White sturgeon (Acipenser transmontanus) are a species of sturgeon in the family Acipenseridae. They are also referred to by location, such as Pacific sturgeon, Kootenai River sturgeon, Columbia River sturgeon, and California white sturgeon. Their habitat ranges from the Aleutian Islands to Central California along the west coast of North America. They are an anadromous fish species; however, several populations became landlocked during the construction of dams which blocked their upriver migratory path to and from ancestral spawning grounds. White sturgeon are the largest freshwater fish in North America, and third-largest species of sturgeon after the beluga and kaluga sturgeons. White sturgeon are known to reach weights up to 816 kg (1,799 lb) and lengths up to 6.1 m (20 ft).
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Physical appearance
The white sturgeon has a slender, torpedo-shaped body that is smooth-skinned, scaleless and armored with 5 lateral rows of bony plates called skutes. Its 11-14 dorsal scutes are all anterior to the dorsal fin, and 38-48 lateral scutes and 9-12 ventral scutes are on each side. The dorsal color of a white sturgeon is gray, pale olive, or gray-brown whereas their underside is white. The fins are customarily a dusky, opaque gray. They have distinctive characteristics that date back to their early ancestors, such as a heterocercal caudal fin similar to that of sharks, a flat rostra, and a large toothless, rubbery-like mouth which they can protrude for vacuuming up food from the bottom substrate. Located just in front of the mouth are four barbels, which are covered in sensory organs used for finding food.
Sturgeons are classified as a bony fish, but actually are more cartilaginous than bony, their internal bone structure being more like a shark's. Sturgeon have changed very little since they first appeared over 175 million years ago, thus have the appearance of a very ancient fish.
Columbia River Sturgeon Fishing Video
Habitat
The white sturgeon lives on the bottom of slow-moving rivers, bays, and estuarine areas, including the brackish water at the mouths of large rivers. Other sturgeon spend most of their time in a marine environment, only coming into rivers to spawn. They are well-adapted to finding food drifting by with their excellent sense of smell and taste. When the food supply is insufficient, sturgeon have been known to move into shallow water to eat freshwater clams.
During the spawning season, the white sturgeon moves to clean, fast-moving areas of rivers, such as just below rapids, with gravel or larger rocks along the bottom.
White sturgeon spawn many times in their lives. As they age, the females spawn less often, but produce more eggs in each spawning. In the late spring or early summer, they congregate in areas of rivers with a heavy current, gravel bottom, and a water temperature of 58 to 66 °F (14 to 19 °C). The fish broadcast spawn in these areas, with males releasing sperm as the outnumbered females release 100,000 to a million eggs. The fertilized eggs then sink and adhere to the gravel at the bottom. The eggs are brown in color and hatch in about a week, depending on water temperature. Female white sturgeon do not spawn every year.
Upon hatching, the larvae are around 0.5 in. (1.3 cm) long, with a tadpole-like appearance. They drift downstream with the current until they reach a suitable habitat. When the rearing habitat is reached, the larvae typically take around 25 days for the yolk sac to be absorbed. About a month after hatching, the sturgeon have a full set of fins, rays, and scutes. As small juveniles, they feed on insects, small fish, and small crustaceans. Maturity is reached between 5 and 11 years, depending on the gender of the fish and the temperature of the water.
White sturgeon can live to be over 100 years old. The rate of growth is dependent on water temperature. Typically, they reach six feet long around 25 years of age, showing that these fish do not grow as quickly as many other fish. They are anadromous, meaning they spawn in fresh water and migrate to salt water to mature. Sturgeon may migrate in and out of salt water many times in their lives. However, since the building of many dams along the Columbia and Snake Rivers, the populations above the dams have become landlocked.
Unexpected social behavior has been observed in white sturgeon of the lower Columbia River. Up to 60,000 sturgeon massed in a dense "sturgeon ball" at the base of the Bonneville Dam in early 2008. Scientists do not know what the reason for the behavior was, but predator avoidance is one theory.
Diet
A sturgeon's taste buds are located on the outside of its mouth. This, along with the barbels, allows it to see if a possible food source is edible before sucking it up into its mouth. As adults, the white sturgeon's diet somewhat varies. This is dependent upon the river systems where it lives. In the Columbia River system, dead fish, crustaceans, and mollusks are all popular prey. Lampreys, primitive eel-like fish, come into rivers to spawn at the same time as the white sturgeon, and are a popular food source then. Smelt is another abundant food around spawning time. Shad come into the Columbia River system in throngs of several million each spring. The extremely large shad runs are often cited as an example of why the lower Columbia River has such a large population of sturgeon. Like the smelt, these fish often die, and the remains are an easy meal for sturgeon.
Fishing
Historically, sturgeons have been an important natural resource, both commercially and as a sportfish. Prior to stringent fishing regulations imposed by state and federal resource agencies, white sturgeon populations in the Columbia River system had reached critical status as a threatened species due to overfishing. Commercial fishing for white sturgeon began in the 1880s. In 1892, this fishery reached a peak, when over 5.5 million pounds (2,500 metric tons) of sturgeon were harvested. By the start of the 20th century, the seemingly endless supply of sturgeon was severely depleted. In the 1940s, a six-foot maximum size restriction was put in place. Sportfishing regulations have also been implemented in order to maintain healthy sportfishing populations.
