| Summary: | Thesis (Ph.D.)--University of Washington, 2020 Understanding the life histories of exploited aquatic taxa is important to sustainable fisheries management. Life history diversity has been shown to stabilize population dynamics through ‘portfolio effects’ which can maintain robust fishery yields despite environmental variability. Moreover, the reproductive life histories of fishes can be important to shaping management-relevant properties such as the steepness of the stock-recruit relationship, genetic diversity, age and size structure, and stock rebuilding potential. Despite the importance of life history information to conservation and management, achieving a practical understanding of the evolutionary and ecological factors that maintain particular life histories can be challenging. This difficulty is exemplified by widespread declines in size-and-age-at-maturity of many commercially valuable fish stocks, the causes of which are seldom be reliably discerned. In this dissertation, I seek to better understand the factors that control the frequencies of alternative maturation and reproductive life histories in sockeye salmon (Oncorhynchus nerka) populations. In chapter 1, I used Bayesian hierarchical modelling to identify the basis of variation in early maturation rates among sockeye salmon populations in Bristol Bay, Alaska. In my second chapter, I developed an age-structured Bayesian state space model to assess the causes of elevated early maturation rates in Kodiak sockeye salmon. Finally, in my third chapter I developed an individual-based population dynamics framework to explore the ecological and evolutionary factors that regulate frequencies of alternative maturation and reproductive life histories in age-structured populations. Collectively, my results demonstrate that the maintenance of alternative life histories within populations may be more complex than existing evolutionary frameworks suggest, and reveal a novel role of population dynamics in the evolution and maintenance of complex mating systems.
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