Impaired reproductive fitness despite high fecundity in European eel (Anguilla anguilla L.) from a Baltic Sea drainage area

The reproductive fitness of female European eels (Anguilla anguilla L.) from the Warnow River, Germany, Baltic Sea region, was evaluated by estimating fecundity and applying a spawning model. Individual fecundity ranged from 1,440,000 to 7,455,000 oocytes and mean relative fecundity equalled 5,956,015 oocytes kg(-1). Modelling suggests that 43% of eels hold insufficient energy storages or are within 10% of complete depletion. The fraction of eels with insufficient energy supply increases from 19% to 35% if the effect of parasitic infection is considered.