Shortnose cisco (Coregonus reighardi) COSEWIC assessment and status report: chapter 6

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Biology

General

Maximum known age is 11 years for females and 9 years for males (Webb and Todd 1995). Maximum known length and weight is 265mm TL and 420g (Scott and Crossman 1998).

Reproduction

The shortnose cisco was the only known spring-spawning cisco in lakes Huron, Michigan and Ontario (Webb and Todd 1995). Spawning occurred from May to June in lakes Huron and Michigan (Koelz 1929, Jobes 1943, Scott and Crossman 1998), and April to May in Lake Ontario (Pritchard 1931). Spawning occurred at depths of 52-146m in Lake Michigan (Jobes 1943), and predominantly at 73m in Lake Ontario (Pritchard 1931). Spawning depths in Lake Huron are unknown (Scott and Crossman 1998). Age at maturity was reported as 2+ to 3+ years in Lake Michigan (Hile and Deason 1947).

Survival

Maximum known age is 11 years for females and 9 years for males (Webb and Todd 1995).  Since sexual maturity is reached at 2 to 3 years (Hile and Deason 1947) and information on reproductive senescence is not known, the average age of reproducing individuals may be in the order of 5 years.

Physiology

Unknown.

Movements/dispersal

Based on skewed sex ratios, and the different depths at which the species was found, outside of spawning season, the shortnose cisco likely underwent a spawning migration to deeper waters (Webb and Todd 1995).

Nutrition and Interspecific Interactions

Prey items in lakes Huron and Ontario were predominantly the freshwater crustaceans Mysis relicta and Diporeia hoyi (Koelz 1929, Pritchard 1931). As the result of their preferred deepwater habitat, the shortnose cisco likely had limited interactions with other fish species, except in the shallowest part of their range. It was likely a prey item for burbot (Lota lota) and deep water forms of lake trout (Salvelinus namaycush). Periodic increases in lake trout numbers in the Great Lakes likely increased the predation pressure on the deepwater ciscoes (Christie 1973, Selgeby et al. 1994). Shortnose cisco may have competed with lake whitefish (Coregonus clupeaformis), deepwater sculpin (Myoxocephalus thompsoni) and other deepwater ciscoes for benthic prey.  Remnant shortnose cisco populations may have competed with, or have been preyed upon by, introduced fish species in lakes Huron, Michigan and Ontario (Smith 1964, Christie 1973, Todd and Stedman 1989, Todd and Smith 1992). As the shortnose cisco did occur in relatively shallow depths (< 40m at times), it is possible that it may have interacted with introduced pelagic fishes such as the sea lamprey (Petromyzon marinus), alewife (Alosa pseudoharengus), and rainbow smelt (Osmerus mordax). The decline of lake trout in lakes Huron and Ontario may have shifted sea lamprey predation to deepwater ciscoes and other species (Christie 1973). Smith (1995) noted that the decline in deepwater ciscoes in Lake Ontario coincided with the increasing abundance of alewife. He postulated that this may have been the result of competition for plankton, or predation on, larval ciscoes. However, the decline of deepwater ciscoes in Lake Superior prior to colonization by the sea lamprey, alewife and rainbow smelt (Lawrie and Rahrer 1973) suggests that these introduced species may not have had a significant impact on deepwater ciscoes, including shortnose cisco, in the Great Lakes.