Pallid sturgeon
Encyclopedia
The pallid sturgeon is an endangered species
of ray-finned fish
, endemic to the waters of the Missouri
and lower Mississippi River
basins of the United States. Named for its pale coloration, the pallid sturgeon is closely related to the relatively common shovelnose sturgeon
(Scaphirhyncus platorhynchus), but is much larger, averaging between 30 and 60 in (76.2 and 152.4 cm) in length and 85 pounds (38.6 kg) in weight at maturity. The pallid sturgeon takes 15 years to mature and spawns infrequently, but can live for up to a century. A member of the Acipenseridae (sturgeon)
family of fish that originated during the Cretaceous period 70 million years ago, the pallid sturgeon has remained essentially unchanged. The species is considered to be a relict
of the dinosaur
era, and has been called "one of the ugliest fish in North America".
In 1990, the U.S. Fish and Wildlife Service (USFWS) placed the pallid sturgeon on the endangered species list, because few young individuals had been observed in the preceding decade, and sightings had greatly diminished; the species is now rarely seen in the wild. It was the first fish species in the Mississippi River drainage area to be listed as endangered, and a loss of its habitat is thought to be responsible for its decline. The vast majority of the Mississippi River drainage system has been channeled and dammed
, reducing the gravel deposits and slow-moving side channels that are its favored spawning
areas. Until the middle of the 20th century, pallid sturgeon were common and anglers found catching such a large fish in fresh water
a rewarding experience. The species is considered to be good-tasting, and its eggs have been used as caviar
, although less commonly than those of many other sturgeon.
Efforts to prevent the species from becoming extinct have had modest success. Pallid sturgeon are actively being raised in a dozen hatcheries
and the offspring are being released back to the wild every year. To better understand pallid sturgeon behavior, researchers have implanted GPS
transmitters to track their movements and help identify possible spawning areas. Federal and state agencies are working together to improve habitat by restoring spawning areas since restoration of these areas is required if the species is to survive in the wild.
and R. E. Richardson classified the pallid sturgeon in 1905, grouping it in the Scaphirhynchus
genus
and the Acipenseridae family
, which includes all sturgeon
worldwide. 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 soon become extinct
. These three species belong to the Scaphirhynchinae
subfamily, which has only one other genus, Pseudoscaphirhynchus
, represented by three species found in west-central Asia
.
The word pallid means "deficient in color", and compared to other species of sturgeon, the pallid is noticeably paler. The scientific name for the fish is derived from Scaphirhynchus, a Greek
word meaning "spade snout" and albus which is Latin
for "white".
and that of other closely related species was conducted to assess the differences within various populations of pallid sturgeon, and the differences between pallid and shovelnose sturgeon. Early DNA research indicated that pallid sturgeon and shovelnose sturgeon were a single species. However, a 2000 study comparing DNA sequences in the three members of the Scaphirhynchus genus (pallid, shovelnose and Alabama sturgeon) showed that the three are distinct species. Between 2001 and 2006, several studies examined two populations of pallid sturgeon located in the upper Great Plains
section of the Missouri River and compared them to a southern population located in the Atchafalaya River
in Louisiana
. These DNA studies concluded that the northern populations of pallid sturgeon are reproductively isolated
and are genetically distinct from the Atchafalaya population. However, the genetic variability among pallid sturgeon was found to be far less than that between them and the shovelnose sturgeon.
Another reason for DNA testing was to determine the rates of hybridization between pallid and shovelnose sturgeon. The southern populations have more hybrids than are found in the middle sections of the Missouri River
basin, while the northernmost populations have had few reports of hybrids. Hybrids are most common in the Atchafalaya River in Louisiana and DNA sequencing in these hybrids showed a genetic distinction from pallid sturgeon, but based on the genetic markers assessed, they were genetically indistinguishable from shovelnose sturgeon. Because of this ability of two species to hybridize, some biologists have expressed concern that it is a violation of the Endangered Species Act
to protect one species that may not be genetically isolated from another. It is not known if the hybrids are able to reproduce or not, although they appear to be the result of pallid sturgeon eggs
being fertilized by shovelnose sturgeon males.
The pallid sturgeon is one of the largest freshwater fish species in North America. They are generally between 30 and 60 in (76.2 and 152.4 cm) in length and weigh as much as 85 pounds (38.6 kg). The species is ancient and has remained virtually unchanged for 70 million years, since the Cretaceous
period. The pallid sturgeon has a distinctive appearance that has been referred to as "primitive", "dinosaur-like" and even "ugly". Although visually similar, the shovelnose sturgeon is much smaller and usually weighs no more than 5 pounds (2.3 kg). Pallid sturgeon are much paler in coloration with grayish white backs and sides, while shovelnose sturgeon are brown. Pallid sturgeon turn whiter as they age and younger specimens are easily confused with adult shovelnoses sturgeon since they are similar in color. Like the shovelnose sturgeon, their tails are heterocercal, with the top tail fin being longer than the bottom fin, though this is more pronounced in pallid sturgeon.
As with other sturgeon, pallid sturgeon are lacking the scales
or bones found in more modern species of fish. Instead, they have cartilaginous
skeletons with five rows of thick cartilage plates that extend along their sides, undersides and backs, as well as over most of the head. These thick cartilage plates are covered by the skin and serve as a protective armor. The bony cartilage also extends along the backside, from the dorsal fin
to the tail.
The pallid sturgeon's snout and head are longer than that of the shovelnose sturgeon. In both species, the mouth is located well back from the tip of the snout. Lacking teeth they use their extendable mouths to suck up small fish, mollusks and other food sources from river bottoms. Both species 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. On pallid sturgeon, the two inner barbels are approximately half as long as the outer ones, while on the shovelnose sturgeon, all four barbels are the same length. The inner barbels of the pallid sturgeon are positioned in front of the outer ones, whereby those on the shovelnose sturgeon are all located in essentially a straight line. The length and positioning of the barbels is one of the best ways to distinguish the two species.
