Cédric Briand

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.

Role of Eel Odour on the Efficiency of an eel, Anguilla anguilla, Ladder and Trap

The influence of eel odour on the efficiency of a freshwater eel ladder and trap was assessed during two glass eel and yellow eel springtime upstream migration seasons in the Vilaine estuary, France. This test consisted of alternatively directing the outflow from the trap holding bin, away from, or onto the trap access ladder and comparing catches. Catches were 1.4 higher for both glass eels and juvenile eels when the trap water was directed towards the pass. The experiment had little influence on predicting ladder catches when compared to the environmental parameters. The distance of detection of the scent was calculated to range between 0 and 5 m from the ladder.

Point sampling the abundance of European eel ( Anguilla anguilla ) in freshwater areas

The European eel population is in decline. Urgent management actions are required. To monitor their effect, we developed a fast sampling method, applicable in shallow rivers and tributaries. We compared the Carle & Strub estimator from 35 double pass electric fishing samples with Point Abundance Sampling by Electrofishing or PASE (24 point samples on average by section) which we adapted for the eel. The correlation between both methods was highly significant (r2=94%, p<0.001) for densities lower than 150 eels .100 m-2. PASE, being a cheaper sampling method, thus constitutes an efficient and cost-effective method for evaluating management actions and further biological studies.

Modelling the recruitment of European eel (Anguilla anguilla) throughout its European range

European eel (Anguilla anguilla) recruitment has been declining at least since the early 1980s at the scale of its distribution area. Since the population is panmictic, its stock assessment should be carried out on a range-wide basis. However, assessing the overall stock during the continental phase remains difficult given its widespread distribution among heterogeneous and separate river catchments. Hence, it is currently considered by the International Council for the Exploration of the Sea (ICES) more feasible to use glass eel recruitment data to assess the status of the overall population. In this study, we used Glass Eel Recruitment Estimation Model (GEREM) to estimate annual recruitment (i) at the river catchment level, a scale for which data are available, (ii) at an intermediate scale (6 European regions), and (iii) at a larger scale (Europe). This study provides an estimate of the glass eel recruitment trend through a single index, which gathers all recruitment time-series available at the European scale. Results confirmed an overall recruitment decline to dramatically low levels in 2009 (3.5% of the 1960-1979 recruitment average) and highlighted a more pronounced decline in the North Sea area compared to elsewhere in Europe.