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Should all fish in mark-recapture experiments be double-tagged? Lessons learned from tagging coastal cod (Gadus morhua)
Björnsson, B.; Karlsson, H.; Thorsteinsson, V.; Solmundsson, J. (2011). Should all fish in mark-recapture experiments be double-tagged? Lessons learned from tagging coastal cod (Gadus morhua). ICES J. Mar. Sci./J. Cons. int. Explor. Mer 68(3): 603-610. hdl.handle.net/10.1093/icesjms/fsq187
In: ICES Journal of Marine Science. Academic Press: London. ISSN 1054-3139, more
Peer reviewed article  

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Keyword
    Marine

Authors  Top 
  • Björnsson, B.
  • Karlsson, H.
  • Thorsteinsson, V.
  • Solmundsson, J.

Abstract
    Cod (Gadus morhua) were tagged outside and inside “herds” formed by anthropogenic feeding in an Icelandic fjord. Recapture rates were twice as high for fish double-tagged with one surgically implanted electronic tag and one anchor tag (46.6 and 62.2%) than with fish tagged with only a single anchor tag (20.0 and 29.2%) outside and inside the herds, respectively. The two main reasons for the differences observed in recapture rates were higher detection and reporting rates for the double-tagged fish. In cage experiments, 8% of the fish receiving implanted tags died during the first 2 d after tagging. For double-tagged fish, tag loss was ~10% for both tag types. About 80% of the tags were returned by fishers and 20% by fish processors. The tag detection rate by fishers was estimated at ~45 and ~80% for single- and double-tagged fish, and the reporting rate at ~74 and ~100% for single- and double-tagged fish, respectively. It is proposed for future tagging studies to double-tag all fish routinely, placing one tag dorsally and one ventrally, to enhance the detection rate and to account for tag loss.

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