Population Expansion and Diets of Deepwater Sculpin, a Rare Native Fish, in Lake Ontario

Deepwater sculpin (Myoxocephalus thompsonii) were abundant in Lake Ontario in the 1920’s and at least common into the 1940’s.  By the 1960’s, they were extremely rare, and by the 1970’s the population was considered extirpated.  The species was ‘rediscovered’ when three individuals were collected in 1996.  A recent summary of deepwater sculpin records from literature, commercial fishing records, and fisheries surveys in Lake Ontario documents sporadic captures of deepwater sculpin during 1996-2004.  The possible recovery of deepwater sculpin was thought to be limited by abundance of predators on pelagic larvae (alewife, Alosa pseudoharengus) and benthic adults (lake trout, Salvelinus namaycush) and the absence of its historically preferred prey, Diporeia spp.  However, catches of deepwater sculpins in sampling conducted by US and Canadian agencies became more consistent and increased steadily during 2005-2010, and distribution of the species has also expanded from isolated locations to broad geographic coverage.  The continued presence of juvenile deepwater sculpins in catches indicates that conditions for survival of young deepwater sculpins are favorable, perhaps because of reduced abundances of alewife.  Deepwater sculpin diets in 2010 were dominated by the native mysid, Mysis diluviana, but also contained dipterans, chironomids, and ostracods  The use of available prey resources and observed population recent population expansion point toward ongoing recovery of this native species, despite the absence of Diporeia spp.