Coregonus zenithicus (Jordan and Evermann, 1909)
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Basis for Listing
The Shortjaw Cisco (Coregonus zenithicus) has a restricted distribution across its range due to overfishing and introduction of the Sea Lamprey (Petromyzon marinus), Alewife (Alosa pseudoharengus), and Rainbow Smelt (Osmerus mordax). Beginning around 1870, the species supported a valuable commercial fishery and was once the dominant deepwater cisco in Lake Superior. It was subsequently overexploited and between the mid-1930s and late 1950s the Shortjaw Cisco experienced marked population declines (Becker 1983). Populations have also been adversely affected from predation by the parasitic Sea Lamprey and from competition for food and habitat with the introduced Alewife and Rainbow Smelt, which also prey on Shortjaw Cisco eggs.
The Shortjaw Cisco has an elongated, elliptically shaped, laterally compressed body. It is olive green dorsally, with large, silvery scales on the sides, and white ventrally. The pelvic and anal fins are sometimes pigmented black, especially in older, larger specimens. The Shortjaw Cisco's small mouth lacks teeth, and its straight snout has a lower jaw shorter than the upper jaw. Males, and sometimes females, have tubercles (small, hardened, breeding growths) during the breeding season. Adults are typically over 30 cm (11.8 in.) in total length and weigh approximately 300 g (10.6 oz.). Females tend to be larger and longer-lived than males.
The Shortjaw Cisco is very similar in appearance to the Cisco (Coregonus artedi), Bloater (Coregonus hoyi), and Kiyi (Coregonus kiyi) (Lyons et al. 2012). Shortjaw Cisco differs from other ciscoes by a usually blunt and angled snout, which rarely may be pointed. The upper jaw is usually longer than the lower, but (rarely) may be equal in length.
Shortjaw Ciscos occur in the deep water, 20-150 m (66-492 ft.) in depth, of large lakes. Spawning probably occurs at 37-73 m (121-240 ft.) deep, over clay bottoms (Becker 1983).
Biology / Life History
The life history of the Shortjaw Cisco is not well known. Their diet includes primarily Opossum Shrimp (Mysis relicta) and Pontoporeia hoyi (an amphipod crustacean) but also planktonic crustaceans, insect larvae, and some aquatic vegetation. Natural predators are Lake Trout (Salvelinus namaycush) and Burbot (Lota lota). Spawning time in Lake Superior is variable. During spawning, Shortjaw Cisco move to shallower waters, approximately half the depth they usually inhabit. Males arrive first to spawning grounds. Eggs are deposited on the bottom and abandoned. Growth is fairly rapid within the first year and then slows down. Weight increase is not pronounced until after the first four years. Males and females grow at about equal rates, however, due to their increased longevity, females attain a greater size. Sexual maturity is reached by the fifth or sixth year. In Lake Superior, Shortjaw Cisco migrate seasonally from 110-144 m (360-472 ft.) deep water in spring, to 55-71 m (180-233 ft.) deep water in summer, and 73-90 m (240-295 ft.) deep water during winter (Scott and Crossman 1973).
Conservation / Management
In addition to overfishing, competition and predation by introduced fishes have adversely affected populations of the Shortjaw Cisco. Disposal of dredged material and sedimentation may also deposit silt on spawning beds, smothering eggs and reducing the level of dissolved oxygen by introducing organic matter. Many hazardous chemicals present in the Great Lakes may also threaten this species.
Recent genetic research failed to differentiate Cisco from Shortjaw Cisco. These results suggest all ciscoes (Coregonus spp.) might not be multiple species, but rather a single species that has adapted to fill multiple open niches. The authors advocate an ecosystem approach of management, which focuses on maintaining niches in lakes with different cisco forms (not individual species) co-habiting. Status assessments should identify and designate lakes with multiple forms as special management units based on morphological, biological, ecological, and genetic evidence (Turgeon et al. 2015).
Conservation Efforts in Minnesota
The Minnesota DNR Section of Fisheries records any occurrences of Shortjaw Cisco found while conducting their annual fish surveys. The North American Native Fishes Association conducted cisco surveys from 2009-2014. Based on meristic and morphological characteristics, Shortjaw Cisco were identified from specimens collected from 2009-2014 in 14 northeastern Minnesota and Minnesota-Ontario border lakes (Schmidt 2016).
General fish surveys are necessary to determine the distribution of the Shortjaw Cisco in Minnesota, and more intensive research is needed on its general biology. In addition, genetic information needs to be obtained. Extant populations should be carefully monitored and protected from overcollection via incidental catch. Preventing further introductions of non-indigenous species while continuing current efforts to suppress existing exotic species populations in Lake Superior should also be a high priority.
Author: Dr. Peter Berendzen, 2008
Revised: Konrad P. Schmidt, 2016
Becker, G. C. 1983. The fishes of Wisconsin. University of Wisconsin Press, Madison, Wisconsin. 1052 pp.
Hoff, M. H., and T. N. Todd. 2004. Status of the Shortjaw Cisco (Coregonus zenithicus) in Lake Superior. Annales Zoologici Fennici 41(1):147-154.
Houston, J. J. 1988. Status of the Shortjaw Cisco, Coregonus zenithicus, in Canada. Canadian Field-Naturalist 102:97-102.
NatureServe. 2015. NatureServe Explorer: an online encyclopedia of life [web application]. Version 7.1. NatureServe, Arlington, Virginia. <http://www.natureserve.org/explorer>. Accessed 25 May 2016.
Scott, W. B., and E. J. Crossman. 1973. Freshwater fishes of Canada. Fisheries Research Board of Canada Bulletin 184, Ottawa, Canada. 966 pp.
Turgeon, J., S. M. Reid, A. Bourret, T. C. Pratt, J. D. Reist, A. M. Muir, and K. L. Howland. 2016. Morphological and genetic variation in Cisco (Coregonus artedi) and Shortjaw Cisco (C. zenithicus): multiple origins of Shortjaw Cisco in inland lakes require a lake-specific conservation approach. Covservation Genetics 17(1)45-56.
U.S. Forest Service. 1999. Population viability assessment in forest plan revision. Statement of purpose and reason. Draft species data records: Coregonus zenithicus. United States Forest Service, Region 9.