Reference | Ross, Robert M., and J.H. Johnson. 1995. Seasonal and annual changes in the diet of double-crested cormorants: Implications for Lake Ontario's fishery. Great Lakes Research Review 2(1): 1-9. |
Abstract | Regurgitated digestive pellets of double-crested cormorants (Phalacrocorax auritus) at Little Galloo Island in Lake Ontario were collected from 1992 to 1994 and analyzed for fish remains to determine the diet composition and total consumption. Otoliths, bones, scales and eye lenses from 38,301 fish of two dozen species were observed in 3,827 pellets. The mean number of fish per pellet during the chick-feeding phase of the nesting cycle fell substantially (about 43%) from the pre-chick feeding period, representing a transfer of energy from adults to young. Species composition also changed over the nesting cycle, with alewife (X = 20% increase in percent composition) replacing yellow perch (X = 14% decrease) during the chick feeding period. The diet composition of cormorants varied among years with alewife decreasing in importance in the diet and yellow perch increasing in importance from 1992 to 1994. Forage fishes made up 50% of the diet and panfish contributed 33% of the diet for the 3-year period. Gamefish, mainly smallmouth bass (1.3%) and salmonines (0.3%) made up only 1.6% of the diet of cormorants. Cormorants consumed an estimated 3.60 million lbs. of fish in 1993 and 1.97 million lbs. in 1994 in the eastern basin of Lake Ontario. The 45% drop in fish consumption in 1994 may be related to reduced availability of alewife in Lake Ontario. Predation losses on individual releases of stocked salmonines were found to reach 9% but probably can be reduced through alteration of existing stocking practices. |
Tag | Coded Wire Tag (CWT) |
Objective | Evaluate habitat use |