Document Type

Thesis

Abstract

Chinook Salmon Oncorhynchus tshawytscha have experienced population declines across their range in recent decades, including Alaska where they are a critical subsistence, commercial, and sport fish species. The Alaska Board of Fisheries has listed Yukon River Chinook salmon as a "stock of yield concern" since 2000 prompting the implementation of escapement goals for key spawning tributaries in 2001. Additionally, research efforts across the basin have increased to better understand potential mechanisms behind these declines and provide information to facilitate management decisions. To help fill a critical data gap in the overall understanding of the fishery, this research investigated various freshwater juvenile life history factors including patterns in post-emergence summer body size, movement, and fish size during spring outmigration in the Chena River, Alaska. This research also identified links between these biological factors and freshwater processes that are affected by climate change, including stream temperature and discharge, with the intention of documenting benchmark information as conditions continue to change. Juvenile Chinook Salmon movement among four key rearing areas was observed during summer and fall 2019 and early spring 2020. Despite differences in early summer size patterns, by the end of September mean fork lengths were not statistically different among all rearing areas (ANOVA; all P > 0.05). Additionally, mean September weight varied among six years of empirical data and ranged from 3.19 g in 2018 (0.03 SE) to a maximum of 5.10 g in 2009 (0.05 SE). September weight was simulated across years with variable stream temperatures and discharge (2003 to 2020) using a bioenergetics model, and compared to observed data. Weight simulations were within <0.40 g of observed mean end of summer weight for all years except in 2019 when the predicted weight was 1.38 g greater than the observed mean September weight. Generally, both observed and simulated weights were lower in years with higher flows. Peak spring outmigration dates ranged from 13 to 29 May (mean = May 18 ± 2.6 d; 95% CI). Fish length, weight, and body condition during outmigration varied among years; fish were smallest in 2019 and largest in 2014. Catch per unit effort also varied with discharge and among years; typically, fewer fish were caught on days with higher discharge. In Spring 2020, catches were compared between minnow traps fished in close proximity to a continuously operating screw trap and found that the screw trap caught more and larger fish than minnow traps and was able to operate during periods of high discharge, while minnow traps had to be pulled. Climate change will continue to affect Chinook Salmon in the northern extent of their range via increasing variability in flow regimes and increasing water temperatures. Understanding how these changes to key freshwater processes may impact the juvenile life stage and ultimately population productivity is critical for conservation and management of this important species. Specifically, the results of this study will help optimize sampling methods for future monitoring and provide benchmark information to track changes in summer fish size and peak outmigration timing. This information may be useful for making inseason management decisions and forecasting future changes in Yukon River Chinook Salmon production.

Publication Date

8-17-2023

Handle

http://hdl.handle.net/11122/14625

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