Estimates of escapement, exploitation rate, and number of downstream migrating European eels Anguilla anguilla in Ichkeul Lake (northern Tunisia)

The European eel (Anguilla anguilla) stock has been declining for the last three decades and today, it is currently listed as endangered. The objective of this study was to quantify the escapement rate of silver eels to obtain an estimate of the future spawners migrating from the southern part of its distribution area in Tunisia. A mark-recapture experiment was conducted in Ichkeul Lake (Tunisia) between December 2013 and February 2014, covering the winter downstream run of eels. The size range of the downstream migrating eels was between 33 and 79 cm with 585.3 +/- 156.77 g mean weight. The number of migrating silver eels was estimated to 342 221 (297 956-386 486), corresponding to a biomass of 200.2 (174.3-226.1) t, with a density of 23.55 (20.51-26.6) kg ha(-1). The commercial fishing rate was estimated to be 18.8% (16.6-21.5%), which translates into an escapement rate of 81.2% (78.5-83.4%). The ratio current/pristine escapement was 0.69 for the entire migration period.