Long-term Retention of Passive Integrated Transponder Tags Injected into the Pelvic Girdle of Adult Walleye

Long-term retention of passive integrated transponder (PIT) tags injected into the subcutaneous musculature between the pelvic fins of adult Walleye Sander vitreus was assessed via collecting fish from natural lakes in northwestern Iowa during April 2015, examining fish for the presence of an existing visual implant tag (used as secondary mark), implanting PIT tags in a representative subsample of previously marked fish, and recapturing fish during subsequent annual surveys. Of the 332 Walleye (range = 444-706 mm; mean TL = 544 mm; standard deviation = 43) PIT-tagged in 2015, 87 of 88 (98.9%) recaptured from one to four years post-tagging retained their tag. Twenty-three Walleye were captured more than once (≥ 2 years post-tagging) and all Walleye had retained their tag on their second or third recapture. This study and others demonstrate that the pelvic girdle was an effective PIT tagging location for long-term studies evaluating adult Walleye population dynamics. In addition, the low probability of tags being encountered in fish fillets by anglers make this a desirable tag location for Walleye studies where Walleye are often targeted for consumption. These studies collectively demonstrate that PIT tags inserted into the pelvic girdle of a range of Walleye sizes yield retention rates suitable for advanced population modeling or stocking evaluations.