Migration of eels tagged in the Baltic Sea and Lake Mälaren
(English)Manuscript (preprint) (Other academic)
Eels (Anguilla spp) are in decline worldwide and the signs of a reduced recruitment have been observed in continental Europe ever since the early 1970s. In order to protect and recover the European eel, EU (the European Union) decided in 2007 to establish a recovery plan, aiming at protection and restoration. Stocking is, together with reduced fisheries and higher survival when passing hydro-electrical power plants, a measure accepted by the EU, and is today used by many European countries, according to their management plans. In the early 20th century eel stocking programs started in Sweden and in other countries around the Baltic Sea, and in Sweden the responsible authorities encouraged stocking activities already at the end of 19th century.In this study, tagging experiments were conducted to follow eel migration from Lake Mälaren and from four sites along the Swedish east coast in the Baltic Sea. Recaptured tagged eels were retrieved from the fishermen, allowing for the opportunity to investigate origin by otolith microchemistry and to discover morphological differences after tagging. Several changes took place; e.g. eye index increased while weight and condition decreased with migrated distance and time until recapture.A majority of the tagged eels in Lake Mälaren did not migrate out of any of the outlets in the eastern part of the lake, irrespective of their origin. Most of them were caught in the opposite direction and continued to be caught in the lake 1-3 years after tagging, with significant weight losses. Overwintering is suggested to be a poorly chosen option, but it is uncertain whether this is a natural behaviour or a result of translocation and restocking.Concerning coastal eels, origin had no effect on the migration behaviour; a majority of the tagged eels migrated towards the outlet of the Baltic Sea. Interestingly, a minority of the recaptured eels originated from stocked fish. Instead, they were dominated of natural immigrants who had spent most of their lives in brackish waters.
Anguilla anguilla, silver eel, Carlin tagging, stocking, otolith microchemistry, strontium
Research subject Marine Ecology
IdentifiersURN: urn:nbn:se:su:diva-113823OAI: oai:DiVA.org:su-113823DiVA: diva2:787843