Abstract
The use of internal telemetry has greatly advanced fisheries research in the past two decades, permitting researchers to observe movements and distributions of organisms in their natural environment. For many years, the prevailing opinion has been that internal tags should not weigh more than 2% of the dry body weight of a fish. Some studies indicate that tags weighing up to 12% dry body weight do not have a negative effect on swimming performance, but few authors have examined impacts to fish physiology and health. This study investigated how tags greater than 2% body mass affected the mortality, tag retention, swimming performance, and physiological indicators of stress in brook trout (Salvelinus fontinalis Mitchill). No mortality was observed between treatment groups, but tag retention was lowest in the heavy tag treatment group in which 80% (12 fish) lost tags. Swimming performance and physiological indices of stress were not significantly impacted by tag mass. Fish tagged with heavy tags showed slower growth in the 3 weeks after tagging, but growth rates appeared to recover by the end of the study, although this result may be confounded by tag loss. The results of this study suggest that for brook trout, the 2% rule is a highly conservative guideline that can be substantially extended but should not exceed 7% body weight due to concerns about tag retention.
Highlights
The use of internal telemetry has greatly advanced fisheries research in the past two decades, permitting researchers to observe movements and distributions of organisms in their natural environment
One tag was lost in each treatment group within the first 2 days post tagging, and all tags were lost by day 14 (Figure 1)
It is likely that this fish would have lost its tag shortly thereafter. Though it was not included in the tag loss group for this analysis, it was excluded from all further analyses due to its abnormally poor condition
Summary
The use of internal telemetry has greatly advanced fisheries research in the past two decades, permitting researchers to observe movements and distributions of organisms in their natural environment. The prevailing opinion has been that internal tags should not weigh more than 2% of the dry body weight of a fish. Some studies indicate that tags weighing up to 12% dry body weight do not have a negative effect on swimming performance, but few authors have examined impacts to fish physiology and health. Researchers must clearly understand the potential consequences associated with each tag attachment method prior to an experiment as internal tags that are not of the proper size relative to species may cause loss of tags and increased mortality, biasing the results of the study
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