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image of a shortjaw cisco

Shortjaw Cisco (Coregonus zenithicus)

Appearance As its name suggests, the shortjaw cisco has a lower jaw shorter than its upper jaw. Its elliptical body is covered in large, smooth scales. Its appearance is silver with a bluish-green back and white underbelly. A member of the trout and salmon family Salmonidae, it has an adipose fin, which is fleshy and does not contain rays. This species can weigh up to 10 ounces and grow as long as 13 inches.

Shortjaw ciscoes can be distinguished from other ciscoes by counting their gillrakers, a series of projections along the gill arch's front edge. Shortjaw ciscoes have fewer gillrakers than other species of ciscoes.

Range and Habitat Shortjaw ciscoes live in deep freshwater lakes. Up until 1970 they were reported from the Great Lakes northwest to Great Slave Lake in the Northwest Territory of Canada. Today, shortjaw ciscoes are considered extirpated in all of the Great Lakes except Lake Superior, where their populations are declining. Small populations also exist in cold, deep inland lakes within Minnesota.

Lake Superior shortjaw ciscoes move seasonally. They are typically found at depths of 360 to 375 feet in spring, 180 to 230 feet in summer, and 240 to 295 feet in winter. These changes in depth reflect the movement of their prey and also their preferred spawning depth.

Biology and Life History Shortjaw ciscoes spawn from September to late November in Lake Superior. Males and females reach sexual maturity around 5 years of age.

Shortjaw ciscoes feed on zooplankton and other crustaceans. They collect food with their gillrakers, which strain out food organisms as water passes through the gills near the back of the throat. Alternately, shortjaw ciscoes are an important food source for predators such as lake trout, salmon, and burbot.

Males can reach sexual maturity in one year, while the slower growing females take two years. Gilt darters can live up to four years, but in Minnesota most gilt darters only make it to their second year -- perhaps a consequence of living on the northern edge of their range.

Status Ciscoes have been an important part of the commercial fishery in the Great Lakes since the mid-1800s. Because commercial catches historically combined all ciscoes, the exact contribution of shortjaw ciscoes to the catch cannot be determined.

Today the shortjaw cisco is listed as a species of special concern in Minnesota waters. Threats to its survival include commercial fishing, nonnative invasive aquatic species such as spiny waterflea and smelt, and diseases such as viral hemorrhagic septicemia. In addition, global warming will affect the temperature of Lake Superior, which in turn will affect shortjaw ciscoes, their predators, and their prey.

Roland Sigurdson
DNR MinnAqua aquatic education specialist

A Closer Look at Critical Habitat

The shortjaw cisco lives in Lake Superior and lakes within the Border Lakes ecological subsection highlighted in Tomorrow's Habitat for the Wild and Rare: An Action Plan for Minnesota Wildlife. Though rare, shortjaw ciscoes have been found in Gunflint, Saganaga, Basswood, and Magnetic lakes. Other fish in the Border Lakes in greatest conservation need include the Nipigon cisco, lake chub, and deepwater sculpin. Learn more.

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