Strategy of recreational anglers and estimated eel (Anguilla anguilla) catches in a large European catchment basin, the Loire (France)

The European Council Regulation (18 September 2007) for the recovery of eel stocks required European states to report on eel stocks and anthropic mortalities. The data sources for France reveal gaps in our knowledge about angling in the public domain, and catches from privately-owned rivers. We tested a simple method, using a survey, for estimating the strategy employed and the catches landed by the 350 000 anglers fishing in the Loire catchment area. The first findings show that the answers of the fishermen varied between 1 and 2% in the departments with the most eels, and between 0.1 and 0.2% in the departments located further upstream. The interest in eel fishing, the average weight of the eels caught by the fishermen, and the total catch all decreased from downstream to upstream. Finally, we estimated the annual average weight of eel caught by anglers, which ranged from 0.8 to 5.3 kg per year depending on the department and the local interest in eel fishing. This preliminary study shows that it is possible to estimate the different fishing strategies used and the quantities caught by means of a survey

Un outil d’aide à la gestion de l’anguille : le tableau de bord anguille du bassin Loire

L’anguille européenne (Anguilla anguilla, L.) est longtemps apparue comme une espèce commune, représentant une composante majeure des milieux littoraux et des eaux continentales. La prise de conscience de la diminution de son abondance est réelle et engendre l’émergence de processus de gestion. Ce constat situe l’enjeu du Tableau de Bord Anguille du Bassin Loire mis en place en avril 2002 sous l’égide du COmité de GEstion des POissons MIgrateurs du Bassin de la Loire, des Côtiers Vendéens et de la Sèvre Niortaise. Son objectif in fine est de contribuer à une gestion et à un développement durable de l’espèce et de ses habitats. Il vise à surveiller les caractéristiques des stocks locaux présents et des habitats disponibles au moyen d’une collecte régulière et objective de données synthétisées sous forme d’indicateurs de population et de milieu. Le concept, le fonctionnement actuel et les applications de ce tableau de bord sont ici présentés

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 environmentmay 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 7% 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

Spatial organisation of European eel (Anguilla anguilla L.) in a small catchment

Modelling governing patterns of European eel (Anguilla anguilla L.) distribution of four eel size classes ( 450 mm) in the Frémur basin (North-West France) was done using artificial neural network (ANN) techniques and ecological profiles. Our results demonstrate the high predictive power of the ANN models. Some macro and micro-scale factors, like distance from the sea, depth and flow velocity have the most significant influence in the models. Influence of distance from the sea appears to be very different from the spatial organisation usually described in river systems. In fact, the general tendencies of total eel densities according to distance from the sea showed that densities weakly increase upstream. Another outcome was the variations of habitat preference according to the eel size, even if this species is spread over practically every type of micro-habitat. Small eels were mainly found in shallow habitats with strong abundance of aquatic vegetation, whereas large eels tend to be found in intermediate to high depth with small to intermediate abundance of aquatic vegetation. Finally, we hypothesize that European eels change behaviour and microhabitat characteristic preference around a size of 300 mm

Migration delays and mortality of adult Atlantic salmon (Salmo salar) en route to spawning grounds on the River Allier, France

During summer periods when water temperatures are high, Atlantic salmon Salmo salar are forced to halt their migration. This phenomenon was observed in our study in the River Allier in France. Between 200 and 1200 S. salar have come to spawn in the River Allier every year for the last 2 decades, but the population has suffered a severe decline. In 2009, 30 individuals were radio tracked; of these, 11 died during the summer period, while the other 19 resumed their migration in the fall. This mortality level was higher amongst the S. salar that arrived towards the end of the migration period, i.e. those individuals that tended to spend the summer in the lower, warmer stretch of the river. In view of the continuing rise in freshwater temperatures, measures are urgently needed to reduce the impact of increased temperatures on fish in the River Allier. This could be achieved by (1) promoting summer delays further upstream by making it easier for fish to pass through dams and (2) by protecting the spawning adults, particularly in the locations of summer halt. This study is consistent with a growing body of literature that suggests that climate change could have devastating effects on the upstream migration phase of anadromous salmonids

A Review of Upstream Migration and Movements in Inland Waters by Anguillid Eels: Toward a General Theory

Anguillid eels are well known as catadromous highly migratory species, with marine spawning grounds well separated from inshore and inland growth areas. However, invasion mechanisms of river systems are poorly documented. This theory is based upon the identification of four distinct movement behaviors: "founders" that colonize rivers until they settle in the first available suitable habitat they encounter; "pioneers" that migrate upstream to the upper boundaries of the system; "home range dwellers" that establish in a given area for several months to several years; and „nomads;“ which are erratic eels that perform a general upstream shift as they search for suitable areas to forage or to settle. These behaviors are not mutually exclusive, any eel shifting from one behavior to another, depending upon ontogenetic attributes (age, experience, morphology, physiological stage, etc.), population parameters that determine density-dependent movements; and environmental parameters such as food availability, temperature, flow, and the carrying capacity of the ecosystem

Contrasting trends between species and catchments in diadromous fish counts over the last 30 years in France

The decline and collapse of populations have been reported for a large range of taxa. Diadromous fishes migrate between fresh water and the sea and encounter many anthropogenic pressures during their complex life cycle. In spite of being of ecological, cultural and economic interest, diadromous fishes have been in decline for decades in many parts across the world. In this study, we investigated the change in five diadromous fish counts in France over a 30-year period using 43 monitoring stations located in 29 rivers across 18 catchments. Our hypothesis was that the counts of these species evolved in a contrasting way between catchments. We also tested the effect of five drivers potentially contributing to the observed trends: catchment, latitude, presence of commercial fisheries, improvement of ecological continuity and salmon stocking. We found contrasting trends in fish counts between species at the national scale, with some taxa increasing (Anguilla anguilla and Salmo trutta), some showing a slight increase (Salmo salar) and some decreasing (Alosa spp. and Petromyzon marinus). For each taxon, except Anguilla anguilla, we highlighted a significant catchment effect indicating contrasting trends between catchments and stations. However, we found no significant effect of catchment characteristics for any of the studied taxa

Diadromous fish modified timing of upstream migration over the last 30 years in France

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