Retention Rates for Passive Integrated Transponder Tags in Three Body Locations and Visible Implant Elastomer Tags for Wild Trout of Spawning Size

Tagging fish is a common method to identify individuals or groups of fish, but the utility of tags can be compromised if tags are shed over time, or provide consumption risks for anglers. We evaluated retention rates for three injection sites of passive integrated transponder (PIT) tags and for visible implant elastomer (VIE) tags in stream-dwelling Cutthroat Trout Oncorhynchus clarkii and Rainbow Trout O. mykiss of spawning size. In three streams in southeastern Idaho, 2,893 fish ≥150 mm (total length) were marked with VIE in the lower jaw, and PIT tagged in the (1) body cavity, (2) muscle tissue immediately posterior to the cleithrum, or (3) muscle tissue immediately ventral to the dorsal fin. Maxillary clips provided additional secondary marks. Retention of PIT tags was highest in the dorsal musculature for fish at large one year (93%), followed by cleithrum (82%), and body cavity (70%) locations. Most body cavity PIT tag loss occurred in females ≥200mm. Annual retention of VIE was 95% and maxillary clips 93%.  The likelihood of a PIT tag being encountered by an angler harvesting fish for consumption was highest for the dorsal musculature (67%), followed by cleithrum (60%) and body cavity (4%) locations.