Escapement Rate and Population Size of Silver European Eel in Ichkeul Lake (Northern Tunisia)

The stock of European eel has faced a dramatic decline over the three last decades. Thus, this species is currently considered endangered (CITES, 2007; IUCN, 2010). It seems necessary to quantify the escape rate of silver eels to assess the stock status of these future broodstocks in its distribution area.

Unlike some European countries, little information is available on the downstream migrating fractions in the south part of its distribution area, especially North Africa. We propose here to provide preliminary information regarding Tunisian eel population.

A mark-recapture experiment was conducted in Ichkeul Lake (Tunisia) during the migration season 2013/2014. The size range of the downstream migrating eels is between 33 and 79 cm with 585g mean weight, and composed by 97% females. The size of the population considered was estimated to 404858 silver eels, corresponding to a mean biomass of 2367 Tons, with a density of 28 kg/ha. The commercial fishing rate is estimated to 17%, which allows estimating an escapement rate of 83%. This rate represents the double of the European Commission recommended level, which corresponds to 40% of the pristine biomass. This first estimation shows thereby the good operational management of the eel stock in this Lake.