Research Update

Mapping Forage Fish in the Upper Great Lakes

The success of restoring lake trout and other native Great Lakes predators depends in part on a stable prey base, or forage fish, including native species such as bloater, herring, stickleback, and sculpin. These fish have historically been a major component of native predator diets, explains Michigan State University scientist Kim Scribner, and play a vital role in the Great Lakes aquatic food web.

With Sea Grant funding, Scribner is leading a large-scale multidisciplinary project to utilize genetic markers to identify differences among stocks of important forage fish species. The information provides fisheries managers with a better idea of the degree of isolation and movements of the stocks within each species.

“What’s unique about this study is that it’s a comparative analysis across five species of fish,” says Scribner. With co-investigator Wendy Stott of the USGS Great Lakes Science Center, Scribner’s team is analyzing bloater, herring, sculpin, stickleback, and alewife. The far-reaching study has capitalized on long-term data collection conducted by the USGS at sampling sites throughout the upper Great Lakes.

To date, researchers have genetically analyzed 4,500 fish. Laboratory results reveal how isolated or genetically different certain fish stocks are.

“We’re essentially testing the extent of interbreeding among populations,” says Scribner. “Estimates of genetic affinities between populations provide a measure of whether a fish from one geographic location is reproductively isolated from fish from other parts of the lake basin.”

Improving Fisheries Management
This degree of detail helps fisheries managers set harvest quotas and make stocking decisions that ultimately impact lake trout, salmon and other economically important species. It also improves predictive capabilities. If a fish population declines, managers might be able to predict how fast it can be expected to rebound based on immigration from other populations, which can be inferred based on the degree of genetic affinity to other populations.

Some fundamental genetic distinctions have already emerged. The biggest difference, according to researchers, is the clear dividing line between fish in Lake Superior and those in Lakes Huron and Michigan. They’ve also found that within a lake basin, slimy sculpin, lake herring and bloater showed the most spatial structuring, or distinct populations with some degree of genetic difference.

Another unique component of the collaborative project involves correlating genetic information with environmental data. Researchers hope that by looking at environmental variables such as productivity and water temperature, or ecological factors such as habitat or water depth, the information will further explain the spatial genetic relationships, making it even more usable by management agencies.

The researchers are currently analyzing the genetic data. “These data are very valuable,” notes Stott. “We now have a shared resource. Any other data collected can build on this.”