M/V Spencer F. Baird is on the Job!
Lake Michigan-Hydroacoustic and Mid-water Trawl Survey
BY DALE HANSON, GREEN BAY FWCO
The U.S. Geological Survey, Michigan Department of Natural Resources, and U.S. Fish and Wildlife Service (FWS) recently collaborated on a lakewide hydroacoustic and midwater trawl survey to monitor the relative abundance of Lake Michigan’s preyfish communities. Green Bay Fish and Wildlife Conservation Office (FWCO) biologist Dale Hanson was aboard the USFWS fish stocking and fishery assessment vessel, the M/V Spencer F. Baird, to lead the USFWS effort from August 4th – 18th, 2014. During this time the vessel surveyed five transects in northern Lake Michigan and four transects in Green Bay waters.
Preyfish generally spend the daylight hours at or near the lake bottom, but at night they move up in the water column and become detectable using the ship’s scientific sonar equipment. These sonars are well suited to measuring the density of fish targets in the water column but midwater trawls are typically needed to determine which species are present. Preliminary findings suggest fish densities in northern Lake Michigan were generally sparse though higher density patches of alewives were also observed along the Wisconsin side of the lake. Green Bay waters were markedly different with dense areas of lake whitefish below the thermocline in southern waters of Green Bay and moderate densities of alewives near the islands in northern Green Bay.
After the data have been analyzed, more definitive results will show how alewife, bloater, and other pelagic species have fared over the last year. Lake managers, and anglers, eagerly await these results that estimate the amount of prey available to the lake’s salmonid predators.