Biological / Geospatial Projects

aimed at answering important environmental questions

Relationship Between Salmonid Smolt Condition, Predation-related Mortality and Survival

Project: Relationship Between Salmonid Smolt Condition, Predation-related Mortality and Survival

Client: USACE - Walla Walla District & Grant County PUD

Year: 2007 - 2019

Location: Mid-Columbia and Lower Snake Rivers

Investigated the use of rapid, nonlethal examination techniques to assess the condition and overall health of juvenile salmonids migrating from the Snake and Columbia rivers, including an evaluation of biotic (e.g., fish size and condition, run-timing) and abiotic (e.g., river discharge, water clarity, water temperature) factors that influence predation and fish survival.

Study compared the external condition (e.g., body injuries, descaling, external signs of disease, and ectoparasite infestations) of fish sampled at hydroelectric dams to the internal condition of fish measured by the presence of selected pathogens detected by histopathology and polymerase chain reaction analysis. Study then estimated out-migration survival and smolt-to-adult return rates, as related to fish size, fish condition and specific mortality threats (e.g., avian predation).

Individual fish characteristics measured during juvenile salmonid out-migration were linked to a host of juvenile and adult performance metrics in the Columbia River basin. Specifically, results from this study supported the conclusion that external fish condition, measured non-destructively via high resolution digital photography, is associated with quantifiable differences in the general health status and fitness of fish. Furthermore, juvenile fish in degraded condition (those with descaling, body injuries, and other types of damage) were found to be more susceptible to predators as compared to healthy fish, indicating condition-dependent mortality during outmigration. The study also found that the probability of a juvenile surviving to adulthood was positively related to length, negatively related to condition, and was higher for wild fish compared to hatchery fish, indicating that individual fish characteristics play a key role in predicting fish survival. Finally, results indicate that mark-recapture modeling techniques should include both population-level and individual-level variables to more accurately identify mechanisms that influence fish survival.

Project was conducted with Oregon State University and University of California – Davis and required close coordination and collaboration with the Corps, Grant County PUD, NOAA Fisheries, and Washington Department of Fish and Wildlife.

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