Surprisingly Low Resiliency to Commonly Used Tagging Methods in Northern Pike

Assumptions about negligible impacts of common tagging methods on fish should be tested to avoid biased inferences from mark-recapture studies. In northern pike, a range of studies have reported limited to no tagging effects with various tagging methods. To repeat these findings in age-0 pike, we compared tagging effects on fitness-related traits using passive integrated transponder (PIT), T-bar anchor, opercular, and streamer tags in ponds. To estimate tag loss all pike, except the control group, were marked with a partial fin clip. The external T-bar anchor tag performed best with tag loss rates of 6.0 % and 15.2 % after 159 and 325 days, respectively. No PIT tag loss was observed. Fin clipping significantly elevated mortality relative to control fish, but the mortality increase was statistically independent of type of external tag employed. In a separate study with adult pike, surgically implanted transmitters negatively affected individual growth. Overall, our result show that PIT tags may be the most successful marking technique in age-0 and adult pike. If external visibility is required, T-bar anchor tags may be the second most appropriate, but age-0 pike should not be fin clipped. Moreover, our study raises a cautionary note about surgically implanted transmitters in pike as they may affect performance negatively.