CIAA sought funding to monitor sockeye salmon smolt and adults at Shell Lake and explore the consequences of suppression of invasive northern pike on native salmonids. This proposal is part of a broader ongoing rehabilitation project working since 2012 to restore the once healthy sockeye salmon population to Shell Lake by seeking to suppress invasive northern pike, circumventing disease occurrences, and by stocking the lake with progeny of the Shell Lake stock. This proposal is being submitted to evaluate the success of the rehabilitation program and how this translates into future returns and future production. The evaluation will provide information on what can be expected from similar projects which is especially critical for the Matanuska-Susitna Valley because of the extent of the northern pike invasion and their propensity to prey on native salmonids.
Timeline: November 2015-March 2018
2016: CIAA staff estimated the number of sockeye salmon at Shell Lake to be no less than 134 fish. Approximately 88,000 eggs were fertilized with milt collected from 33 pairs of Shell Lake sockeye salmon. Using gillnets, hoop nets, and hook and line angling, a total of 759 northern pike were harvested and data regarding age, sex, length, and weight were collected. Notably, the mean length and weight of harvested pike has decreased for most year classes from 2014-2016 which suggests suppression may be increasing the proportion of smaller northern pike in Shell Lake. Because smaller northern pike tend to eat more juvenile salmon, this trend needs to be monitored closely to ensure that netting is not exacerbating the invasive northern pike issue in Shell Lake.2017: Between May 23 and June 21, 2017 15 sockeye smolt and 6 coho smolt were enumerated as they emigrated from Shell Lake. Video weir footage documented 575 sockeye and 411 coho salmon passing the weir. Approximately 30,000 eggs were fertilized with milt collected from 25 females and 14 male sockeye salmon. A total of 780 northern pike were harvested and data was collected on age, sex, length, and weight. Because literature indicates that smaller northern pike tend to eat more juvenile salmon, CIAA partnered with UAF to determine what impacts the netting is having on Shell Lake northern pike and salmon populations. The models developed through that analysis indicate CIAA's netting effort has reduced the potential of northern pike predation on Shell Lake smolt by 81% since 2012. UAF also concluded that suppression strategies targeting all size classes of pike are more likely to be effective at reducing consumption of salmon.