Pallid sturgeon

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Pallid sturgeon
Conservation status
Endangered (IUCN 3.1)
Scientific classification
Kingdom: Animalia Phylum: Chordata Class: Actinopterygii Order: Acipenseriformes Family: Acipenseridae Subfamily: Scaphirhynchinae Genus: Scaphirhynchus Species: S. albus
Binomial name
Scaphirhynchus albus Forbes and Richardson, 1905

The Pallid sturgeon (Scaphirhynchus albus) is an endangered species of fish that exists in the waters of the Mississippi and Missouri River basins in the United States. In 1990, the U.S. Fish and Wildlife Service placed the pallid sturgeon on the endangered species list, because very few young pallids were being found and all sightings of the fish had greatly lessened in the preceding decade.^[1] The pallid was the first fish species in the Mississippi River drainage that was listed as endangered. Current populations of the fish are small, and the fish is now rarely seen in the wild.

The pallid sturgeon is closely related to the relatively common Shovelnose sturgeon (Scaphirhyncus platorhynchus), however the pallid is much larger. Evolving during the Cretaceous period 70 million years ago, the pallid is one of the largest fish found in the Mississippi River drainage. The pallid is a relic of the dinosaur era and has been called the ugliest fish in North America.^[2]

The pallid sturgeon is believed to have become endangered due to a loss of habitat. The vast majority of the Mississippi River drainage system has been channeled and dammed, reducing gravel deposits and slow moving side channels that are favored spawning areas. The fish was relatively common until the middle of the 20th Century, and anglers found the prize of landing such a large fish in fresh water a rewarding experience. The pallid is also considered to be an excellent tasting fish, and like many sturgeon, the eggs have been used as caviar, though this is uncommon with this species.^[3]

Efforts to restore the species have yet to yield positive results. Capturing a young pallid has become a rare event since the 1980s. With the major alterations to natural spawning areas that have occurred throughout their native habitat, restoration of spawning areas throughout the Mississippi River drainage basin will be mandatory if the species is to be expected to survive in the wild. Active efforts using fish hatcheries for spawning may help to ensure the species continues to exist, but this existence is heavily dependent on human assistance. In at least one situation, researchers have implanted sonic transmitters in sturgeons, making it easier to track their movements and help identify possible spawning areas.

Contents 1 Taxonomy and Etymology 2 Biology 2.1 Physical characteristics 2.2 Reproduction and life cycle 3 Ecology 3.1 Distribution, habitat and food preferences 3.2 Conservation efforts 4 Habitat destruction 5 Recent research on the pallid sturgeon 6 Management Practices on the Pallid Sturgeon 7 References 8 External links

[edit] Taxonomy and Etymology

The pallid sturgeon's closest relatives are the shovelnose sturgeon (Scaphirhyncus platorhynchus), which is still relatively common, and the critically endangered Alabama sturgeon (Scaphirhynchus suttkusi), which may now be extinct.^[4] Taxonomists S. A. Forbes and R.E. Richardson classified the pallid sturgeon in 1905, and along with the shovelnose, grouped them in the Scaphirhynchus genus and the Acipenseridae family, which includes all sturgeon worldwide. Pallid and shovelnose sturgeon can produce hybrid offspring, however DNA sequencing has determined that all three species of sturgeon in the Scaphirhynchus genus are distinct.^[5] Since the 1970s, the rates of hybridization between the pallid and shovelnose have increased and this is attributed to changes in the Mississippi and Missouri Rivers, forcing pallids into areas where they have a greater liklihood of encountering shovelnose.

The word pallid means "deficient in color",^[6] and compared to other species of sturgeon, the pallid is noticeably less colorful in appearance.^[7] Pallid sturgeon are some of the most primitive and ancient fish species, having originated during the Jurassic Period 200 million years ago.^[8] The pallid is a relic of the dinosaur era and has remained virtually unchanged over the past 70 million years. The scientific name for the fish is derived from Scaphirhynchus, a Greek word meaning "spade snout" and albus is Latin for the color white.^[9]

