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The Use of Three Types of PIT Tag Antennas at Zosel Dam on the Okanogan River

Jeffrey K. Fryer

Columbia River Inter-tribal Fish Commission, 700 NE Multnomah Street Suite 1200, Portland, OR 97232

Zosel Dam, located on the Okanogan River near the Canadian border, is a critical point to estimate abundance of both upstream and downstream migrating Sockeye Salmon as well as Chinook and steelhead.  Adult salmon arriving at this dam have already passed 9 mainstem Columbia River dams followed by 132 km of Okanogan River where temperatures during the upstream migration often exceed 25C.  Despite these challenges, Okanagan Sockeye for the past 25 years have often been the largest naturally produced run of salmonids in the Columbia Basin.  Due to the high temperatures, migration timing and survival through the Okanogan River are highly variable, making good escapement estimates important.  Given that there were PIT tagging programs for species of interest (especially Sockeye Salmon) PIT tag antennas were installed in the two fish ladders in 2010.  However, this was followed by several years when high flows resulted in most of the Sockeye migration passing undetected through open spillways.  Floating antennas immediately upstream of the spillways were installed beginning in 2014 which detected PIT-tagged juveniles (and became important in estimating juvenile mortality and timing), but adults migrated too deep for detection.  In 2021, PIT tag antennas were installed across the spill basin immediately downstream of the dam but upstream of the fish ladder entrances.  These antennas have been plagued by problems with shed tags lodged underneath the antennas which generate continuous detections and have been thus far impossible to remove.  In addition, 4 of the 6 spill basin antennas have failed.  Despite these problems, valuable PIT tag detection data has been obtained from these newest antennas, some of which suggests that salmon may have trouble passing upstream through the fish ladders. Experience with the three antenna types will be compared in terms of cost, installation and maintenance issues, and data collected.