Commercial fishery
In the 1800s, there was a small subsistence fishery that was utilized by Native American populations. As the salmon fisheries grew during the mid-1800s, the numbers of sturgeon bycatch grew exponentially as did the local markets for caviar and sturgeon meat. Exports to markets in the eastern US began during the late 1800s. By the turn of the 19th Century, the white sturgeon fishery had peaked with over I,000,000 pounds (453,515 kg) recorded in 1897. By the beginning of the 20th Century, the fishery experienced sharp declines with only 65,000 pounds (29,478 kg) recorded in 1901. Annual harvests fluctuated thereafter but never again reached the numbers recorded in the late 1800s. Reports indicate that overfishing from 1880 to 1900 depleted the numbers necessary to sustain a healthy breeding population.
In 1992, commercial fishing for white sturgeon was valued as a US$10.1 million industry. Non-Indian commercial fisheries for white sturgeon occur in the mainstem Columbia River downstream from Bonneville Dam. These fisheries use gillnets. Commercial sturgeon fishing may be done in conjunction with commercial salmon fishing or may be a targeted fishery. Release mortality on undersize and oversize sturgeon is estimated by state fish and wildlife managers to be low. Generally, fisheries are managed with weekly landing limits per fisher. Green sturgeon are sometimes caught but must be released unharmed.
Tribal sturgeon fisheries occur in the mainstem Columbia River between Bonneville Dam and McNary Dam. Tribal fisheries primarily use gillnets and setline gear. Some sturgeon are caught with hook and line gear or hoopnets from platforms along the shore. The tribes have subsistence and commercial fisheries for sturgeon.
Worldwide, sturgeon commercial fisheries use sturgeon for meat and eggs, the eggs being most sought after. Caviar is considered a delicacy in many parts of Europe and North America. In the Columbia River, size restrictions make it very unlikely any fishers ever legally retain egg-bearing fish. The fish caught legally by sport and commercial fishers are too small and not yet sexually mature enough to make harvesting for eggs worthwhile.
As in Oregon and Washington, a commercial sturgeon fishery began in the 1880s, the sturgeon populations declined shortly thereafter, and the fisheries were substantially limited in an effort to protect and rebuild the populations. In California, though, the commercial sturgeon fishery has been closed for many decades and remains closed.
For Sport
Fishing for white sturgeon is a popular sport throughout the Northwest and Canada. It is regulated by the US Fish & Wildlife Service and the National Marine Fisheries Service (NMFS) in cooperation with the respective state resource agencies, all of which are dependent on population surveys and conservation programs that are in place for a specific area.
Toxicity
The threat of toxics bioaccumulation is especially high in sturgeon meat. Because of its eating habits, sturgeon accumulate toxins in their flesh as they feed. They feed on any sort of organic material found while scavenging; this includes raw sewage, dead fish, paper mill wastes, and plants sprayed by pesticides. Dioxins and dioxin-like compounds are unintentional byproducts of paper bleaching and pesticides. It is also one of the most commonly found toxics in fish populations. PCB is also found in fish. It is used as a plasticizer in paint, rubber, and plastic products. Before the government ceased its production in 1977, more than 1,500,000,000 pounds (680,000 tonnes) were produced. Methylmercury is one of the more commonly known toxics found in fish's flesh. Some have speculated that it is also the most dangerous. Sturgeon and other fish in the Columbia and Willamette Rivers have registered 0.05 to 0.50 parts per million. Although most accumulation in sturgeon happens in the liver, pancreas, and other organs, the toxics still accumulate in the edible flesh. The Oregon Department of Fish and Wildlife has issued warnings on all fish caught in the Willamette River. "Women of childbearing age, children under six, and people with liver and kidney damage should avoid eating fish from these waters. Healthy adults should eat no more than one eight ounce meal per month". Also for areas with high concentrations of PCBs, dioxins, and pesticides: "All persons should reduce or avoid eating fatty parts of fish. Exposure can be reduced by removing the skin and all fat, eggs, and internal organs".
Conservation
In Oregon and Washington
In addition to overfishing, dams constructed along the Columbia and Snake Rivers have become a threat to sturgeon. The dams block passage to and from the ocean, leaving landlocked populations. The higher water levels have, as a result, destroyed areas that once had rapid currents, eliminating spawning grounds. Now, the only healthy population of white sturgeon on the Columbia River and its tributaries is the lower Columbia River population. These fish are still able to move freely between marine, estuarine, and freshwater environments. All other populations have become landlocked because of the dams. These populations have suffered from the inaccessibility of many food sources, inability to migrate, and destruction of their habitat. As a result, none of the populations above Bonneville Dam are considered to be abundant. White sturgeon in the Kootenai River are at such a low level, they were listed as endangered under the Endangered Species Act in 1994. Some white sturgeon populations, however, do support fisheries. The Oregon Department of Fish and Wildlife has worked together with the Washington Department of Fish and Wildlife and the Columbia River Treaty Tribes to impose size restrictions as well as season and quota restrictions on all sturgeon caught in the Columbia River. The objective of size restrictions is to minimize fishing impacts on large sturgeon that comprise the spawning population. Poaching is also partly responsible for declining numbers.
Fishery management agencies have implemented more restrictive commercial and recreational fishing regulations such as closed areas to protect spawning fish to help protect this magnificent creature. These fishery regulations in conjunction with hydrosystem management actions taken by the Corps of Engineers and restoration funding provided by the Bonneville Power Administration will help alleviate the over harvest of sturgeon and destruction of sturgeon habitat.
State and tribal fishery managers have experimented with spawning sturgeon artificially and raising sturgeon in hatcheries with the goal of releasing juvenile sturgeon in the upstream areas of the Columbia and Snake Rivers to help rebuild sturgeon populations in these areas. Initial results are promising, but no full-scale hatchery production has been funded.
In British Columbia
The Fraser River Sturgeon Conservation Society is active in monitoring their local white sturgeon population and producing research on the behaviour of the animal.
Source of the article : Wikipedia
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