Marine-entry timing and growth rates of juvenile chum salmon in Alaskan waters of the Chukchi and northern Bering Seas

Abstract

Recent climate change is most pronounced in the Arctic, with many implications for juvenile salmon life-history patterns, such as altered timing of migrations and/or timing and success of life-history stages. The objectives of this study were to determine the timing of marine entry and early marine growth of juvenile Chum Salmon Oncorhynchus keta in the Chukchi and northern Bering seas. Sagittal otoliths were collected from juvenile Chum Salmon in summers 2007, 2012, and 2013 via surface trawls in the southern Chukchi and northern Bering seas. Inductively coupled plasma-mass spectrometry (ICP-MS) was used to discriminate between freshwater and marine environments, and daily growth increments were counted to determine marine-entry dates and growth rates of juvenile Chum Salmon to make temporal and regional comparisons of juvenile characteristics. Marine-entry dates ranged from mid-June to mid-July, with all region and year combinations exhibiting similar characteristics with respect to entry timing, i.e., larger individuals at the time of capture entered the marine environment earlier in the growing season than smaller individuals. Juvenile growth rates were estimated to be, on average, 4.9 % body weight per day in both regions in summers 2007 and 2012, and 6.8% body weight per day in the Chukchi Sea in 2013. This study shows consistent conditions among regions with respect to juvenile Chum Salmon marine-entry timing, with some variation in growth rates. These results provide a novel and more thorough evaluation of juvenile Chum Salmon early life-history characteristics in the Alaskan Arctic and provide a baseline for comparisons with future climate change studies.