Silver eel migration behaviour in the Baltic

No abstracts are to be cited without prior reference to the author.

During the 2005 eel migration season 16 female silver eels (Anguilla anguilla L.) were tagged with data storage tags (Lotek LTD 2410) and released on the Swedish east coast at longitude 56o 30’ N. Until now 8 (50 %) of the eels have been recaptured and the data of 6 tags were possible to recover. In all 71 days of migration is documented and the data show a very consistent and regular behaviour, both between individuals and over time. Essentially all swimming activity was between dusk and dawn, starting when the light level at the surface equalled the civil twilight limit and stopping in the morning at approximately the same light level. In the daytime the eels stayed quiet at the bottom, in bottom depths varying between 2 and 36 m. The only exception to this diurnal behaviour was one eel during one day, moving in an area where the bottom depth was in excess of 30 m. In this case the eel continued migration during daylight, following the thermocline in 8-12 m depth. Two of the eels stayed stationary at the bottom from 1 to 4 full days before resuming migration.