Basis for Listing

Little information exists about the population status of the Least Darter (Etheostoma microperca) in Minnesota or throughout North America. As of 2008, it had been documented at a limited number of sites across the southern three-fourths of Minnesota, but most of its populations occurred in the west-central portion of the state in the Otter Tail River and Upper Mississippi River drainages. Minnesota populations represent the northwestern limit of the species' range and are disjunct from those of the Ozark and eastern Great Lakes regions (Becker 1983). In addition to being a major center of abundance for this species, the Otter Tail River supports a population that exhibits life history characteristics substantially different from those that occur near the center of the species' range (Johnson and Hatch 1991). For these reasons, the Least Darter was designated as special concern in Minnesota in 1996.

  Description

The Least Darter is the smallest vertebrate fish species native to Minnesota, averaging 3.75 cm (1.5 in.) in total length. It has no lateral line, and its body is stout and laterally compressed. Least Darters are a light, creamy color, with an olive green back, and they have 6-9 irregular blotches on their midline. Females are slightly larger than males, and breeding females have yellow fins (Eddy and Underhill 1974). Breeding males have a large, orange, pelvic fin, orange spots on the membranes between each dorsal fin spine, and tubercles (small, hardened, breeding growths) on the pelvic and anal fins.

The Least Darter is very similar in appearance to the Western Sand Darter (Ammocrypta clara), Crystal Darter (Crystallaria asprella), Bluntnose Darter (E. chlorosoma), Iowa Darter (E. exile), and Johnny Darter (E. nigrum) (Lyons et al. 2012).  Least Darters differ from similar species in having 5-6 anal fin rays and 0-7 pored, lateral scales.

  Habitat

Least Darters prefer crystal clear, freshwater streams and lakes, with cool to warm waters. They are strongly associated with waterbodies that have dense, submerged, aquatic vegetation such as eelgrass (Vallisneria americana), Canadian elodea (Elodea canadensis), and pondweed (Potamogeton spp.) in streams; and muskgrass (Chara spp.) in lakes (Becker 1983; Johnson and Hatch 1991).  In Minnesota, Least Darters are usually found in low-velocity streams that are part of a connected lake or stream system. They typically use weedy, shallow pools during the spawning season and deeper pools outside of the spawning season (Johnson and Hatch 1991).

  Biology / Life History

Least Darters migrate from the deeper pools of streams to shallow, weedy habitats from March to May. During spawning, males develop three-dimensional territories of about 30 cm (11.8 in.) in diameter and defend them from other males. Females enter a male's territory and spawn on pieces of aquatic vegetation. Females will travel through many male's territories and can lay about 30 eggs per day (Petravicz 1936). Least Darters are a short-lived species; in Minnesota, they live 2-3 years. The Least Darter's diet includes aquatic, invertebrate larvae, particularly midge larvae, and microcrustaceans (Johnson and Hatch 1991).

  Conservation / Management

Habitat loss and degradation are the greatest threats to Least Darter populations. They are vulnerable to pollution, pesticides, agricultural and urban run-off, eutrophication, and loss of habitat elements such as low-velocity waters and aquatic vegetation. Other potential threats to this species include loss of forested habitats around streams, stream reclamation, and the introduction of non-native and predatory fish species. Maintenance of high quality water systems is recommended for this species. Water systems with large populations of Least Darters should be protected from human disturbances and development.

  Conservation Efforts in Minnesota

Prior to 1990, the Least Darter was known from 31 sites in 10 streams and nine lakes scattered across the southern three-fourths of the state. Surveys from 1990-2002 added 47 sites in nine new streams and 41 new lakes, mostly in the Otter Tail River system and the Upper Mississippi River drainage. A collection from Long Lake on the border of Itasca and St. Louis counties was the first record of the Least Darter in the Lake Superior drainage (Hatch et al. 2003). DNR Surveys completed from 1997-2008 found new sites for this species (Schmidt and Proulx 2009), but also learned that at least one population had been lost in a highly developed area (i.e., Crystal Lake in Hennepin County). More thorough sampling is needed to obtain accurate population estimates. Additionally, the identification of specific environmental stressors is needed. Genetic analysis may also aid in the conservation of this rare species. Currently, there are no specific management plans for the Least Darter in Minnesota.

The recent inception of Minnesota’s Clean Water Legacy Program will eventually yield benefits to Least Darter Habitats through nutrient and sediment load reductions. Shoreline owners are encouraged to explore the DNR’s Restore your Shore web page, which offers step by step suggestions in creating buffer strips to protect their lake’s water quality and explains why maintaining both terrestrial and aquatic vegetation is vital to Least Darters and other aquatic species.

A volunteer effort of the North American Native Fishes Association successfully established the species in six Twin Cities Metro Area lakes via donor stock from Fish Lake in Le Sueur County. The Least Darter and suite of four additional sensitive species will serve as environmental indicators to reflect the success of the restoration efforts in lakes where natural colonization is no longer possible (Nelson 2013; Schmidt 2014).

  References and Additional Information

Becker, G. C. 1983. The fishes of Wisconsin. University of Wisconsin Press, Madison, Wisconsin. 1052 pp.

Eddy, S., and J. C. Underhill. 1974. Northern fishes, with special reference to the Upper Mississippi Valley. Third edition. University of Minnesota Press, Minneapolis, Minnesota. 414 pp.

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.

Johnson, J. D., and J. T. Hatch. 1991. Life history of the Least Darter Etheostoma microperca at the northwestern limits of its range. American Midland Naturalist 125:87-103.

Lyons, J., P. Hanson, E. White, J. F. Kitchell, and P. Moy. 2012. Wisconsin fish identification database [web application]. <http://wiscfish.org>. Accessed 18 May 2016.

NatureServe. 2015. NatureServe Explorer: an online encyclopedia of life [web application]. Version 7.1. NatureServe, Arlington, Virginia. <http://www.natureserve.org/explorer>. Accessed 17 May 2016.

Nelson, D. 2013. For love of minnows. Minnesota Conservation Volunteer 76(448):56-61.

Petravicz, J. J. 1936. The breeding habits of the Least Darter, Microperca punctulata Putnam. Copeia 1936(2):77-82.

Schmidt, K. P. 2014. Noah's Fish Ark. American Currents 39(1):8-12.

Schmidt, K. P., and N. Proulx. 2009. State Wildlife Grant final report; status and critical habitat of Special Concern and rare fish species in lakes within seven counties in Minnesota. 16 pp, including photos and maps. Minnesota Department of Natural Resources, Division of Ecological Resources.