Shortjaw Cisco

Description
Habitat
Threats
Further Information
Scientific Information

Description

The Shortjaw Cisco (Coregonus zenithicus) is a widespread species in the Salmonidae subfamily, Coregoninae. It has the following characteristics:

• Often silver in colour, with olive or tan on the back and white on the stomach; however, colour variations occur across their distribution;
• Elliptically shaped body that is laterally compressed and covered with large, smooth scales;
• Mouth is small and toothless; lower jaw is usually shorter than, or even with, the upper jaw;
• Gill rakers number between 32 and 46 (comb-like structure on the inner surface of the bony arch supporting the gill), fewer than most other cisco species;
• Gill rakers are moderate or short in length, compared to other cisco species;
• In Ontario, maximum length is highly variable; ranging from 400 mm (Lake Nipigon) to less than 100 mm (White Partridge Lake);
• Weight is generally less than 300 g, although exceptionally large specimens can reach 1 kg; and
• Little is known about the growth of the species in northern and prairie lakes, with the exception of Barrow Lake, Alberta, where individuals have been reported greater than 400 mm in length.

Shortjaw Cisco, Yellowknife Bay variant

Illustration by: Paul Vescei, Golder Associates

Habitat

The Shortjaw Cisco has a widespread distribution in Canada, ranging from the Laurentian Great Lakes throughout central Canada to the Northwest Territories. In the Great Lakes, it is currently found in lakes Superior and Nipigon and has been reported in Lake Huron after not being collected since 1982. It is believed to be extirpated from lakes Michigan and Erie, and is in serious decline in lakes Superior and Huron.  In addition to the Great Lakes, Shortjaw Cisco have been reported in 10 other lakes in Ontario.  In the Prairies, Shortjaw Cisco have been reported in numerous lakes in Manitoba and Saskatchewan (Lake Athabasca, Reindeer Lake, Lake Athapapuskow, Clearwater Lake, Lake Winnipeg and George Lake) and one lake in Alberta (Barrow Lake). In the Northwest Territories, it has also been documented in Great Slave Lake and Great Bear Lake.

The map indicates the distribution of the Shortjaw Cisco in the Northwest Territories, Alberta, Saskatchewan, Manitoba and Ontario.

Most life history information has been collected from the Great Lakes, with much less understanding of history and habitat requirements from other locations. The Shortjaw Cisco generally inhabits the deep waters of large lakes, between 55 and 180 m. In Lake Superior, seasonal depth differences have been recorded including movement into shallower water during spawning. In Lake Nipigon, it inhabits depths of 10 to 60 m, and occasionally deeper. This species usually spawns in the fall, however spring spawning has also been reported. Fecundity is likely similar to other deepwater ciscoes: 3,200 to 18,800 eggs depending on fish length. Eggs are deposited on the lake bottom and left unattended to develop for three-to-four months. Females grow faster, larger and heavier, and live longer than males. Age of maturity varies widely by location, from two years (Barrow Lake), to four years (Lake Winnipeg) to  five or six years (Great Lakes). Its lifespan was previously estimated between 10 and 13 years; however, recently Shortjaw Cisco have been aged up to 25 years old in lakes Superior and Nipigon.  The Shortjaw Cisco is prey for Lake Trout (Salvelinus namaycush) and Burbot (Lota lota).

Their diet includes the Opposum Shrimp (Mysis diluviana) and the Scud (Diporeia spp.), along with copepods, cladocerans and aquatic insect larvae.

Threats

In the early 1900s, commercial overfishing in the Great Lakes had a negative impact on Shortjaw Ciscos. More recently, habitat degradation (including eutrophication), and competition with/predation from exotics, such as the Rainbow Smelt (Osmerus mordax), Alewive (Alosa pseudoharengus) and Sea Lamprey (Petromyzon marinus) have imposed additional stresses.The historical and present abundances of the Shortjaw Cisco in the Prairies and the Northwest Territories are not known. Consequently, there is no direct evidence of its decline in these areas, and defining potential threats is difficult. Nonethless, many of the same types of threats may apply. 

Further Information

For more information, visit the SARA Registry at www.SARAregistry.gc.ca.

Text Sources: Murray and Reist 2003; COSEWIC Status Report 2003; Alberta Wildlife Status report
No. 41 2002; T. Pratt, pers comm.

Scientific Information:

Scientific Name: Coregonus zenithicus
SARA Status: Threatened* (schedule 2)
COSEWIC Status: Threatened, May 2003

* Shortjaw Cisco are listed in Schedule 2, defined as species that had been designated as endangered or threatened, and have yet to be re-assessed by COSEWIC using revised criteria. Once these species have been re-assessed, they may be considered for inclusion in Schedule 1 under SARA.