Use of Stable Isotopes and Otolith Micro-Chemistry to Evaluate Migration in Male Chinook Salmon,Oncorhynchus tshawytscha,from an Alaskan River

Abstract

Abstract In salmonid fishes, males display much more variation in age and size at maturity than females, including a greater proportion of non-anadromous individuals, and those spending fewer years at sea than females. The life history of Chinook salmon is especially variable among Pacific salmon species, including non-anadromous (precocious parr) and early maturing anadromous males (jacks) but these have been studied primarily in populations towards the central and southern part of their range. In this study we investigated reports of small and putatively non-anadromous male Chinook salmon in Lake Creek, Alaska, using otolith microchemistry and stable isotopes. Small males (ca. 300–350 mm fork length) displayed otolith Sr:Ca ratios and δ15N values consistent with anadromy; indeed, the δ15N values of these “mini-jacks” that had spent a year at sea and larger jacks (ca. 500 mm) were more enriched than those of the larger, older conspecifics. Thus the multiple alternative anadromous male life history patter...