Potential Effects of Habitat Use and Geographical Location on the Fecundity of European Eel

Declining recruitment of European eel (Anguilla anguilla) has focused attention on the conservation of potential spawners (silver eels) leaving continental waters. However, stock recovery is complex, as A. anguilla display considerable variation in biological characteristics across habitat types and range. In this regard, knowledge of silver eel fecundity is incomplete, with few estimates available from wild A. anguilla. Furthermore, there has been no systematic investigation of the effects habitat use and geographical location have on silver eel fecundity. To assess the former, we estimated the fecundity of silver eels which had predominantly been resident in either freshwater (Lake Mälaren, Sweden) or brackish (Baltic Sea) habitats. Despite Lake Mälaren silver eels generally being larger, there was no difference in the fecundity-body size relationship between these habitats. Secondly, we determined if fecundity differed geographically between Baltic region (Lake Mälaren and Baltic Sea), eastern Mediterranean (Vistonis Lake, Greece) and north-west European (River Shannon, Ireland) sub-populations. No latitudinal trend was apparent, but Baltic region and eastern Mediterranean silver eels were more fecund than those from north-west Europe. Consequently, though many factors affecting eel reproductive potential differ between freshwater and brackish residents, integration of fecundity in spawner stock management should primarily reflect geographic origin.