[edit] Biology

[edit] Physical characteristics

Pallid sturgeon are generally between 30 and 60 inches (76 to 152 cm) in length and weigh as much as 85 pounds (39 kg).^[10] Though similar in appearance, the shovelnose sturgeon is much smaller and usually weighs no more than 5 pounds (2.25 kg). Pallids are also much paler in coloration than shovelnose and have greyish white backs and sides while shovelnose are brown.^[3] Pallids turn whiter as they age and younger specimens are easily confused with adult shovelnose since they are similar in color.^[11] Pallids have a shark-like appearance and are distantly related to sharks. Like sharks, pallids do not have scales or bones as are found in more modern species of fish. Instead, pallids have cartilaginous skeletons and 5 rows of thick cartilage plates that extend along their sides, undersides and backs, as well as most of the head. These thick cartilage plates are covered by the skin and serve as a protective armor.^[12] The bony cartilage also extends along the backside of the pallid, from the dorsal fin to the tail.^[9] The tail of the pallid is much longer on the top than on the bottom.^[12]

The pallid snout and head are longer than that of the shovelnose sturgeon.^[11] Pallids have no teeth and instead use their extendable mouths to suck small fish, mollusks and other food sources from the bottom of rivers. The mouth is located well back from the tip of the snout. Like the shovelnose, pallids also have four barbels which descend from the snout near the front of the mouth. The barbels are believed to be sensory features to locate food sources.^[12] On pallids, the two inner barbels are only about half as long as the outer ones, while on the shovelnose, all four barbels are the same length.^[3] The inner barbels of the pallid are also positioned ahead of the outer ones, whereby those on the shovelnose are all located in essentially a straight line. Examining the characteristics of barbels is one of the best ways to identify the differences between the pallid and the shovelnose.^[11]

[edit] Reproduction and life cycle

Pallid sturgeon have very long lifespans but it is unclear exactly how long they live. A lack of bones and scales has made exact age determination difficult in those fish that have been researched.^[13] It is generally believed that pallids live in excess of 50 years.^[14][15] As is true for many long lived species, pallids take many years before they reach reproductive maturity.^[16] Male pallids reach sexual maturity between the ages of 5 and 7 years, while females are believed to not become capable of reproduction until they are at least they 15 years old. Research on 5 male and 9 female pallids in one study indicated that female pallids can begin egg development between the ages of 9 and 12 years, but do not reach reproductive maturity until 15.^[17]

Pallid spawning areas have been greatly disturbed from dam construction and river rechannelization projects. Pallids apparently prefer rocky or hard surfaces for spawning in swift currents. Pallids spawn between the months of June and August and can produce hundreds of thousands of eggs when spawning.^[18] One female pallid that was caught in the upper Missouri River was estimated to be carrying 170,000 eggs, representing over 11% of it's total body weight.^[19] Reproduction is not known to occur every year and research indicates that pallids spawn every third year at a minimum. After fertilization, pallid eggs hatch in 5 to 8 days.^[3]For several decades, no known natual reproduction of pallids had been observed, since all the pallids that had been captured were older specimens. However, in the late 1990s, young pallids were discovered living in a restored riparian area of the lower Missouri River. This was the first documented example of wild spawned pallids in 50 years.^[15] In 2007, two female pallids were reported to have apparently spawned in the Missouri National Recreational River area located downstream from Gavins Point Dam on the Missouri River.^[20]

After pallids hatch, their larval tend to drift downstream and settle into deeper water after a couple of weeks, depending on local water velocities. The rates of survival to maturity for pallids is extremely low and of the hundreds of thousands of eggs spawned, only a small handful live to adulthood.^[15]

[edit] Ecology

[edit] Distribution, habitat and food preferences

The pallid sturgeon's historical range spanned the entire Missouri and into the Mississippi Rivers. The species was historically rare to nonexistent in the upper Mississippi, probably due to a lack of proper habitat. As of 2008, pallids can still be found throughout their original range, but their population numbers have been severely reduced from what they were in the mid 20th century. The Missouri and Mississippi Rivers from Montana to Louisiana as well as the Atchafalaya River in Louisiana continue to have an aging population of pallids.^[16] Pallids have never been very common, and even as early as 1905 when the species was first identified, they represented only 1 in 5 of all sturgeon in the lower Missouri River and as few as 1 in 500 where the Illinois River meets the Mississippi.^[21] Between 1985 and 2000, the ratio of pallids to all sturgeon netted declined from 1 in about 400 to 1 in nearly 650. A 1996 study concluded that between 6,000 and 21,000 pallids were believed to exist in their natural habitat at that time.^[22]

