U.S. Fish & Wildlife Service Comparison of Genetic Diversity between Chum and Coho Salmon in the River Potential Impacts of Land-Use Activities

Introduction Tanana River System Loss of freshwater habitat is a common factor associated with the decline in abundance and genetic diversity of Pacific salmon throughout their range. The impact of localized habitat degradation on genetic diversity may vary among species depending on how populations are structured. Species 200km composed of populations that occupy large geographic regions and exhibit moderate to high levels of genetic exchange are less likely to lose genetic Innoko River System diversity as a result of local habitat Species System Tributary LS Year N Chum Salmon Innoko R California Cr. A 1997 52 degradation than those composed Tolstoi Cr. A 1997 50 of isolated populations occurring Tanana R. Chena R. A 1997 57 on small geographic scales with low Salcha R. A 1997 50 rates of genetic exchange. Therefore, species-specific population structure Coho Salmon Innoko R. Illinois Cr. J 1997 78 is a critical factor in assessment of the California Cr. J 1996 84 potential loss to genetic diversity for a Tanana R. R. A 1997 56 Clearwater Cr. A 1997 56 given species when habitat is impacted by land-use activities (e.g., mining, logging, development). Figure 1. Map of sampling areas in the Yukon River drainage. The Conservation Genetics Laboratory of the U.S. Fish and Wildlife populations of coho salmon have used microsatellites and mitochondrial Service, Alaska Region, initiated a been detected at both small and large DNA (mtDNA) to estimate the degree study to examine genetic diversity geographic scales in river systems of of population structure within and and population structure of chum the Pacific Northwest and Alaska. In among the four collections made for (Oncorhynchus keta) and coho (O. this study, we test the hypothesis that each species. kisutch) salmon that co-occur in the chum and coho salmon in the Yukon

Innoko and Tanana Rivers, tributaries River exhibit population structure The statistic FST is a relative of the Yukon River in Alaska at different spatial scales. If this measure of population structure (Figure 1). This study was part of a hypothesis is true, then the risk of ranging between zero (no population comprehensive assessment designed losing genetic diversity because of structure) and one (completely to evaluate the possible environmental localized habitat degradation in the isolated populations). This statistic and biological impacts of a gold mine Yukon River drainage could differ was used to quantify the amount on a Yukon River tributary near the between these species. of genetic variation resulting from Innoko National Wildlife Refuge. population divergence. Variation Methods was hierarchically partitioned into Previous genetic analyses indicate that three components: 1) among all chum salmon populations, with some Fin tissue samples (non-lethal) were eight collections; 2) between the two exceptions, appear to be organized on collected (1996 and 1997) from chum tributary collections within each of large geographic scales encompassing and coho salmon in both the Innoko and the two rivers, and 3) between the two multiple river systems. In contrast, Tanana River tributaries (Figure 1). We rivers.

Conservation Genetics Laboratory - Alaska Region Results Among Between Between All Rivers Tributaries Our study indicates that genetic diversity Within is structured at different spatial scales Collections for chum and coho salmon in the Yukon Rivers River (Figure 2). Genetic diversity in Yukon River chum salmon appears to be distributed over a relatively broad Chum geographic area. The estimate of Microsatellites overall population structure from the 0.021 0.021 0.000

microsatellite loci (FST = 0.021) while significant, is low, and due entirely to genetic differences between the two rivers and not to genetic differences within rivers (i.e., between tributaries). This large-scale population structure mtDNA 0.000 0.000 0.000 should serve to buffer chum salmon from the loss of genetic diversity if some spawning aggregations are lost because of localized habitat degradation. However, it must be emphasized that Coho regardless of whether or not overall genetic diversity is lost, the loss of Microsatellites 0.091 0.061 0.032 chum salmon from a tributary would likely reduce the overall abundance of Yukon River chum salmon. Such a loss would have other negative impacts (e.g. ecological, cultural, or economic). mtDNA 0.586 0.564 0.052 In contrast, the data indicate that coho salmon collections in the Yukon River are highly differentiated, suggesting that population structure occurs on a No Completely much smaller geographic scale than for Population Isolated chum salmon (Figure 2). Because coho Structure Populations salmon populations are relatively small and discrete, the likelihood of localized Key F Value 0.000 0.500 1.000 habitat degradation affecting an entire ST population is greater with coho salmon than with chum salmon. It appears that gene flow between populations is Figure 2. Genetic diversity comparisions for chum and coho salmon in extremely low and, if exterminated, Yukon River tributaries. the vacant habitat is unlikely to be re- colonized rapidly by other coho salmon populations. such as mining in the Innoko River conservation plans may be required to drainage, would impact the genetic maintain genetic diversity of salmon Conclusions diversity of coho salmon to a much species occupying the same geographic greater degree than chum salmon. area. Thus, a multi-species approach is This study suggests that habitat Similarly, the geographic scale of recommended for evaluating the potential degradation resulting from land-use management units will differ between impact of localized habitat degradation on activities in the Yukon River drainage, these two species. Species-specific the genetic diversity of Pacific salmon.

For additional details, see: For more information contact: Olsen JB, Spearman WJ, Sage GK, Jeff Olsen Miller SJ, Flannery B, Wenburg JK U.S. Fish and Wildlife Service (2004) Variation in the population Conservation Genetics Laboratory structure of Yukon River chum and 1011 E. Tudor Road coho salmon: evaluating the potential Anchorage, Alaska 99503 impact of localized habitat degradation. 907/786 3598 Transactions of the American Fisheries [email protected] Society 133, 476-483. alaska.fws.gov/fisheries/genetics

November 2010