Sean Brennan Ph.D. Defense June 2

May 30, 2014 • Filed under: News — melanie.rohr

Sean Brennan will defend his thesis, “Using Strontium Isotopes to Track Pacific Salmon Migrations in Alaska”, at the Murie Auditorium on Monday, June 2, 2014 at 1:00pm.

Pacific salmon (Oncorhyncus spp.) are an important cultural, ecological, and economic natural resource in Alaska. Not only do salmon maintain an important mechanism of nutrient transport between marine, aquatic, and terrestrial ecosystems, but they also provide a sustainable food and economic resource for human communities. A challenging issue in the management, conservation, and research of Pacific salmon is tracking their responses to perturbations across the multiple scales of population structure that characterize these species. Research has shown how the inherent biodiversity of Pacific salmon imparts resiliency to environmental change, and temporal stability to their overall productivity and the human systems dependent upon such productivity (e.g., fisheries). The vast biodiversity of salmon arises primarily via precise natal homing of adults to their rivers of origin, resulting in locally adapted populations. Thus, there have been considerable efforts to develop methods to effectively manage and monitor Pacific salmon biodiversity. One important example is using genetic differentiation among populations to discern the relative contributions of genetically distinct stocks in mixed stock fishery harvests. In the Bristol Bay region, sockeye salmon (O. nerka) harvests can be discerned at the watershed level (i.e., the nine major watersheds contributing to the fishery). However, tens to hundreds of locally adapted populations exist within each of these watersheds and there are no methods to discern this finer scale population structure in fishery harvests. This dissertation presents a new method in Alaska to discern fine-scale population structure of Chinook salmon (O. tshawytscha) (i.e., within watersheds) using a naturally occurring geochemical tracer in rivers, strontium (Sr) isotopes (87Sr/86Sr). Because of the conservative nature of the 87Sr/86Sr ratio during physical and biological processes, the development of this method is applicable not only to Chinook salmon, but also to other salmon species (e.g., sockeye and coho salmon, O. kisutch). Additionally, the development of baseline 87Sr/86Sr information and an overall research framework to employ this tracer, have statewide implications for the research and management of other migratory animals.