Eric Feunteun

Management and restoration of European eel population (Anguilla anguilla): An impossible bargain

Abstract The European eel panmicitic population has been declining at least since the 1980s throughout its distribution area. The stocks are now ten times lower than they were initially. The causes of this decline are reviewed in this paper: marine causes such as Gulf Stream shifts are thought to reduce survival of leptocephali larvae during their transoceanic migration, but inland causes are also suspected, i.e. overfishing of all continental stages, obstructions to upstream and downstream migrations, habitat loss, water quality, parasite and xenobiotic contamination, which together contribute to reducing quality and quantity of spawner escapement from European inland waters to sea. Restoration programs have been conducted in several inland hydrosystems in Europe. If local fisheries have been sustained mainly by stocking elvers and glass eels, no significant restoration of the population has been observed suggesting that restoration plans are inefficient, despite significant efforts and relevant technologies (fish passage). The causes for the failure of restoration projects are listed and discussed, and it is shown that the minimum scale to work at is the catchment area. But international cooperation is required to coordinate programs, to determine common objectives and policies. Concepts for sustainable restoration and management are provided and discussed together with the general interest of eel population as a biointegrator of the quality and integrity of inland hydrosystems.

Sublethal Effects of Exposure to Chemical Compounds: A Cause for the Decline in Atlantic Eels?

Because of their unusual life cycle, American and European eels (Anguilla rostrata Lesueur and A. anguilla L.), are particularly exposed to pollutant effects. Because silver eels fast when they leave the freshwater system, the transoceanic migration forces them to constitute energy reserves in the form of muscle lipids, that are needed for successful spawning. Using species biological data, toxicological and ecotoxicological information, hypotheses are given to assess the contribution of pollution from freshwater sources to the recorded decline in the American and European eels fisheries since the 1980s. This paper first describes the lipid storage problems and the relative migratory capacities. Then several studies on the accumulation of xenobiotics in various anatomical compartments, on the biological half-lives of these compounds, and on their sublethal toxicity, are reviewed. During migration, lipid mobilization returns persistent lipophilic pollutants back into circulation, these being concentrated particularly in gonads at the crucial time of gametogenesis. Extrapolation of toxicological analysis (individual physiology) to the population level (spawning success) suggests that the quality of future spawners leaving freshwaters is one of the prime factors for the conservation of this threatened species.

European salt marshes diversity and functioning: The case study of the Mont Saint-Michel bay, France

The macrotidal Mont Saint-Michel bay has beenstudied intensively since 1990. The objectives ofthis study, supported by the European Union, wereto understand various processes underlying thefunctioning of this hydrosystem with a special focuson organic matter and nutrient fluxes betweensaltmarshes and marine waters. This paper presents asynopsis of these studies. The tidalflats are unvegetated and primary production isexclusively due to microphytobenthos communitiesdominated by diatoms. Halophile plant communitiescolonize the top parts of the tidal flats. Theircomposition and production vary according to amaturity gradient and sheep grazing. In ungrazedsaltmashes, production ranged from 1080 gDW m-2·yr-1in the lower marsh to 1990 gDW m-2·yr-1in the upper marsh whereas it was only 200 to500 gDW m-2·yr-1in Salicorniaspp.dominated pioneer zones and sheep grazed areas. Mostof this organic matter (OM) was trapped in situ,processed by fungi and bacteria, and then releasedseaward via tidal fluxes, groundwater and runoff as particulate OMand nutrients: –497 kg N, –1200/–1000 kg P-PO4and –9900/–4200 kg inorganic carbon). A small amount ofOM was exported to the bay as macrodetritus. Fattyacids and stable isotopes, used as markers, showedthat OM produced by the marsh halophytes contributedto the diet of all the tidal flats invertebrates thatwere studied. Transient fish species were shown tocolonize the saltmarshes to forage or graze, exporting about 50 tons POM (DW)·y-1. Therefore,it is assumed that the saltmarsh production enhancesthe production of the whole bay. But the functioningis still poorly known because the nutrient sinks havenot all been identified. Part of the nutrients inputwas provided by precipitation (+327 kg y-1), butthe contribution of the catchments was not quantifieddespite the fact that their influence was shown by thepresence of lindane in all the compartments of thesystem. Dynamics of saltmarshes are mainly influencedby natural sedimentation (1.5 million m3·y-1in the bay), plant community succession, and management (i.e., reclamation and agricultural activities).

