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COSEWIC Assessment and Update Status Report on the Blackfin Cisco in Canada

Limiting Factors and Threats

Factors known to have caused the decline of blackfin cisco in the Great Lakes are over-exploitation by the commercial fisheries and sea lamprey predation (Smith 1964; Berst and Spangler 1972; Lawrie and Rahrer 1972; Christie 1972). Smith (1964) also suggested that, in Lake Michigan, the extirpation of blackfin cisco may have been through introgressive hybridization with C. artedi. Continued capture of blackfin cisco as an incidental catch species in lake whitefish nets on Lake Nipigon may have a detrimental effect on species populations in this lake over time; however, present information is insufficient to quantify this effect.

Introduced species, such as alewife (Alosa pseudoharengus) and rainbow smelt (Osmerus mordax), may have competed for food with deepwater cisco populations in Lake Huron (Berst and Spangler 1972; Christie 1972). This threat, along with potential sea lamprey predation, may, in part, be suppressing a recovery of remnant deepwater cisco populations, populations that may once have included blackfin cisco, within the Great Lakes. Rainbow smelt may also be impacting blackfin cisco populations in Lake Nipigon.