Production and Yield of Juvenile Chinook Salmon in Two Alaskan Lakes

Age‐0 chinook salmon Oncorhynchus tshawytscha (mean length, 52.4 mm; mean weight, 1.4 g) were stocked in two small lakes in southeastern Alaska to determine whether the lakes could produce chinook salmon smolts. The lakes were without fish before 15 July 1982 when 4,714 fish/hectare of lake area were stocked in Tranquil Lake (1.4 hectares) and 4,561 fish/hectare were stocked in Larry Lake (3.4 hectares). The fish ate large (> 1.5‐mm‐long) zooplankton and grew rapidly during the first 3 weeks. However, growth rates declined markedly when large zooplankton disappeared from both lakes. Then fish primarily ate benthic invertebrates and cladocerans in shallow lake areas, even though small (< 1.5‐mm) copepods were abundant. Of the chinook salmon stocked in Tranquil Lake, 42% emigrated as age‐I smolts; of those stocked in Larry Lake, 38% emigrated as age‐I smolts. Smolts from Tranquil Lake were twice as large (14.3 g versus 7.1 g) as those from Larry Lake. Net yield emigrating smolts was 21.1 kg/hectare in Tranquil Lake and 6.7 kg/hectare in Larry Lake. The large number of chinook salmon stocked in the lakes prematurely depleted the large zooplankton, thereby limiting size and number of smolts produced. Shoal, defined here as the area of lake bounded by the shoreline and a bottom contour equivalent to the maximum compensation depth (99% extinction of surface light), was important in determining smolt yields because most fish foraged in shallow (<3‐m‐deep) water. For greatest tissue production of juvenile chinook salmon and subsequent yield of smolts in lakes similar to Larry and Tranquil lakes, 2,500 fish should be stocked for each hectare of shoal.