Green Bay Fisheries Resources Office staff measure the abundance of adult lake trout on spawning reefs in Lake Michigan in October. - FWS photo

Chuck Bronte and Mark Holey , both from the Green Bay Fishery Resources Office, took the lead in analysis and publishing of an interagency cooperative research project that evaluated the lake trout restoration effort on Lake Michigan. 

The project, funded by the Great Lakes Fishery Trust, teamed the Service with biologists from the the Departments of Natural Resources from Wisconsin, Michigan, Illinois and Indiana, Chippewa/Ottawa Authority, Little River Band of Ottawa Indians, Grand Traverse Bay Band of Indians, and the U.S. Geological Survey, on a three-year project which compares the relative abundance of lake trout  spawners at 19 stocked spawning sites to 25 unstocked sites. 

This was done to evaluate how effective site-specific stocking was to re-colonizing historically important spawning reefs.  The results indicated that adult fish were more abundant on stocked sites than on unstocked sites.  This suggested that site-specific stocking is more effective at establishing spawning aggregations than the ability of hatchery-reared lake trout to find spawning reefs, especially those offshore. 

Spawner densities were generally low and relatively young in age at most sites to expect significant natural reproduction.  However, densities were sufficiently high at some sites to expect reproduction and therefore the lack of recruitment was attributable to other factors. 

Less than 3% of all spawners could have been wild fish and indicates little natural reproduction occurred in past years.  Sea lamprey wounding was generally lower for fish of the Seneca Lake strain and highest for strains from Lake Superior. 

Fish captured at offshore sites in southern Lake Michigan had the lowest probability of wounding, while fish at onshore sites in northern Lake Michigan had the highest wounding.  The relative survival of the Seneca Lake strain was higher than that of the Lewis Lake or the Marquette strains for older year classes examined. 

Survival differences among strains were less evident for younger year classes. Recaptures of coded-wire tagged fish of five strains indicated that most fish returned to their stocking site or to a nearby site, and that dispersal from stocking sites during spawning was about 100 km. 

The paper concluded that future restoration strategies should rely on site-specific stocking of lake trout strains with good survival at selected historically important offshore spawning sites to increase egg deposition and the probability of natural reproduction in Lake Michigan. The paper will be published in the North American Journal of Fisheries Management in early 2007.