External attachment of acoustic tags to deepwater reef fishes : an alternate approach when internal implantation affects experimental design

Implanting internal acoustic tags is often a preferred method for tracking fish; however, this procedure can present issues with respect to surgical incision that affect experimental design. This is particularly the case when testing for the effects of barotrauma, where the incision for an internal tag would inadvertently “vent” the fish, precluding an “unvented” or control treatment. The rise of barotrauma experimentation has increased the need for methods facilitating this design. Here, we develop and test a novel technique to externally attach acoustic tags, without causing the release of gasses from the fish's body cavity. In addition, this method does not require anesthetics, thereby allowing researchers to eliminate artifacts associated with sedation when trying to more accurately replicate “real-world” fishery conditions. We used accelerometer/depth tags to provide information on how long an externally tagged fish would retain its tag in situ. Changes in acceleration or changes in depth were used as a proxy to determine whether the fish was alive or dead or had shed its tag. Results showed that 80% of the fish (n = 20) detected retained their tags for at least 48 h. Seventy-five percent of the fish tagged retained their tags for at least 23 d. After 23 d, tags were shed periodically until day 49. Thirty-three percent of fish tagged retained their tags until day 57, when the experiment was ended. The ability of these modified tags to stay attached for at least 23 d suggests that the technique would be successful for maintaining a balanced experimental design for measuring postrelease mortality or changes in behavior in deepwater fishes while eliminating artifacts typically associated with internal tag implantation.