The Afognak Lake sockeye salmon Oncorhynchus nerka run severely declined in 2001. Concerns expressed by local subsistence users to the Alaska Department of Fish and Game and the US Fish and Wildlife Service Office of Subsistence Management prompted an investigation of the lake’s rearing environment in 2003 followed by subsequent annual studies. This report provides 2011 project results.
An estimated 329,948 sockeye salmon smolt (95% CI 288,393–371,502) emigrated from Afognak Lake in 2011, based on the same mark-recapture techniques used in prior years. The emigrating sockeye salmon smolt population was composed of 250,741 age-1. and 79,207 age-2. smolt. Age-1. smolt had a mean weight of 3.1g, a mean length of 72 mm, and a mean condition factor of 0.81. Age-2. smolt had a mean weight of 3.8 g, a mean length of 78 mm, and a mean condition factor of 0.77. The total sockeye salmon escapement into Afognak Lake was 49,193, of which 40.2% were age 1.2 and 28.5% were 1.3.
Lake limnology data was collected during five monthly sampling events from May to September. In 2011, seasonal total phosphorus concentrations and seasonal zooplankton densities remained low, chlorophyll-a concentrations remained moderate, the seasonal nitrogen concentrations rose, and the body condition of emigrating smolt remained at healthy levels.
Two years of diet and bioenergetic analysis of juvenile sockeye salmon have revealed that juveniles of all ages primarily consumed insects in the spring, gradually shifting to zooplankton as their primary prey. Additionally, juveniles of all ages consumed the greatest volume of food in June, with their stomach fullness decreasing as prey shifted to zooplankton.
Further assessment of photosynthetically active radiation, nutrient availability, phytoplankton population, and available forage species versus actual forage species will occur over the next two years (2012–2013) of this project. This additional information, coupled with annual smolt health and abundance estimates, will provide greater insight into Afognak Lake’s freshwater environment and factors affecting smolt production.