Bull trout

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 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 halos on the brook trout. Bull trout lack the deeply forked tail fin of lake trout (S. namaycush, another char).[6]

Core distribution of bull trout (Salvelinus confluentus) in U.S. 2005[8]

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.[5][6] 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.[2][9]

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.[9] 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 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 suitable spawning 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 of genetic 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 trout ecology.[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 to gene flow between isolated populations, maintaining genetic diversity and increasing the species’ resilience.[18]

Understanding bull trout dispersal patterns is crucial for effective conservation and management strategies.[14] Conservation efforts can be focused on protecting critical habitats and maintaining connectivity between populations.[13] Conservation biologists use various techniques to study bull trout dispersal, including radio telemetry, genetic analysis, and mark-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, and ecosystem health.[20] 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.[14]

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, some of the southernmost populations of bull trout feed heavily on salmon eggs and fry, as well as fish.

Bull trout sign at Lake Pend Oreille in Idaho

The bull trout is listed as a threatened species under the U.S. Endangered Species Act throughout its range in the contiguous United States.[6] In 1998, the Klamath River distinct population segment (DPS) and Columbia River DPS were federally listed as threatened.[21] This finding followed a legal challenge[22] to the U.S. Fish & Wildlife Sevice's (USFWS) decision in 1994[23] to assign a lower priority to the species' listing. The Jarbidge 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 and St. 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, including Boise National Forest and Sawtooth National Forest (Sawtooth National Recreation Area). They can also be found in the Glacier National Park.[26] 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.[10] Bull trout populations are also in danger from hybridization 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 the National Forest Management Act and Wild and Scenic Rivers Act by approving grazing plans in Oregon's Malheur National Forest. In April 2018, U.S. District Judge Michael W. Mosman dismissed the complaint.[27]

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".[28]

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.[29]^: 71–72 By the recommendation of COSEWIC,[29]^: iv the Saskatchewan-Nelson Rivers population in Alberta was listed as threatened under the Species at Risk Act in 2019.[7]