Salmon Lake Limnology
Unlike other salmon species, sockeye salmon require a lake habitat during the juvenile phase of their lifecycle. Salmon Lake plays an integral part in determining the quantity of sockeye salmon that return to the Pilgrim River each year. As a result of the depleted sockeye returns in the 1990s, Norton Sound Economic Development Corporation (NSEDC) helped sponsor a limnology study of Salmon Lake from 1994 to 1996. Based on the study looking at the health of the lake, it was decided that fertilization of the lake would be an appropriate way to increase sockeye salmon returns. Limnology studies continue today to determine the amount of fertilization applied to Salmon Lake each year and to ensure that fertilization does not have any negative impacts on the lake ecosystem.
Salmon Lake Fertilization
Fertilization of Salmon Lake leads to an increase in the growth of phytoplankton and zooplankton, which, in turn, leads to an increase in the growth of salmon. Salmon fry feed on zooplankton, which feed on phytoplankton that rely on nitrogen and phosphorous in the waters for growth. NSFR&D simply puts nitrogen and phosphorous in the lake to sustain an adequate amount of phytoplankton and zooplankton to support a healthy population of juvenile sockeyes. Since 1996, NSEDC has sponsored 50% or more of the cost of lake fertilization.
It is NSFR&D’s aim to provide for stable sockeye salmon runs that meet the area’s subsistence and escapement needs every year.
Pilgrim River and Salmon Lake Smolt
To evaluate the effectiveness of Salmon Lake fertilization, NSFR&D looks at the health condition of salmon lake smolts that outmigrate from the lake in the spring. A larger smolt has a better chance of survival in the ocean than a smaller smolt; therefore, the NSFR&D crew looks at the age and size of smolts leaving the lake. These data are used to gauge the effectiveness of the fertilization applied in previous summers.
Pilgrim River Weir
The most sure-fire way to gauge the effectiveness of the Salmon Lake fertilization project is to determine the yearly adult returns. To find out how many sockeye salmon return to the Pilgrim River, NSFR&D operates a weir counting station, employing fisheries technicians every summer. Their counts not only determine the effectiveness of the fertilization program, but the counts also help the Alaska Department of Fish and Game manage the subsistence fishery.