Impacts of Environmental and Social Factors on Fish Movement and Behavior Over Three Timescales

Abstract

The ability to move influences essential behaviors in fish, including foraging, predator escape, migration, mating, and breeding. These behaviors occur over various timescales, from the immediate response to predators to migrations over a longer timescale. Environmental factors like temperature impact both instantaneous and long-term behaviors. Additionally, social factors, such as the presence and behavior of other fish, also play a significant role in these behaviors. This dissertation explores the impacts of environmental and social factors on fish movement and behavior across three distinct timescales. In the first chapter, I examine how temperature affects the collective response of fish to a predation threat in the timescale of seconds. Using lab experiments I found that while fish can move faster in higher temperatures, during a predation threat, fish at lower temperatures are able to compensate for the lower speeds by increasing their probability to startle. In the second chapter, I explore the influence of social cues on the juvenile migration of salmon on a daily timescale in three rivers in Washington state. I use hatchery releases as a way to test the ‘pied-piper’ hypothesis that the large number of hatchery salmon moving downstream motivates wild salmon to migrate along with them. Our findings support the ‘pied-piper’ hypothesis, demonstrating that both environmental and social cues stimulate downstream migration in salmon. In the third chapter, I investigate the influence of temperature, cumulative flow, and hatchery releases on the timing of peak migration and the duration of migration of juvenile salmon at the seasonal timescale. The results show that increased temperatures have a negative effect on the timing of migration of sub-yearling Chinook salmon and sub-yearling chum salmon. Similarly, increased flow has a negative effect on the timing of migration of coho salmon. Larger and earlier hatchery releases have a negative effect on the duration of migration of coho salmon. Broadly, this research shows us both environmental factors and social factors influence the movement and behavior of fish in nuanced ways. By understanding these relationships across various timescales, we can make better management strategies to reduce the impact of various anthropogenic stressors on fish populations.