Pallid sturgeon have a long lifespan, living in excess of 50 years and perhaps as long as 100 years. They lack bones and scales which makes it more difficult to establish their age and determine exactly how long they live. As is true for many long-lived species, pallid sturgeon reach reproductive maturity relatively late. Males reach sexual maturity between the ages of 5 and 7 years, while females are believed to become capable of reproduction when they are at least 15 years old. One study of 9 females indicated that they begin egg development between the ages of 9 and 12 years, but do not reach reproductive maturity until they are 15 years old. Reproduction does not take place every year; the average interval between spawnings is three years, although other studies suggest an interval as long as ten years. Spawning usually takes place between the months of May and July.
Prior to the construction of dams on the Missouri, pallid sturgeon migrated hundreds of miles upstream to spawn, and would seek out rocky or hard surfaces to deposit hundreds of thousands of eggs. One female pallid sturgeon that was caught in the upper Missouri River was estimated to be carrying 170,000 eggs, representing over 11 percent of its total body weight. After fertilization, pallid sturgeon eggs hatch in 5 to 8 days, after which the larvae drift back downstream for several weeks. As the larvae develop tails, they seek out slower moving waterways and slowly mature over a period of a dozen years. The rate of survival to maturity for pallid sturgeon larvae is extremely low and of the hundreds of thousands of eggs spawned, only a small handful lives to adulthood.
For several decades, no natural reproduction of pallid sturgeon was observed, since all the pallid sturgeon that had been captured were older specimens. However, in the late 1990s, young pallid sturgeon were discovered living in a restored riparian area of the lower Missouri River. This was the first documented example of wild spawned pallid sturgeon in 50 years. In 2007, two female pallid sturgeon were also reported to have spawned in the Missouri National Recreational River
area located downstream from Gavins Point Dam
on the Missouri River.
spanned the entire Missouri and into the Mississippi Rivers. Historically, the species was rare to nonexistent in the upper Mississippi, probably due to a lack of proper habitat. Currently, the species is considered imperiled throughout its entire range. As of 2008, pallid sturgeon can still be found throughout their original range, but their population numbers have severely declined from the mid 20th century. The Missouri and Mississippi Rivers from Montana
to Louisiana, as well as the Atchafalaya River in Louisiana, continue to harbor an aging population of pallid sturgeon. Pallid sturgeon have never been very common; 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. Recently, between 1985 and 2000, the ratio of pallid sturgeon 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 pallid sturgeon remained in their natural habitat at that time.
Six areas were studied for wild pallid sturgeon population estimates and recovery recommendations by the United States Fish and Wildlife Service
between 1990, when the species was declared endangered, and 2006. The USFWS has referred to these six areas of wild pallid sturgeon population studies as Recovery Priority Management Areas (RPMA's). In the northernmost region of the study, known as RPMA 1, located between the Marias River
in Montana to the western reaches of Fort Peck Reservoir, only 45 wild (non-hatchery) individuals remain. Of these, no juveniles were observed and the population was declining. In RPMA 2, located between Fort Peck Dam, the headwaters of Lake Sakakawea
and the lower Yellowstone River
up to the confluence of the Tongue River
, Montana, only 136 wild specimens remain. In RPMA 3, stretching from upstream of the Niobrara River
to Lewis and Clark Lake
along the Missouri River, no native populations were recorded. All collected specimens appeared to be hatchery raised. However, the hatchery raised specimens were apparently maturing and adjusting well to this section of the river. RPMA 4 extends from Gavins Point Dam to the confluence of the Missouri and Mississippi Rivers. This region also includes the Platte River. Here, at least 100 unique non-hatchery specimens were collected during the study period. There is also evidence that some wild reproduction is ongoing in this region. In RPMA 5, between the confluence of the Missouri and Mississippi and the Gulf of Mexico
, several hundred specimens were documented. Here again, some evidence suggests that natural reproduction is occurring, as demonstrated by the recovery of a few examples of immature, non-hatchery raised individuals. The Atchafalaya River basin is designated as RPMA 6 and the findings there were similar to those in Recovery Priority Management Areas 4 and 5 but with greater numbers of unique individuals, near 500 in total.
waterways and water depths between 3 and 25 ft (0.9144 and 7.6 m). The species is more commonly found where sandy substrates are plentiful but also lives in waterways that are predominately rocky. Pallid sturgeon prefer swift river currents more often than do shovelnose sturgeon.
In a study based in Montana
and North Dakota
conducted on both the pallid and shovelnose sturgeon, both species were fitted with radio transmitters so researchers could track their swimming habits. Pallid sturgeon were found to prefer wider river channels, mid-channel sandbars and numerous islands and were most commonly recorded in water depths between 2 and 47 ft (0.6096 and 14.3 m). The study also showed that the pallid sturgeon moved as much as 13 miles (20.9 km) a day and up to 5.7 mi/h. Pallid sturgeon are believed to have preferred the muddy and generally warmer waters that existed prior to Missouri River dam construction.
s, 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 thought to be opportunistic feeders. One study which examined the contents from the stomachs of juvenile pallid sturgeon revealed that their diets were seasonally dependent. Various insects were consumed during some seasons and various fish species during others. These results support the description of the pallid sturgeon's eating habits as opportunistic. Fish is a more important dietary staple for pallid sturgeon than it is for shovelnose sturgeon. In one study comparing dietary tendencies between adult shovelnose sturgeon and immature pallid sturgeon, the pallid sturgeon was found to consume far greater numbers of small fish such as Cyprinid
s (minnows). In another study conducted in the upper Missouri River region, an examination of the stomach contents of hatchery reared pallid sturgeon showed that 82% of the wet weight was small fish and the balance was mosquito-like insects
, mayflies
and caddis flies
and small amounts of detritus and plant material.
