Picture by Chad Thomas, Texas State University-San Marcos

Scaphirhynchus platorynchus

shovelnose sturgeon

Type Locality

“Ohio, Wabash, and Cumberland rivers, seldom reaching as high as Pittsburg; also in Mississippi and Missouri rivers” (Rafinesque 1820); no specific locality designated (Lee 1980).

Etymology/Derivation of Scientific Name

Scaphi – a shovel, rhynchus – snout; platy – broad, rhynchus – snout (Scharpf 2005).

Synonymy

Acipenser platorynchus Rafinesque 1820:80.

Scaphirhynchus platorunchus (Rafinesque) Cope and Yarrow 1875:639.

Scaphirhynchus platorhynchus

See Bailey and Cross (1954) for detailed synonymy.

Characters

Maximum size: 1,080 mm (42.5 in) TL (Page and Burr 1991).

Coloration: Light brown above and on sides, white underside; fins similar in color to surrounding body parts (Page and Burr 1991; Plieger 1975).

Counts: 30-36 dorsal soft fin rays; 18-23 anal soft fin rays (Pfliger 1975; Page and Burr 1991).

Mouth position: Subterminal (Goldstein and Simon 1999).

Body shape: Flat, shovel-shaped snout, long, slender caudal peduncle flat in cross section and covered with bony scutes (Plieger 1975; Page and Burr 1991).

Morphology: Four fleshy lobes on lower lip; four fringed barbels; long filament on upper lobe of caudal fin (sometimes broken off); no spiracle (small opening above and slightly behind eye); scalelike scutes on belly (except in smallest young); bases of outer barbels in line with, or ahead of inner barbels (Pflieger 1975; Page and Burr 1991). Observations of swimming ability in shovelnose sturgeon indicated that the streamlined body shape, flat rostrum, and large pectoral fins allows it to exploit river bottoms as refugia from current and to maintain position in high velocities (Adams et al. 1997); species is well adapted for maintaining its position in fast flowing water on river bottoms (Weisel 1978, 1979).  Intersex (having both male and female gonads) individuals reported (Harshbarger et al. 2000; Stahl 2008).

Distribution (Native and Introduced)

U.S. distribution: Once occurred throughout most of the Mississippi and Missouri river drainages; two specimens were obtained from the Rio Grande in Albuquerque, New Mexico during 1872-1874 fish surveys (Cope and Yarrow 1875; Bailey and Cross 1954; Nelson et al. 2004; Hubbs et al. 2008).

Texas distribution: Found only in the Red River below Dennison Dam (Lake Texoma Reservoir; Hubbs et al. 2008); Red River system (Bonn and Kemp 1952). Evidence of the presence of this species in the lower Pecos River, during prehistoric times, strongly suggests that it likely occurred in many Texas rivers (Jurgens 2005; Hubbs et al. 2008).

Abundance/Conservation status (Federal, State, Non-governmental organizations)

State Threatened (Texas; Hubbs et al. 2008). Apparently secure (Scharpf 2005); however, status is Endangered in Mexico and Ohio; Special Concern status in Oklahoma; and extirpated in Alabama, New Mexico, Pennsylvania, and West Virginia. Special Concern status in Mississippi (Ross 2001). Currently Stable in the southern United States (Warren et al. 2000). According to Morrow et al. (1998), the species was apparently abundant at the two lower Mississippi (Mississippi) locations sampled. Keenlyne (1997) reported that  shovelnose sturgeon were classified as a sport fish in 12 of the 24 states in which it occurred and as a commercial species in 7; the species was considered extirpated in 3 states, was fully protected in 4 states, and was considered rare, threatened, or of special concern in 8 states; some states had dual classifications for shovelnose sturgeon and some classified the species differently in various waters. According to Keenlyne (1997), populations throughout most of the upper Mississippi, lower Missouri, Red, and Atchafalaya rivers were considered stable; further, Wyoming, West Virginia, and New Mexico had developed plans to reintroduce the species into areas were it had been extirpated. Page and Burr (1991) reported this species as common in the Mississippi basin, rare in the Mobile Bay drainage, and extirpated in the Rio Grande.

