Alewife (Alosa pseudoharengus) and Rainbow Smelt (Osmerus mordax) are the most abundant pelagic planktivores in Lake Ontario (Weidel et al 2017), and the most important prey for salmon and trout, making up greater than 90% of the diet of the top predator, Chinook salmon (Lantry 2001, Brandt 1986), and supporting a multimillion dollar sportfishery. Alewife are also important prey for warm water predators, notably Walleye (Sander vitreus). Abundance of Alewife and smelt has declined since the 1980s, likely due to reduced nutrient loading, proliferation of invasive dreissenid mussels, and predation by stocked salmon and trout. Cisco (Coregonus artedi), a native planktivore, historically dominated the offshore pelagic prey fish of Lake Ontario, but their populations were severely reduced in the mid-20th century due to overfishing and competition with Alewife and smelt. Remnant populations of Cisco still exist, mostly in the eastern basin, and Cisco produce periodic strong year classes once or twice per decade (Owens et al 2003, most recently in 2012 and 2014 (OMNRF, 2017).

Alewife (Alosa pseudoharengus) and Rainbow Smelt (Osmerus mordax) are the most abundant pelagic planktivores in Lake Ontario (Weidel et al 2017), and the most important prey for salmon and trout, making up greater than 90% of the diet of the top predator, Chinook salmon (Lantry 2001, Brandt 1986), and supporting a multimillion dollar sportfishery. Alewife are also important prey for warm water predators, notably Walleye (Sander vitreus). Abundance of Alewife and smelt has declined since the 1980s, likely due to reduced nutrient loading, proliferation of invasive dreissenid mussels, and predation by stocked salmon and trout. Cisco (Coregonus artedi), a native planktivore, historically dominated the offshore pelagic prey fish of Lake Ontario, but their populations were severely reduced in the mid-20th century due to overfishing and competition with Alewife and smelt. Remnant populations of Cisco still exist, mostly in the eastern basin, and Cisco produce periodic strong year classes once or twice per decade (Owens et al 2003, most recently in 2012 and 2014 (OMNRF, 2017).