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Migration of eels tagged in the B altic S ea and L ake M älaren—in the context of the stocking question
Author(s) -
Sjöberg Niklas B.,
Wickström Håkan,
Asp Anders,
Petersson Erik
Publication year - 2017
Publication title -
ecology of freshwater fish
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.667
H-Index - 55
eISSN - 1600-0633
pISSN - 0906-6691
DOI - 10.1111/eff.12296
Subject(s) - stocking , otolith , overwintering , fishery , context (archaeology) , brackish water , fish migration , fish <actinopterygii> , biology , geography , ecology , salinity , paleontology
Abstract Eels ( A nguilla spp.) are in decline worldwide, and the signs of reduced recruitment have been observed in continental E urope since the early 1970s. To aid recovery of the E uropean eel, stocking is used by many E uropean countries as a management option. In this study, tagging experiments were conducted to follow eel migration from L ake M älaren and four sites along the S wedish east coast in the B altic S ea. The recaptured tagged eels were retrieved from fishermen, allowing for the opportunity to investigate their origin (brackish water, stocked in freshwater or a mix in between) by otolith microchemistry and to assess for morphological differences after tagging. Several changes took place; for example, eye index increased while weight and condition decreased with migrated distance and time until recapture. In L ake M älaren, the majority of tagged eels did not migrate out of the outlets, 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. Overall, overwintering is suggested to be an inferior option, but it is uncertain whether this is a natural behaviour or a result of translocation and restocking. For coastal eels, origin had no effect on migratory 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, recaptures were dominated by natural immigrants that had spent most of their lives in brackish waters.