Yukon Chinook Strontium and Genetics

It is currently unclear which regions of the Yukon River produce the most Chinook salmon and how spatial patterns of production change over time. As part of a series of AYK-SSI funded projects, we built a strontium (Sr) isotope watershed model, coupled to Sr isotope records from otoliths of fish captured in downriver fisheries, to reconstruct the production patterns and life history strategies of Chinook salmon annually at high spatial resolution across the basin. However, some regions of the Yukon basin are not differentiable based only on their Sr isotope characteristics, thereby requiring complementary information to assign fish to natal tributaries at fine spatial resolution. Here, we integrated genetic and isotopic data on the same individual fish to enhance our power to determine fine scale natal origins and quantify the spatio-temporal patterns of Chinook salmon production across the Yukon River. We analyzed the production patterns of Chinook salmon returning to the Yukon River in 2015 and 2017, which are the years for which we have paired genetic and isotope data for all fish sampled (n=250 per year). Genetic and isotopic variation were highly spatially complementary across the Yukon River basin. Genetics was able to determine the broad geographic region of origin (i.e., Lower, Middle, and Upper Yukon), while the isotopes refined these estimates to relatively small spatial scales within these large areas, sometimes to individual tributaries. Combining genetic and isotopic data, also indicated that Chinook salmon production for each return year was heterogeneously distributed across the basin, and this variability was expressed at multiple spatial scales (e.g., Canada versus USA, the major sub basins, and individual tributaries). Furthermore, the spatial pattern of production shifted substantially among years, illustrating that some parts of the basin are disproportionately important for any given return year. These results highlight that the entire Yukon River is involved in producing Chinook salmon, and that the habitat complexity across the basin and its associated biological diversity are integral in stabilizing the total production of Chinook salmon year-to-year. Although the reasons why patterns of production show complementary dynamics overtime is unclear, the analytical framework presented here, especially the integration of isotopes and genetics on individual fish, could provide critical insights as Yukon River Chinook salmon populations respond to the rapid environmental change occurring across the Arctic and Subarctic.

The project was fully executed and delivered although funds were not fully spent. No compliance or other issues of concern remaining. The project end date changed from April 30, 2018, to April 30, 2019 because the mass spectrometer instrument the Principle Investigators were using to complete their objectives went down and they had to order a new one from Germany and do quality assurance and quality control on the data. This delayed the timeline of the project.

It is currently unclear which regions of the Yukon River produce the most Chinook salmon and how spatial patterns of production change over time. As part of a series of AYK-SSI funded projects, we built a strontium (Sr) isotope watershed model, coupled to Sr isotope records from otoliths of fish captured in downriver fisheries, to reconstruct the production patterns and life history strategies of Chinook salmon annually at high spatial resolution across the basin. However, some regions of the Yukon basin are not differentiable based only on their Sr isotope characteristics, thereby requiring complementary information to assign fish to natal tributaries at fine spatial resolution.
Here, we integrated genetic and isotopic data on the same individual fish to enhance our power to determine fine scale natal origins and quantify the spatio-temporal patterns of Chinook salmon production across the Yukon River. We analyzed the production patterns of Chinook salmon returning to the Yukon River in 2015 and 2017, which are the years for which we have paired genetic and isotope data for all fish sampled (n=250 per year).
Genetic and isotopic variation were highly spatially complementary across the Yukon River basin. Genetics was able to determine the broad geographic region of origin (i.e., Lower, Middle, and Upper Yukon), while the isotopes refined these estimates to relatively small spatial scales within these large areas, sometimes to individual tributaries. Combining genetic and isotopic data, also indicated that Chinook salmon production for each return year was heterogeneously distributed across the basin, and this variability was expressed at multiple spatial scales (e.g., Canada versus USA, the major sub basins, and individual tributaries). Furthermore, the spatial pattern of production shifted substantially among years, illustrating that some parts of the basin are disproportionately important for any given return year. These results highlight that the entire Yukon River is involved in producing Chinook salmon, and that the habitat complexity across the basin and its associated biological diversity are integral in stabilizing the total production of Chinook salmon year-to-year. Although the reasons why patterns of production show complementary dynamics overtime is unclear, the analytical framework presented here, especially the integration of isotopes and genetics on individual fish, could provide critical insights as Yukon River Chinook salmon populations respond to the rapid environmental change occurring across the Arctic and Subarctic.