| Bull trout | |
|---|---|
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Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Actinopterygii |
| Order: | Salmoniformes |
| Family: | Salmonidae |
| Genus: | Salvelinus |
| Species: | S. confluentus |
| Binomial name | |
| Salvelinus confluentus | |
Thebull trout (Salvelinus confluentus) is achar of the familySalmonidae native to northwesternNorth America.[4] Historically,S. confluentus has been known as the "Dolly Varden" (S. malma), but was reclassified as a separate species in 1980.[5] Populations of bull trout in the lower 48 states are listed asthreatened under the U.S.Endangered Species Act,[6] and bull trout overall are listed as vulnerable to extinction on theIUCN Red List of Threatened Species.[1] The Saskatchewan-Nelson Rivers population inAlberta, Canada is listed as threatened under theSpecies at Risk Act.[7]
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 103 cm (41 in) in length and weighing 14.5 kg (32 lb).[4] 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.[6] Migratory bull trout are typically much larger than resident bull trout, which rarely exceed 2 kg (4.4 lb).[5] Bull trout can be differentiated frombrook trout (S. fontinalis) by the absence of distinct spots on thedorsal fin, as well as yellow, orange, or salmon-colored spots on the back as opposed to red spots with blue halos on the brook trout. Bull trout lack the deeply forked tail fin oflake trout (S. namaycush, another char).[6]
S. confluentus is found in the cold, clear waters of the high mountains and coastal rivers of northwesternNorth America, includingYukon,Alberta,British Columbia,Washington,Oregon,Idaho, and westernMontana, as well as theJarbidge River of northernNevada and perhapsAlaska.[5][6] A population of bull trout exists east of theContinental Divide inAlberta, where it is the provincial fish. The historical range of bull trout also included northernCalifornia, but they are likelyextirpated.[2][9]
Bull trout have exacting habitat demands, requiring water temperatures generally below 55 °F (13 °C), cleangravel beds, deep pools, complex cover such assnags andcut banks, and large systems of interconnected waterways to accommodate spawning migrations.[9] Thus, they favor the deep pools of cold lakes and large rivers, as well as high, cold mountain headwaters. Bull trout may beanadromous in coastal rivers, and individual bull trout have been found to have migrated from one coastal river to another by the ocean.[10]
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.[11] During the early life stages, bull trout are often found in small, low-gradient streams or near the shores of larger rivers and lakes.[12] As they grow and mature, they start to disperse in search of suitablespawning grounds and feeding habitats.[12]
One of the primary reasons for bull trout dispersal is the need to find appropriate spawning areas. Bull trout rely on clean, cold water and gravels of specific sizes for successful reproduction.[13] Once mature, they migrate upstream to spawn in the same streams where they were born.[11] This behavior ensures that the population remains connected and allows for the exchange ofgenetic material.[14] The dispersal distances can vary greatly, with some individuals traveling only a few miles while others undertake extensive migrations of over a hundred miles.[15]
Long-distance dispersal is also an essential aspect of bull troutecology.[16] 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.[16] In some cases, bull trout have been observed moving between different river basins, crossing over mountain ranges, and even traversing large lakes.[17] These long-distance dispersal events contribute togene flow between isolated populations, maintaininggenetic diversity and increasing the species' resilience.[18]
Understanding bull trout dispersal patterns is crucial for effectiveconservation andmanagement strategies.[14] Conservation efforts can be focused on protectingcritical habitats and maintainingconnectivity between populations.[13] Conservation biologists use various techniques to study bull trout dispersal, includingradio telemetry,genetic analysis, andmark-recapture studies.[14] By tracking the movements of individual fish and analyzing their genetic makeup, researchers can gain valuable insights into dispersal patterns, population dynamics, and potential barriers to migration.[19]
Bull trout dispersal is a complex and vital aspect of their life history. Their movements are critical to maintaining population connectivity,genetic diversity, andecosystem health.[20] Protecting and restoring essential habitats, ensuring the connectivity of river systems, and managinganthropogenic influences in bull trout habitats are all crucial steps in conserving this iconic species.[14]