Though never believed to be common, pallid sturgeon populations rapidly declined during the late 20th century and the species was listed as endangered on September 6, 1990. The U.S. Government and most of the states with pallid sturgeon populations have commenced restoration efforts to save the species from extinction. Wild reproduction of pallid sturgeon is rare to nonexistent in most areas; therefore, human intervention is needed to ensure the survival of the species. Pallid sturgeon were previously considered a prized trophy game fish species, until their numbers declined and they were placed on the endangered species list. All captured pallid sturgeon must now be released back to the wild. The species was known for being very palatable and the roe
from females was used as caviar
.
The route and the environmental characteristics of Missouri River in the northern Great Plains
states of North and South Dakota
, Nebraska
and Montana, have been significantly altered. The resultant changes to the Missouri River in the upper Great Plains from channelization and impoundment prevent upstream migration. The reduced water flow rates and sediment loads and has brought an end to the seasonal flooding of the flood plains in the region. Since the construction of the Fort Peck Dam
in Montana in 1937, and subsequent damming and channelization, the Missouri river has lost over 90 percent of its wetland and sandbar ecosystems. More than 2000 miles (3,218.7 km) of the Missouri River has been altered and only that stretch of the river above Fort Peck Reservoir in Montana remains relatively unchanged. These alterations of the river have had a detrimental impact on a number of native fish species. In the 13 U.S. state
s that the pallid sturgeon is found, only a few other fish species are listed as endangered. Although substantial efforts are being implemented to ensure the survival of this species, the rarity of self-sustaining populations of pallid sturgeon ensures that it will remain federally protected for many decades.
s of Montana are both at risk of extinction and current projections are that wild pallid sturgeon populations in Montana will be extinct by 2018. Though a vigorous stocking effort was implemented in 1996, until pallid sturgeon females reach reproductive maturity sometime after they are 15 years of age, recovery efforts in Montana will not be readily measurable. The U.S. Bureau of Reclamation has been conducting spring pulse water releases from the Tiber dam
every four to five years to try and recreate a semblance of an annual spring flood to restore and rejuvenate downstream floodplains. These pulse releases are done in an effort to restore suitable habitat for numerous fish species.
In Nebraska, a small number of pallid sturgeon have been captured along the lower reaches of the Platte River
. Unlike most rivers in the Mississippi-Missouri river system, the Platte River has only a few dams and they are well upstream from its confluence with the Missouri River. The lower Platte River is shallow with numerous sand bars and small islands. Though pallid sturgeon prefer more turbulent and deeper rivers than the Platte River, between 1979 and 2003 over a dozen pallid sturgeon, including some from hatcheries, have been captured from the Platte River. A number of these pallid sturgeon have been fitted with radio transmitters
which track their return to the Platte River when water levels and turbidity conditions are favorable. Coinciding with the majority of the pallid sturgeon that have been captured, this period that is generally most favorable is during the spring and early summer months. By mid-summer, a reduction in water levels and turbidity on the Platte River encourages pallid sturgeon to return to the Missouri River.
The lower reaches of the Platte River, a more than 30-mile (48 km) stretch from the Elkhorn River
to its confluence with the Missouri River, has suitable spawning habitat for pallid sturgeon, although no conclusive evidence has been found that spawning is occurring in this region. Along with the lower Yellowstone River, the lower Platte River was identified as one of the best of the remaining regions with the potential for the natural spawning.
In Missouri, at the Lisbon Bottoms section of the Big Muddy National Fish and Wildlife Refuge
, wild pallid sturgeon larvae were collected in 1998. These non-hatchery raised larvae were the first recovered on the lower Missouri River in the previous 50 years. The recovery was made along a side channel of the Missouri River that had been developed to provide suitable habitat for pallid sturgeon and other fish spawning. The side channel was apparently being used by the larva pallid sturgeon for protection from the swifter currents of the Missouri River.
In 2007, the U.S. Fish and Wildlife Service concluded that hatchery-based reproduction efforts should be continued, along with monitoring of any population changes, to determine the effectiveness of human intervention. The 2007 findings also emphasized the need to determine the most likely areas of spawning, to identify any parasite or disease that may be impacting the reproductive capabilities of pallid sturgeon and to examine engineering possibilities that may permit recreation of suitable habitats without reducing the USFWS ability to protect people from harmful and destructive flooding, and to maintain its ability to provide adequate water impoundment for irrigation and recreation purposes.
Endangered species
An endangered species is a population of organisms which is at risk of becoming extinct because it is either few in numbers, or threatened by changing environmental or predation parameters...
of ray-finned fish
Actinopterygii
The Actinopterygii or ray-finned fishes constitute a class or sub-class of the bony fishes.The ray-finned fishes are so called because they possess lepidotrichia or "fin rays", their fins being webs of skin supported by bony or horny spines , as opposed to the fleshy, lobed fins that characterize...
, endemic to the waters of the Missouri
Missouri River
The Missouri River flows through the central United States, and is a tributary of the Mississippi River. It is the longest river in North America and drains the third largest area, though only the thirteenth largest by discharge. The Missouri's watershed encompasses most of the American Great...
and lower Mississippi River
Mississippi River
The Mississippi River is the largest river system in North America. Flowing entirely in the United States, this river rises in western Minnesota and meanders slowly southwards for to the Mississippi River Delta at the Gulf of Mexico. With its many tributaries, the Mississippi's watershed drains...
basins of the United States. Named for its pale coloration, the pallid sturgeon is closely related to the relatively common shovelnose sturgeon
Shovelnose sturgeon
The shovelnose sturgeon, Scaphirhynchus platorynchus, is the smallest species of freshwater sturgeon native to the United States of America. It is often called "hackleback", "sand sturgeon", or "switchtail." Switchtail refers to the long filament found on the upper lobe of the caudal fin...
