Shortjaw cisco COSEWIC assessment and status report: chapter 8
Population Size and Trends
Shortjaw ciscoes have been an important part of the food fishery in the Great Lakes since at least the mid-1800s (Milner 1874; Koelz 1926). Landing records, on the whole, were not recorded by species, but were lumped into a general category, “chubs”, for all the deepwater cisco species that excluded the shallow-water lake herring (Baldwin et al. 1979). Shortjaw ciscoes seem to have been relatively uncommon in Georgian Bay waters of Lake Huron, but reached levels of up to 17% of chub catches from Lake Huron proper (Koelz 1929). Collections in U.S. waters of Lake Huron in 1956 revealed that shortjaw ciscoes constituted 19% (including fish identified as C. alpenae) of the total chub catch--66% of which was bloaters (U.S.G.S., Great Lakes Science Center, unpublished data). Only individual specimens were taken in the 1970s, and a lone individual was taken in Lake Huron in 1982 off Ausable Pt., Michigan (Todd 1985). In Lake Michigan, the species (including fish identified as C. alpenae) made up about 21% of the chub catch in the 1930s, dropping to 6% in the 1950s, 2% by the early 1960s, and disappeared from the lake in the 1970s (Smith 1964; Todd 1985). Other than the few specimens reported from the original paper on Lake Erie shortjaw ciscoes (described as longjaw ciscoes, C. alpenae), no subsequent specimens were ever collected, and so no information is available on the population trends in Lake Erie (Scott and Smith 1962; Scott and Crossman 1973). The species still persists in Lake Superior, but has declined in relative abundance from nearly 90% of the chub catch in the 1920s (Koelz 1929), to about 25% of the catch in the late 1950s (Hoff and Todd 2004), to 6-11% in Michigan waters in the 1970s (Peck 1977). Two small collections made in Michigan waters in 1997 revealed abundances of 5% and 11%, in the same range as the 1970s (Hoff and Todd 2004). The abundance of the species in Lake Superior has not been adequately studied, however, and, other than its definite presence in the lake and a drastic decline since the 1920s, little can be said about recent trends. While the general trend of extirpation in the Great Lakes has been reasonably well documented, the causes for the decline are not well understood. Early fisheries selectively exploited the larger individuals of all the cisco species and had driven the larger species (C. johannae and C. nigripinnis) nearly to extinction by the 1920s (Koelz 1929; Hile and Buettner 1955). As these preferred species declined, the fishery shifted to the smaller species and increased their exploitation (Smith 1964, 1968). Proliferation of introduced rainbow smelt (Osmerus mordax) and alewife (Alosa pseudoharengus) in the 1930s through the 1950s provided additional stress from competition and predation. Also, beginning in the late 1940s, ecological changes brought about by extirpation of nearly all lake trout (Salvelinus namaycush) by introduced sea lamprey (Petromyzon marinus) resulted in the extinction of the large species, C. johannae and C. nigripinnis, and the selective proliferation of the bloater (Smith 1964, 1968) because of a preference for larger prey species by the sea lamprey. As a further consequence of the population destabilizations, hybridization became a factor in the final demise of these species (Smith 1964; Todd and Stedman 1989). The bloater is now the only deepwater cisco species in Lakes Michigan and Huron, and dominates in Lake Superior (Fleischer 1992).
Populations of shortjaw ciscoes in Lake Nipigon are still abundant and coexist with lake herring, bloaters, and blackfin ciscoes (C. nigripinnisregalis), as well as lake whitefish (C. clupeaformis) and round whitefish (Prosopium cylindraceum), rather like the situation in the other Great Lakes (with the exception of blackfin ciscoes). Extensive, long-term data on the species are lacking, although periodic population assessments have been made since the 1970s. Examination of commercial catches (large-mesh nets) and experimental sets in 1973 revealed that shortjaw ciscoes comprised 31% of the total catch of ciscoes (U.S.G.S., Great Lakes Science Center, unpublished data). More recent assessments (1997) from graded-mesh research nets have provided values of 3.4%, although these values are probably biased on the low side because of uncertain identifications (R. Salmon, Ontario Ministry of Natural Resources, Lake Nipigon Assessment Unit, personal communication).
Population trends in other lakes that the species inhabits are generally unknown. Steinhilber and Ruhde (2001) noted that the species formed 4.2-5.7% of cisco collections in Barrow Lake, Alberta in 1996-1997 and 11.6% in 2000 with many immature specimens in all years that suggested good reproduction and juvenile survival. Cisco collections in Barrow Lake in 1966 contained 21% shortjaw ciscoes (Turner 1967; Paterson 1969). Steinhilber and Ruhde (2001) concluded that different sampling methods in the 1960s selectively caught more shortjaw ciscoes and that the species has been stable over the past few decades. The species undoubtedly forms a portion of food-fishery captures in some of the larger lakes, such as Great Slave Lake, that have either assessment programs or fishery statistical offices, but identification of such catches to individual species is apparently not done. Some recent collections from Great Slave Lake have not contained any shortjaw ciscoes while others have (Murray and Reist 2003).
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