Too short to spawn? Implications of small body size and swimming distance on successful migration and maturation of the European eel Anguilla anguilla.

Individual net fat reserves after migration and reproductive investments were calculated for migrating female silver eels Anguilla anguilla (n = 387) collected in the outlet region of the Baltic Sea during the autumn run. It is estimated that 20·4% of the A. anguilla had completely exhausted all initial fat reserves and that 45·0% of A. anguilla were within 90% of complete energy depletion after migration and reproduction. This study concludes that a combination of body size and distance (6900 km) to the spawning area in the Sargasso Sea explains the results. An increase in the costs of migration due to heavy infection with Anguillicoloides crassus was also evaluated in an additional scenario with results showing that 26·4% of the A. anguilla had completely depleted all fat reserves. It is hypothesized that a large proportion of female silver A. anguilla from the Baltic Sea catchment area will have inadequate or suboptimal reserves for successful migration and reproduction.