Burbot Growth and Diets in Lakes Michigan and Huron: An Ongoing Shift from Native Species to Round Gobies
Stephen R. Hensler, David J. Jude, and Ji He
Abstract.—Burbot Lota lota is a native species of cod (Gadidae) found in the coldwater regions of all five Laurentian Great Lakes. Burbot age-at-length data from along western Lake Huron showed that fish reached 18 years of age. Fish age 7 and younger grew more slowly in southern Lake Huron than in north-central and northern Lake Huron, while this trend was reversed for fish ≥ 8 years old. Burbot growth and diet data were recorded for fish collected near Leland, Fairport, and Bridgman (D. C. Cook nuclear power plant), Michigan and Washington Island, Wisconsin in Lake Michigan and Alpena, Michigan in northern Lake Huron to determine changes in growth and diet with the recent invasion of the nonindigenous round goby Neogobius melanostomus. We compared burbot growth at four length intervals (500–800 mm) among these locations and found significantly lower growth at Alpena compared with the other sites; burbot from Bridgman at 500 and 600 mm were the lightest among all sites. Burbot diets have changed substantially in some areas from native fish and invertebrate species to a diet that includes large proportions of the nonindigenous round goby (77% by wet weight in Lake Huron near Alpena, 53% in Lake Michigan near Fairport). Establishment of round gobies in the open waters of the Great Lakes is likely to change coldwater food webs, including replacement of sculpins (Cottus spp.) at depths up to 70 m, where round gobies have been found. Burbot, whose diets were composed of large amounts of round gobies, showed lower growth, and there is a potential for decreased bioaccumulation of toxic substances because round gobies consume zebra mussels Dreissena polymorpha and quagga mussels D. bugensis, which are lower in the food chain than organisms that native species eat.