Role of fish communities in particulate organic matter fluxes between salt marshes and coastal marine waters in the Mont Saint-Michel Bay

Among the 90 fishspecies censused in the Mont Saint-Michel Bay (France), 23 colonise and forage in the salt marshes during flood. Therefore, this environment may play an important trophic and nursery role for these species. This community is largely dominated by mullets (81% of the biomass), Liza ramada and secondarily L. aurata. But gobies (mainly Pomatoschistus minutus and P. lozanoï) and sea bass (Dicentrarchus labrax) are also present; they represent respectively 11% and 4% of the biomass. During the tide cycles, mullets export from salt marshes about % of their body weight (FW) containing a mixture of sediment (43%), organic matter (24%) and water (33%). Gobies and sea bass mainly feed on dwelling macro-invertebrates, and they export respectively 4.5% and 10% of their body weight during a tide cycle. Thus, we estimated that 50 tonnes year-1 of particulate organic matter (dry weight POM) are exported from the 4000 ha of salt marshes to the marine coastal waters. These fish communities appear to be POM transporters and could play a significant role in the global energy budgets of coastal environments such as Mont Saint-Michel Bay. According to the seasons and the years, the energy exported by fish communities is assumed to range between 0 and 10% of the total POM output.

Feeding ecology of 0-group sea bass, Dicentrarchus labrax, in salt marshes of Mont Saint Michel Bay (France)

Abstract0-group sea bass,Dicentrarchus labrax, colonize intertidal marsh creeks of Mont Saint Michel Bay, France, on spring tides (e.g., 43% of the tides) during flood and return to coastal waters during ebb. Most arrived with empty stomachs (33%), and feed actively during their short stay in the creeks (from 1 to 2 h) where they consumed on average a minimum of 8% of their body weight. During flood tide, diet was dominated by mysids,Neomysis integer, which feed on marsh detritus. During ebb, when young sea bass left tidal marsh creeks, the majority had full stomachs (more than 98%) and diet was dominated by the most abundant marsh (including vegetated tidal flats and associated marsh creeks) resident amphipod,Orchestia gammarellus. Temporal and tidal effects on diet composition were shown to be insignificant. Foraging in vegetated flats occurs very rarely since they are only flooded by about 5% of the tides. It was shown that primary and secondary production of intertidal salt marshes play a fundamental role in the feeding of 0-group sea bass. This suggests that the well known nursery function of estuarine systems, which is usually restricted to subtidal and intertidal flats, ought to be extended to the supratidal, vegetated marshes and mainly to intertidal marsh creeks.

Biodiversity in salt marshes: from patrimonial value to ecosystem functioning. The case study of the Mont-Saint-Michel bay

Until 1979, European salt marshes were known only through the inventories of fauna and especially of flora. On such criteria, the salt marshes of the Mont-Saint-Michel bay (France) were regarded as most significant of the French coasts. However, it took 20 years of research on the role of these wetlands of the estuaries-salt marsh systems to highlight the ecological, social and economic interest of this ecotone, between continental and marine systems, a long time considered as territory without value, except for stock breeders or hunters.

Assessment of Grey Heron predation on fish communities : the case of the largest European colony

