Delineation of Yakutat foreland coho salmon (Oncorhynchus kisutch) stocks using otolith chemistry

Abstract

Otolith chemistry was utilized to identify suspected coho salmon sub-stock populations on the Yakutat Foreland of southeast Alaska. In order to demonstrate that otolith chemistry might be successful in sub-stock differentiation, water samples were collected from four adjacent river systems and chemically segregated by collection site. Juvenile coho salmon and adult coho salmon were collected from the same four river systems and were subsequently analyzed for levels of select Ba, Ca, Mg, and Sr isotopes in all otolith edge and core regions using laser ablation-inductively coupled plasma-mass spectrometry. Otolith Sr⁸⁷/Ca⁴⁸ and Mg²⁴/Ca⁴⁸ were used to segregate collection sites, identify sub-stock populations, and infer straying rates for coho salmon on the Yakutat Foreland. Juvenile core and edge otolith chemistry returned moderate to high classification accuracy for three out of four collection' sites (60%-92%) in statistical discriminant analyses. Adult core otolith chemistry could not segregate samples according to collection site in three out of four sites (7%-50%). Yakutat Foreland otolith chemistry analysis results allowed for (1) differentiation of adjacent freshwater systems, (2) a significant amount of coho salmon stock delineation, and (3) a higher suggested rate of straying from natal sites than coho salmon in other locations.