Bull Trout
Last Update/Review: June 17, 2002
Status | Description | Habits | Reproduction | Food | Limiting Factors | Management and Outlook
Status
Did you know the bull trout isn't really a trout? Instead, it belongs to a branch of the trout family called "chars," along with the lake trout, (eastern) brook trout, and Dolly Varden (which was once considered to be the same species as the bull trout).
The bull trout is special for other reasons, too. It claims distinction among its char relatives and more distant trout cousins, by possessing the most extensive natural range in Alberta. Many people consider the bull trout to be the most "homegrown" of any sport fish in the province and therefore uniquely Albertan. It is perhaps the best candidate we have for Alberta's official fish emblem.
Bull trout live in cold mountain headwaters where food is scarce and most species must struggle to survive. Because the bull trout is a native species that evolved in these waters, it has adapted to these harsh conditions. However, bull trout are slow to mature and, consequently, many of the lakes and streams they inhabit can support only a limited harvest of fish.
At one time, bull trout were common to all the major river systems flowing from the Eastern Slopes of the Rocky Mountains. Before the turn of the century, when numbers were probably at their highest, its range extended down the waterways and out into Alberta's prairie and parkland. However, during the last 30 years there has been a significant reduction in both the number and distribution of bull trout, primarily as a result of over fishing. Changes in habitat contributed to the species' decline, and so did the attitudes held by Albertans in the first part of this century.
In the early 1900s, fish-stocking programs brought new species to many streams. Some anglers saw bull trout as unwanted predators that fed on the more savoured trout species introduced by people. From the 1930s to the 1950s, the removal of large bull trout from some streams was an accepted practice, because it was believed this removal would improve the survival of the other fish. Although the stocking of trout in these waters provided anglers with a greater variety of fishing opportunities, it also greatly increased the fishing pressure on the bull trout to the extent that its numbers began to decline steadily. At present, most anglers are not aware of the vulnerable state of bull trout populations, and they have difficulty distinguishing this species from other trout and char.
In the United States, the American Fisheries Society considers the bull trout to be a "species of special concern" throughout its range. In Alberta, this species is not in immediate danger of extinction but could easily disappear from some of our lakes and streams. Many populations are unable to maintain current numbers and will continue to diminish unless managed wisely. Natural Resources Service is protecting the bull trout from further decline and is taking steps to ensure its population recovery.
Description
Bull trout are known to thrive in cold mountain lakes and streams, where they can reach ages of more than 20 years and lengths of 30 to 70 cm, depending on the food available and growing conditions in their environment. They can weigh up to 10 kg. The largest bull trout recorded for Alberta was caught in 1947 from the Muskeg River. It weighed 11.7 kg! (Compare this to record catches of 5.9 kg for Brook Trout, 7.9 kg for brown trout, and 9.2 kg for rainbow trout.)
The
bull trout is a long slender fish. Its head and jaws are large in comparison
to its body and long ago this shape inspired the term "bull." The
tail fin is only slightly forked, and even less so in young fish. Adult
fish are generally plumper (fatter) than juveniles.
A typical bull trout can be quite pale in appearance but if you glance upward from its white belly to its dorsal fin, you will notice a hint of color beginning with olive-green and turning to blue-gray. Along the sides and back, pale round spots in shades of yellow, orange, pink or red can be seen. Occasionally, the spots along the back may be elongated or wormlike in shape.
Some variations in colour and appearance do occur. For example, in spawning males, the spots on the sides are brighter and the belly may be red or orange. Lake-dwelling bull trout may have a silver sheen to their sides and young bull trout often have 7 to 10 pale dark bands along their sides, separated by narrow light stripes.
bull trout are often misidentified, especially juveniles. The key to correctly identifying this species, however, is the absence of black spots on its dorsal fin. In fact, the Alberta bull trout Task Force uses the slogan "No black, put it back!" to help anglers identity bull trout so they may be released in support of population recovery plans for this species.