(Scaphirhyncus platorhynchus), but is much larger, averaging between 30 and 60 in (76.2 and 152.4 cm) in length and 85 pounds (38.6 kg) in weight at maturity. The pallid sturgeon takes 15 years to mature and spawns infrequently, but can live for up to a century. A member of the Acipenseridae (sturgeon)
Sturgeon
Sturgeon is the common name used for some 26 species of fish in the family Acipenseridae, including the genera Acipenser, Huso, Scaphirhynchus and Pseudoscaphirhynchus. The term includes over 20 species commonly referred to as sturgeon and several closely related species that have distinct common...
family of fish that originated during the Cretaceous period 70 million years ago, the pallid sturgeon has remained essentially unchanged. The species is considered to be a relict
Relict
A relict is a surviving remnant of a natural phenomenon.* In biology a relict is an organism that at an earlier time was abundant in a large area but now occurs at only one or a few small areas....
of the dinosaur
Triassic
The Triassic is a geologic period and system that extends from about 250 to 200 Mya . As the first period of the Mesozoic Era, the Triassic follows the Permian and is followed by the Jurassic. Both the start and end of the Triassic are marked by major extinction events...
era, and has been called "one of the ugliest fish in North America".
In 1990, the U.S. Fish and Wildlife Service (USFWS) placed the pallid sturgeon on the endangered species list, because few young individuals had been observed in the preceding decade, and sightings had greatly diminished; the species is now rarely seen in the wild. It was the first fish species in the Mississippi River drainage area to be listed as endangered, and a loss of its habitat is thought to be responsible for its decline. The vast majority of the Mississippi River drainage system has been channeled and dammed
River engineering
River engineering is the process of planned human intervention in the course, characteristics or flow of a river with the intention of producing some defined benefit. People have intervened in the natural course and behaviour of rivers since before recorded history - to manage the water resources,...
, reducing the gravel deposits and slow-moving side channels that are its favored spawning
Spawn (biology)
Spawn refers to the eggs and sperm released or deposited, usually into water, by aquatic animals. As a verb, spawn refers to the process of releasing the eggs and sperm, also called spawning...
areas. Until the middle of the 20th century, pallid sturgeon were common and anglers found catching such a large fish in fresh water
Fresh Water
Fresh Water is the debut album by Australian rock and blues singer Alison McCallum, released in 1972. Rare for an Australian artist at the time, it came in a gatefold sleeve...
a rewarding experience. The species is considered to be good-tasting, and its eggs have been used as caviar
Caviar
Caviar, sometimes called black caviar, is a luxury delicacy, consisting of processed, salted, non-fertilized sturgeon roe. The roe can be "fresh" or pasteurized, the latter having much less culinary and economic value....
, although less commonly than those of many other sturgeon.
Efforts to prevent the species from becoming extinct have had modest success. Pallid sturgeon are actively being raised in a dozen hatcheries
Fish hatchery
A fish hatchery is a "place for artificial breeding, hatching and rearing through the early life stages of animals, finfish and shellfish in particular". Hatcheries produce larval and juvenile fish primarily to support the aquaculture industry where they are transferred to on-growing systems...
and the offspring are being released back to the wild every year. To better understand pallid sturgeon behavior, researchers have implanted GPS
Global Positioning System
The Global Positioning System is a space-based global navigation satellite system that provides location and time information in all weather, anywhere on or near the Earth, where there is an unobstructed line of sight to four or more GPS satellites...
transmitters to track their movements and help identify possible spawning areas. Federal and state agencies are working together to improve habitat by restoring spawning areas since restoration of these areas is required if the species is to survive in the wild.
Taxonomy and etymology
Taxonomists S.A. ForbesStephen Alfred Forbes
Stephen Alfred Forbes was the first Chief of the Illinois Natural History Survey, a founder of aquatic ecosystem science and a dominant figure in the rise of American ecology. His publications are striking for their merger of extensive field observations with conceptual insights...
and R. E. Richardson classified the pallid sturgeon in 1905, grouping it in the Scaphirhynchus
Scaphirhynchus
Scaphirhynchus is a genus of threatened sturgeons native to the United States of America. It contains three species:*Scaphirhynchus albus...
genus
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
and the Acipenseridae family
Family (biology)
In biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...
, which includes all sturgeon
Sturgeon
Sturgeon is the common name used for some 26 species of fish in the family Acipenseridae, including the genera Acipenser, Huso, Scaphirhynchus and Pseudoscaphirhynchus. The term includes over 20 species commonly referred to as sturgeon and several closely related species that have distinct common...
worldwide. The pallid sturgeon's closest relatives are the shovelnose sturgeon (Scaphirhyncus platorhynchus), which is still relatively common, and the critically endangered Alabama sturgeon
Alabama sturgeon
The Alabama sturgeon, Scaphirhynchus suttkusi, is a critically endangered species of sturgeon native to the United States of America and now only believed to exist in of the lower Alabama River. The fish has a distinctive yellowish-orange color, grows to a size of about 30 inches long and 2 to 3...
(Scaphirhynchus suttkusi), which may soon become extinct
Extinction
In biology and ecology, extinction is the end of an organism or of a group of organisms , normally a species. The moment of extinction is generally considered to be the death of the last individual of the species, although the capacity to breed and recover may have been lost before this point...
. These three species belong to the Scaphirhynchinae
Scaphirhynchinae
Scaphirhynchinae is a subfamily of sturgeon which includes two genera comprising a total of six species.*Genus Scaphirhynchus Heckel, 1835 **Scaphirhynchus albus...
subfamily, which has only one other genus, Pseudoscaphirhynchus
Pseudoscaphirhynchus
Pseudoscaphirhynchus is a genus of fish in the Acipenseridae family. The three species, all of which are threatened, are restricted to west-central Asia.-Species:*Pseudoscaphirhynchus fedtschenkoi...
, represented by three species found in west-central Asia
Asia
Asia is the world's largest and most populous continent, located primarily in the eastern and northern hemispheres. It covers 8.7% of the Earth's total surface area and with approximately 3.879 billion people, it hosts 60% of the world's current human population...
.
