Evaluation of the Effects of Marking Pacific Lamprey Ammocoetes with Visual Implant Elastomer, Coded Wire Tags, and Passive Integrated Transponders

Populations of Pacific Lamprey Entosphenus tridentatus have declined in multiple portions of the Columbia River basin and some Pacific coastal rivers due to a variety of factors. Given the ecological and cultural significance of the species, federal, state, and tribal resource managers have increased conservation efforts, though a lack of basic information about the biology of wild lampreys hinders some of these actions. Multiple tagging technologies have been used to mark migrating metamorphosed juvenile lampreys for research, but these methods have not been experimentally tested for use on the smaller ammocoete stage. Lamprey ammocoetes (total length range = 29-83 mm) were assigned to groups marked with three common tags (visible implant elastomer [VIE], coded wire tags [CWT], and passive integrated transponders [PIT]) or to untagged controls, and mortality and tag retention were monitored. Growth and burrowing ability were also measured to determine the potential for sublethal effects of tagging. At the end of the 137-d study, no mortality was measured in the VIE group and tag retention was 100%. Fish in the CWT group also exhibited no mortality, though tag retention was 64%. Fish in both of these groups did not exhibit any differences in growth or burrowing performance when compared with controls. The PIT group was the only group to experience mortality at a rate of 62.5%. While the larger fish within the PIT group displayed higher survival, the smallest fish that survived PIT implantation was 70 mm. Tag retention was 89% for surviving lampreys in the PIT group. All three techniques were successfully used to mark small ammocoetes, though researchers should carefully consider the benefits and potential effects on animal behavior when choosing which method to use.