Abstract

Mortalities resulting from internally tagging a fish on a boat may be due to barotrauma injuries, increased stress from prolonged handling times, or predation after a fish has been released back into the water. Conducting in situ internal acoustic tagging at depth of capture removes barotrauma stresses and simplifies the release method. In this study, we used eight years of acoustic tagging data to determine if the tagging method (in situ versus on the boat) influenced fish survivorship and evaluated the role of other tagging variables. Cox proportional hazard models indicated that tagging method was the only variable to significantly affect survival probability, with fish tagged in situ ~75% less likely to have an ‘event’ (mortality, tag loss, or emigration) compared to fish tagged on the boat at both 4 and 6-days after tagging. Examining tagging methods separately, handling time only marginally influenced survival probability of boat tagged fish and no variables had a significant effect on survival of in situ tagged fish. Implanting internal acoustic tags in situ is not a practical method for every species and for every environment, but given the increased fish survivorship demonstrated here, we suggest it be considered where applicable.

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