Water Resources Research Act Program

Details for Project ID 2011AK98B

Developing high-resolution strontium isotope maps of Alaskan Rivers to track pacific salmon migrations: The Nushagak River as a case study to evaluate spatial and seasonal variability.

Institute: Alaska
Year Established: 2011 Start Date: 2011-03-01 End Date: 2012-01-29
Total Federal Funds: $20,098 Total Non-Federal Funds: $9,949

Principal Investigators: Matthew Wooller

Abstract: We propose developing the use of strontium isotope (87Sr/86Sr) variation of waters within and among Western Alaskan Rivers as a tool to track natal sources of Pacific salmon (Oncorhynchus spp.) caught in mix-stock fisheries. Western Alaskan Rivers provide important rearing and spawning habitats for some of the world’s largest wild salmon populations. Salmon not only maintain an important mechanism of nutrient transfer between marine, aquatic and terrestrial ecosystems, but are also valuable to Alaskan subsistence communities. Tracking population responses to mix-stock fisheries is especially difficult due to the complex migratory life cycle (anadromy: freshwater-marine-freshwater) and population structure of salmon. Spawning salmon exhibit high fidelity with their natal freshwater streams resulting in a complex genetic hierarchy composed of distinct local breeding populations (the basic reproductive unit of salmon). Over-fishing by humans poses real threats to the biodiversity and overall success of these species, and to subsistence human communities of Alaska. Thus, a State need exists to develop tools to track the natal origins of salmon to better conserve salmon biodiversity and the natural resource they represent. This proposed research aims to use the Nushagak River, which flows into Bristol Bay, as a case study to develop the use of strontium isotopes to track salmon natal sources. 87Sr/86Sr in otoliths (the auditory structure of fish) continually record aqueous environmental variation experienced during the lifetime of a fish in distinct accretionary bands of calcium carbonate. Our proposed research uses strontium isotope time-series analyses of otoliths of fish species with differing migratory patterns (anadromy, seasonally migratory and sedentary) to evaluate seasonality of a river’s isotopic signature and seasonal movements of fish. Evaluating how otoliths record seasonal isotopic variation in river water and seasonal movements of fish between rearing streams will be imperative, as these could mislead natal source predictions of salmon. To evaluate spatial variation within the Nushagak River we propose collecting water and otolith samples from its major tributaries. Additionally, using the proposed water collections and analyses we will validate the accuracy of a priori modeled 87Sr/86Sr variation within the Nushagak River. This model uses high-resolution geologic maps and rock geochemistry data to predict spatial variation of 87Sr/86Sr values of river waters. To feasibly and accurately geochemically characterize all potential salmon natal sources of Western Alaskan Rivers necessitates the development of a geospatial model in ArcGIS. To this end, we will also use 25 water samples collected in the summer of 2010 from around Alaska to further develop such a model. All of the funds in this proposal are dedicated to supporting fieldwork and research to be conducted by a graduate student (Sean Brennan) in the Water and Environmental Research Center (WERC) at the University of Alaska Fairbanks (UAF). The ultimate goal of our study is to develop a technique, based on the hydro-geochemistry of otoliths to relate salmon stocks to the rivers they originated from, which will have practical applications in the management of water and salmon resources.