Effects of commercial fishing and predation by cormorants on the Anguilla anguilla stock of a shallow eutrophic lake

13-year population survey of the critically endangered European eel in the southern Mediterranean region (Algeria)

A 13-year biomonitoring survey was carried out on the European eel, Anguilla anguilla for the first time in North Africa (Algeria) where there is a serious lack of information on the species. The study targeted specimens populating the only four sites where the species is both potentially present and legally exploited (Lake Oubeira, Lake Tonga, Mellah lagoon and Mafragh estuary). A total of 1370 individuals were sampled ranging from 17 to 113 cm in length, 19 to 2642 g in weight and 0.7 months to 6.6 years old, age being estimated from otolith growth marks. Otolith interpretation and age estimation were generally unambiguous at all four sites. According to the EELREP silvering index, the highest proportion of silver females was captured in fresh water (46% in Lake Oubeira and 25% in Lake Tonga), whereas a third were present in brackish water (Mafragh and Mellah). The sex ratio was in favour of females, and silver males were found to mature early (mean length 40 ± 1 cm, mean weight 123 ± 28 g and mean age 2 ± 0.6 years). Growth differed at the four sites, and the growth rate was highest in Lake Oubeira and asymptotic length highest in Mellah lagoon. Metamorphosis from the yellow resident stage to the silver migrating stage occurred very early in the eels' continental life (between 3 and 4 years of age). Results highlight rapid growth in these Algerian sites, and earlier silvering than in eels living in European waters, suggesting different life-history traits of A. anguilla in North African waters, influenced by environmental conditions.