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Traceability of stocked eels – the Swedish approach
Author(s) -
Wickström Håkan,
Sjöberg Niklas B.
Publication year - 2014
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.12053
Subject(s) - stocking , fishery , stock (firearms) , anguillidae , biology , fish <actinopterygii> , geography , archaeology
Stocking of eels is one of the management measures in the eel regulation (EC No 1100/2007) to recover the stock. The Swedish Eel Management Plan doubles the numbers stocked to 2.5 million eels per year. Whether stocked eels contribute to the spawning stock or not has been questioned: stocked eels might not migrate as successful as wild recruited eels. The EIFAAC/ICES Working Group on Eel (2011) recommended ‘that all stocked eel should be marked and thereby separable from wild eel in subsequent sampling’. Since 2009, eels stocked in Sweden have been bathed in a strontium (Sr) solution, which gives a detectable mark in their otoliths. So far, 5.5 million eels have been marked in Sweden; Finland imports eels for stocking via Sweden, and these 0.6 million eels were marked by two Sr rings. We present results on marking success and recapture rates and also from marking with alizarin complexone and PIT tags in combination with Sr. If all eels stocked in the Baltic are marked, their contribution to the spawning run can be estimated. Using different combinations of marks in different regions, the relative contribution from separate stocking programmes can be evaluated. To increase the set of suitable marks, barium was tested as an additional tracer.