This method to distinguish bull trout from other fish is also related to the fact that it is a char and not a trout. True trout, like the rainbow, cutthroat and brown trouts, have dark spots on their bodies and dorsal fins. Char, like the bull trout, generally have only light-colored spots on their bodies. An exception to this rule is the Brook Trout, which has dark spots on its dorsal fin even though it is a char. It also has a dark stripe that appears just behind the white leading edge of each of its lower fins. This black stripe, as well as the dark spots on the dorsal fin, are absent in the bull trout. So, the bull trout slogan "No black, put it back!" is very fitting indeed.
Habits
Three
distinct life patterns have been identified for bull trout and are
based on where they live as adults. Some mature adults remain in small
streams, very near their spawning grounds, for their entire lives.
Other adults move into larger streams and rivers. Still other adult
bull trout can be found in lakes and reservoirs.
Larger waterways generally provide more food, space and shelter. Differences in these habitat components can affect the rate at which bull trout grow and mature. In addition, adult fish living in the larger rivers and lakes can face greater distances and encounter obstacles as they travel back upstream to spawn.
Regardless of where a bull trout makes its home, it prefers cold waters (18° C or lower) and usually can be found in the deeper pools and slower backwaters. In adapting to its environment, where food supplies are often limited, bull trout have become hardy individuals that don't often pass up a meal. As a result, anglers find the bull trout to be an easy catch.
Reproduction
The reproductive potential for bull trout is naturally low. The fish mature slowly, often spawning for the first time in their fifth or sixth year. Those fish living in more unproductive waters may not spawn until their eighth year (compared to brook trout, which mature at 2 to 4 years). In addition, some female bull trout do not spawn in consecutive years. Although no one is certain how widespread this phenomenon of skipping a year might be, it appears that, in unproductive habitat, it sometimes takes more than one year for eggs to mature inside a female's body.
bull trout require stable, flowing water to reproduce successfully. They seek out small, spring-fed streams that can provide a continuous supply of oxygen for their developing eggs (in water with too much sediment, silt may cover the eggs and suffocate them.) Therefore, suitable spawning streams will have steady winter flows, free-flowing spring-time flash floods, and clean gravel areas. Mature fish instinctively return to these areas in autumn; often to the very streams where their lives began. Water temperatures below 9°C trigger spawning, which occurs between mid-August and mid-October.
Once a suitable site has been chosen, the female bull trout digs a nest or "redd" in an area where there is medium- to large-sized gravel without much sediment. The larger size of some females allows them to choose sites farther from the shore, to move larger stones, and to dig a deeper redd than the females of other fish species. This ability increases the chance of survival of the eggs. Once the female is satisfied that the depression is deep enough, she deposits up to 5000 eggs in the redd. Male fish swim nearby, and release milt (milky-white sperm) to fertilize the newly laid eggs. The female then positions herself directly upstream from the redd. With the help of the current, she covers the fertilized eggs with gravel. When spawning is complete, males and females move downstream to overwinter.
For the next six or seven months, bull trout eggs incubate in their gravel nests. Water temperatures of 2° to 4°C are ideal and the eggs begin to hatch during March and April. Young bull trout can remain in their nursery streams for one to five years. Some remain here for their entire lives, and others venture downstream into larger rivers or lakes.
Another interesting aspect about this species' reproduction is that it can hybridize with brook trout. There is concern that the sterile hybrids produced could contribute to the decline of some bull trout populations, by reducing the reproductive potential of current and future generations.
Food
Bull trout have voracious appetites and take full advantage of any and all food sources available to them. They feed primarily along the bottom and up to mid-water levels, consuming insects and other fish species such as suckers, sculpins, minnows, burbot, and trout. Mountain whitefish are probably their favourite meal. Bull Trout occasionally take food from the surface. They have even been known to eat small mammals such as mice that may have accidentally fallen into the water!
