| Bull trout | |
|---|---|
| Bull trout in Oregon | |
| Conservation status | |
| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Actinopterygii |
| Order: | Salmoniformes |
| Family: | Salmonidae |
| Genus: | Salvelinus |
| Species: | S. confluentus |
| Binomial name | |
| Salvelinus confluentus Suckley, 1859[1] |
|
The bull trout, Salvelinus confluentus, is a char of the family Salmonidae native to northwestern North America.[2] Historically, S. confluentus has been known as the "Dolly Varden" (S. malma), but was re-classified as a separate species in 1980.[3] Bull trout are listed as a threatened species under the U.S. Endangered Species Act.[4]
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S. confluentus is found in the cold, clear waters of the high mountains and coastal rivers of northwestern North America, including Yukon, British Columbia, Washington, Oregon, Idaho, western Montana, as well as the Jarbidge River of northern Nevada.[3][4] A population of bull trout exists east of the Continental Divide in Alberta, where the bull trout is the provincial fish. The historical range of bull trout also included northern California, but they are likely extirpated.[5]
Like other species of char, the fins of bull trout have white leading edges. Its head and mouth are unusually large for salmonids, giving it its name. Bull trout have been recorded measuring up to 103 centimetres (41 in) in length and weighing 14.5 kilograms (32 lb).[2] Bull trout may be either migratory, moving throughout large river systems, lakes, and the ocean, or they may be resident, remaining in the same stream their entire lives.[4] Migratory bull trout are typically much larger than resident bull trout, which rarely exceed 2 kilograms (4 lb).[3] Bull trout can be differentiated from brook trout (S. fontinalis) by the absence of distinct spots on the dorsal fin, as well as yellow, orange, or salmon-colored spots on the back as opposed to red spots with blue haloes on the brook trout. Bull trout lack the deeply forked tail fin of lake trout (S. namaycush, another char).[4]
Bull trout have exacting habitat demands, requiring water temperatures generally below 55 °F (13 °C), clean gravel beds, deep pools, complex cover such as snags and cut banks, and large systems of interconnected waterways to accommodate spawning migrations.[5] Thus, they favor the deep pools of cold lakes and large rivers, as well as high, cold mountain headwaters. Bull trout may be anadromous in coastal rivers, and individual bull trout have been found to have migrated from one coastal river to another via the ocean.[6]
Young bull trout feed on zooplankton and zoobenthos, especially chironomids. As they grow larger, they begin to feed heavily upon other fish. In coastal Washington state, some of the southernmost populations of bull trout feed heavily on salmon eggs and fry, as well as fish.
Bull trout are listed as a threatened species under the U.S. Endangered Species Act throughout their range in the contiguous United States.[4] Bull trout are used as a management indicator species for several national forests, including Boise National Forest and Sawtooth National Forest (Sawtooth National Recreation Area). Bull trout reproduction requires cold water and very low amounts of silt, both of which are negatively impacted by road building and logging. Additionally, the bull trout's need to migrate throughout river systems may be hindered by impassible fish barriers such as dams.[6]
Bull trout populations are also in danger from hybridization with non-native brook trout.[5]
They are a prized game fish in Northern Canada. Indeed, the fish was once maligned out of fear that they threatened populations of other native species more prized by anglers.
There has been historic confusion between S. confluentus and Salvelinus malma malma, today commonly called the Dolly Varden trout. This was likely due to over-lapping ranges and similar appearances among members of the two species.
The first recorded use of the name "Dolly Varden" for a fish species was applied to members of S. confluentus caught in the McCloud River in northern California in the early 1870s. In his book, Inland Fishes of California, Peter Moyle recounts a letter sent to him on March 24, 1974 from Mrs. Valerie Masson Gomez:
My grandmother's family operated a summer resort at Upper Soda Springs on the Sacramento River just north of the present town of Dunsmuir, California. She lived there all her life and related to us in her later years her story about the naming of the Dolly Varden trout. She said that some fishermen were standing on the lawn at Upper Soda Springs looking at a catch of the large trout from the McCloud River that were called 'calico trout' because of their spotted, colorful markings. They were saying that the trout should have a better name. My grandmother, then a young girl of 15 or 16, had been reading Charles Dickens' Barnaby Rudge in which there appears a character named Dolly Varden; also the vogue in fashion for women at that time (middle 1870s) was called 'Dolly Varden,' a dress of sheer figured muslin worn over a bright-colored petticoat. My grandmother had just gotten a new dress in that style and the red-spotted trout reminded her of her printed dress. She suggested to the men looking down at the trout, 'Why not call them "Dolly Varden"?' They thought it a very appropriate name and the guests that summer returned to their homes (many in the San Francisco Bay area) calling the trout by this new name. David Starr Jordan, while at Stanford University, included an account of this naming of the Dolly Varden Trout in one of his books.
In 1874, Livingston Stone, a naturalist working for the U.S. government wrote of this fish:[7]
Also called at (Upper) Soda Springs the 'Varden' trout. … The handsomest trout, and, on the whole, having the most perfect form of all the trout we saw on the McCloud. Also, the only fish that had colored spots. This one was profusely spotted over most of the body with redish [sic?] golden spots. ... The local name at (Upper) Soda Springs is the Dolly Varden.
It is currently unknown whether the name "Dolly Varden" was later applied to S. m. malma because of its similar appearance to S. confluentus; the two may have even been believed to be the same species. The name "Dolly Varden" may have also been given to S. m. malma independent of the McCloud River fish.
Ironically, it appears that the original "Dolly Varden" trout (i.e., S. confluentus) likely became locally extinct in the McCloud River in the 1970s, although reports continue of its being caught. Other fish species, typically introduced trout, will out-compete S. confluentus, and can interbreed resulting in sterile hybrids. An attempt to re-introduce S. confluentus to the McCloud was unsuccessful, and no additional attempts are expected.[8]
The "Dolly Varden" name is also applied to the other subspecies of S. malma: S. m. krascheninnikova, and S. m. miyabei, found on the island of Hokkaidō in Japan.[9]
The name has also been applied to S. alpinus, today more commonly known as Arctic char.
The name "bull-trout" was also given in the past to some of the large sea-trout (Salmo trutta) that run the River Tweed and other rivers in Scotland and North East England. Victorian anglers and others classified these as a separate race, but today they are biologically classified along with all other UK brown and sea-trout as Salmo trutta. This does not deny that populations of S. trutta can differ appreciably in habits, size and appearance from place to place, or indeed in the same river or lake.