Date of Award

Spring 2023

Project Type

Thesis

Program or Major

Biological Sciences

Degree Name

Master of Science

First Advisor

Nathan B Furey

Second Advisor

Adrienne I Kovach

Third Advisor

Scott G Hinch

Abstract

Understanding behavior and quantifying survival is vital to the conservation of anadromous fishes. Sockeye Salmon (Oncorhynchus nerka) are one of the most economically and culturally important fish in the world, but some populations are declining, particularly in the Fraser River watershed in British Columbia, Canada. Within the Fraser River basin, Chilko Lake is one of the most prolific Sockeye Salmon populations, and Fisheries and Oceans Canada (DFO) has operated a counting fence at the mouth of the river for several decades to enumerate outmigrating smolts. Previous studies identified the clear water landscapes immediately downstream of the fence as high-risk, with high mortality of migrating smolts relative to larger, more turbid systems further downstream. In this thesis, I used passive integrative transponder (PIT, n = 358 age-1 smolts and n = 251 age-2 smolts) and acoustic telemetry (n = 208 age-2 smolts) to assess behavior and estimate survival of Chilko Lake Sockeye Salmon smolts in the 1.3-km upstream of the counting fence. Mark-recapture Cormack-Jolly-Seber models indicate that this 1.3-km stretch of the migration is high-risk (survival ranging from 37.7% - 62.2%). Survival estimates were similar among age classes and tag types, but age-2 fish may experience slightly higher survival than age-1 fish, with age-1 fish representing ~96% of the outmigrating population. Travel duration from release to the counting fence varied widely (1.3 hours – ~18 days days), suggesting complex behavioral patterns in this specific area. After investigating several covariates, fork length, mass, and a condition metric (residuals of a mass-length relationship) appeared correlated with survival, but the directions of relationships were not consistent across age and tag types. Further investigations of fine-scale behavioral patterns revealed that it is common for smolts to make several attempts to pass the fence, potentially causing delay and a depletion of energy stores. Consistent with previous studies, I presented evidence that increased co-migrant density appears to promote successful escapement at the fence. I identified a new high-mortality landscape and showed that a counting fence used by fisheries managers annually over the past 70 years is likely negatively affecting survival and the timely passage of out-migrating smolts.

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