Food Habits of Walleye and Freshwater Drum in Northeast South Dakota

Establishing a walleye (Sander vitreus) year class in Mina Lake, South Dakota has been a challenge during the past decade.  Despite annual fry and fingerling stockings, the number of age-0 walleye sampled during fall night time electrofishing runs is low (range = 0 - 0.2 walleye/hour), indicating poor survival.  In addition, fall gill net surveys from the past decade indicate a low abundance (range= 0.2-1.3 fish/net night) of stock length walleye.  Considering the money invested in stocking walleye and the popularity of fishing for walleye in South Dakota, factors contributing to poor survivability of Mina Lake walleye need to be addressed.  Freshwater drum (Aplodinotus grunniens) is the most abundant fish species in Mina Lake and shows an increased abundance (range = 2.7-30.2 fish/net night) within the past decade.  It is unknown how increases in omnivorous freshwater drum influence the assemblage of prey available for walleye.  To identify specific prey items important to walleye and freshwater drum, diets of 98 freshwater drum and 197 walleye were examined.  For each prey item identified, percent by weight and number, frequency of occurrence, and relative importance was calculated.  Morista’s index of niche overlap was determined between walleye and freshwater drum in Mina Lake to conclude if significant diet overlap is occurring. If prey items considered important to walleye are the same as those important to freshwater drum, an increasing abundance of freshwater drum may limit prey for walleye and contribute to low abundance of Mina Lake walleye.