Couesius plumbeus (Agassiz, 1850)
Basis for Listing
The Lake Chub (Couesius plumbeus) has the most northern distribution of any minnow in North America. A glacial relict population reported in northeastern Iowa is now presumed extirpated (Harlan and Speaker 1956). In Minnesota, the Lake Chub occurs in Lake Superior and North Shore tributary streams (North Shore Highlands Subsection). Minnesota DNR fish surveys have reported occurrences in the Hudson Bay drainage from Skull Lake in 1974 and Tofte Lake in 1973 and 1991. However, there are no extant specimens, and both lakes are managed for stream trout species (LakeFinder 2013). The distribution of the Lake Chub appears to be receding northward in Minnesota. It has not been reported from the Baptism River since 1983, Beaver River (1940), Cross River (1955), French River (1940), Gooseberry River (1940), Grand Lake (1955), Lester River (1955), Onion River (1941), Poplar River (1941) and St. Louis Bay (1992). Currently, only populations in the Brule and Pigeon river systems appear stable. These populations are isolated and morphologically distinct from the Lake Superior population (Hatch and Schmidt, in preparation). The unique inland populations and reduction in range, which may be linked to climate change, prompted listing the Lake Chub as a special concern species in Minnesota in 2013.
The Lake Chub is a large minnow, with adults ranging from 10.0-17.5 cm (3.9-6.9 in.), and can reach a maximum size of 22.5 cm (8.9 in.) total length. Distinguishing characteristics include a small and slightly subterminal mouth, inconspicuous barbels at the corners of the mouth, flanks have a faint mottling and sometimes a diffuse lateral stripe, lateral line has 60-67 scales in lateral series. Breeding adults exhibit a rosy color around mouth and gill cover and rosy spots at the base of pectoral and pelvic fins. Fine tubercles are present on head, body, and pectoral and pelvic fins. A lateral stripe may be more pronounced in males (Lyons et al. 2006). Inland stream populations in Minnesota exhibit the rosy colors throughout the year, including lower flanks (Hatch and Schmidt, in preparation).
The Lake Chub occupies a wide range of habitats and is usually a shallow water species. However, northern and higher altitude populations are more often found in streams, while southern populations prefer lakes. In Lake Superior, along Wisconsin’s South Shore, the species inhabits stream mouths and shore areas over sand with scattered boulders but has also been found in permanent and intermittent streams up to 22 km (13.7 mi.) inland (Becker 1983). In Minnesota, Lake Chubs are occasionally found in bedrock surf pools along the North Shore. However, isolated populations above barrier falls prefer headwater streams in riffles and pools with moderate gradient and substrates of gravel and cobble (Hatch and Schmidt, in preparation).
Biology / Life History
In Lake Michigan, Lake Chubs mature at age three, when both sexes average about 13.2 cm (5.2 in.) total length. They live up to five years, with females living longer and attaining a larger size than males (Stasiak 2006). In Minnesota, the species feeds mostly on small crustaceans (opossum shrimp, water fleas, copepods) and midge larvae. Large individuals even consume small fish (Anderson and Smith 1971). Spawning periods varied across the species range from April into September but were reported in Minnesota from mid-June into July. Spawning also initiates at a wide range of water temperatures, from 9-19° C (48.2-66.2° F). Both sexes congregate in deep water over boulders before moving into shallows to spawn (Hatch and Schmidt in preparation).
Conservation / Management
Maintaining habitat and good water quality within the Lake Chub's range should be a high priority. Research needs include life history and genetic studies of Lake Superior and inland stream populations. Lake Chubs may also serve as a climatic change indicator because of its northward receding distribution.
Conservation Efforts in Minnesota
The Minnesota DNR and Pollution Control Agency (PCA) stream surveys collect information on population structure and long-term trends in distribution and abundance.
References and Additional Information
Anderson, E. D., and L. L. Smith, Jr. 1971. A synoptic study of food habits of 30 fish species from western Lake Superior. Minnesota Agricultural Experiment Station Technical Bulletin 279, University of Minnesota, St. Paul. 199pp.
Becker, G. C. 1983. The fishes of Wisconsin. University of Wisconsin Press, Madison, Wisconsin. 1052 pp.
Harlan, F. R., and E. B. Speaker. 1956. Iowa fish and fishing. Iowa Department of Natural Resources. 377 pp.
Hatch, J. T., and K. P. Schmidt. Lake Chub Couesius plumbeus (Agassiz, 1850). In J. T. Hatch, G. P. Phillips, K. P. Schmidt, M. C. McInerny, and J. C. Underhill, editors. The Fishes of Minnesota (in preparation).
Hatch, J. T., K. P. Schmidt, D. P. Siems, J. C. Underhill, R. A. Bellig, and R. A. Baker. 2003. A new distributional checklist of Minnesota fishes, with comments on historical occurrence. Journal of the Minnesota Academy of Science 67:1-17.
LakeFinder. 2013. Lake survey database [web application]. Division of Ecological and Water Resources, Minnesota Department of Natural Resources, St. Paul, MN. <http://www.dnr.state.mn.us/lakefind/indes.html>. Accessed 10 April 2013.
Lyons, J., P. C. Hanson, E. A. White. 2006. A photo-based computer system for identifying Wisconsin fishes. Fisheries 31(6):269-275.
NatureServe. 2009. NatureServe Explorer: an online encyclopedia of life [web application]. Version 7.1. NatureServe, Arlington Virginia. <http://www.natureserve.org/explorer>. Accessed 29 May 2009.
NatureServe. 2013. NatureServe Explorer: an online encyclopedia of life [web application]. Version 7.1. NatureServe, Arlington Virginia. <http://www.natureserve.org/explorer>. Accessed 09 April 2013.
Stasiak, R. H. 2006. Lake Chub (Couesius plumbeus): a technical conservation assessment. USDA Forest Service, Rocky Mountain Region, Lakewood, Colorado.
Underhill, J. C. 1989. The distribution of Minnesota fishes and late Pleistocene glaciation. Journal of the Minnesota Academy of Science 55:32-37.