Diet composition and fish consumption of double-crested cormorants from three St. Lawrence River colonies in 2013

NYSDEC Lake Ontario Annual Report 2013- 15
By: , and 



Double-crested Cormorants (Phalacrocorax auritus) were first observed nesting in the upper St. Lawrence River at Strachan Island in 1992. Cormorants now nest at a number of islands in the Thousand Islands section of the river. Griswold, McNair, and Strachan islands are among the largest colonies in the upper river. Until 2011, nest counts had remained relatively stable, ranging from 200 to 603 nests per colony. However, since 2011 the number of nests at McNair Island have exceeded 700 each year. Although the size of cormorant colonies in the upper St. Lawrence River is smaller than those in the eastern basin of Lake Ontario, the close proximity of islands in the upper river that have colonies may cause a cumulative fish consumption effect similar to a larger colony. Because of increasing numbers of Double-crested Cormorants in the upper St. Lawrence River and the possible effects on fish populations, studies were initiated in 1999 to quantify cormorant diet and fish consumption at the three largest colonies. From 1999 to 2012, these studies have shown that cormorants consumed about 128.6 million fish including 37.5 million yellow perch (Perca flavescens), 17.4 million rock bass (Ambloplites rupestris) and 1.0 million smallmouth bass (Micropterus dolemieu) (Johnson et al. 2012). During this same time period fish assessment studies near some of these islands have shown a major decrease in yellow perch populations (Klindt 2007). This occurrence is known as the halo effect and happens when piscivorous birds deplete local fish populations in areas immediately surrounding the colony (Ashmole 1963). This paper describes the diet and fish consumption of cormorants in the upper St. Lawrence River in 2013.

Study Area

Additional publication details

Publication type Report
Publication Subtype State/Local Government Series
Title Diet composition and fish consumption of double-crested cormorants from three St. Lawrence River colonies in 2013
Series title NYSDEC Lake Ontario Annual Report
Series number 2013
Chapter 15
Year Published 2014
Language English
Publisher New York State Department of Environmental Conservation
Publisher location Albany, NY
Contributing office(s) Great Lakes Science Center
Description 12 p.
Larger Work Type Report
Larger Work Subtype State/Local Government Series
Larger Work Title 2013 Annual report: Bureau of Fisheries, Lake Ontario unit and St. Lawrence River unit, to the Great Lakes Fishery Commission’s Lake Ontario Committee
First page 15-1
Last page 15-12
Conference Title Lake Ontario Committee Meeting
Conference Location Windsor, ON
Conference Date March 26-27, 2014
Country Canada, United States
State New York
Other Geospatial Griswold Island, McNair Island, St. Lawrence River, Strachan Island
Google Analytic Metrics Metrics page