Coregonus zenithicus    (Jordan and Evermann, 1909)

Shortjaw Cisco 


MN Status:

special concern
Federal Status:
none
CITES:
none
USFS:
yes


Group:

fish
Class:
Actinopterygii
Order:
Salmoniformes
Family:
Salmonidae
Habitats:

(Mouse over a habitat for definition)


Coregonus zenithicus Coregonus zenithicus Coregonus zenithicus

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Map Interpretation

Map Interpretation

  Synonyms

  Basis for Listing

The shortjaw cisco 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 950s, 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.

Today, the shortjaw cisco is rare throughout its range and there is no current fishery. Extant populations are only known to occur in Saganaga, Gunflint, and Basswood lakes in northeastern Minnesota and in Lake Superior. It has been extirpated from Lakes Huron and Michigan, and the populations in Lake Superior are thought to be declining. Given its dramatic population decline, limited distribution, and concerns over competition with exotic species, the shortjaw cisco was listed as a special concern species in Minnesota in 1996.

  Description

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 (10.5 oz.). Females tend to be larger and longer-lived than males.

  Habitat

Shortjaw ciscos occur in deep water, 20-150 m (66-492 ft.) in depth, of large lakes. Spawning probably occurs at 37-73 m (121-239 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, 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 4 years. Males and females grow at about equal rates, but 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 (180-232 ft.) deep water in summer, and 73-90 m (239-295 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.

Other common names for the shorjaw cisco include shortjaw chub, longjaw, Lake Superior longjaw, lightback tullibee, and paleback tullibee.

  Conservation Efforts in Minnesota

The Minnesota DNR Section of Fisheries records any occurrences of shortjaw cisco found while conducting their annual fish surveys. Additionally, documenting new occurrences of this species will be a priority of the Minnesota Biological Survey during future surveys in regions where this species is thought to exist. Surveys in the Border Lakes ecological subsection started in 2009.

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 and continuing current efforts to suppress existing exotic species populations in Lake Superior should also be a high priority.

  References

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.

Scott, W. B., and E. J. Crossman. 1973. Freshwater fishes of Canada. Fisheries Research Board of Canada Bulletin 184, Ottawa, Canada. 966 pp.

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.