Age, Growth, and Productivity of Juvenile Sockeye Salmon in Two High Latitude Lakes, Alaska

Sockeye salmon (Oncorhynchus nerka) from Salmon and Glacial lakes on the Seward Peninsula, Alaska are an important subsistence resource for local residents. Despite their regional importance, little is known about the factors that influence production and recent dramatic fluctuations in abundance. Possible factors include fertilization of Salmon Lake and the extensive estuarine environment available at the Pilgrim River outlet. The objectives of this study were to determine if 1) Salmon Lake limnological factors and fertilization affected the first year of fry growth, 2) first year of fry growth was important to adult returns, 3) total freshwater or the first year of marine growth of Salmon Lake sockeye salmon was greater than for Glacial Lake sockeye salmon, and 4) total freshwater growth was greater for returning adults than for emigrating smolts.  Annual juvenile sockeye salmon growth was represented by scale radii measurements from the focus to the first freshwater annulus, last freshwater annulus, and first marine annulus. Salmon Lake environmental conditions were represented by annual mean Nome airport temperature anomalies, and total cladoceran and Bosmina species specific annual mean zooplankton biomasses.  Salmon Lake sockeye salmon population dynamics were explored using escapement and return data. Salmon Lake age-0 sockeye salmon fry growth was significantly related to Bosmina biomass (P = 0.006).  Total freshwater growth was greater for returning adults than for emigrating smolts for both populations. Glacial Lake age-1 smolts were the same size as Salmon Lake age-1 smolts at the end of their first freshwater year but were larger at the end of their first saltwater year.  Age-2 smolts were larger at Glacial Lake but there was no difference in the growth between these populations in the ocean. These growth histories do not show changes in Salmon Lake fry growth due to fertilization but do suggest population and age specific adaptations and size dependent mortality.