Molly Martha Cobleigh
Introduction
Columbia River chinook salmon (Oncorhynchus tshaswytscha) stocks have been declining for several decades. These declines have been linked to ocean conditions (Beamish and Boullion 1993, Francis and Hare 1994, Hare and Francis 1995, Adkinson et al. 1996, Beamish et al. 1997a, Beamish et al. 1997b, Mantua et al. 1997; Pearcy 1997, Johnson 1998, Beamish et al. 1999, Beamish et al. 2000, Anderson 2000b, Batchelder and Powell 2002). to river conditions (Zabel and Williams 2001, Budy et al. 2002) and to fish condition (Beckman et al. 1998, Beckman et al. 1999, Zabel and Williams 2001). The motivation for this research was the hypothesis that there is a link between the three. In-river experiences must affect most juvenile salmon's (Oncorhynchus spp.) condition and its condition when it hits the ocean must affect its further survival. At the most basic level, I tested whether the initial conditions of a fish affect its ability to survive its next experience.
Although Columbia River salmon inspired this work, the results are broadly applicable. Intuitively, most can accept that stressful events impact an individual's fitness, but quantifying how this occurs is difficult. Understanding the effects of stress on survival of an individual is critical to exploring the effects of life history events on a population. This information is crucial for conservation biology, stewardship of wild populations and aquaculture.
In the first chapter I review the literature, outlining the hypotheses that inspired my research. I investigated in-river survival, ocean conditions and their correlation with adult return rate, correlations of size and growth with survival, salmonid metabolism and starvation, stress effects on survival and evidence that passage of hydroelectric dams is stressful. In addition I introduce the concept of vitality, which attempts to quantify the effects of stressors on an animal's survivability.
In the second chapter, I describe the methods used to investigate my hypothesis. I used several approaches. I performed two fasting and temperature challenge experiments on juvenile chinook salmon at the University of Washington (UW) to test the hypothesis that feeding history affects a fish's ability to survive under a secondary stress. I analyzed otolith samples of migrating juvenile chinook salmon from a National Marine Fisheries Service (NMFS) experiment at Bonneville Dam to investigate whether relative growth history (determined from otoliths) was related to survivability in sea water tanks. Lastly, I analyzed the survival results of all of those experiments using the vitality model.
The third chapter describes in detail the 20º C challenge experiments performed at the University of Washington. It demonstrates the effects of feeding history on survival and examines the implications of such effects.
In the fourth and fifth chapters I show the results of the otolith analysis, and the second UW challenge experiment. Although the results of these investigations were not statistically significant, they were useful for establishing methods to pursue this research in the future.
Finally I provide brief conclusions and discuss management implications. Decisions about instream flow, hatchery release timing, barging, and spill, could all be influenced by results of studies on cumulative stress and delayed mortality.