Habitat Associations

Macrohabitat: Bottom of main channels and embayments of large, turbid rivers (Bailey and Cross 1954; Pflieger 1975; Page and Burr 1991; Keenlyne 1997). According to Riggs and Bonn (1959), this species was unknown in Lake Texoma, but occasionally seen or caught in the tailwaters.

Mesohabitat: Frequently inhabits flowing water over sandy bottoms or near rocky points or bars (Bailey and Cross 1954; Pflieger 1975; Page and Burr 1991; Keenlyne 1997). In Pool 13 of the upper Mississippi River, shovelnose sturgeon were frequently located at water depths of 2-7 m (6.5-23 ft), where currents were .2-.4 m/s (.65-1.3 ft/s) at the bottom and .4-.7 m/s (1.3-2.3) at the surface (Hurley et al. 1987); during spring high-river stages, fish were most frequently located downstream from both wing dams and closing dams, and at the border of the main channel within 50 m (55 yd) of shore; during low river stages in summer, they were found usually found close to or in the main channel or in upstream side of wing dams and closing dams. During extreme low flow conditions in Pool 13 of the upper Mississippi River (Iowa-Illinois), species was often found in the main channel and tailwaters (during the spring) where water velocities were highest; this was in contrast to other studies which indicated this species did not occupy those areas during years with normal spring flow (Curtis et al. 1997). Quist et al. (1999) studied overwinter habitat use in the Kansas River (at water temperatures of 2-9°C, 35.6°F-48.2°F): 80% of S. platorynchus locations were in water depths of 1-2 m (3.3-6.5 ft), where current velocities were 0.01-1.11 m/s at the surface and 0.02-0.79 m/s at the bottom; 92% of shovelnose sturgeon locations were over sand substrate; during high discharge (>150 m³/s), fish appeared to move near shore or downstream of instream cover; movement (km/d) and directional movement (i.e. upstream or downstream) were unrelated to discharge or water temperature; data indicated that the species utilizes channel-crossover macrohabitats and areas with bottom velocities of 0.02-0.79 m/s regardless of discharge; fish apparently do not congregate in deep waters at water temperatures less than 9°C (48.2°F). Allen et al. (2007) investigated the influence of substrate type, water depth, light, and relative water velocity on microhabitat selection in juvenile shovelnose sturgeon in an artificial stream system and reported an overall selection for sandy, deep, or heavily shaded habitats. Larval fish drift in the water column for up to 12 days after hatching before settling out of the water column to begin the benthic phase of life (Kynard et al. 2002; Braaten et al. 2007).

Biology

Spawning season: Occurs in spring at temperatures between 17-21°C (62.6-70.0°F)(Keenlyne 1997); occurs April to early July (Lee 1980); spawning in May (Pflieger 1975). Stahl (2008) provided evidence indicating that a fall spawning may occur in the middle Mississippi River, Illinois.

Spawning habitat: In channels of large rivers in a strong current over rocky or gravelly bottoms (Pflieger 1975; Lee 1980). Over rock or gravel substrate downstream from dams, near rock structures, or in tributaries (Keenlyne 1997).

Spawning behavior: Nonguarders; Open substratum spawner; lithopelagophil – rock and gravel spawner with pelagic free embryos (Simon 1999). Adults do not spawn every year; frequency of spawning influenced by food supply and ability to store adequate fat to produce gametes (Keenlyne 1997).

