Abstract
A systematic review and meta-analysis was conducted to evaluate the appropriate tag:fish size ratio when tagging juvenile salmonids (genera Oncorhynchus, Salmo, and Salvelinus). The review yielded 18 publications with 211 control and treatment groups reporting results from laboratory studies on the effects of passive integrated transponder (PIT) tags, plus a small number of additional studies on acoustic transmitters. A meta-analysis of the PIT tagging studies showed significant heterogeneity among studies with respect to mortality. Meta-regression revealed that juvenile salmonid mortality increased curvilinearly with the tag:fish length ratio, indicating that mortality risk is rapidly enhanced as smaller fish or larger tag sizes are used. The tag:fish length ratio effect on daily length or mass gain increased linearly. The results provide an estimate of the effects of the tag:fish length ratio on mortality and growth parameters in juvenile salmonids. Based on this, we suggest that researchers can follow best practices for tagging juvenile salmonids with tags that are not greater than 17.5% of fish total length (TL). This equates a minimum size threshold of 131 mm TL for tagging salmonids with 23-mm PIT tags, and 69 mm TL with 12-mm PIT tags. This information can assist researchers, managers, and welfare agencies striving to use the best possible evidence to make informed decisions regarding fish tagging.
Highlights
Given their ecological and cultural importance (Verspoor et al 2008; Forseth et al 2017), salmonids have been important focal species of tagging efforts for centuries (Walton 1653)
Time was an important predictor on its own, which is intuitive given that the outcome was cumulative mortality, which can only increase with time
The strong interaction between tag:fish length ratio squared and time suggests that the impact of tag:fish length ratio on mortality dropped off substantially over time, and was primarily high during a period shortly after tagging
Summary
Given their ecological and cultural importance (Verspoor et al 2008; Forseth et al 2017), salmonids have been important focal species of tagging efforts for centuries (Walton 1653). Small tags can be used in comparatively small fish and potentially have lesser impact on the animals’ performance in terms of growth, survival, and behaviour, but usually have shorter detection ranges, and depending on the type may have short life span. Effects of the tagging process and physical impacts of tags themselves on animal health and performance, and the validity of study results, have been of scientific interest since tagging became a common practice among fisheries scientists (e.g. Markus 1933; Pechacek 1956; Jepsen et al 2015). Data from individuals negatively affected by tagging may provide false inferences about growth, survival rates, and behaviour of wild fish. Procedures such as capture, handling, and tagging elicit physiological and behavioral responses of animals, and the tagged individual requires time and suitable conditions
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