Pallids prefer moderate to swift river currents and most captured specimens have been recovered in rivers and streams in which the current averages between 0.33 to 2.9 feet (10 and 90 centimeters) per second. They also prefer turbid waterways and in water depths between 1 and 8 meters (3 to 25 ft). The species is more commonly found where sandy substrates are common but can also be found in waterways that are predominately rocky. Pallids tend to prefer swift river currents more often than do shovelnose sturgeon.^[16] In a Montana and North Dakota based study conducted on both the pallid and shovelnose sturgeon, both species were fitted with radio transmitters. Pallids were found to prefer wider river channels, mid channel sandbars and numerous islands. Pallids were most commonly recorded in water depths between 2 and 47 feet (.6 and 14.5 m).^[23] The study also showed that both species moved up as much as 9.3 miles (15 km) a day and that they were both less active in the fall and winter.^[23]

Pallids are generally bottom feeders, skimming the sandy reaches of the various rivers and streams in their habitat. Though little is known about the precise eating habits of the species, they are believed to be opportunistic feeders.^[16] One study which examined the contents from the stomachs of juvenile pallids reveiled that their diets were seasonally dependent. Various insects were consumed during some seasons and other fish species during others. The results indicated that pallids are opportunistic in their eating habits.^[24]

[edit] Conservation efforts

Though never believed to be common, pallid sturgeon populations nosedived during the late 20th century and the species was listed as endangered on September 6, 1990.^[3]

The Pallid Sturgeon’s population has declined due to habitat loss and man’s alteration of the larger river systems. Damming, channelizing, and diking have destroyed much of the natural function of the river. This has destroyed the spanning beds, reduces the amount of woody debris, organic material, and inorganic sediments. This is disrupting flow and temperature regimes and also lowering the turbidity which is preferred by the Pallid Sturgeon. (http://fwp.mt.gov/wildthings/tande/pallid.html)

The Pallid Sturgeon was enlisted on the endangered species list in 1990. There has been some spawning documented with a few Pallid Sturgeon fry, but no recruitment has been documented in the last 30 years. The current population of the two Pallid Sturgeon populations are anywhere from 30 to 200. With one of the populations being in Missouri River above Fort Peck Reservoir and in the Missouri River and lower Yellowstone River below Fort Peck Dam. With many of these fish being old it is projected that the wild population of Pallid Sturgeon will be extinct by 2018. (http://fwp.mt.gov/wildthings/tande/pallid.html)

[edit] Habitat destruction

Habitat destruction for the pallid sturgeon is the leading cause in the decline in the population. Some of the problems are the channelizing of the river, damning of the rivers, reducing the gravel deposits, the decline of slow moving side channels that favored spawning. Another cause of the decline is the caviar industry, which pallid sturgeon eggs are considered to be a delicacy. The channelizing of the river is due to the increase in the use of the Missouri and Mississippi rivers as industrial tools. The uses of the river for barges and other boats that have traveled the river have had an impact on the pallid sturgeon’s habitat. The damning of the river for hydroelectric power has also caused destruction to the pallid sturgeon’s habitat. The damning of the river prevents the pallid sturgeon from migrating up or down the river. (Status of the Pallid Sturgeon, L. Kallemeyn)

The reducing of the gravel deposits of the river have also caused a decline in the population because according to the study by Bramblett and White it is known that the pallid sturgeon use gravel deposits for spawning as well as areas to hang out. The channelizing of the rivers has led to the loss of the slow moving side channels that sturgeon need for spawning. The removing of these side channels not only have an effect of the pallid sturgeon but is also messing with the rivers natural made flood plain. With out these side channels not only does the pallid sturgeon suffer but when the river floods there is no place for the water to go except into surrounding areas which are mostly agricultural land. (Status of the Pallid Sturgeon, L. Kallemeyn)

[edit] Recent research on the pallid sturgeon

As from the readings from up above there has been many different studies that have been conducted on the pallid sturgeon to determine their movements, preferred habitat, sexual maturity as well as other studies. In one of the studies that was compiled to see what kind of habitat pallid sturgeon preferred; they attached Global Positioning System transmitters to the pallid sturgeon. After they let the sturgeon go back to their normal life. Then they tracked then using telemetry to see what habitat the pallid sturgeon preferred. After the pallid sturgeon was pin pointed by the telemetry then they recorded their exact coordinates and also the habitat present. (Habitat Use and Movements of Pallid and Shovelnose Sturgeon in the Yellowstone and Missouri Rivers in Montana and North Dakota, R. Bramblett and R. White)