Young bull trout feed onzooplankton andzoobenthos, especiallychironomids. As they grow larger, they begin to feed heavily upon other fish. In coastal Washington, some of the southernmost populations of bull trout feed heavily onsalmon eggs and fry, as well as fish.[citation needed]
The bull trout is listed as a threatened species under the U.S. Endangered Species Act throughout its range in thecontiguous United States.[6] In 1998, theKlamath Riverdistinct population segment (DPS) andColumbia River DPS were federally listed as threatened.[21] This finding followed a legal challenge[22] to the U.S. Fish & Wildlife Service's (USFWS) decision in 1994[23] to assign a lower priority to the species' listing. TheJarbidge River DPS was listed as endangered under an emergency rule in 1998,[24] and was subsequently downgraded to threatened in 1999.[24] Finally, in determining that the Coastal-Puget Sound andSt. Mary-Belly River DPS were threatened, the USFWS issued a threatened listing for all bull trout in the lower 48 states in 1999.[25]
In the United States, bull trout are used as a management indicator species for several national forests, includingBoise National Forest andSawtooth National Forest (Sawtooth National Recreation Area). They can also be found in theGlacier National Park.[26] Bull trout reproduction requires cold water and very low amounts ofsilt, 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.[10] Bull trout populations are also in danger fromhybridization with non-native brook trout.[9] Several of these issues were raised in a long-running lawsuit where in 2003, the Oregon Natural Desert Association and the Center for Biological Diversity sued the U.S. Forest Service claiming they violated theNational Forest Management Act andWild and Scenic Rivers Act by approving grazing plans inOregon'sMalheur National Forest. In April 2018, U.S. District JudgeMichael W. Mosman dismissed the complaint.[27]
They are a prizedgame fish innorthern 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".[28]
Within Canada, bull trout have been designated as a "species of Special Concern" by both theGovernment of Alberta and theGovernment of British Columbia.[29]: 71–72 By the recommendation ofCOSEWIC,[29]: iv the Saskatchewan-Nelson Rivers population in Alberta was listed as threatened under theSpecies at Risk Act in 2019.[7]
Historically, confusion has existed betweenS. confluentus andSalvelinus malma malma, today commonly called theDolly Varden trout. This was likely due to overlapping ranges and similar appearances among members of the two species.[citation needed]
The first recorded use of the name "Dolly Varden" for a fish species was applied to members ofS. confluentus caught in theMcCloud River in northern California in the early 1870s. In his bookInland Fishes of California,Peter Moyle recounted a letter from Mrs. Valerie Masson Gomez:
My grandmother's family operated a summer resort atUpper Soda Springs on theSacramento River just north of the present town ofDunsmuir, 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 readingCharles Dickens'Barnaby Rudge in which there appears a character namedDolly 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 atStanford 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:[30]
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 toS. m. malma because of its similar appearance toS. confluentus; the two may have even been believed to be the same species. The name "Dolly Varden" may have also been given toS. m. malma independent of the McCloud River fish.[citation needed]
Ironically, the original "Dolly Varden" trout (i.e.,S. confluentus) apparently likely becameextirpated in the McCloud River in the 1970s, although reports continue of its being caught. Other fish species, typically introduced trout, outcompeteS. confluentus, and can interbreed with them, resulting in sterile hybrids. An attempt to reintroduceS. confluentus to the McCloud was unsuccessful, and no additional attempts are expected.[31]
The "Dolly Varden" name is also applied to the other subspecies ofS. malma, theS. m. krascheninnikova, andS. m. miyabei, found inLake Shikaribetsu on the island ofHokkaidō inJapan.[32]
The name has also been applied toS. alpinus, today more commonly known asArctic char.[citation needed]
The name "bull trout" was also given in the past to some of the large sea trout that run theRiver Tweed and other rivers inScotland andNorth 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 asSalmo trutta. This does not deny that populations ofS. trutta can differ appreciably in habits, size, and appearance from place to place, or indeed in the same river or lake.
Trout and char of the world | ||
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| Trout of Europe andAtlantic basin Salmo |   .png) | |
| Trout of thePacific basin Oncorhynchus | ||
| True char Salvelinus | ||
| Media related toTrout at Wikimedia Commons | ||
Authority control databases: National |
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