Shortjaw cisco COSEWIC assessment and status report: chapter 10
General Biology
Spawning occurs in either the fall or spring in the Great Lakes. Shortjaw ciscoes in Lakes Michigan, Huron, and Erie spawned solely in the fall (Koelz 1929; Scott and Smith 1962). However, Lake Superior fish have been found spawning in either the spring or the fall--a fact noted by Koelz (1929), although he considered it unusual and concluded, along with VanOosten (1936), that Lake Superior shortjaw ciscoes spawned in the fall. Todd and Smith (1980) reported a more extensive occurrence of spring spawning in this species. Eggs are deposited over the lake bottom (generally clay in the Great Lakes) and left to develop without parental care for a period of three or four months, depending on temperature (Berlin et al. 1977). Fecundity of shortjaw ciscoes is likely similar to that of other deepwater species such as the bloater, ranging from 3,230 eggs for a fish 241 mm total length (TL) to 18,768 for a fish 305 mm TL (Emery and Brown 1978).
As in most fish species, shortjaw ciscoes grow quickly in their first year of life. While the sexes have been found to have similar growth in length, females grew faster in weight than the males--growing an average of about 30 g a year in mature fish with an annual length increase of about 25 mm (VanOosten 1936). Maturity occurred in about the fifth year and resulted in additional growth in weight, primarily due to gonadal development--nearly 60% of potential maximum weight gain occurred after age five compared to growth in length that reached about 80% of its potential maximum value at age five and increased only slowly thereafter (VanOosten 1936). Maximum size for Lake Superior fish has been recorded at 276 g for males 368 mm TL, and females at 292 g (VanOosten 1936). Lake Nipigon shortjaw ciscoes exhibit larger sizes, and have been recorded at weights of 500 g to 1.0 kg and up to 400 mm TL (R. Salmon, Ontario Ministry of Natural Resources, Lake Nipigon Assessment Unit, pers. comm.). Some populations of shortjaw ciscoes mature at much smaller sizes--adult fish in George Lake, Manitoba, for example averaged only 158 mm (127-173 mm) SL (U.S.G.S., Great Lakes Science Center, unpublished data).
Coregonines are opportunistic, particulate feeders that generally ingest prey one item at a time. Availability is important, and seasonal prey such as insects show up in the diets of fish in small lakes. Because shortjaw ciscoes may live in the deeper parts of lakes, terrestrial input is limited, and limnetic crustacea (copepods and cladocerans) and benthic organisms (Mysis and Diporeia) dominate their diets (Koelz 1929; Bersamin 1948; Anderson and Smith 1971; Wain 1993; Turgeon et al. 1999; Hoff and Todd 2004). Such prey has been found to dominate the diet of shortjaw ciscoes even in shallower habitats--Barrow Lake, Alberta, for example (Steinhilber et al. 2002).
In addition to the species’ importance in general food fisheries, shortjaw ciscoes form an important part of the forage base for predators such as lake trout and burbot (Lota lota). In the Great Lakes, the species was one of several that functioned in this role, but, in smaller Canadian lakes, it is often the main forage for predators. It is also likely that the species became vulnerable to predation from sea lampreys in the Great Lakes as favored individuals of larger species became depleted.
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