Sturgeons

Sturgeons (primitive Acipenseriform) are an ancient group of fishes dating back to the Triassic Period some 245 to 208 million years ago. True sturgeons appear in the fossil record during the Upper Cretaceous (101 to 66 million years ago). There are about twenty-five species of sturgeons, and all belong to the Family Acipenseridae, Order Acipenseriformes. Sturgeons can be found in subtropical, temperate, and sub-Arctic rivers, lakes, and coastlines of North America, with the greatest diversity in Eurasia. In North America, there are eight species that range along the Atlantic Coast from the Gulf of Mexico to Newfoundland, as well as along the West Coast in major rivers from California and Idaho to British Columbia, Canada. The family contains four genera as follows: Acipenser (with five species in North America and eleven in Eurasia), Scaphirhynchus (three species confined to North America), Huso (two species), and Pseudoscaphirhynchus (three species), with the latter two occurring in Europe. Sturgeons are considered “primitive fishes” because their morphological characteristics have remained relatively unchanged since the earliest fossil history. This has earned them an informal status as “living fossils.” Three sturgeon species inhabit the state of Arkansas.

Sturgeons are the largest freshwater fishes, with several species growing quite large; many typically range from 2.0 to 3.5 m (7 to 12 ft.) in length. The largest on record was a beluga sturgeon (Huso huso) female collected in a Volga (central Russian) estuary in 1827 that was 7.2 m (24 ft.) and weighing upwards of 1,571 kg (3,463 lbs.). This species, occurring in the Black and Caspian seas, is also long-lived (some are more than 150 years old).

Sturgeons are late-maturing fishes (attaining sexual maturity at age twenty or more) with distinctive characteristics, such as a spiral valve, a mostly cartilaginous skeleton, and a heterocercal caudal fin (like a shark’s) that contains posterior vertebrae that have continued out into the dorsal lobe. They also have an elongated spindle-like body that is smooth and scaleless, but armored with five lateral rows of scutes (bony plates). These scutes are sharp in young fish but are worn and smooth in larger adults. Sturgeons have a protrusible mouth with fleshy lips, and adults are toothless. Its prominent snout has four barbels positioned about midway between the mouth and tip of the snout that serve as sensory organs. They navigate their riverine habitats traveling just off the bottom with their barbels dragging along gravel or murky substrate.

Sturgeons have a tolerance for wide ranges of temperature and salinity. Most species are at least partially anadromous bottom-feeders that migrate upstream to spawn in freshwater but spend most of their lives feeding in brackish water estuaries and river deltas. Some, however, spend their entire lives in freshwater environments (e.g., Lake Sturgeon), while others primarily inhabit marine environments near coastal regions and are known to take to the open ocean.

Sturgeons are primarily non-visual benthic feeders, with a diet of shells, crustaceans, and small fish. Exceptions are the white sturgeon and pallid sturgeon, and both Huso species that feed primarily on other fish as adults. Without teeth, they are unable to seize prey, though larger individuals and more predatory species can swallow very large prey items, including whole salmon. Feeding is accomplished with the use of a combination of sensors, including olfactory, tactile, and chemosensory cues detected by the four barbels, and electroreception using their ampullae of Lorenzini.

Sturgeons are a global human food fish, with several species harvested for their roe, which is eaten as caviar (salt-cured mature eggs), but also for their flesh, particularly in Eurasia. The most expensive and rarest form of caviar comes from the critically endangered beluga sturgeon. Commercial fisheries in the midwestern United States take small numbers of shovelnose sturgeons (genus Scaphirhynchus), with a limited amount of caviar being produced from their catch. The combination of slow growth and reproductive rates and the extremely high value placed on mature, egg-bearing females make sturgeon particularly vulnerable to overexploitation and other threats, including pollution and habitat fragmentation. Therefore, most species are considered to be at risk of extinction. Indeed, a 2013 study on the critically endangered sturgeon populations in the Danube River Basin reported that ongoing illegal fishing activity and the caviar trade is threatening the future of Danube sturgeons.

In general, sturgeons are broadcast spawners and do not spawn every year because they require specific conditions. A single gravid female has the ability to produce 100,000 to three million eggs, but not all will be fertilized. These fertilized eggs become sticky and will adhere to the aquatic substrate upon contact. It takes between eight and fifteen days for the embryos to mature into larvae. River currents carry the larvae downstream into backwater areas such as sloughs and oxbows, where the free-swimming fry will spend their first year feeding on larval insects and crustaceans. During their first year of growth, they will reach 18 to 20 cm (7.1 to 7.9 in.) in length and migrate back into the swift-flowing currents in the mainstem watershed.