The fish predation rate by Grey Heron Ardea cinerea was studied during two breeding seasons (1987–88) in the largest European colony at the Lake of Grand-Lieu (Loire-Atlantique, France). The herons diet was compared to the available fish population of its main feeding area, the marsh of Bourgneuf (16000 ha) which is composed of former salt pans and meadows drained by a dense network of shallow ditches. This study is the first attempt to assess the predation exerted by an ardeid colony on a fish community over such an extensive natural environment. It also provides the first data about the abundance and the structure of fish communities in shallow coastal dyked marshes. For this purpose, two different sampling methods were used according to the waters salinity. In fresh waters, electrofishing was used as the removal method, and density estimates were calculated with Carle & Strub estimator (1978). Fish were caught in randomly selected stations (sections of ditches enclosed by two 5 mm mesh nets). In brackish waters, pools and ditches were drained. The distribution of the herons at the feeding areas was determined by direct observations, by counting flights from the colony, and by radio-tracking. The diet was investigated by observing adult herons on the foraging areas, and by analyzing the prey regurgitations of the young at the nests. The global food consumption was assessed from Marion (1988), according to the birds activity determined during 5 years of radio-tracking. Altogether, at least 39 species of fish were available in the herons feeding area (during the reference period, 87–88) and the mean fish biomass was 270 kg per ha of open water, or 30 kg per ha of marsh (open water = 11.2% of the marsh area). The fish community was dominated by eel Anguilla anguilla (145 kg ha−1, 50,8% of the total biomass), and catfish Ictalurus melas (40 kg ha−1, 14%). Except for small and inaccessible species (living in the deepest parts of the marsh), heron diet was very similar to fish species composition of the community occurring in the marsh. The catfish was the species captured most frequently by the heron (45% of the mass), the eel was second with 28% of the mass. The catfish was probably over represented in the diet considering that they are caught in catfish-dumps created by professional fishermen at Grand-Lieu lake, in order to reduce the density of this undesirable species. Inversely, small species such as Gasterosteus aculeatus were not found in the diet whereas they are very numerous in the marsh. On average herons of Grand-Lieu colony catch 1.92 kg of fish per ha of marsh (6% of the fish standing crops in the marsh) during the breeding season, the main predation period.RésuméLe taux de prédation exercé par la plus grande colonie européenne de Hérons cendrés (800 à 1300 couples reproducteurs) du lac de Grand-Lieu (Loire-Atlantique, France) a été étudié pendant deux saisons de reproduction (1987 et 1988), en comparant le régime des hérons et la population de poissons dans la principale aire dalimentation, le marais de Bourgneuf. Ce dernier est constitué de marais salants et de prés bas drainés par un réseau dense de fossés étroits et peu profonds. Cette étude est la première tentative dévaluation de la prédation exercée par une colonie dArdéidés sur une aire géographique aussi étendue (16000 ha), et fournit les premiers résultats concernant la structure et labondance du peuplement ichtyologique dun marais littoral endigué. Deux methodes déchantillonnage des poissons ont été utilisées en fonction de la salinité de leau dans une zone représentative de 3660 ha. En milieu dulçaquicole, des pêches électriques ont été conduites de façon à pouvoir utiliser la méthode destimation des stocks de Carle & Strub (1978) dans des stations sélectionnées au hasard (sections de fossés isolés par deux filets droits de 5 mm de maille). En eau saumâtre, des vidanges de pièces en eau (anciens marais salants) ont été réalisées. Le régime des hérons a été étudié par observation directe des adultes sur les zones alimentaires, et par lanalyse des régurgitations de proies par les jeunes au nid. Les besoins alimentaires quoditiens des adultes ont été déterminés à laide dun modèle bioénergétique (Marion, 1988) basé sur le rythme dactivité observé directement ou par radio-tracking pendant 5 saisons de reproduction. La répartition des adultes sur les zones alimentaires a été étudiée par les mêmes méthodes ainsi que par les comptages de vols alimentaires sur la colonie pendant trois saisons de reproduction (1976–78).Durant la période de référence, au moins 39 espéces de poissons sont disponibles dans le marais et la biomasse moyenne du peuplement en mai est de 270 kg par ha deau, soit 30 kg par ha de marais (leau représentant 11,2% du marais). Ce dernier est largement dominé par languille Anguilla anguilla (145 kg ha−1 deau et 50% du peuplement) puis par le poisson-chat Ictalurus melas (40 kg ha−1 et 14,0%). Si lon excepte les espèces de petite taille, et celles qui ne sont pas accessibles (vivant dans les zones les plus profondes), la composition du régime alimentaire des hérons est proche de celle du peuplement de proies disponibles dans le milieu, les espèces les plus consommées étant le poisson-chat (45% du poids de poisson dans le régime), et secondairement languille avec 28%. Cependant le poisson-chat est surreprésenté par rapport au milieu, en raison de lartéfact des décharges de Cette espèce à Grand-Lieu, créées par les pêcheurs professionnels pour limiter Cette espèce indésirable. A linverse certaines petites proies comme lépinoche sont délaissées dans les marais. La proportion pondérale du prélèvement des hérons reste très faible: en moyenne 1,92 kg de poissons par ha de marais pendant la période de reproduction des hérons, qui représenté la période essentielle de prédation, soit environ 6% de lichtyomasse totale.

