Multi-objective assessment of conservation measures for the European eel (Anguilla anguilla): an application to the Camargue lagoons

The European eel (Anguilla anguilla) stock has declined since the early 1970s and is presently considered outside safe biological limits. The European Commission proposed a regulation (COM 2005/472 final) to establish measures for the recovery of the stock, with the aim to achieve the escapement to the sea of a 40% of adult eel biomass (with respect to undisturbed conditions) from each river basin. The proposed regulation imposes an effective reduction of fishing activities until implementation of an approved eel management plan. We use a demographic model, explicitly accounting for age, length and sex structure and for the peculiar features of the continental phase of eel life cycle, to assess the effectiveness of the regulation proposal. We explore alternative management options with reference to the Camargue (Southern France) eel population. Using multi-criteria methods we compare different fishing policies with respect to two potentially conflicting objectives: preserving a sufficient spawner escapement and guaranteeing an acceptable harvest to fishermen. We show that the current fishery is inefficient and that appropriate management policies (like limiting the fishing season and increasing the mesh size of the fishing gears) are likely to have a doubly positive effect, by achieving the conservation target of the regulation and increasing fishermen revenues

Age and growth of Anguilla anguilla in the Camargue lagoons

Age and total length (L-T) data from a 11 year monitoring of the Anguilla anguilla eel population of the Camargue lagoons (Rhone delta, southern France) were collected for glass, yellow and silver eels. Three distinct models were calibrated to describe the growth process of undifferentiated eels, females and males, respectively. Uncertainty of parameter estimates was evaluated by bootstrapping. Females were characterized by larger asymptotic body size (L-T) than males (580 +/- 50 v. 388 +/- 13 mm) and faster growth, whilst the Brody growth coefficient was larger for males than for females (means +/- S. D. 3.00 10(-3) +/- 1.68 10(-3) v. 1.73 10(-3) +/- 0.50 10(-3)). Sexual differentiation was estimated to begin at 204 +/- 38 mm mean +/- S. D., i.e. at the end of the second year in the lagoons, well before the LT at which macroscopic differentiation became possible (c. 300 mm). Males probably leave the lagoon or die (due to either natural or fishing mortality) within the first 3 years, whilst females can remain up to 5 years. Sexual differentiation and maturation have a major role in shaping the LT structure of the population. The LT and mass (M) data were fitted by allometric curves (M = a(LT)(b)). The calibration of distinct curves for data from different years indicated that the allometric coefficient a was subject to wider interannual fluctuations than the allometric exponent b. A negative correlation linked the average LT and the allometric exponent (r = 0.58, P < 0 01). (c) 2006 The Fisheries Society of the British Isles

Sex differentiation of the European eel in brackish and freshwater environments : a comparative analysis

Body growth parameters, age and total length at sex differentiation were compared in three European eel Anguilla anguilla populations from Mediterranean sites with different salinity. Whilst body growth was faster in brackish than in freshwater environments, the present analysis shows that body size at sex differentiation might be a physiological invariant. (c) 2006 The Fisheries Society of the British Isles