Coregonus nipigon (Koelz, 1925)
Basis for Listing
The Nipigon Cisco (Coregonus nipigon) had been reported from three Canadian lakes: Nipigon and Black Sturgeon in Ontario and Winnipeg in Manitoba (Koelz 1929). Then, in 1964, MN DNR fish surveys of Saganaga Lake (Cook County) reported what appeared to be at least two distinct cisco forms. Additional surveys and analysis of specimens revealed the presence of three forms: Cisco (C. artedi), Nipigon Cisco, and Shortjaw Cisco (C. zenithicus). Nipigon Cisco was also collected downstream in Saganagons Lake, Ontario (Etnier and Skelton 2003). Recent fish surveys of 75 lakes have found Nipigon Cisco in the following Minnesota lakes: Basswood, Gneiss, Gull, Lac la Croix, Namakan and Red Rock as well as in Northern Light Lake, Ontario (D. Etnier, pers. comm.). Despite the recent number of new occurrences, Nipigon Cisco occupies a very small range in Minnesota (Border Lakes Subsection), Manitoba, and Ontario. Furthermore, very little is known of the species life history or potential impacts from recent invasions of exotic species such as Rainbow Smelt (Osmerus mordax) and Spiny Waterflea (Bythotrephes longimanus). These factors prompted listing the Nipigon Cisco a special concern species in Minnesota in 2013.
A high gill raker count on the first arch (range: 45-70 and usually more than 50) distinguishes Nipigon Cisco from Cisco and Shortjaw Cisco (Page and Burr 2011). Gill rakers are long and closely spaced, except for 1-2 much shorter rudiments at each end of the arch. Total gill rakers usually range from 51-64 and average 59. Pectoral, pelvic, and anal fins are black and much darker than those of Cisco and Shortjaw Cisco where they co-occur. Lateral-line scales usually range from 68-78 and average 74, versus usually 74 or fewer and average 69 or fewer in co-occurring cisco species. Nipigon Cisco is also the largest of the three species, attaining a maximum size of 47.0 cm (18.5 in.) total length (Etnier and Skelton 2003) in Minnesota.
Nipigon Cisco occurs in large deep lakes, with surface areas ranging from 7,120-13,788 ha (17,594-34,071 ac.) and depths from 34-85 m (112-279 ft.). In Saganaga Lake, the species prefers shallower eutrophic bays, rather than the deeper more oligotrophic basins (Etnier and Skelton 2003). It has also been found in small shallow lakes such as Gneiss, Gull, and Red Rock, which all have stream connections with Saganaga Lake.
Biology / Life History
Based on egg development, spawning probably occurs in late fall in Lake Saganaga, where sexual maturity is reached at about 22 cm (8.7 in.) total length for both sexes. As would be predicted for a species with such numerous long and closely spaced gill rakers, primary food based on stomach analysis of a dozen or so adults from Lake Saganaga consists of tiny (nearly microscopic) crustaceans, such as water fleas (cladocerans) and copepods.
Conservation / Management
Lakes with Minnesota populations are protected within the U. S. boundaries of the Boundary Waters Canoe Area Wilderness, Voyageurs National Park, and Ontario boundaries of Quetico and La Verendrye provincial parks. Future research needs include life history study and assessment of potential impacts from established exotic species. The Nipigon Cisco appears to have benefitted from the temporary population explosion of Rainbow Smelt as a forage base (Etnier and Skelton 2003). However, the suspected dietary and nutritional impacts on fish populations from the more recent Spiny Waterflea invasion have yet to be determined.
Conservation Efforts in Minnesota
Regularly scheduled DNR lake surveys can provide data on population structure, long-term trends, species depth preferences, and impacts of exotic species.