Cycleptus elongatus (Lesueur, 1817)
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Basis for Listing
The distribution of Blue Sucker (Cycleptus elongatus) in Minnesota includes the Mississippi River downstream of St. Anthony Falls, Minnesota River downstream of Granite Falls, and St. Croix River downstream of Taylors Falls. Historically, it occurred in the St. Croix River upstream of Taylors Falls, but has not been reported there since 1979 (Lyons et al. 2012a). The species has also been found in lower reaches of the Cannon and Zumbro rivers in southeastern Minnesota and in Wisconsin’s Chippewa River (Hatch et al. in preparation).
Historically, the Blue Sucker was common and a highly prized commercial species known locally as “Sweet Sucker”. However, in the 1930’s, the construction of the U.S. Lock and Dam system for navigation on the Upper Mississippi River drastically altered the species’ habitat from a free-flowing river into a series of reservoirs. This, in conjunction with widespread water pollution over several decades, decimated populations. Since the passage of the Clean Water Act in 1972, the Blue Sucker has exhibited a remarkable recovery. However, its abundance remains far below historical accounts, and it is generally rare throughout its range. For these reasons, the Blue Sucker was listed as a special concern species in 1984.
The Blue Sucker is unique in having many more rays in its dorsal fin than other Minnesota sucker species (28-33) as well as elongated, anterior rays (Lyons et al. 2012b). The body is blue or bluish black in color and has a small, slender head that tapers to a fleshy snout. The mouth is protractile, surrounded by a distinct groove, and the lips are thick and directed downward. The species may reach a length of more than 60 cm (23.6 in.). The largest specimen taken from Minnesota waters was 77.2 cm (30.4 in.) long, 51.3 cm (20.2 in.) in girth, and weighed 6.4 kg (14 lbs. 2 oz.) (Hatch et al. in preparation).
The Blue Sucker prefers deep, swift water in channels of large rivers with sand, gravel, or rubble bottoms. The species are often associated with wing dams on the Mississippi River and with woody snags in the St. Croix River. They are tolerant of high turbidities, if currents are swift enough to prevent siltation (J. T. Hatch, in preparation).
In Mississippi River Pools 4 and 8 from 1992-2015, 109 of 167 Blue Suckers were found along main channel borders, while 83 fish exhibited a preference for sites with wing dams. The species was also reported along side-channel borders (36), tailwater zones of dams (14), impoundments (6), and backwaters (2). Secchi disc readings (transparency) ranged from 26-137 cm (10.2-53.9 in.), depths from 0.2-19.0 m (0.7-62 ft.) (154 fish at 3.5 m (11.5 ft.) or less), and velocities from 0.0-0.85 m/s (0.0-2.8 ft./s) (LTRMP 2016).
Biology / Life History
The life history of the Blue Sucker is not fully known, and some life stages are based on assumptions derived from multiple sources. The species spawns in turbid and swift water during the spring, when water temperatures reach 10-13°C (50-55°F), which usually coincides with rising stream flows. Groups of multiple males and one or more females spawn in shoals and rapids comprised of gravel, cobble, or boulder substrate. However, in areas lacking rocky substrates, adults may migrate over 300 km (185 mi.) in search of suitable spawning habitat. Females broadcast their eggs, which are fertilized from males releasing milt. Adults provide no parental care. In Wisconsin, during normal years, spawning lasts 3-4 weeks, from mid-April to mid-May. Hatching larvae are thought to drift into backwaters and sloughs with aquatic vegetation and little or no current. Juveniles greater than 4.5 cm (1.8 in.) abandon slack-water habitats for swifter currents in riffles, side channels, and dam tailwaters (Lyons 2014).
Breeding males darken and develop small tubercles (small, hardened, breeding growths) sprinkled on the head, scales, and rays of all fins. Presumably a bottom feeder, the Blue Sucker’s diet likely includes aquatic insects, insect larvae, crustaceans, plant material, and algae. Young Blue Suckers are likely preyed on by Walleye (Stizostedion vitreum) and Small Mouth Bass (Micropterus dolomieu) as well as by fish-eating birds.
Conservation / Management
The Blue Sucker is extremely sensitive to pollution, and its presence indicates a healthy environment. The decline of the Blue Sucker in the 20th century was probably caused by siltation, pollution, physical changes in the environment (such as the partial filling of channels by floods), and dams; which slow the current, increase silting, and block migration.
Restoring Blue Suckers to historic habitats in Minnesota will require dam removal or installation of fish passage features such as ladders or lifts on the St. Croix River at Taylors Falls, the Minnesota River from Granite Falls to Big Stone Lake, and the Mississippi River at Lock and Dam 1.
Additional research needs for the Blue Sucker in Minnesota include life history studies, identification of habitat guilds, and identification of limiting factors and opportunities for fish passage around dams on the Minnesota, Mississippi, and St. Croix rivers.
Conservation Efforts in Minnesota
Fish surveys of the Minnesota, Mississippi, and St. Croix rivers have shown increasing numbers of Blue Sucker since the early 1990s. Large tracts of the Mississippi River are protected within the boundaries of the Upper Mississippi River National Wildlife and Fish Refuge, and the St. Croix River is afforded some protection by its designation as a National Scenic Riverway, as well as by three State Parks and a state Scientific and Natural Area. The recent inception of Minnesota’s Clean Water Legacy Program will eventually yield benefits to Blue Sucker habitats through nutrient and sediment load reductions.