Diets of Angler-Caught Predators in Lake Huron, 2009-2010

We analyzed diets of over 4,500 predators caught by anglers in Lake Huron during 2009 and 2010 to determine how predators have responded to recent changes in the prey base, especially the near absence of Alewife and low biomass of other fish prey. Anglers captured primarily Chinook Salmon, Lake Trout, Walleye, Steelhead, and Atlantic Salmon. During 2009, prey fish were scarce, and predators relied on non-traditional prey; most fish consumed Round Goby, but there was surprising reliance on invertebrate prey. Small, recently stocked Lake Trout and Chinook Salmon comprised a substantial proportion of diets, and were occasionally the most prominent prey observed in stomachs after stocking events. During 2010, Gizzard Shad and Rainbow Smelt were more abundant and their dietary proportions increased, but predators continued to consume non-traditional prey. Predators in Lake Huron appear to be prey-limited, and large-bodied prey seemed especially rare. Prey limitation may be most severe for Walleye, Chinook Salmon, and Lake Trout, because their diet breadth was narrow. Atlantic Salmon and Steelhead may be less affected because of their wider diet breadth. Our results may also explain recent declines in survival of stocked salmonids because predation on them seemed especially severe.