Are Lithuanian eels fat enough to reach the spawning grounds?

Abstract

Stocks of the European eel Anguilla anguilla have been in a steep decline since the 1980s. Stocking of water bodies with juvenile eels captured in the wild to establish or enhance local populations has been a common practise in Europe for many decades. However, the degree of contribution by stocked eels to natural spawning capacity is poorly known and extensively debated. There have been suggestions that eels derived from stocking are less likely to contribute to the spawning stock due to a lack of navigational capability and lower fitness related to insufficiency of energetic resources. Results of the current study indicated that eels translocated long distances from the point of capture and released into inland waters in Lithuania are successfully undergoing the silvering process. A proportion of 23.7% (N = 27) among all migrating eels were described to be at the yellow (SI, SFII or SFIII) eel stage and downstream movements of these eels should be attributed to local movements, rather than spawning migration; 76.3% were assigned to the silver eel stage. This study suggests that 36.8% (N = 32) of downstream migrating silver eels of stocked origin had accumulated sufficient energetic resources for spawning migration and gonadal development and should be able to traverse the 7900-km distance to the presumptive spawning grounds in the Sargasso Sea. The rest of migrating silver eels (63.2%, N = 55) had insufficient energetic resources; the average potential swimming range of these eels was estimated to be 6135 ± 683 km.