Double-crested Cormorants (Phalacrocorax auritus) began to recolonize Leech Lake, Minnesota, in the 1990s and reached 2,524 breeding pairs before control measures started in 2005. Walleye (Sander vitreus) recruitment concurrently declined, creating concern in the local community. To better understand the impacts of cormorants on fish, a cormorant diet analysis was conducted and two models were compared: Madenjian and Gabrey (1995) and Niche Mapper™ for estimating cormorant consumption of fish. Stomach content analysis revealed Yellow Perch (Perca flavescens) to be the most dominant species, providing 80% and 40% of the overall diet in 2005 and 2006, respectively. The Madenjian and Gabrey and the Niche Mapper™ models showed similar results in estimating daily food consumption of cormorants despite their different approaches and complexity levels. In both models, consumption estimates were greater in 2005 than in 2006, with 26 to 33% of their total body mass in 2005 and 18 to 22% of their total body mass in 2006. Likely the variation was caused by the variation in diet found in cormorant stomachs and the difference in the caloric densities of their diet between the two years, with Lake Herring (or Cisco, Coregonus artedi) being more prevalent in the diet in 2006. The most sensitive parameters in the Madenjian and Gabrey model were daily energy expenditure, assimilation efficiency, caloric density of fish and weight of cormorants. In the Niche Mapper™ model, core body temperature of cormorants and caloric density of fish were the most sensitive parameters. The strengths and weaknesses of both models are discussed, while providing guidance for researchers to select the method most applicable to their specific site and available data.
You have requested a machine translation of selected content from our databases. This functionality is provided solely for your convenience and is in no way intended to replace human translation. Neither BioOne nor the owners and publishers of the content make, and they explicitly disclaim, any express or implied representations or warranties of any kind, including, without limitation, representations and warranties as to the functionality of the translation feature or the accuracy or completeness of the translations.
Translations are not retained in our system. Your use of this feature and the translations is subject to all use restrictions contained in the Terms and Conditions of Use of the BioOne website.
Vol. 35 • No. sp1