Feasibility of passive integrated transponder technology to study in situ movements of larval sea lamprey

Abstract

In the Laurentian Great Lakes, sea lamprey Petromyzon marinus is an invasive species controlled primarily through application of selective toxicants (lampricides) to tributaries expected to contain the most large larvae (>100 mm). Current assessment techniques make the assumption that larvae occupy all stream habitats in the same proportion irrespective of size or life history stage. Testing this assumption relies on the availability of a marking method to determine individual animal movement between habitats over time. To evaluate the feasibility of using passive integrated transponder (PIT) technology to detect sea lamprey larvae in situ, we implanted two sizes of PIT tags (8 and 9 mm) in larvae of less than 120-mm average length to assess survival, tag loss, behavior, and detectability in situ. Larval mortality and tag loss were lower when smaller tags were used, but mortalities were still high (60%) due to the small body cavity severely restricting internal tag implantation. Burrowing performance of 8-mm PIT-tagged larvae and untagged larvae was compared, and tagged larvae spent significantly more time moving (35 vs. 21 s) and more total time (71 vs. 31 s) to completely burrow into the substrate than untagged larvae. Detectability of those 8- and 9-mm PIT-tagged larvae in situ was evaluated by releasing them in a simulated stream and using a portable PIT tag antenna on three occasions to relocate them at a detection rate that ranged from 47 to 100%. Feasibility of tracking individual larval sea lamprey movements was evaluated by tagging larvae with either 9-mm PIT tags, visible implant alpha tags, or visible implant elastomer tags; releasing them in a natural stream; and relocating them by PIT antenna or recapturing them by electrofishing. In the natural stream, a total of 36% of 9-mm PIT-tagged larvae were relocated in situ during the study period, whereas less than 7% of larvae tagged with other tag types were recaptured. The smallest currently available PIT tags are not suitable for tracking movements of individual sea lamprey larvae less than 120 mm in average length because of the significant effects of tagging on behavior and survival rates. We are unaware of other tagging technologies currently available to track individual sea lamprey larvae of this size range in situ over time.