Tag Retention of T-Bar Anchor Tags and PIT Tags in Shovelnose Sturgeon

Capture/recapture methods are commonly used to estimate population parameters and often provide some of the most reliable estimates if the necessary assumptions are followed.  The broadest assumption of all capture/recapture models is that tags are not lost or over-looked.  Therefore, it is essential to understand tag retention so that estimates can be adjusted if tag loss occurs.  Our objectives were to 1) determine retention rates of T-bar anchor tags and PIT tags inserted dorsally into shovelnose sturgeon Scaphirhynchus platorhynchus, and if retention was poor, 2) determine if other locations on the body and/or tagging methods would provide higher retention.  Sturgeon were captured from the wild and transported to a large circular holding tank (1,550-L; 1.8-m diameter; 0.6-m deep).  Shovelnose sturgeon were then randomly selected to receive one of two treatments:  fish handled but not implanted with either tag (control fish; N=10) and fish implanted with both tag types (N=22).   Shovelnose sturgeon were inspected for tag loss every 14 days following implantation for a total of 98 days.  T-bar anchor tags had a retention rate of 100%; whereas PIT tags had a retention rate of 64%.  Follow-up experiments testing other PIT placement locations like the operculum or using super glue to plug the insertion point of dorsally PIT-tagged fish resulted in 92% and 85% tag retention after 98 days, respectively.  These results imply that dorsally-inserted PIT tags provide the lowest retention and that alternate tagging locations or procedures are warranted.