Acipenser fulvescens Rafinesque, 1817
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Basis for Listing
Once very common throughout the state, overfishing and pollution in Lake of the Woods and the St. Louis River estuary in the Lake Superior drainage nearly extirpated the Lake Sturgeon (Acipenser fulvescens) from Minnesota. The Lake Sturgeon is a long-lived, slow-growing, late-maturing, fish species that does not do well under heavy exploitation. Catch estimates since the early 1890s have declined 99.4%. Siltation, some agricultural practices, and dam construction also reduced habitat availability for the species, resulting in the extirpation or reduction of populations throughout its range. For these reasons, the Lake Sturgeon was listed as a special concern species in Minnesota in 1984 (Hatch et al. in preparation).
The Lake Sturgeon is a primitive fish, with a cartilaginous skeleton. It has 5 rows of large, prominent, bony plates (or scutes) on its body. A small aperture, the spiracle, is present between the eye and the upper corner of the gill cover. The region from the anus to the tail fin is thick and not entirely covered with bony plates. Lake Sturgeon have a flattened snout, with large, fleshy barbels and a protractile mouth located under the head. The lower lip has 2 slightly papillose lobes. The Lake Sturgeon is Minnesota's largest fish and can reach a total length of 2 m (6.6 ft.) and weigh over 45 kg (99 lbs.).
Lake Sturgeon prefer moderately clear, large rivers and lakes. They are most often found over firm sand, gravel, or rubble bottoms. The Lake Sturgeon is a migratory species, present in all drainages in Minnesota except the Missouri. It was recently found after a long absence in the Minnesota River, downstream of Granite Falls. Lake Sturgeon are also present in limited numbers in the Mississippi, St. Croix, Red, and Rainy rivers as well as Lake Superior, Lake of the Woods, and some lakes in the Boundary Waters Canoe Area.
In Mississippi River pools 4 and 8, fish surveys from 1994-2015 reported 57 Lake Sturgeon. The species overwhelmingly preferred tailwater zones of dams (51 fish), followed by backwaters (5), and main channel border (1). Secchi disk readings (transparency) ranged from 18-108 cm (7.1-42.5 in.), depths from 0.9-20.0 m (3-66 ft.) (52 fish captured at 3.4 m (11.2 ft.) or deeper), and velocities from 0.4-0.7 m/s (1.3-2.2 ft. /s) (LTRMP 2016).
Adult Lake Sturgeon prefer deep pools of 1.50 m (5 ft.) or greater. Spawning adults favor raceways 60-149 cm (2-5 ft.) deep and velocities of 30 cm/s (1ft/s) or greater (Aadland and Kuitunen 2006).
Biology / Life History
Found in Minnesota waterways year-round, Lake Sturgeon travel widely in loose aggregations within their range. They require extensive areas of shallow water to find food, lightly dragging their barbels along the bottom in search of prey. Their diet includes insect larvae and other invertebrates, snails, leeches, small mussels, and small fish. Spawning occurs between April and early June, and aggregations can be seen in shallow water (0.3-4.6 m (1-15 ft.)) near shorelines (Becker 1983). Lake Sturgeon are thought to return to natal areas to spawn, and individuals migrate long distances (as far as 201 km (125 mi.)) upstream to spawning grounds. Males arrive at spawning sites before females, often cruising the shallows in groups of eight or more. Spawning begins as soon as a ripe female enters the group, and several males attend one female. Fertilized eggs are adhesive and attach to gravel or rocks until hatching. Females may spawn for 5-8 hours over one or more days. Lake Sturgeon are slow-growing and late-maturing, and they only spawn intermittently. Females spawn once every 4-6 years and typically reach sexual maturity at 24-26 years old, when they are about 140 cm (55 in.) long (Becker 1983). Males spawn every 2-3 years and typically reach sexual maturity at 8-17 years, when they are around 114 cm (45 in.) long. Only 10-20% of adults within a population are sexually active and spawn during a given season (U.S. Fish and Wildlife Service 2008). The largest Lake Sturgeon specimen documented in Minnesota's official angling records was caught in the Kettle River and weighed 42.8 kg (94 lbs. 4 oz.). It measured 178 cm (70 in.) long and 67 cm (26.5 in.) in girth. The largest historical record was from 1903, weighed 181.4 kg (400 lbs.), and measured 457.2 cm (180 in.) long. The maximum life span of Lake Sturgeon is typically 55 years for males and may be more than 150 years for females.
