Potential Effects of Jaw Tag Loss on Exploitation Estimates for Lake Erie Walleyes

Abstract

We used mark–recapture data collected from 1992 to 1995 to evaluate the potential effects of jaw tag loss on exploitation (u) estimates for walleyes Sander vitreus migrating from Lake Erie into the Grand River, Ohio. Loss of small jaw tags (size 10) detected during tagging periods was less than 17%. The annual loss rate of small tags exceeded 49% during each of the 2 years in which they were used. We detected no loss of large tags (size 12) during tagging periods, and annual rates of large-tag loss ranged from 23% to 50%. Exploitation rates adjusted for tag loss ranged from 14% to 39%, and unadjusted estimates ranged from 7% to 20%. Failure to adjust for annual tag loss rates resulted in 25–59% underestimation of u; however, error rates may be inflated due to a lack of knowledge concerning temporal patterns in tag loss. Our findings indicate that jaw tag loss rates must be accounted for when estimating population parameters such as u from mark–recapture studies. Furthermore, if agency personnel are able to analyze large samples of harvested fish for tags, the use of internal tag types that typically exhibit higher retention rates than jaw tags could reduce tag loss and eliminate biases due to nonreporting.