Fecundity: Gravid females from the middle Mississippi River, Illinois, had a mean oocyte diameter of 2.58 mm; mean fecundity estimate of 20,277 ± 7,570 (Stahl 2008). Kennedy et al. (2006) examined females (49 specimens, measuring from 601-858 mm, 23.6-33.8 in, fork length) from the upper Wabash River, Indiana: relative fecundity ranged from 11,220- 23,956 eggs kgˉ¹ (mean 18,156 eggs kgˉ¹); absolute fecundity ranged from 14,294-65,490 eggs femaleˉ¹ (mean 30,397 eggs femaleˉ¹) and was positively related to fork length (r² = 0.76) and wet weight (r² = 0.82); number of eggs gˉ¹ of ovary weight ranged from 72-170 (mean = 98 eggs gˉ¹) and was negatively correlated with gonadosomatic index (GSI); GSI values ranged from 9.4-27.2 (mean = 19.3) and were positively correlated to fork length (r² = 0.18). Stahl (2008) reported that mean fecundity estimates for gravid females in populations from Missouri, Illinois, and Indiana ranged from 18,000-30,000 or 15-22 oocytes per gram of fish with positive relationships with fork length and/or weight. In South Dakota, Zweiacker (1967) reported mean total egg count per spawning female 9,210 (range 6,709-15,637); mean egg diameter was 2.45 mm.

Age/size at maturation: In the middle Mississippi River, Illinois, age at maturation was 10 years for males and 9 years for females (Stahl 2008). Females from the upper Wabash River, Indiana, reached sexual maturity at approximately 600 mm (23.6 in) and age-at-maturity ranged from ages 6-12 (median age = 9; Kennedy et al. 2006). Males in the Mississippi River reached maturity at a length ranging from 495-559 mm (19.4-22.0 in) SL; smallest adult female collected was 635 mm (25 in) in length (Barnickol and Starrett 1951). Individuals mature and spawn at 5-7 years of age (Pflieger 1975; Lee 1980); most males at 5 years, and most females at 7 years (Keenlyne 1997). In areas where food is not abundant, males and females may become sexually mature at a smaller size (Keenlyne 1997). Zweiacker (1967) reported that fish in South Dakota ranged from 5-13 years old at first spawning attempt.

Migration: Pflieger (1997) noted that this species does not have a restrictive home range: a specimen tagged in 1978 in the Missouri River near Easley, Boone Co., Missouri, was captured 13 years later, 560 miles upstream in Nebraska; while another specimen tagged in 1978, in the Mississippi River at the mouth of the Ohio River was caught in 1985 in the Wasbash River near Vienciennes, Indiana. Although the species is capable of rapid, long-distance movements, it is found to be generally sedentary (Hurley et al. 1987), with greatest movement rates in the upper Mississippi River occurring in May, probably during the spawning period (based on capture of young-of-year specimens in mid-June). In the Missouri River, greatest movement occurred during the spawning season and lower rates of movement took place in early spring and summer (Moos 1978; Hurley et al. 1987).

Growth and Population structure: Two-hundred specimens captured from the lower Mississippi River near Rosedale and Vicksburg, Mississippi, ranged in age from 2-16 years; mean fork lengths at capture ranged from 338 mm (13.3 in) at age 2 to 707 mm (27.8 in) at age 16; annual mortality was 20% for ages 7 and greater (Morrow et al. 1998). Individuals from the upper Mississippi River reported to average 211 mm (8.3 in) fork length when one year old, and averaged 315 mm (12.4 in), 409 mm (16.1 in), 485 mm (19.1 in), 541 mm (21.3 in), and 599 mm (23.6 in) in years 2-6, respectively (Pflieger 1997). Carlander (1969) summarized growth data from Missouri River specimens collected as reservoirs were filling: 213 mm (8.3 in) TL at age 1, 274 mm (10.7 in) TL at age 2, 399 mm (15.7 in) at age 5, and 503 mm (19.8 in) at age 10 (Keenlyne 1997). 4,849 specimens were captured in the upper Wabash River, Indiana: ages ranged from 2-30, with 95% of fish between ages 9-20; fork length of captured fish ranged from 273-858 mm, 10.7-33.8 in (median 683 mm, 26.9 in), but few fish less than 550 mm (21.6 in) were captured; wet weight of fish ranged from 52-3,381 g (median 1,208 g; Kennedy et al. 2007).

