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 this species. 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.
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 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 (78 in.) 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.
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 miles)) upstream to spawning grounds. Males arrive at spawning sites before females, often cruising the shallows in groups of 8 or more. Spawning begins as soon as a ripe female enters the group, and several males attend 1 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 to 3 years and typically reach sexual maturity at 8-17 years, when they are around 114 cm (44 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 42.7 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 and measured 457.2 cm (180 in.) long and weighed 181.4 kg (400 lbs.). 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 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 each year from the St. Croix River or Canada-Minnesota border waters. 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.