Author: Darin Ruhl

Publisher:

Published: 2016

Total Pages: 88

ISBN-13:

Concerns expressed by local subsistence users over declines in Afognak Lake sockeye salmon Oncorhynchus nerka prompted the Alaska Department of Fish and Game to investigate Afognak Lake's rearing environment. Funded through the U.S. Fish and Wildlife Service Office of Subsistence Management and Alaska Sustainable Salmon Fund, this report provides results from the 2015 season. Based on established mark-recapture techniques, an estimated 133,880 sockeye salmon smolt outmigrated from Afognak Lake in 2015. From 2010 to 2014, the outmigration averaged 258,042 and ranged from 127,861 to 329,948 smolt. Age-1 smolt comprised 84.9% of the outmigration in 2015 and averaged 74.9% of the outmigration from 2010 to 2014. Although age, weight, and condition data indicate fairly healthy, robust smolt, a life-history based model produced a significantly larger estimate, which could indicate poor survival prior to the outmigration. Limnological sampling was conducted during 5 monthly events from May to September in 2015. Phosphorus concentrations and zooplankton densities remained low, while chlorophyll-a levels were slightly above average. Nitrogen concentrations, lake temperatures, and phytoplankton biovolume were above average for the third consecutive year. Nutrient loading in Afognak Lake was influenced mainly by precipitation events (runoff), spring/fall turnover events, and to a lesser extent, wind-induced disturbance and mixing of the benthic substrate. Afognak Lake sockeye salmon returned in sufficient numbers to meet the escapement goal of 20,000-50,000 sockeye salmon and support subsistence, sport, and commercial harvests. The escapement of 38,151 fish in 2015, was slightly below the average of 44,300 sockeye salmon (2014-2014) and predominately composed of age-1.3 and age-1.2 fish.