Relative Survival of Lake Trout Stocked at Different Sizes and Quality in Lake Michigan

Abstract

Beginning in 1995, the size of yearling lake trout ( Salvelinus namaycush) stocked into the upper Great Lakes was increased based on the assumption that these fish would be healthier and survive better since natural mortality is thought to be inversely proportional to body size. We compared the postrelease, relative survival of paired stockings of lake trout reared to 44 fish/kg (standard size) with larger fish reared to 22–26 fish/kg (enhanced size) in Lake Michigan. About 60,000 lake trout each of the standard and enhanced sizes for the 1994–1997 year classes were released as yearlings in spring near Clay Banks Reef, Wisconsin, and identified with coded-wire tags and an adipose fin-clip. Recaptures were made from 1997 to 2003 in four gill net surveys conducted in spring and fall near the release location. Comparisons of catch-per-unit of effort corrected for numbers stocked generally indicated no significant differences in relative survival of standard and enhanced lake trout. An autopsy-based assessment of overall fish health and condition indicated few measures where significantly different between standard and enhanced lake trout prior to stocking. Size differences between standard and enhanced fish remained statistically significant at all observed ages at recapture; however growth rates were the same for the two groups. Stocking numbers at certain sites on Lake Michigan were reduced concurrent with the change to larger yearlings with the expectation of increased survival, which did not occur; hence recruitment was essentially reduced in these areas for the restoration program.