The word pallid means "deficient in color", and compared to other species of sturgeon, the pallid is noticeably paler. The scientific name for the fish is derived from Scaphirhynchus, a Greek
Greek language
Greek is an independent branch of the Indo-European family of languages. Native to the southern Balkans, it has the longest documented history of any Indo-European language, spanning 34 centuries of written records. Its writing system has been the Greek alphabet for the majority of its history;...
word meaning "spade snout" and albus which is Latin
Latin
Latin is an Italic language originally spoken in Latium and Ancient Rome. It, along with most European languages, is a descendant of the ancient Proto-Indo-European language. Although it is considered a dead language, a number of scholars and members of the Christian clergy speak it fluently, and...
for "white".
DNA studies
To better protect the pallid sturgeon from extinction, research on its DNADNA
Deoxyribonucleic acid is a nucleic acid that contains the genetic instructions used in the development and functioning of all known living organisms . The DNA segments that carry this genetic information are called genes, but other DNA sequences have structural purposes, or are involved in...
and that of other closely related species was conducted to assess the differences within various populations of pallid sturgeon, and the differences between pallid and shovelnose sturgeon. Early DNA research indicated that pallid sturgeon and shovelnose sturgeon were a single species. However, a 2000 study comparing DNA sequences in the three members of the Scaphirhynchus genus (pallid, shovelnose and Alabama sturgeon) showed that the three are distinct species. Between 2001 and 2006, several studies examined two populations of pallid sturgeon located in the upper Great Plains
Great Plains
The Great Plains are a broad expanse of flat land, much of it covered in prairie, steppe and grassland, which lies west of the Mississippi River and east of the Rocky Mountains in the United States and Canada. This area covers parts of the U.S...
section of the Missouri River and compared them to a southern population located in the Atchafalaya River
Atchafalaya River
The Atchafalaya River is a distributary of the Mississippi River and Red River in south central Louisiana in the United States. It flows south, just west of the Mississippi River....
in Louisiana
Louisiana
Louisiana is a state located in the southern region of the United States of America. Its capital is Baton Rouge and largest city is New Orleans. Louisiana is the only state in the U.S. with political subdivisions termed parishes, which are local governments equivalent to counties...
. These DNA studies concluded that the northern populations of pallid sturgeon are reproductively isolated
Reproductive isolation
The mechanisms of reproductive isolation or hybridization barriers are a collection of mechanisms, behaviors and physiological processes that prevent the members of two different species that cross or mate from producing offspring, or which ensure that any offspring that may be produced is not...
and are genetically distinct from the Atchafalaya population. However, the genetic variability among pallid sturgeon was found to be far less than that between them and the shovelnose sturgeon.
Another reason for DNA testing was to determine the rates of hybridization between pallid and shovelnose sturgeon. The southern populations have more hybrids than are found in the middle sections of the Missouri River
Missouri River
The Missouri River flows through the central United States, and is a tributary of the Mississippi River. It is the longest river in North America and drains the third largest area, though only the thirteenth largest by discharge. The Missouri's watershed encompasses most of the American Great...
basin, while the northernmost populations have had few reports of hybrids. Hybrids are most common in the Atchafalaya River in Louisiana and DNA sequencing in these hybrids showed a genetic distinction from pallid sturgeon, but based on the genetic markers assessed, they were genetically indistinguishable from shovelnose sturgeon. Because of this ability of two species to hybridize, some biologists have expressed concern that it is a violation of the Endangered Species Act
Endangered Species Act
The Endangered Species Act of 1973 is one of the dozens of United States environmental laws passed in the 1970s. Signed into law by President Richard Nixon on December 28, 1973, it was designed to protect critically imperiled species from extinction as a "consequence of economic growth and...
to protect one species that may not be genetically isolated from another. It is not known if the hybrids are able to reproduce or not, although they appear to be the result of pallid sturgeon eggs
Egg (biology)
An egg is an organic vessel in which an embryo first begins to develop. In most birds, reptiles, insects, molluscs, fish, and monotremes, an egg is the zygote, resulting from fertilization of the ovum, which is expelled from the body and permitted to develop outside the body until the developing...
being fertilized by shovelnose sturgeon males.
Physical characteristics
Cretaceous
The Cretaceous , derived from the Latin "creta" , usually abbreviated K for its German translation Kreide , is a geologic period and system from circa to million years ago. In the geologic timescale, the Cretaceous follows the Jurassic period and is followed by the Paleogene period of the...
period. The pallid sturgeon has a distinctive appearance that has been referred to as "primitive", "dinosaur-like" and even "ugly". Although visually similar, the shovelnose sturgeon is much smaller and usually weighs no more than 5 pounds (2.3 kg). Pallid sturgeon are much paler in coloration with grayish white backs and sides, while shovelnose sturgeon are brown. Pallid sturgeon turn whiter as they age and younger specimens are easily confused with adult shovelnoses sturgeon since they are similar in color. Like the shovelnose sturgeon, their tails are heterocercal, with the top tail fin being longer than the bottom fin, though this is more pronounced in pallid sturgeon.
As with other sturgeon, pallid sturgeon are lacking the scales
Scale (zoology)
In most biological nomenclature, a scale is a small rigid plate that grows out of an animal's skin to provide protection. In lepidopteran species, scales are plates on the surface of the insect wing, and provide coloration...
or bones found in more modern species of fish. Instead, they have cartilaginous
Cartilage
Cartilage is a flexible connective tissue found in many areas in the bodies of humans and other animals, including the joints between bones, the rib cage, the ear, the nose, the elbow, the knee, the ankle, the bronchial tubes and the intervertebral discs...
skeletons with five rows of thick cartilage plates that extend along their sides, undersides and backs, as well as over most of the head. These thick cartilage plates are covered by the skin and serve as a protective armor. The bony cartilage also extends along the backside, from the dorsal fin
Dorsal fin
A dorsal fin is a fin located on the backs of various unrelated marine and freshwater vertebrates, including most fishes, marine mammals , and the ichthyosaurs...
to the tail.
