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Utilizing PIT Tag Arrays to Evaluate Translocated Adult Pacific Lamprey in the Clearwater River Basin, ID

Michael Kosinski, Tod Sween, Ryan Kinzer

Nez Perce Tribe, Post Office Box 365, Lapwai, ID 83540

Over two million Pacific Lamprey once entered the Columbia River and were a highly coveted traditional food source for the Nez Perce Tribe. Pacific Lamprey have encountered massive challenges since the onset of large dam construction and basin-wide habitat alterations, with abundances approaching zero above Lower Granite Dam. In response, the Nez Perce Tribe, in 2006, initiated an adult lamprey translocation program to provide some level of natural production, thwart local extirpations, and preserve cultural values in the Snake River basin. Collections occur at lower mainstem Columbia River dams during the summer months, and adults are typically held in Nez Perce Tribe hatchery facilities until the following spring when they are released into suitable spawning streams. In 2018 and 2020 collections at the dams exceeded hatchery over-wintering holding capacity and these additional fish were direct released into the mainstem Clearwater River, Idaho. We were able to PIT tag 212 of these direct-released adult lamprey in July 2018 and 200 in July of 2020. These PIT tagged lampreys were released months prior to spawning and provided an ability to gain valuable unknown information about adult lamprey prespawn movement, distribution, and spawning stream preference.

Instream PIT Tag Detection Systems (IPTDS) in the Clearwater River basin of Idaho cover many of the major spawning basins for salmonids and provided good coverage to detect adult lamprey migration patterns into their ultimate spawning destination. Over one year after release, we estimated 87% (2018 release) and 72% (2020 release) of PIT tagged adults were detected at various Clearwater River tributary arrays. The lamprey showed a preference for the larger Lochsa and Selway Rivers, but were also detected in smaller streams, such as Lolo Creek and the South Fork of the Clearwater River. Lamprey passed arrays in as little as 6 days after release and as late as 383 days after release. Travel time from direct release sites to ending IPTDS detection, time of passage, and individual stream choice were the main information learned from this study. Future adult lamprey PIT tagging efforts and research in the Snake River basin face dedicated funding challenges but can show a wealth of information on these little-studied ancient fish.