Invasive species sustain double-crested cormorants in southern Lake Michigan

Advisors: Holly P. Jones.Committee members: Nicholas A. Barber; Owen T. Gorman; Carl von Ende.Double-crested cormorants (Phalacrocorax auritus ) have long and often been implicated in having detrimental effects on fisheries. Resulting persecution, as well as DDT water contamination, led to a major decline of the species throughout its range. Research shows that the main components of cormorant diets vary significantly among forage, invasive, or economically important fish species. A recent, rapid increase in cormorant abundance in the Great Lakes has led, in some instances, to calls for the management of cormorant populations. Thus the objective of this study was to determine the prey composition of the double-crested cormorant colony in East Chicago, Indiana. This study builds on previous work in the north basin of Lake Michigan by focusing on cormorant diet composition at their only significant nesting colony in the southern basin where cormorant diet has been unstudied. Regurgitated pellets were collected from the colony and diagnostic bones were used to elucidate diet composition. Alewife (Alosa pseudoharengus ), round goby (Neogobius melanostomus), Lepomis spp., white perch (Morone americana) and yellow perch (Perca flavescens) were the most frequently found prey items depending on cormorant breeding stage. Invasive species (i.e., alewife, round goby, white perch) contributed over ninety percent of the individuals and eighty percent of the biomass to cormorant diet over the study period. No salmonine species were detected suggesting that negative effects on this important fishery would likely occur only via direct competition for prey (e.g., alewife). Predation on yellow perch, which occurred mainly prior to and during the perch spawning season (i.e., of age-1 and older individuals), may warrant further study to quantify the effects on the local recreational yellow perch fishery. However, because yellow perch abundance is thought to be currently limited by poor recruitment at age-0, these results do not support active management of the cormorants at this colony to protect local fisheries.M.S. (Master of Science