The pallid sturgeon's snout and head are longer than that of the shovelnose sturgeon. In both species, the mouth is located well back from the tip of the snout. Lacking teeth they use their extendable mouths to suck up small fish, mollusks and other food sources from river bottoms. Both species also have four barbels
Barbel (anatomy)
A barbel on a fish is a slender, whiskerlike tactile organ near the mouth. Fish that have barbels include the catfish, the carp, the goatfish, sturgeon, the zebrafish and some species of shark...
which descend from the snout near the front of the mouth. The barbels are believed to be sensory features to locate food sources. On pallid sturgeon, the two inner barbels are approximately half as long as the outer ones, while on the shovelnose sturgeon, all four barbels are the same length. The inner barbels of the pallid sturgeon are positioned in front of the outer ones, whereby those on the shovelnose sturgeon are all located in essentially a straight line. The length and positioning of the barbels is one of the best ways to distinguish the two species.
Reproduction and life cycle
Prior to the construction of dams on the Missouri, pallid sturgeon migrated hundreds of miles upstream to spawn, and would seek out rocky or hard surfaces to deposit hundreds of thousands of eggs. One female pallid sturgeon that was caught in the upper Missouri River was estimated to be carrying 170,000 eggs, representing over 11 percent of its total body weight. After fertilization, pallid sturgeon eggs hatch in 5 to 8 days, after which the larvae drift back downstream for several weeks. As the larvae develop tails, they seek out slower moving waterways and slowly mature over a period of a dozen years. The rate of survival to maturity for pallid sturgeon larvae is extremely low and of the hundreds of thousands of eggs spawned, only a small handful lives to adulthood.
For several decades, no natural reproduction of pallid sturgeon was observed, since all the pallid sturgeon that had been captured were older specimens. However, in the late 1990s, young pallid sturgeon were discovered living in a restored riparian area of the lower Missouri River. This was the first documented example of wild spawned pallid sturgeon in 50 years. In 2007, two female pallid sturgeon were also reported to have spawned in the Missouri National Recreational River
Missouri National Recreational River
The Missouri National Recreational River is located on the border between Nebraska and South Dakota. The designation was first applied in 1978 to a 59-mile section of the Missouri River between Gavins Point Dam and Ponca State Park. In 1991, an additional 39-mile section between Fort Randall Dam...
area located downstream from Gavins Point Dam
Gavins Point Dam
Gavins Point Dam is a hydroelectric dam on the Missouri River in the U.S. states of Nebraska and South Dakota. Built from 1952 to 1957, it impounds Lewis and Clark Lake. The dam is on the Nebraska-South Dakota border, west of Yankton, South Dakota....
on the Missouri River.
Distribution
The pallid sturgeon's historical rangeRange (biology)
In biology, the range or distribution of a species is the geographical area within which that species can be found. Within that range, dispersion is variation in local density.The term is often qualified:...
spanned the entire Missouri and into the Mississippi Rivers. Historically, the species was rare to nonexistent in the upper Mississippi, probably due to a lack of proper habitat. Currently, the species is considered imperiled throughout its entire range. As of 2008, pallid sturgeon can still be found throughout their original range, but their population numbers have severely declined from the mid 20th century. The Missouri and Mississippi Rivers from Montana
Montana
Montana is a state in the Western United States. The western third of Montana contains numerous mountain ranges. Smaller, "island ranges" are found in the central third of the state, for a total of 77 named ranges of the Rocky Mountains. This geographical fact is reflected in the state's name,...
to Louisiana, as well as the Atchafalaya River in Louisiana, continue to harbor an aging population of pallid sturgeon. Pallid sturgeon have never been very common; 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
Illinois River
The Illinois River is a principal tributary of the Mississippi River, approximately long, in the State of Illinois. The river drains a large section of central Illinois, with a drainage basin of . This river was important among Native Americans and early French traders as the principal water route...
meets the Mississippi. Recently, between 1985 and 2000, the ratio of pallid sturgeon 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 pallid sturgeon remained in their natural habitat at that time.
Six areas were studied for wild pallid sturgeon population estimates and recovery recommendations by the United States Fish and Wildlife Service
United States Fish and Wildlife Service
The United States Fish and Wildlife Service is a federal government agency within the United States Department of the Interior dedicated to the management of fish, wildlife, and natural habitats...
between 1990, when the species was declared endangered, and 2006. The USFWS has referred to these six areas of wild pallid sturgeon population studies as Recovery Priority Management Areas (RPMA's). In the northernmost region of the study, known as RPMA 1, located between the Marias River
Marias River
The Marias River is a tributary of the Missouri River, approximately 210 mi long, in the U.S. state of Montana. It is formed in the Blackfeet Indian Reservation in Glacier County, in northwestern Montana, by the confluence of the Cut Bank Creek and the Two Medicine River...
in Montana to the western reaches of Fort Peck Reservoir, only 45 wild (non-hatchery) individuals remain. Of these, no juveniles were observed and the population was declining. In RPMA 2, located between Fort Peck Dam, the headwaters of Lake Sakakawea
Lake Sakakawea
Lake Sakakawea is a reservoir in the Missouri River basin in central North Dakota. Named for the Shoshone-Hidatsa woman Sakakawea, it is the third largest man-made lake in the United States, after Lake Mead and Lake Powell. The lake lies in parts of six counties in western North Dakota: Dunn,...
and the lower Yellowstone River
Yellowstone River
The Yellowstone River is a tributary of the Missouri River, approximately long, in the western United States. Considered the principal tributary of the upper Missouri, the river and its tributaries drain a wide area stretching from the Rocky Mountains in the vicinity of the Yellowstone National...
up to the confluence of the Tongue River
Tongue River (Montana)
The Tongue River is a tributary of the Yellowstone River, approximately 265 mi long, in the U.S. states of Wyoming and Montana. The Tongue rises in Wyoming in the Big Horn Mountains, flows through northern Wyoming and southeastern Montana and empties into the Yellowstone River at Miles City,...
