Early Marine Ecology and Regional Discrimination of Chum Salmon

Chum salmon Oncorhynchus keta exhibit lower genetic divergence than other Pacific salmon, thereby reducing reliable stock delineation using standard genetic methods.  In addition, little is known about the early marine life history of this species.  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 groups that were independent of location, further supporting the mixing of stocks within regions.