The bull trout (Salvelinus confluentus) is a char of the family Salmonidae native to northwestern North America. Historically, S. confluentus has been known as the "Dolly Varden" (S. malma), but was reclassified as a separate species in 1980. Populations of bull trout in the lower 48 states are listed as threatened under the U.S. Endangered Species Act,
Description
Like other species of char, the fins of a 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 in length and weighing .]]
S. confluentus is found in the cold, clear waters of the high mountains and coastal rivers of northwestern North America, including Yukon, Alberta, British Columbia, Washington, Oregon, Idaho, and western Montana, as well as the Jarbidge River of northern Nevada and perhaps Alaska. A population of bull trout exists east of the Continental Divide in Alberta, where it is the provincial fish. The historical range of bull trout also included northern California, but they are likely extirpated.
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.
Dispersal
Bull trout are known for their extensive movements within river systems. They exhibit short-distance and long-distance movements, which are crucial in maintaining healthy populations and genetic diversity. During the early life stages, bull trout are often found in small, low-gradient streams or near the shores of larger rivers and lakes. As they grow and mature, they start to disperse in search of suitable spawning grounds and feeding habitats. Once mature, they migrate upstream to spawn in the same streams where they were born. The dispersal distances can vary greatly, with some individuals traveling only a few miles while others undertake extensive migrations of over a hundred miles.
Long-distance dispersal is also an essential aspect of bull trout ecology. These movements often occur during the non-spawning season when the fish search for suitable feeding grounds or escape unfavorable conditions such as high water temperatures or low oxygen levels. These long-distance dispersal events contribute to gene flow between isolated populations, maintaining genetic diversity and increasing the species' resilience.
Understanding bull trout dispersal patterns is crucial for effective conservation and management strategies.
Bull trout dispersal is a complex and vital aspect of their life history. Their movements are critical to maintaining population connectivity, genetic diversity, and ecosystem health. Protecting and restoring essential habitats, ensuring the connectivity of river systems, and managing anthropogenic influences in bull trout habitats are all crucial steps in conserving this iconic species. This finding followed a legal challenge to the U.S. Fish & Wildlife Service's (USFWS) decision in 1994 to assign a lower priority to the species' listing. The Jarbidge River DPS was listed as endangered under an emergency rule in 1998, and was subsequently downgraded to threatened in 1999.
In the United States, 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). They can also be found in the Glacier National Park. Bull trout reproduction requires cold water and very low amounts of silt, both of which are negatively impacted by road building and logging. Additionally, its need to migrate throughout river systems may be hindered by impassible fish barriers, such as dams.
They are a prized game fish in northern Canada. It was once maligned out of fear they threatened populations of other native species more prized by anglers. Some jurisdictions publicize the requirement to release with the slogan "No black, put it back".
Within Canada, bull trout have been designated as a "species of Special Concern" by both the Government of Alberta and the Government of British Columbia. By the recommendation of COSEWIC,
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, the original "Dolly Varden" trout (i.e., S. confluentus) apparently likely became extirpated in the McCloud River in the 1970s, although reports continue of its being caught. Other fish species, typically introduced trout, outcompete S. confluentus, and can interbreed with them, resulting in sterile hybrids. An attempt to reintroduce S. confluentus to the McCloud was unsuccessful, and no additional attempts are expected.
Other uses of "Dolly Varden"
The "Dolly Varden" name is also applied to the other subspecies of S. malma, the S. m. krascheninnikova, and S. m. miyabei, found in Lake Shikaribetsu on the island of Hokkaidō in Japan.
The name has also been applied to S. alpinus, today more commonly known as Arctic char.
"Bull trout" in Europe
The name "bull trout" was also given in the past to some of the large sea trout 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.