Salmon Stock Discrimination

Chinook Salmon Early Life History Correlation to Canadian-origin Harvest
Chum Salmon Stock Discrimination Through Microchemistry

Chinook Salmon Stock Discrimination

Jim Murphy and Katie Howard

Juvenile Chinook salmon variation in length.

Final Report:
Murphy, J. M., Howard, K. G.,Gann, J. C., Cieciel, K., Templin, W. D., Guthrie III, C. M. 2015. Juvenile Chinook salmon abundance in the northern Bering Sea: Implications for future returns and fisheries in the Yukon River. US Dept. of the Interior, Bureau of Ocean Energy Management, Alaska OCS Region. OCS Study BOEM 2011-AK-11-08 a/b. 51 pp. – DRAFT REPORT

Juvenile Chinook salmon (Oncorhynchus tshawytscha) abundance is estimated in the northern Bering Sea and used to provide guidance for future returns and fisheries on Canadian-origin Chinook salmon in the Yukon River. Abundance estimates are based on surface trawl catch data, mixed layer depth adjustments, and genetic stock composition of juveniles in the northern Bering Sea near the end of their first summer at sea (September). Estimated annual abundance range from 0.6 million to 2.55 million juveniles with an overall average of 1.44 million juvenile Chinook salmon from 2003 to 2014. Comparisons of juvenile and adult abundance provide an unique insight into the survival of Chinook salmon. Although the estimates of juvenile survival rates are relatively low (average of 5.2%), juvenile abundance is significantly correlated (r = 0.88, p < 0.001) with adult returns, indicating that much of the variability in survival occurs during earlier life stages (freshwater and initial marine). Survival of Chinook salmon during these early life-history stages has increased along with juvenile abundance and has important implications for future returns and fisheries in the Yukon River. The number of juveniles per spawner increased from an average of 26 (2003 to 2012) to an average of 54 in 2013 and 2014. Recent production declines in Chinook salmon have triggered closures of commercial, sport, and personal use fisheries and severe restrictions on subsistence fisheries in the Yukon River. The number of adults projected to return from juvenile abundance estimates indicate that fishing opportunities on the Canadian-origin stock group of Chinook salmon in the Yukon River could be restored as early as 2016.

Chum Salmon Stock Discrimination using Microchemistry

Trent Sutton and Kevin Pangle

Juvenile Chum salmon variation in length.

Final Report:
Sutton, T. M., Pangle, K. L. 2015. Regional Discrimination of Chum Salmon in Alaskan Waters of the Bering and Chukchi Seas Using Otolith Elemental Analysis. US Dept. of the Interior, Bureau of Ocean Energy Management, Alaska OCS Region. OCS Study BOEM 2011-AK-11-08 a/b. 37 pp. – DRAFT REPORT

Chum Salmon Oncorhynchus keta exhibit lower genetic divergence than other Pacific salmon, thereby reducing reliable stock delineation using standard genetic methods. The objectives of this study were to examine the utility of using otolith elemental analysis to examine the early marine ecology of juvenile Chum Salmon and determine the feasibility for differentiating among and within-region variability of fish collected from the Chukchi Sea, North and South Bering Sea, and Bristol Bay. Elemental concentrations (particularly Strontium and Barium) along otolith transects provided a clear indication of the timing of ocean entry. Consistent peaks in Strontium concentration at the otolith core were indicative of maternal effects. Based on the otolith element composition associated with early life history in freshwater, accuracy of discrimination from neighboring regions was relatively high (mean = 85.8%). In contrast, the ability to discriminate fish among sites within a region was relatively poor (mean = 28.7%). These results suggest regional separation among Chum Salmon stocks, but a mixed-stock assemblage within regions. Hierarchical cluster analysis of otolith elemental composition revealed distinct Chum Salmon groups that were independent of location, further supporting the mixing of stocks within regions.

Chum salmon support important commercial and subsistence fisheries in Alaska. Although genetic methods have historically been the primary means for resolving stock mixtures for salmonids (Shaklee et al. 1999; Seeb et al. 2004; Templin et al. 2006; Beacham et al. 2008), chum salmon exhibit lower genetic divergence than other Pacific salmon, which reduces stock delineation (A. Gharrett, University of Alaska Fairbanks, unpublished data). As a result, it is essential to identify an approach that allows for reliable differentiation of chum salmon stocks in Alaskan waters.

Using a combination of trace element, rare earth element, and stable isotope ratio composition data for otoliths, we will use multivariate statistical analyses to determine whether (1) there are differences in otolith chemical composition for chum salmon captured in the north versus the south Chukchi Sea (region-level variation) and (2) within each region, if there is sufficient variability in otolith chemical composition to suggest stock-level differentiation.

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