One interesting behavior is that many sturgeons leap completely out of the water, usually making a loud splash. It is unknown why they do this, but some have suggested it functions as a method of communication to maintain group cohesion, catching airborne prey, in display of courtship, or to help shed eggs during spawning. Others have suggested that sturgeons may be escaping from predators, shedding parasites, or gulping or expelling air. Leaping sturgeons are known to occasionally cause injuries to humans in boats; a five-year-old girl died in 2015 after a sturgeon leapt from the Suwannee River in Florida and struck her.

For several reasons—including long reproductive cycles, long migrations, and sensitivity to environmental conditions—many species of sturgeons are under severe pressure. In addition, threats from overfishing, poaching, water pollution, and damming of rivers have led to their demise in some areas. As the demand for caviar increases, there has been a noticeable decline in sturgeon populations. According to the International Union for Conservation of Nature, over eighty-five percent of sturgeon species are classified as at risk of extinction, making them more critically endangered than any other group of fishes.

Three sturgeon species inhabit the state of Arkansas: the lake sturgeon (Acipenser fulvescens), pallid sturgeon (Scaphirhynchus albus), and shovelnose sturgeon (S. platorhynchus). Each plays a vital ecological role in the aquatic ecosystems of the state. Sturgeons are among the poorest-known fishes in Arkansas because of the difficulty of collecting them in their big river habitat and the apparent rarity of two of the three species in the state.

Lake Sturgeons
The lake sturgeon (A. fulvescens) is a large grayish-olive fish with a yellow-to-white belly. It is easily differentiated from the other two sturgeon species in the state by its possession of spiracles, a caudal peduncle not completely covered with scutes, a lower lip with two lobes, and an upper lobe of the caudal fin without a filament. This sturgeon is primarily a northern species and reaches the southern limit of the range in Arkansas. It is one of the rarest sturgeons in the state—ranked by NatureServe as S1 (critically imperiled)—and is approaching extinction in Missouri, Ohio, and in the middle Mississippi River drainages. In Arkansas, it is considered a “Species of Greatest Conservation Need.” To date, only six records of A. fulvescens have been reported from the state. One weighing 61.2 kg (135 lbs.) with a length of 198 cm (6 ft., 6 in.) was taken in the Little Missouri River near Chidester (Ouachita County), two specimens were collected from the Mississippi River near Mellwood (Phillips County), two from the lower White River (Desha and Prairie counties), and one from the Caddo River (Pike County). This sturgeon prefers the bottom of lakes and large rivers over a substrate of gravel, mud, and sand.

Pallid Sturgeons
The pallid sturgeon (S. albus) is rarely observed and infrequently taken with fishing tackle. It is a pale, grayish-white fish that is similar to the shovelnose sturgeon but differs in having a larger head, wider mouth, more numerous (37 or more) dorsal and (24 or more) anal rays, and no scalelike scutes on its belly; it also generally achieves a larger size. This sturgeon’s four barbels are staggered, with the two short center barbel bases positioned slightly closer to the front of the snout than those of the shovelnose sturgeon, whose barbels are about equal in length and set in a straight line. The pallid sturgeon may weigh more than 31 kg (68 lbs.). It was not formally distinguished from the S. platorhynchus until 1905. It has a restricted range to the main channels of the Missouri River and lower Mississippi River from Montana to Louisiana. Only two records are known from the state, one from the main channel of the Mississippi River (Phillips County) and one from the St. Francis River (St. Francis County). It is apparently rare throughout its entire range (ranked imperiled by NatureServe in every state) and may be threatened by channelization of the Mississippi River. This sturgeon prefers the deep and large turbid river channels, typically with strong current over gravel and firm sand. In 1990, S. albus was added to the federal endangered-species list and protected by federal law. Fishermen should be aware that possession of this fish or any of its parts is prohibited, and anyone who catches any sturgeon that cannot be positively identified should release it unharmed immediately. A 1992 recovery plan by the Missouri Department of Conservation, which first artificially spawned the species, has produced over 2,000 juvenile pallid sturgeon a year, which are stocked in the Missouri and Mississippi rivers.

Shovelnose Sturgeons
Although the shovelnose sturgeon (S. platorhynchus) is common in the Mississippi basin from western Pennsylvania to Montana and south to Louisiana, it has been extirpated in the Rio Grande River in New Mexico. However, S. platorhynchus remains common in the larger Arkansas rivers such as the Black, Mississippi, Red, and White, and is ranked S3 (vulnerable) by NatureServe. A second record of this sturgeon was collected from the Mississippi River at Sans Souci Landing near Osceola (Mississippi County). This species is the state’s smallest sturgeon, and the state rod and reel record is a 2.3 kg (5 lb) specimen caught in 2008 in the Spring River.

