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Chapter 1:  Quantifying habitat use and preferences of spawning sockeye salmon (Oncorhynchus nerka) using individual movement data: a case study in Bristol Bay, Alaska

Map of the study sites located on Little Togiak Lake within the Wood River System in Southwest Alaska.

Alaska’s Bristol Bay salmon fisheries control many ecological processes that support the livelihoods and economies with which they are connected. Yet the impact of changing climate threatens the sustainability of this area’s fisheries management. Researching the mechanisms behind how individual salmon chooses a habitat under different environmental conditions and levels of population density has been relatively understudied. It is critical to understand the nature and extent of salmon movement, habitat selection, and preference on which reproductive success and population productivity rely. Applying a discrete choice model to twenty years of annual fish tagging data of two spawning sockeye salmon populations at A and C creeks on Little Togiak Lake, we: (1) identify stream habitat features (e.g., slope) that influence the spatial distribution and population densities of spawning sockeye salmon; and (2) share results on how salmon select a habitat among varying degrees of reproductive habitat and protection from predators. These preliminary findings have implications for fisheries management, including predicting population abundance and occupancy of spawning habitat; and establishing effective habitat restoration goals and strategies. These results also have the potential to inform management of a range of systems prior to initiation of proposed human development (e.g., mining) which causes a major threat to the world’s freshwater habitats.

Chapter 2:  The effects of reproductive strategies on Pacific salmon reproductive success

Breeding animals can detect and respond to a variety of signals of predators in the wild. The behavior of breeding animals can be adjusted to perceived predation risk and influence the selection of breeding habitat. Mating has the potential to cause the change of an individual’s reproductive investment during their lifetime, especially under varying predation intensities. Animals have been found to not mate and reproduce due to increased predation risk; or decrease the number of eggs deposited in excavated depressions in the river bed gravels called redds (i.e., nests). A few studies have investigated the effect of predation risk on the fitness of different breeding behavioral strategies but variation in antipredator behavioral strategies employed by animals in the wild have rarely been studied due to the logistical constraints of measuring antipredator activities and reproductive success in the same individuals over time.

 

In this second chapter, we evaluate whether the risk of predation affects the fitness of different breeding reproductive strategies. We ask if spawning salmon that exhibit cyclic movements between instream habitats lead to higher reproductive success. By combining the same two sockeye salmon populations in the Wood River system in Alaska, U.S.A, we used: (1) in-stream antennas and remote camera data from Bentley et al. (2014) to identify ‘movers’ and ‘non-movers’ at A and C Creeks and (2) estimates of lifespan reproductive success from a multigenerational pedigree. The data generated as part of this research would add information on the number of returning offspring and thus the reproductive success of the individuals studied by Bentley et al. (2014).