, Montana, only 136 wild specimens remain. In RPMA 3, stretching from upstream of the Niobrara River
Niobrara River
The Niobrara River is a tributary of the Missouri River, approximately long, running through the U.S. states of Wyoming and Nebraska. The river drains one of the most arid sections of the Great Plains, and has a low flow for a river of its length...
to Lewis and Clark Lake
Lewis and Clark Lake
Lewis and Clark Lake is an impoundment on the Missouri River above Gavins Point Dam, near Yankton, South Dakota. It is located on the border of South Dakota and Nebraska. The reservoir is approximately long, with a surface area of 31,000 acres ; it has a maximum depth of . It is the smallest of...
along the Missouri River, no native populations were recorded. All collected specimens appeared to be hatchery raised. However, the hatchery raised specimens were apparently maturing and adjusting well to this section of the river. RPMA 4 extends from Gavins Point Dam to the confluence of the Missouri and Mississippi Rivers. This region also includes the Platte River. Here, at least 100 unique non-hatchery specimens were collected during the study period. There is also evidence that some wild reproduction is ongoing in this region. In RPMA 5, between the confluence of the Missouri and Mississippi and the Gulf of Mexico
Gulf of Mexico
The Gulf of Mexico is a partially landlocked ocean basin largely surrounded by the North American continent and the island of Cuba. It is bounded on the northeast, north and northwest by the Gulf Coast of the United States, on the southwest and south by Mexico, and on the southeast by Cuba. In...
, several hundred specimens were documented. Here again, some evidence suggests that natural reproduction is occurring, as demonstrated by the recovery of a few examples of immature, non-hatchery raised individuals. The Atchafalaya River basin is designated as RPMA 6 and the findings there were similar to those in Recovery Priority Management Areas 4 and 5 but with greater numbers of unique individuals, near 500 in total.
Habitat
Pallid sturgeon 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 and 2.9 ft/s (0.100584 and 0.88392 m/s). They also prefer turbidTurbidity
Turbidity is the cloudiness or haziness of a fluid caused by individual particles that are generally invisible to the naked eye, similar to smoke in air. The measurement of turbidity is a key test of water quality....
waterways and water depths between 3 and 25 ft (0.9144 and 7.6 m). The species is more commonly found where sandy substrates are plentiful but also lives in waterways that are predominately rocky. Pallid sturgeon prefer swift river currents more often than do shovelnose sturgeon.
In a study based in Montana
Montana
Montana is a state in the Western United States. The western third of Montana contains numerous mountain ranges. Smaller, "island ranges" are found in the central third of the state, for a total of 77 named ranges of the Rocky Mountains. This geographical fact is reflected in the state's name,...
and North Dakota
North Dakota
North Dakota is a state located in the Midwestern region of the United States of America, along the Canadian border. The state is bordered by Canada to the north, Minnesota to the east, South Dakota to the south and Montana to the west. North Dakota is the 19th-largest state by area in the U.S....
conducted on both the pallid and shovelnose sturgeon, both species were fitted with radio transmitters so researchers could track their swimming habits. Pallid sturgeon were found to prefer wider river channels, mid-channel sandbars and numerous islands and were most commonly recorded in water depths between 2 and 47 ft (0.6096 and 14.3 m). The study also showed that the pallid sturgeon moved as much as 13 miles (20.9 km) a day and up to 5.7 mi/h. Pallid sturgeon are believed to have preferred the muddy and generally warmer waters that existed prior to Missouri River dam construction.
Food preferences
Pallid sturgeon are generally bottom feederBottom feeder
Demersal fish live on or near the bottom of the sea or lakes. They occupy the sea floors and lake beds, which usually consist of mud, sand, gravel or rocks. In coastal waters they are found on or near the continental shelf, and in deep waters they are found on or near the continental slope or along...
s, 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 thought to be opportunistic feeders. One study which examined the contents from the stomachs of juvenile pallid sturgeon revealed that their diets were seasonally dependent. Various insects were consumed during some seasons and various fish species during others. These results support the description of the pallid sturgeon's eating habits as opportunistic. Fish is a more important dietary staple for pallid sturgeon than it is for shovelnose sturgeon. In one study comparing dietary tendencies between adult shovelnose sturgeon and immature pallid sturgeon, the pallid sturgeon was found to consume far greater numbers of small fish such as Cyprinid
Cyprinid
The family Cyprinidae, from the Ancient Greek kyprînos , consists of the carps, the true minnows, and their relatives . Commonly called the carp family or the minnow family, its members are also known as cyprinids...
s (minnows). In another study conducted in the upper Missouri River region, an examination of the stomach contents of hatchery reared pallid sturgeon showed that 82% of the wet weight was small fish and the balance was mosquito-like insects
Chironomidae
Chironomidae are a family of nematoceran flies with a global distribution. They are closely related to the Ceratopogonidae, Simuliidae, and Thaumaleidae...
, mayflies
Mayfly
Mayflies are insects which belong to the Order Ephemeroptera . They have been placed into an ancient group of insects termed the Palaeoptera, which also contains dragonflies and damselflies...
and caddis flies
Trichoptera
The caddisflies are an order, Trichoptera, of insects with approximately 12,000 described species. Also called sedge-flies or rail-flies, they are small moth-like insects having two pairs of hairy membranous wings...
and small amounts of detritus and plant material.
Conservation
Roe
Roe or hard roe is the fully ripe internal egg masses in the ovaries, or the released external egg masses of fish and certain marine animals, such as shrimp, scallop and sea urchins...
from females was used as caviar
Caviar
Caviar, sometimes called black caviar, is a luxury delicacy, consisting of processed, salted, non-fertilized sturgeon roe. The roe can be "fresh" or pasteurized, the latter having much less culinary and economic value....
.
The route and the environmental characteristics of Missouri River in the northern Great Plains
Great Plains
The Great Plains are a broad expanse of flat land, much of it covered in prairie, steppe and grassland, which lies west of the Mississippi River and east of the Rocky Mountains in the United States and Canada. This area covers parts of the U.S...
states of North and South Dakota
South Dakota
South Dakota is a state located in the Midwestern region of the United States. It is named after the Lakota and Dakota Sioux American Indian tribes. Once a part of Dakota Territory, South Dakota became a state on November 2, 1889. The state has an area of and an estimated population of just over...
