status: Endangered, IUCN Endangered, ESA
Description and biology
The pallid sturgeon, also known as the white sturgeon, is so-named because of its light coloring. It is one of the largest fishes found in the areas drained by the Missouri and Mississippi Rivers. Some adults weigh as much as 85 pounds (39 kilograms). The fish's snout is long, flattened, and shovel- shaped. Its toothless mouth is located far under the snout. In front of the mouth is a row of sensory barbels, fleshy feelers the fish uses to detect food on river bottoms. It feeds on fish, snails, and crayfish and other aquatic invertebrates.
Males reach sexual maturity at 7 to 9 years of age, females at 15 to 20 years of age. Biologists (people who study living organisms) know little about the fish's reproductive habits. They do know that the sturgeon spawns (lays eggs) in June and July at the confluence, or junction, of the Mississippi and Missouri Rivers.
Habitat and current distribution
The pallid sturgeon is found in the Missouri River and in the Mississippi River downstream from where the Missouri empties into it. The fish is also found in the lower portion of the Yellowstone River. Biologists do not know how many of these sturgeons currently exist.
Pallid sturgeons seem to prefer to inhabit the sandy or rocky bottoms of large, murky, free-flowing rivers. They have occasionally been found inhabiting sand flats or gravel bars in rivers, streams, lakes, and deep pools.
History and conservation measures
The pallid sturgeon was first identified as a distinct species in 1905. In the 1950s, its range included the middle and lower Mississippi River, the Missouri River, and the lower reaches of the Platte, Kansas, and Yellowstone Rivers. This range extended over a length of about 3,550 miles (5,712 kilometers). Now the sturgeon is considered one of the rarest fish in this range.
The sturgeon has declined in number because its habitat in both the Missouri and Mississippi Rivers has been drastically altered. Areas in both rivers have been dredged (deepened) to allow ships to navigate more easily. Dikes (walls built along rivers to hold back water and prevent flooding) and weirs (fences placed in rivers to catch fish) have been constructed throughout the fish's range. Other areas on these rivers have been enclosed in reservoirs or dams.
All of these modifications have blocked the ability of the sturgeon to swim throughout its range. They have also destroyed spawning areas and reduced the fish's food supply. In addition, portions of both rivers (especially the Mississippi) have high levels of pollution from industrial wastes and pesticide and fertilizer runoff from farms.
To prevent the extinction of this fish, the U.S. Fish and Wildlife Service is developing a captive-breeding program. Officials are hoping to use this program to reintroduce pallid sturgeons into former areas of their habitat.
DID YOU KNOW?
The sturgeon family, composed of 26 species, is a primitive family that has existed on Earth since the Paleozoic era (the division of geologic time occurring between 570 and 240 million years ago). Present-day sturgeons are remarkably similar in appearance to their prehistoric ancestors. Instead of scales, these fish have rows of armorlike bony plates, called scutes, which partially cover their body.
Sturgeons are found only in northern regions of Europe, Asia, and North America. Worldwide, almost every species of sturgeon is currently endangered. The demise of these fish began in the late nineteenth century, when humans began catching sturgeons solely to eat their eggs—a delicacy known as caviar. As a result, most species of this ancient fish family were brought to the edge of extinction in only 30 years.