The Michigan Department of Natural Resources (DNR) goes high-tech when it surveys prey fish on Lake Michigan.
Every year, the DNR uses a hydro-acoustic (sonar) and mid-water trawl to survey alewives and other prey fish in Lake Michigan.
According to the DNR, biologists can estimate alewives in Lake Michigan in just a few weeks. This is thanks to technological advances in fisheries surveys.
Another factor that helps is the DNR's partnership with the U.S. Geological Survey's (USGS).
"In a given night of sampling we can trawl up to 5 miles at depths ranging from 30 to 250 feet and collect up to 100 miles of acoustic data," says Randy Claramunt, DNR fisheries research biologist. "All information is recorded digitally and immediately available for analysis."
The purpose of the survey is to determine the status of prey in the lake's waters. The numbers will aid fisheries managers to determine next steps for Lake Michigan fish populations, in terms of the predator-prey balance.
The survey takes place at night beginning mid-August. It is conducted on board the DNR's S/V Steelhead, based out of Charlevoix, in conjunction with USGS' Great Lakes Science Center's R/V Arcticus.
"Cooperation with the DNR makes this survey possible," says Dave Warner, USGS Great Lakes Science Center research biologist. "If we did not have the ability to use two vessels, then our uncertainty in estimates of prey fish would be much higher because we would not be able to cover an adequate amount of the lake at the same time."