Longevity: 30 years (Kennedy et al. 2007).

Food habits: Goldstein and Simon (1999) listed first and second level trophic classifications as invertivore and benthic, respectively; trophic mode – hunter; feeding behavior – feeds by raking bottom with sensitive barbels. Bulk of diet made up of aquatic insect larvae (Lee 1980). In the Missouri River (South Dakota), annual diet was dominated by aquatic arthropods, particularly larvae of the insect orders Trichoptera, Diptera, and Ephemeroptera; in the fall, fish extensively utilized organisms drifting in the water column; in the winter, feeding behavior was characterized by exploitation of a greater diversity of aquatic and terrestrial invertebrates; and during the late spring and summer, feeding was restricted to benthic foraging (Modde and Schmulbach 1977). In the Missouri River, aquatic insect larvae were found to be the most important, while crustaceans were second (ranked by number, volume and frequency of occurrence), and terrestrial insects were the third most abundant food item volumetrically (Held 1969). Diet items of specimens from the Mississippi River, Iowa: 68% Potamyia flava larvae, 7% Cheumatopsyche campyla larvae, 17% Hexagenia naiads; and 8% other material, which included immature plecopterans, dipterans and odonates (Hoopes 1960). Braaten and Fuller (2007) studied diet composition of larval and young-of-year fish in the upper Missouri River, and reported that fish began exogenous feeding by 16 mm (.62 in), and individuals 16-140 mm (.62-5.5 in) fed exclusively on Diptera and Ephemeroptera.

Phylogeny and morphologically similar fishes

Colombo et al. (2007) described embryological development.

Host Records

shovelnose sturgeon are a host for the parasitic larvae of the hickory-nut mussel (Coker 1930); also, a host for glochidia of Lampsilis teres, Quadrula pustulosa, and Obovaria olivaria (Becker 1983; Keenlyne 1997). Myxidium sp. confirmed in bile ducts of one specimen from the Mississippi River, south of Saint Louis, Missouri, and a helminth parasite was seen in the liver of another (Harshbarger et al. 2000).

Commercial or Environmental Importance

Damming of many rivers within the range of shovelnose sturgeon has resulted in flow alteration and habitat fragmentation which negatively impacts the long-term health of the species, specifically by affecting replacement, reproduction, and gene flow (Keenlyne 1997). Furthermore, due primarily to dam construction (Bailey and Cross 1954; Held 1969), the combination of a reduction in current and the covering of a firm bottom with a heavy layer of flocculent silt occurring behind dams has resulted in a marked decline of this species. Dams are also thought to block spawning migrations (Bailey and Cross 1954).

Shovelnose sturgeon are harvested for meat and roe (Coker 1930; Keenlyne 1997). Keenlyne (1997) reported that commercial harvest of this species was allowable in 7 states, and about 22,680 Kg (50,000 lbs) was harvested annually. In Missouri, this species is the only sturgeon that remains commercially important, with demand often exceeding the supply; market values for this species are among the highest of all commercial species; they are also frequently taken by sport fisherman using trot lines baited with worms or minnows and positioned in drop-off areas near the lower end of sand bars (Pflieger 1997).

Hybridization between shovelnose sturgeon and pallid sturgeon is a concern among sturgeon fishery managers; possible introgression of genes from the more common shovelnose sturgeon is viewed as a threat to the rarer pallid sturgeon (Keenlyne 1997).

References

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Allen, T.C., Q.E. Phelps, R.D. Davinroy, and D.M. Lamm. 2007. A laboratory examination of substrate, water depth, and light use at two water velocity levels by individual juvenile pallid (Scaphirynchus albus) and shovelnose (Scaphirynchus platorynchus) sturgeon. J. Appl. Ichthyol. 23:375-381.

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