Double-crested Cormorant (Phalacrocorax auritus) chick bioenergetics following round goby (Neogobius melanostomus) invasion and implementation of cormorant population control

As the fish community changed in the Beaver Archipelago (northern Lake Michigan), so has the diet of breeding Double-crested Cormorants (Phalacrocorax auritus). In 2000, the energetically dense alewife (Alosa pseudoharengus) dominated the diet, but more recently, the relatively low quality round goby (Neogobius melanostomus) has become the most common prey item. Additionally, cormorant control measures have been underway in the archipelago. This study investigated decreases in cormorant chick numbers and changes in chick bioenergetics in response to this change in diet, as well as the influence of control efforts, and compared these results to an earlier study. Two colonies, one actively controlled the other only controlled following completion of this study, were investigated to determine changes in colony size throughout the breeding season, document chick diet, measure chick growth, and determine chick survivorship to fledging. The bioenergetics model estimated that in 2010, chicks consumed a greater biomass of prey to reach fledging due to the change in diet, but lower biomass overall due to fewer chicks in the system. Control efforts in combination with the change in diet reduced chick numbers. Overall, the impact of cormorant chicks on available fish biomass has declined in recent years due to control efforts. However, the birds have the potential to consume a greater biomass of round goby in the absence of control. The impact of cormorants on fisheries resources is complicated by the abundance and effects of non-native species.