowledge about the downstream migration of sexually mature European eels (Anguilla anguilla) remains incomplete, particularly in still water habitats such as lakes and wetlands subject to water level management. However, for the management of this endangered species, it is important to understand migration dynamics, and contribution to the...

The spawning migration of the European eel (Anguilla anguilla L.) to the Sargasso Sea is one of the greatest animal migrations. However, the duration and route of the migration remain uncertain. Using fishery data from 20 rivers across Europe, we show that most eels begin their oceanic migration between August and December. We used electronic taggi...

In the European eel (Anguilla anguilla, L.), the steep decline of reproductive silver eels is partly due to disorientation and mortality during their downstream migration, when facing turbines, but also reservoirs and dams. In the Frémur, an obstructed river in Brittany, which is representative of the western coastal hydrosystem of France, five hyd...

1. Estimating accurate age-specific survival probabilities and understanding the processes (density dependent or independent) that regulate this demographic parameter are fundamental to propose sustainable management options for the endangered European eel (Anguilla anguilla). 2. In the present study, we used extensive mark-recapture data sets (13...

As a key parameter in the management of fish populations, individual growth rate (GR) variations were examined in the European eel (Anguilla anguilla; > 150 mm) using extensive mark–recapture surveys in the lotic habitats of two small rivers of western France: the Frémur, supposed to be saturated, and at the same latitude, the Oir with densities fi...

Methods to study the migratory behaviourr of fish can be divided in two categories: capture-dependent (based on sampling marked or unmarked fish) and capture-independent methods, such as visual or video observation, resistivity fish counters or hydroacoustics. In this chapter we focus only on capture-dependent methods using marked fish.

Are the distribution of Mazocraes alosae and its impact on the host similar between Alosa alosa and A. fallax according to their resemblances? Parasites were numbered on each gill of shads sampled in North-East Atlantic coastal waters and connected rivers. Their impact on host condition was measured using girth, gonado-somatic ratio, C/N ratio, and...

The decline in the European eel has led the European Union to require that its Member States establish an Eel Management Plan, which includes a set of measures to help preserve and restore the wild eel populations. Stocking has been conducted in France since 2011 as part of this Management Plan. This stocking programme is based on a protocol design...

Length–weight relationships for European silver eel ( Anguilla anguilla ) sub-populations in six countries (13 catchments) along the latitudinal gradient in the area of distribution in this study use three important sampling programs; these results concur with previous studies on European eel with the equation: W = 0.0010 L3.148 for the entire data...

In the last few decades, there has been a marked decline in the number of shad (Alosa alosa and A. fallax) landed in France, which prompted the French committee of the International Union for Conservation of Nature to list shad as a ‘Vulnerable’ species in 2010. The freshwater phases of shad life cycles have been extensively studied, but the marine...

In the last few decades, there has been a marked decline in the number of shad (Alosa alosa and A. fallax) landed in France, which prompted the French committee of the International Union for Conservation of Nature to list shad as a ‘Vulnerable’ species in 2010. The freshwater phases of shad life cycles have been extensively studied, but the marine...

Even though restocking is one of the principal measures proposed to sustain the freshwater eel populations, few studies attempted to demonstrate its efficiency. Here we considered that restocking is useful when stocked eels yield more silver eels than natural migrants and with at least equal reproductive potential. To test this, a restocking experi...

As part of the French Eel Management plan, extensive glass eel restocking was operated since 2010 in French rivers from the Belgium to the Spanish borders. From 34 km to 960 kgs of glass eels were restocked during 29 different operations, totalling 6900 kgs of glass eels. A total of 18 catchments were restocked including lakes, marshes, small and l...

The professional fishery of Loire River has always existed as archaeological remains revealed. This creates a huge diversity of fishing practices, gears and knowledge on river functioning and fish ecology. In the thirties, 15 fisheries imported anchored stownet techniques from the Netherlands in order to focus on silver eel captures. During the eig...

Despite intensive research on eels, their population dynamics in continental waters remain poorly documented which creates serious gaps in planning the restoration of the European eel population. We selected two European sub-populations of western France, at same latitude and separated by 67 km that vary substantially in degree of human development...

During EELIAD project, we examined effects of contamination by metals, POPs (including PCB) and introduced parasites on life history traits of 450 silver eels sampled across Europe. Our results showed a positive relationship between age and latitude, while size & weight at silvering were correlated to catchment characteristics. Growth rate was link...

The Loire River is one of the largest rivers in Western Europe. Its privileged situation with regard to the Gulf Stream leads to high levels of recruitment by glass eels and probably to among the highest level of silver eel biomass in Europe. However, no study attempted to estimate both number and reproductive potential of silver eels produced by t...

