Survival of seaward-migrating PIT and acoustic-tagged juvenile Chinook salmon in the Snake and Columbia Rivers: An evaluation of length-specific tagging effects

Abstract

Background: Acoustic telemetry is a widely used tool for evaluating the behavior and survival of juvenile salmonids in the Columbia River basin. Thus, it is important to understand how the surgical tagging process and the presence of a transmitter affect survival. This study evaluated the effect of fish length on the survival of yearling and subyearling Chinook salmon during their seaward migrations through the Snake and Columbia Rivers during 2006, 2007, and 2008. Fish were collected at Lower Granite Dam on the Snake River (695 river km from the mouth of the Columbia) and implanted with either only a passive integrated transponder (PIT) tag (PIT fish) or both a PIT tag and an acoustic transmitter (AT fish). Results: Across the 3 years, a total of 157,000 yearling and subyearling fish were tagged and designated as PIT fish and 18,500 as AT fish. Survival was estimated from release at Lower Granite Dam to multiple downstream dams using the Cormack-Jolly-Seber single release model, and analysis of variance was used to test for differences among length classes for both tag types. No length-specific tag effect was detected between PIT and AT fish (that is, length affected the survival of PIT fish and AT fish in a similar manner). Fish length was positively correlated with the survival of both PIT and AT fish. Survival was markedly low among the smallest length class (that is, 80 mm to 89 mm) of both PIT and AT subyearling Chinook salmon and the survival of PIT fish was generally greater than that of AT fish. Conclusions: The lack of a length-specific tag effect suggests that under the conditions used in this study, differences in survival between PIT and AT fish may be due to the process of surgically implanting the transmitter rather than the presence of the transmitter.