Conservation / Management
Dam construction has restricted the migration of Lake Sturgeon, resulting in limited access to spawning grounds and destruction or degradation of available feeding and spawning grounds. Siltation, pollution, deforestation, and some agricultural practices have also contaminated aquatic habitats, reducing available habitat. Removing barriers to fish passage and re-connecting river habitats offer the greatest opportunity for restoring Lake Sturgeon populations. Efforts to reduce point and non-point pollution should also be encouraged to improve water quality and the condition of spawning grounds. Research needs for the Lake Sturgeon in Minnesota include identification of habitat guilds and spawning areas and further studies into limiting factors and opportunities for fish passage around dams.
Conservation Efforts in Minnesota
The commercial harvest of Lake Sturgeon in Minnesota was closed in the 1930s. Today, sport fishing harvest requires a special tag and is limited to one fish per year from the St. Croix River or Canada-Minnesota border waters (Rainy River and Lake of the Woods). The Minnesota DNR and various partners, including the U.S. Fish and Wildlife Service and local and tribal governments, have been working since 1990 to reintroduce or restore Lake Sturgeon populations in four Minnesota watersheds: Red River, Lake of the Woods/Rainy River, St. Louis River estuary/western Lake Superior, and St. Croix River. Lake Sturgeon are often tagged to allow an estimate of exploitation and to determine population status, movement patterns, habitat components, growth rate, and spawning chronology. Efforts are also being made to determine and protect the genetic identity of Minnesota's Lake Sturgeon populations.
The spawning success of the Rainy River Lake Sturgeon population rebounded in the 1970s as a direct result of the federal Clean Water Act (Kallok 2008). Results of a 2004 population study, which also included portions of Lake of the Woods, revealed an expanding population, with consistent recruitment over the last 30 years. Given the large proportion of immature fish, however, this population is still considered to be below recovery goals (Stewig 2005).
The Minnesota DNR began stocking Big Stone Lake with fingerlings in 2014 (LakeFinder 2016), and commercial fishermen reported catching juveniles in early 2016 (C. Domeier, DNR Fisheries, personal communication). The last time the species was reported in Big Stone Lake was 1940.
The recent inception of Minnesota’s Clean Water Legacy Program will eventually yield benefits to Lake Sturgeon habitats through nutrient and sediment load reductions.
James C. Underhill, Ph.D., University of Minnesota 1988; Konrad P. Schmidt, 2016
Aadland, L. P., and A. Kuitunen. 2006. Habitat suitability criteria for stream fishes and mussels of Minnesota. Ecological Services Division, Minnesota Department of Natural Resources Special Report 162, Fergus Falls, and St. Paul. 169 pp.
Auer, N. A., editor. 2003. A lake sturgeon rehabilitation plan for Lake Superior. Great Lakes Fishery Commission. Miscellaneous Publication. 2003-02.
Becker, G. C. 1983. The fishes of Wisconsin. University of Wisconsin Press, Madison, Wisconsin. 1052 pp.
Hatch, J. T., G. L. Phillips, and K. P. Schmidt, editors. In preparation. The fishes of Minnesota.
Kallok, M. A. 2008. Sturgeon Status. Minnesota Conservation Volunteer 71(418):13.
Knights, B. C., J. M. Vallazza, S. J. Zigler, and M. R. Dewey. 2002. Habitat and movement of Lake Sturgeon in the Upper Mississippi River System, USA. Trasactions of the American Fisheries Society 131:507-522.
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 17 May 2013.
LTRMP 2016. Mississippi River pools 4 and 8 fish survey data (1989-2015). Long Term Resource Monitoring Program, fisheries database browser [web application]. Upper Midwest Environmental Sciences Center, La Crosse, Wisconsin. <http://www.umesc.usgs.gov/data_library/fisheries/fish1_query.html>. Accessed 17 May 2016.
Minnesota Department of Natural Resources. 2002. Restoration of extirpated lake sturgeon, Acipenser fulvescens, in the Red River of the North Watershed. Section of Fisheries, Minnesota Department of Natural Resources, Bemidji, Minnesota. 10 pp.
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.
Stewig, J. D. 2005. A population assessment of the Lake Sturgeon in Lake of the Woods and the Rainy River, 2004. Division of Fisheries, Minnesota Department of Natural Resources. 38 pp.
U.S. Fish and Wildlife Service. 2008. U.S. Fish and Wildlife Service [web site]. Lake Sturgeon Biology and Population History in the Great Lakes.
U.S. Forest Service. 1999. Population viability assessment in forest plan revision. Statement of purpose and reason. Draft species data records: Acipenser fulvescens. United States Forest Service, Region 9.