Predation by hatchery released salmonids and fallfish on naturalized subyearling Chinook salmon and steelhead in the Salmon River, New York

Natural reproduction of naturalized Chinook salmon (Oncorhynchus tshawytscha) and steelhead (O. mykiss) has been documented in the Salmon River, New York for several decades.  In 2009 we initiated a study to examine predation by recently released yearling hatchery salmonids and fallfish (Semotilus corporalis) on Chinook salmon and steelhead fry.  In May, Chinook fry made up 39.9%, 24.6%, 18.5%, 62.5%, and 48.1% of the diet of yearling steelhead, coho salmon (O. kisutsch), Atlantic salmon (Salmo salar), large fallfish (≥ 150mm), and medium fallfish (100-149mm), respectively.  Fallfish less than 100mm did not consume salmonid fry.  In June yearling steelhead (5.4%), large fallfish (11.5%), and medium fallfish (0.8%) continued to consume Chinook fry.  Steelhead fry were a major component of the diet of yearling steelhead (23.6%), Atlantic salmon (14.6%), brown trout (S. trutta) (59.2%), large fallfish (11.0%), and medium fallfish (10.7%) in June.  Based on the number of yearling salmonids stocked and fallfish population estimates we estimate that approximately 8.2 million Chinook fry (5.7 million and 2.5 million consumed by fallfish and yearling salmonids, respectively) and 2.1 million steelhead fry (1.9 million and 0.2 million consumed by fallfish and yearling salmonids, respectively) were consumed by these species during May and June in 2009.