In the other study that was done by K.D. Keenlyne and L.G. Jenkins they captured fourteen pallid sturgeons and then froze them. After they thawed they were then weighed and measured. Then their reproductive tracts were removed and weighed to the nearest gram to determine the stage development and maturity determined. After that they then take the leading ray of the right pectoral fin and sectioned with a low-speed diamond saw and examined to determine the age of the fish and to also locate spawning bands. Spawning bands are created when energy is diverted into gonadal development, causing annuli to be more closely spaced; after spawning energy is redirected to growth. A gonadosomatic index or gsi was calculated for each of the five males and eight females by dividing the weight of reproductive material by the total body weight. One of the other females was examined and aged, but the GSI could not be calculated because its gonads had been removed and were not available for analysis. (Age at Sexual Maturity of the Pallid Sturgeon, K.D. Keenlyne, L.G. Jenkins)

In other studies that are conducted by state agencies most of the research that is done is by tagging the fish. After the fish are tagged they are then released. When an angler lands the fish they are suppose to call the number on the tag. The state agency will then mark the spot that the fish was caught at and this can tell you how far the fish had migrated as well. State agencies will use the gps transmitter method also. With the decline in the pallid sturgeon population the more research and studies are being implemented to help and determine what we can do to keep the population steady and hopefully increase it.

[edit] Management Practices on the Pallid Sturgeon

There are a few management practices that are being performed to help save the pallid sturgeon. One of them is the releasing of hatchery raised yearlings into the Missouri River just below the Fort Randall Dam. The fish were followed extensively to see what their daily movement and diet was. The following of the fish also led to see what the survival rate of the fish was. This showed that at least 68% of the fish tagged survived the first two and a half years. The study also indicates that range of movements of the juvenile pallid sturgeon based on shorter studies should be interpreted cautiously because the hatchery reared fish may not have acclimated to the riverine environment until the second year of stocking. Based on survival and distribution of juvenile pallid sturgeon throughout the study area, they concluded that this research is suitable for recovery efforts. This is one management practice that could help the population of the pallid sturgeon. If hatchery fish can survive in the wild then this may be an important step into increasing the population of pallid sturgeon. (Poststocking Movements and Habitat Use of Hatchery-Reared Juvenile Pallid Sturgeon in the Missouri River below Fort Randall Dam, South Dakota and Nebraska, G.R Jordan, R.A. Klumb, G.A. Wanner, W.J Stancill)

Some states are installing structures along the sides of the major rivers that help to divert the stronger currents towards the middle of the river. This helps to create spawning areas for the pallid sturgeon along the edge of the rivers. States have also built side channels for pallid sturgeon to spawn in. States have also implemented structures in the river that help to reestablish their habitat.

[edit] References

• http://fwp.mt.gov/wildthings/tande/pallid.html, Montana Fish, Wildlife & Parks.

• Mississippi Interstate Cooperative Resource Association. Pallid Sturgeon, Scaphirhynchus albus. Retrieved on 2006-05-05.
• Hinton, Richard. "Nine endangered pallid sturgeon captured", The Bismarck Tribune, May 5, 2006. 

[edit] External links

Bramblett, R G., R G. White. 2001. Habitat Use and Movements of Pallid and Shovelnose Sturgeon in the Yellowstone and Missouri Rivers in Montana and North Dakota. American Fisheries Society 130 (6) 1006-1025.

Keenlyne, K. D., L. G. Jenkins. 1993. Age at Sexual Maturity of the Pallid Sturgeon. Amercian Fisheries Society 122 (3) 393-396.

Snook, VA., Peters., EJ, Young, LJ. Movements and Habitat Use by Hatchery-Reared Pallid Sturgeon in the Lower Platte River, Nebraska. Biology, Management, and Protection of North American Sturgeon. American Fisheries Society Symposium 28 161-174.

Jordan, GR., RA, Klumb, GA, Wanner, WJ, Stancill. Poststocking. Movements and Habitat Use of Hatchery-Reared Juvenile Pallid Sturgeon in the Missouri River below Fort Randall Dam, South Dakota and Nebraska. American Fisheries Society 135 (6) 1499-1511.

Kallemeyn, L. Status of the Pallid Sturgeon. American Fisheries Society 8 (1) 3-9.

Hurley, KL., RJ, Sheehan, RC, Heidinger, PS, Wills, B, Clevenstine. Habitat use by the Middle Mississippi River Pallid Sturgeon. American Fisheries Society 133 (4) 1033-1041.