Evaluation of Transmitter Application Techniques for Use in Research of Adult Eulachon

Abstract

AbstractThe Eulachon Thaleichthys pacificus is a small anadromous fish whose annual spawning runs historically totaled millions of fish returning to the Columbia River in the Northwest United States. Recent population declines of returning adult Eulachon have been attributed to many factors, leading to the Eulachon being listed as threatened on the U.S. Federal Endangered Species List. However, basic life history information of the Eulachon in freshwater remains unknown, hampering efforts to manage the species. In the current study, we tested common transmitter application techniques (internal implantation versus external attachment) for use on adult Eulachon captured as they approached terminal spawning areas and measured both lethal and sublethal effects of each procedure. Time to mortality, overall mortality, and the proportion of fish that showed external signs of disease did not differ between techniques. Fish from the external attachment group had the lowest concentrations of the plasma ions Na+ and Cl−, potentially indicating increased chronic stress associated with this procedure. Internal implantation of transmitters did not induce increased mortality or sublethal stress, though female fish experienced some egg loss through the incision site. The ultimate effects of transmitter implantation into the egg mass are unknown. Our results suggest that both internal implantation and external attachment of transmitters are viable biotelemetric techniques for use on migrating Eulachon at terminal spawning areas, though various sublethal effects unique to each procedure need to be carefully evaluated by prospective researchers.Received April 5, 2013; accepted July 11, 2013