Clackamas River Bull Trout Reintroduction Project 2018

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Clackamas River Bull Trout Reintroduction Project 2018

Over four decades after the last Bull Trout (Salvelinus confluentus) was documented in the Clackamas River in 1963, a 2007 feasibility study determined the Clackamas River Subbasin to be a favorable candidate for Bull Trout reintroduction. A reintroduction effort launched in 2011, with the goal of re-establishing a self-sustaining population of spawning adults (between 300 and 500) by the year 2030. The final year of translocating Bull Trout from the Metolius River Subbasin to designated reaches in the upper Clackamas River and select tributaries was 2016. The primary objectives during the eighth year of the project (second phase) were to monitor and evaluate the reintroduction effort. During 2018, progress was made toward the project’s goal. The effectiveness of the reintroduction strategy was assessed by describing the seasonal distribution of translocated Bull Trout, assessing reproduction, and characterizing potential impacts to Endangered Species Act-listed salmon and steelhead that currently occupy the Clackamas River Subbasin. A video monitoring weir with an associated adult trap and passive integrated transponder (PIT) antenna was employed in Pinhead Creek to assess the spawning population. The spawning population was comprised of individuals that had been translocated of multiple life stages in 2012 – 2016, confirming survival and recruitment into the adult population. The 25 individuals subsampled at the weir trap were large, migratory fish and ranged in size from 440 – 705 mm TL. A total of 101 individual Bull Trout were captured or observed at the weir of which 54 (53%) were female and 47 (47%) were male. Of the 54 females, 27 (50%) had been previously tagged. Forty-two (89%) of the 47 males had been previously tagged. Since all translocated fish were PIT-tagged, the presence of untagged fish suggests at least some of the spawners may have been locally-born offspring, though the disparity between the ratio of tagged to untagged males and females may indicate an elevated rate of tag shedding among the females. During 2018, 95% of tagged Bull Trout that encountered the Pinhead Creek weir successfully passed upstream during the spawning season. Seventy-three percent of the Bull Trout that encountered the weir, passed during their first encounter and 91% passed upstream by their second encounter. Redd counts have increased substantially since the inception of the reintroduction program and the 84 redds counted during 2018 were near the highest counts to date. Caudal fin tissue was collected from five additional untagged Bull Trout captured at the Pinhead Creek weir during 2018. Combined with samples from 2017, this collection will provide the opportunity for subsequent parentage analysis and possibly the confirmation of naturally produced progeny and recruitment into the spawning population. Monitoring efforts to date have not provided evidence of post-emergent juveniles, or confirmed the recruitment of naturally-reproduced individuals into the spawning population, both of which are major benchmarks in the overall goal of establishing a self-sustaining population of Bull Trout in the Clackamas River Subbasin. These benchmarks may be achieved over time as the reintroduction effort progresses and the population develops. Implementation and monitoring of the reintroduction project will continue to be evaluated on an annual basis and the reintroduction strategy will be adaptively managed.

Kevin Hauser
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