River management is known to have severely fragmented river continuity. The steep decline of temperate eels is caused by a set of factors including dams that reduce accessibility to growth habitats and induce turbine mortality. We studied effects of dams and reservoir on downstream migration behaviour of silver European eels. We used an acoustic te...

Leptocephali are unusual in many ways compared to other fish larvae, and their feeding ecology appears to be based on consuming particulate organic matter, such as marine snow, as their food source. Sampling surveys for leptocephali in the Mascarene Ridge area of the western Indian Ocean and in the western South Pacific were used to examine the sta...

European eels (Anguilla anguilla) undertake a ~5000-km spawning migration from Europe to the Sargasso Sea (Tesch 1977). As details of this marine migration remain unknown, the EELIAD project was built to access the oceanic biology, ecology and movements of eels. This project showed that the eels travelled up to 50 km per day and exhibited a consist...

Helminth parasites were studied in 149 silver eels from five sites in northern Europe. In total, 88% were infected by 12 species including Monogena, Cestoda, Nematoda, and Acanthocephala. Anguillicoloides crassus was most common (56%), then Acanthocephalus clavula (30%) and Pseudodactylogyrus spp. (17%). The body condition (BC) was negatively influ...

Because parasitism is among the reasons invoked to explain the collapse of Anguilla anguilla, we evaluated the parasitic constraint on body condition (BC) of migrant silver eels as a proxy of fitness with inter-site comparisons. Metazoan parasites were studied in 149 silver eels from five sites (northern Europe). In total, 89% were infected by 13 s...

Hydroelectric power plants are often considered a major cause of mortality for migratory fish. The endangered status of European eels Anguilla anguilla forces managers to make efforts to reduce this mortality. Among the mitigation measures used, turbine shutdowns appear to be an efficient method, but they involve a substantial financial loss for hy...

Bilan des connaissances et lacunes sur les phases marines et estuariennes des poissons migrateurs amphihalins

Salt-marsh invasions by the grass Elymus athericus (Poaceae) recently transformed usual areas dominated by Atriplex portulacoides (Chenopodiaceae) into homogeneous meadows. Two wolf spider species, Pardosa purbeckensis and A rctosa fulvolineata, show contrasting densities and habitat preferences in salt marshes (respectively dominant and co-dominan...

This paper describes the assessment of silver European eel (Anguilla anguilla) escapement based on a "sedentary" population fraction analysis in a 60-km2 watershed of northern Brittany (France). Downstream migration fluxes were monitored using eel traps and related to environmental factors. Intensive electrofishing and fyke-net fishing were conduct...

Individual specialisation can lead to the exploitation of different trophic and habitat resources and the production of morphological variability within a population. Although the ecological causes of this phenomenon are relatively well known, its consequences on individual fitness are less recognised. We have investigated the extent of individual...

Summary1. Despite carrying capacity being one of the most important parameters in population management and modelling, we lack substantial evidence for habitat limitations on freshwater species. Here we tested the ideal free distribution (IFD) hypothesis using an indirect behaviour-based method for small closed populations assuming that animals can...

Hepatotoxic microcystins (MCs) produced by cyanobacteria are known to accumulate in gastropods following grazing of toxic cyanobacteria and/or absorption of MCs dissolved in water, with adverse effects on life history traits demonstrated in the laboratory. In the field, such effects may vary depending on species, according to their relative sensiti...

Current models in evolutionary ecology predict life history alterations in response to habitat suitability to optimize fitness. Only few empirical studies have demonstrated how life history traits that are expected to trade off against each other differ among environments. In Europe, many salt marshes have been recently invaded by the grass Elymus...

The influence of environmental factors (mainly the river flow) on the year-to-year variability of European eel Anguilla anguilla fluvial recruitment in a small coastal catchment, the Frémur River (north-west France) was examined. A comprehensive survey of catches from fixed traps at two weirs located at 4.5 km (Pont es Omnes Dam) and 6.0 km (Bois J...

Mortality of eels Anguilla anguilla in a large shallow lake in France due to predation by the cormorant Phalacrocorax carbo was found to be moderate when compared to fishery catches over a 9 year period. The results show that, contrary to previous extrapolations made at the pan-European scale, P. carbo predation in shallow lakes is not invariably a...

This paper assesses potential production of premigrant European eels Anguilla an-guilla based on analysis of sedentary eel populations in two small river systems in western France that are in close proximity. Abundance and biological characteristics were evaluated from electrofishing surveys conducted in three years in September and October, before...