, Nebraska
Nebraska
Nebraska is a state on the Great Plains of the Midwestern United States. The state's capital is Lincoln and its largest city is Omaha, on the Missouri River....
and Montana, have been significantly altered. The resultant changes to the Missouri River in the upper Great Plains from channelization and impoundment prevent upstream migration. The reduced water flow rates and sediment loads and has brought an end to the seasonal flooding of the flood plains in the region. Since the construction of the Fort Peck Dam
Fort Peck Dam
The Fort Peck Dam is the highest of six major dams along the Missouri River, located in northeast Montana in the United States, near Glasgow, and adjacent to the community of Fort Peck...
in Montana in 1937, and subsequent damming and channelization, the Missouri river has lost over 90 percent of its wetland and sandbar ecosystems. More than 2000 miles (3,218.7 km) of the Missouri River has been altered and only that stretch of the river above Fort Peck Reservoir in Montana remains relatively unchanged. These alterations of the river have had a detrimental impact on a number of native fish species. In the 13 U.S. state
U.S. state
A U.S. state is any one of the 50 federated states of the United States of America that share sovereignty with the federal government. Because of this shared sovereignty, an American is a citizen both of the federal entity and of his or her state of domicile. Four states use the official title of...
s that the pallid sturgeon is found, only a few other fish species are listed as endangered. Although substantial efforts are being implemented to ensure the survival of this species, the rarity of self-sustaining populations of pallid sturgeon ensures that it will remain federally protected for many decades.
Efforts to preserve the species from extinction
Two populations of pallid sturgeon in the Missouri and Yellowstone RiverYellowstone River
The Yellowstone River is a tributary of the Missouri River, approximately long, in the western United States. Considered the principal tributary of the upper Missouri, the river and its tributaries drain a wide area stretching from the Rocky Mountains in the vicinity of the Yellowstone National...
s of Montana are both at risk of extinction and current projections are that wild pallid sturgeon populations in Montana will be extinct by 2018. Though a vigorous stocking effort was implemented in 1996, until pallid sturgeon females reach reproductive maturity sometime after they are 15 years of age, recovery efforts in Montana will not be readily measurable. The U.S. Bureau of Reclamation has been conducting spring pulse water releases from the Tiber dam
Tiber Dam
Tiber Dam, located in southern Liberty County in northern Montana, USA, is a dam on the Marias River which forms Lake Elwell, also known as Tiber Reservoir. Construction on the dam began in 1952 and it was complete in 1956. Between 1967 and 1969, a dyke was added to the southern rim of the...
every four to five years to try and recreate a semblance of an annual spring flood to restore and rejuvenate downstream floodplains. These pulse releases are done in an effort to restore suitable habitat for numerous fish species.
Platte River
The Platte River is a major river in the state of Nebraska and is about long. Measured to its farthest source via its tributary the North Platte River, it flows for over . The Platte River is a tributary of the Missouri River, which in turn is a tributary of the Mississippi River which flows to...
. Unlike most rivers in the Mississippi-Missouri river system, the Platte River has only a few dams and they are well upstream from its confluence with the Missouri River. The lower Platte River is shallow with numerous sand bars and small islands. Though pallid sturgeon prefer more turbulent and deeper rivers than the Platte River, between 1979 and 2003 over a dozen pallid sturgeon, including some from hatcheries, have been captured from the Platte River. A number of these pallid sturgeon have been fitted with radio transmitters
Tracking animal migration
For years scientists have been tracking animals and the ways they migrate. One of the many goals of animal migration research has been, of course, to determine where the animals are going; however, researchers also want to know why they are going "there"...
which track their return to the Platte River when water levels and turbidity conditions are favorable. Coinciding with the majority of the pallid sturgeon that have been captured, this period that is generally most favorable is during the spring and early summer months. By mid-summer, a reduction in water levels and turbidity on the Platte River encourages pallid sturgeon to return to the Missouri River.
The lower reaches of the Platte River, a more than 30-mile (48 km) stretch from the Elkhorn River
Elkhorn River
The Elkhorn River originates in the eastern Sandhills of Nebraska and is one of the largest tributaries of the Platte River, flowing and joining the Platte just southwest of Omaha, approximately 1 mile south and 3 miles west of Gretna.Located in northeast and north-central Nebraska, the Elkhorn...
to its confluence with the Missouri River, has suitable spawning habitat for pallid sturgeon, although no conclusive evidence has been found that spawning is occurring in this region. Along with the lower Yellowstone River, the lower Platte River was identified as one of the best of the remaining regions with the potential for the natural spawning.
In Missouri, at the Lisbon Bottoms section of the Big Muddy National Fish and Wildlife Refuge
Big Muddy National Fish and Wildlife Refuge
The Big Muddy National Fish and Wildlife Refuge was established in 1994, and has grown to over . Like pearls on a string, these acres are spread out as individual units along the Missouri River between Kansas City and St. Louis. These pearls of habitat benefit floodplain-dependent fish and wildlife...
, wild pallid sturgeon larvae were collected in 1998. These non-hatchery raised larvae were the first recovered on the lower Missouri River in the previous 50 years. The recovery was made along a side channel of the Missouri River that had been developed to provide suitable habitat for pallid sturgeon and other fish spawning. The side channel was apparently being used by the larva pallid sturgeon for protection from the swifter currents of the Missouri River.
In 2007, the U.S. Fish and Wildlife Service concluded that hatchery-based reproduction efforts should be continued, along with monitoring of any population changes, to determine the effectiveness of human intervention. The 2007 findings also emphasized the need to determine the most likely areas of spawning, to identify any parasite or disease that may be impacting the reproductive capabilities of pallid sturgeon and to examine engineering possibilities that may permit recreation of suitable habitats without reducing the USFWS ability to protect people from harmful and destructive flooding, and to maintain its ability to provide adequate water impoundment for irrigation and recreation purposes.