Impact of sheep grazing on juvenile sea bass, Dicentrarchus labrax L., in tidal salt marshes

The diet of young of the year sea bass, Dicentrarchus labrax L., from sheep grazed and ungrazed tidal salt marshes were compared qualitatively and quantitatively in Mont Saint-Michel Bay. In areas without grazing pressure, the vegetation gradient changes from a pioneer Puccinellia maritima dominated community at the tidal flat boundaries through a Atriplex portulacoides dominated community in the middle of the marsh to a mature Elymus pungens dominated community at the landward edge. The A. portulacoides community is highly productive and provides important quantities of litter which provides a habitat and good supply to substain high densities of the detrivorous amphipod Orchestia gammarellus. In the grazed areas, the vegetation is replaced by P. maritima communities, a low productive grass plant, and food availability and habitat suitability are reduced for O. gammarellus. Juvenile sea bass colonise the salt marsh at flood during 43% of the spring tides which inundate the salt marsh creeks. They forage inside the marsh and feed mainly on O. gammarellus in the ungrazed marshes. In grazed areas, this amphipod is replaced by other species and juvenile sea bass consume less food from the marsh. This illustrates a direct effect of a terrestrial herbivore on a coastal food web, and suggests that management of salt marsh is complex and promotion of one component of their biota could involve reductions in other species.

Do fish communities function as biotic vectors of organic matter between salt marshes and marine coastal waters

The contribution of fish communities to organic matter (OM) fluxes, especially between salt marshes and adjacent marine coastal waters are reviewed. For this a data set from the bay of Mont Saint-Michel and literature is examined and discussed. In a range of macro-tidal coasts of Europe, salt marshes are only flooded at spring tides for a short time. Many animals, including fish, then invade the salt marshes through tidal creeks. They forage there for up to a few hours and swim back to sea at ebb. Meanwhile, organic matter is exported as gut content. In the 4000 ha of salt marshes of the bay of Mont Saint-Michel mullets were responsible for the export of about 8 kg of dry weight OM ha−1 in 1996 and of roughly 12 kg in 1997. Although spatio-temporally variable, the fish communities appear to play a more or less significant role, as ‘biotic vectors’ in the nutrient fluxes between salt marshes and coastal waters.

Preliminary results on a high east–west gradient in the macrozoobenthic community structure of the macrotidal Mont Saint-Michel bay

Abstract Environmental conditions in terms of river inputs, salt marsh development, shellfish cultures, hydrodynamics and sediment characteristics are very different from the western and the eastern part of the Mont Saint-Michel bay. A large scale study on the spatial structure of the intertidal macrozoobenthic community was then performed at the bay scale in order to determinate how these various conditions may modify the community composition and species density. In terms of density, the community was globally dominated by suspension/deposit filter-feeding bivalves, as well as amphipods in the eastern high levels of the intertidal zone. Several biocoenotic assemblage of the Macoma balthica community were described and large differences in the species composition and density were observed between the eastern and the western sectors of the bay. Total density for all species and recruitment were much higher in the eastern sector than in the west. We discussed about these east–west variations in terms of hydrodynamics, sedimentation processes and trophic conditions. Indeed, the large salt marsh extension and river inputs, as well as the lack of shellfish cultures in the east, may favour high food availability for benthic invertebrates of the area whereas the low river inputs and salt marsh development, the high sedimentation process and the intensification of mussel and oyster cultures in the west may create less favourable environments.