Adult S. platorhynchus are typically tan, and the belly is covered with bony plates (except in small juveniles). Its population in the White River near Augusta (Woodruff County) was large enough to support the establishment of a modest sturgeon roe fishery in the early 1980s; from 1980 to 1985, an average of 31,983 pounds (16 tons) of sturgeon per year was taken commercially in Arkansas. In 2010, S. platorhynchus was listed as threatened to try to protect S. albus. Since they are difficult to identify and have overlapping ranges, protecting the shovelnose sturgeon in areas where the ranges overlap will, in theory, potentially help protect the pallid sturgeon as well.

There are five other species of sturgeons in North America: the shortnose sturgeon (A. brevirostrum), green sturgeon (A. medirostris), white sturgeon (A. transmontanus), Atlantic sturgeon (A. oxyrinchus), and Alabama sturgeon (S. suttkusi). The latter species was named in honor of famous fish researcher Royal D. Suttkus, emeritus professor and curator of the Tulane Museum of Natural History in New Orleans, Louisiana.

Sturgeons, in general, harbor a great variety of parasites, including trematodes, tapeworms, nematodes, acanthocephalans, leeches, and crustaceans. Interestingly, an unusual cnidarian parasite, Polypodium hydriforme, has been found in A. fulvescens in Michigan where it infects its eggs. To date, no parasites have been reported from any Arkansas sturgeons.

For additional information:
“Arkansas Endangered, Threatened, Regulated, and Species of Greatest Conservation Need.” Little Rock: Arkansas Game & Fish Commission, 2016.

Bemis, E., K. Findeis, and L. Grande. “An Overview of Acipenseriformes.” Environmental Biology of Fishes 48 (1997): 25–71.

Binkowski, F. P., and S. I. Doroshov. North American Sturgeons: Biology and Aquaculture Potential. Dordrecht (Netherlands): Dr. W. Junk, Publishers, 1985.

Birstein, V. J., R. Hanner, and R. DeSalle. “Phylogeny of the Acipenseriformes: Cytogenic and Molecular Approaches.” Environmental Biology of Fishes 48 (1997): 127–155.

Buchanan, Thomas M., Henry W. Robison, and Ken Shirley. “New Distributional Records for Arkansas Sturgeons.” Journal of the Arkansas Academy of Science 47 (1993): 133. Online at http://scholarworks.uark.edu/jaas/vol47/iss1/34/ (accessed September 4, 2018).

Crump, Betty G., and Henry W. Robison. “Record of the Lake Sturgeon, Acipenser fulvescens Rafinesque, from the Caddo River (Ouachita River Drainage), Arkansas.” Journal of the Arkansas Academy of Science 54 (2000): 146. Online at http://scholarworks.uark.edu/cgi/viewcontent.cgi?article=1731&context=jaas (accessed September 4, 2018).

Douglas, Neil H. The Fishes of Louisiana. Baton Rouge: Claitor’s Publishing Division, 1974.

Etnier, David A., and Wayne C. Starnes. The Fishes of Tennessee. Knoxville: University of Tennessee Press, 1993.

Lee, David S., Carter R. Gilbert, C. H. Hocutt, Robert E. Jenkins, Donald W. McAllister, and Jay R. Stauffer Jr. Atlas of North American Freshwater Fishes. Raleigh: North Carolina State Museum of Natural History, 1980.

Mettee, M. F., P. E. O’Neil, and J. M. Pierson. Fishes of Alabama and the Mobile Basin. Birmingham: Oxmoor House, 1996.

Miller, Rudolph J., and Henry W. Robison. Fishes of Oklahoma. Norman: University of Oklahoma Press, 2004.

Nelson, Joseph S., Terry C. Grande, and Mark V. H. Wilson. Fishes of the World. 5th ed. New York: John Wiley and Sons, 2016.

Pflieger, William L. The Fishes of Missouri. Jefferson City: Missouri Department of Conservation, 1997.

Robison, Henry W., and Thomas M. Buchanan. Fishes of Arkansas. 2nd ed. Fayetteville: University of Arkansas Press, 2020.

Ross, Stephen T. The Inland Fishes of Mississippi. Jackson: University Press of Mississippi, 2001.

Tumlison, Renn, Chris T. McAllister, Henry W. Robison, Matthew B. Connior, D. Blake Sasse, David A. Saugey, and Stephen Chordas, III. “Vertebrate Natural History Notes from Arkansas, 2016.” Journal of the Arkansas Academy of Science 70 (2016): 248–254. Online at http://scholarworks.uark.edu/jaas/vol70/iss1/40/ (accessed September 17, 2018).

Warren, Melvin L., Jr., and Brooks M. Burr. Freshwater Fishes of North America. Vol. 1. Petromyzontidae to Catostomidae. Baltimore: Johns Hopkins University Press, 2014.

Chris T. McAllister
Eastern Oklahoma State College