European eel (Anguilla anguilla): prediction of spawner escapement from continental population parameters

This paper describes the assessment of silver European eel (Anguilla anguil la) escapement based on a "sedentary" population fraction analysis in a 60- km(2) watershed of northern Brittany (France). Downstream migration fluxes were monitored using eel traps and related to environmental factors. Intens ive electrofishing and fyke-net fishing were conducted to assess eel biomas s, densities, and population structure. A total of 564 eels, including 81 s ilver eels, were PIT tagged. In 1996, 616 eels were caught in the catchment including 68 silver eels (11%). During the following downstream migration period, 12 of the PIT-tagged silver eels, among a total of 678, were recapt ured in the downstream traps. Seven were recaptured in the catchment in 199 7. It was shown that (i) only about 20% of the silver eels present in the c atchment emigrated during the following year, (ii) 12% stayed in the catchm ent including two (3.4%) that recovered yellow eel characteristics, and (ii i) the other eels either died or settled in the catchment but were not reca ptured. It was also estimated that 2% (650 eels) of the population (34 000 eels) among 3000 silver eels considered "emigration candidates" emigrated e ach year.