Shortjaw cisco

Description

The shortjaw cisco (Coregonus zenithicus) is a North-American freshwater whitefish in the salmon family. Adult fish range to about 30 cm (12 in) in length and are silver, tinged with green above and paler below. One of the members of the broader Coregonus artedi complex of ciscoes, it is distributed widely in the deeper lakes of Canada, but populations in the Great Lakes have been declining and it is no longer present in Lakes Michigan, Huron, and Erie. It feeds mainly on crustaceans and insect larvae and spawns in the autumn on the lake bed. It is part of the important cisco (chub) fishery in the Great Lakes. The International Union for Conservation of Nature has rated its conservation status as "vulnerable". Shortjaw cisco have however evolved from the cisco Coregonus artedi independently in different lakes and different parts of the range, and conservation assessments therefore should be made on a lake-wise rather than range-wide basis. The shortjaw cisco has large, smooth scales and is iridescent silver, with a greenish back and white belly. The mouth is small and toothless, and the lower jaw is shorter than or equal in length to the upper jaw. It typically weighs approximately 300 g. 11 oz, and ranges from 150 to greater than 300 mm, 6 to 12 inches standard length. Very difficult to differentiate from other cisco species by superficial appearance, this species typically has fewer gillrakers than other ciscoes. Once common throughout the upper Laurentian Great Lakes it is no longer found in Lake Michigan and populations are much lower in Lake Huron than in the past. The population in Lake Superior is known to be lower than historically, based on commercial catch statistics. Its status in Lake Nipigon is uncertain. It has been reported in at least 22 other lakes outside of the Great Lakes, from the Canadian provinces of Ontario, Manitoba, Saskatchewan, Alberta, and the Northwest Territories. It is not known whether the remaining Great Lakes populations are increasing, decreasing or stable. Population trends in other lakes are unknown. The shortjaw cisco is most commonly found in the deeper waters of large lakes. It has been found at depths of between 55 to 114 m (180 to 374 ft) in Lakes Superior, Michigan, and Huron, and is known to exhibit seasonal changes in depth distribution in Lake Superior. Spawning occurs in the autumn. Eggs are deposited over the lake bottom in deep water and develop over three to four months, depending on water temperature.