Effect of internal tagging on egg viability of steelhead

Objective: Acoustic and radio tagging has been used extensively to study movement patterns of fish in marine and freshwater environments and often relies on internal tagging. Intracoelomic implantation of tags in fish requires the surgeon to make an incision, insert a transmitter in the body cavity, and close the incision with one or more sutures. Techniques to safely carry out these procedures along with the effects of surgery and tag burden on mortality and behavior have been well studied, but secondary effects such as reduced reproductive potential have not been documented. Given the growing use of acoustic telemetry and radiotelemetry and increased conservation concern for fish globally, it is important to understand the costs of scientific research on the target species. This study was designed to describe the effect of intracoelomic implantation of acoustic tags on the egg viability of female winter steelhead Oncorhynchus mykiss during their spawning migration. Methods: We monitored egg development of 108 hatchery-origin steelhead implanted with dummy acoustic tags across different abdominal locations. Results: Compared to a nontagged control group, we observed significant mortality of embryos for the majority of the treatment groups; however, when incisions were located on the midbody, ventral surface and sutured, we observed no significant negative effect on egg viability, presumably due to reduced water entering the body cavity during and after surgery. Conclusions: These results provide insight for those tagging fish species of high conservation concern on their spawning migration.