Effects of acoustic tag implantation on lake sturgeon Acipenser fulvescens: lack of evidence for changes in behavior

Abstract

An assumption of studies using acoustic telemetry is that surgical implantation of acoustic transmitters or tags does not alter behavior of tagged individuals. Evaluating the validity of this assumption can be difficult for large fish, such as adult sturgeons, not amenable to controlled laboratory experimentation. The purpose of this study was to determine if and when this assumption was valid for adult lake sturgeon Acipenser fulvescens tagged with large (34 g) acoustic transmitters and released into the St. Clair River during 2011–2014. The hypothesis that activity and reach-scale distributions of tagged and untagged lake sturgeon did not differ was tested by comparing movement frequencies, movement rates (speed-over-ground), and location-specific detection probabilities between newly-tagged lake sturgeon and presumably fully-recovered conspecifics tagged and released in prior years. Activity of acoustic-tagged lake sturgeon did not differ between newly-tagged individuals and conspecifics tagged in prior years. Movement frequencies and movement rates in all comparisons were similar between lake sturgeon observed during the first 15 days after surgery and simultaneously-observed conspecifics tagged in prior years. Likewise, lake sturgeon observed during the first 15 days after release were not more likely than conspecifics tagged in prior years to be distributed upstream or downstream of release sites. However, newly-tagged lake sturgeon were more likely than conspecifics tagged in prior years to be detected near release areas. Whether the cause for this ephemeral difference in detection probabilities was a behavioral response to surgery or a consequence of releasing newly-tagged individuals near receivers could not be determined. Lack of evidence for changes in movement frequencies, movement rates, and distribution after surgical implantation of acoustic tags supported the assumption that movements of acoustic-tagged adult lake sturgeon were representative of untagged conspecifics. Thus, detection data gathered from recently tagged individuals is unlikely to bias data analyses in studies of lake sturgeon spatial ecology using telemetry. Our findings should apply to most tag sizes given that we used some of the largest acoustic tags currently available. The “staggered entry” design used in this study also may be useful for testing fundamental assumptions of biotelemetry studies for other large fish.