Limiting Factors
The disappearance of the bull trout from much of its natural range in Alberta has not occurred overnight. Dwindling populations are the result of the unique habitat requirements combined with certain biological constraints and our earlier attitudes toward this species. The bull trout can recover, but all the elements involved in its decline must be clearly understood and effective management strategies must be initiated to deal with the limiting tractors.
In order to spawn, bull trout require cold, flowing groundwater-fed streams that are clean and free of sediment. Alberta has a limited number of such mountain headwaters. Any alteration that causes erosion, increased siltation, removal of stream cover, or changes in water flow or temperature, affects the number of bull trout that hatch and their ability to survive to maturity. Typically, the spawning and nursery streams are small and cold, and provide little in the way of food, space, and shelter. These stream characteristics limit the number of fingerling bull trout that can be supported even when successful spawning has taken place. Bull trout overwater in deep pools that are limited in number and capable of sustaining only a small number of fish.
Culverts and reservoirs put in place without consideration for migration routes can strand some bull trout populations. When this happens, adult fish cannot reach their spawning grounds and the survival of their populations is threatened.
Bull trout grow slowly and take a long time to mature! When they spawn, they produce relatively few eggs and there is no guarantee that successful spawning will occur every year. For any population to sustain itself, the number of individuals that are removed must be replaced through growth and reproduction. The removal of too many fish can result in a declining population, and for the bull trout, the recovery of a population can take more than 20 years.
Management and Outlook
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Garrie Gillund holds a male bull trout captured during
a spawning run in September, 1993. Mr. Gillund along with
his son Brad, and other members of the Westwind Flyfishers
of Calgary, worked as volunteers on a study of the bull trout
in Lower Kananaskis Lake for Natural Resources Service.Natural Resources Service has a management and recovery plan for the bull trout. The goal of this plan is to restore healthy, self-sustaining populations of bull trout in areas with suitable habitat.
Bull trout, because of their large and varied appetite, eagerly take most baits and lures and are much more vulnerable to capture and overfishing than other species. When anglers catch and keep bull trout that have not yet reached spawning age (and this was often the case), the reproductive potential of the population is reduced. The past introduction of exotic (nonnative) fish into the habitat of bull trout has increased fishing pressure on this species with disastrous results. Numbers continue to decline and other fish species are extending their range into vacant bull trout habitat.
The first step is to achieve population recovery through strict conservation measures. Current stocks will be protected from further losses and, where feasible, bull trout populations will be re-established in parts of their former range. Habitat for all lifestages will be protected, enhanced, or restored. Recreational fishing opportunities for bull trout and other species sharing their habitat will be permitted when this angling does not interfere with conservation efforts.
Following are some specific management strategies:
- Catch-and-release fishing for bull trout was implemented throughout the province in 1995. This means that no one is allowed to keep bull trout until populations have recovered and can withstand some harvest.
- Critical bull trout spawning areas will be closed to all fishing on a seasonal or yearly basis.
- The use of bait will be restricted in order to reduce hooking mortality in bull trout caught by anglers. (bull trout are more likely to take baited hooks and swallow these hooks more deeply than artificial lures. Fish caught with bait and then released, may not survive.)
- Information on bull trout identification and status has been provided to Albertans to help them understand and participate in management strategies.
- The Alberta government will work with industry and other land users, to prevent stream disturbances and repair damaged habitat.
- Obstacles and blockages that occur along bull trout migration routes will be corrected or removed (where this is feasible).
- Regulations protecting the bull trout and its habitat will be strictly enforced.
- Where practical, abundant food sources will be maintained for bull trout (e.g., prey species such as mountain whitefish).
- The harvest of fish species that compete with bull trout will be permitted.
The future of Alberta's bull trout is no longer uncertain; its populations will recover with the support of government, industry and the public. Information and education programs, strict compliance with fishing and environmental regulations, and the protection and enhancement of bull trout habitat will each play a part in achieving this goal. Anglers, the scientific community and government are already working together on behalf of the bull trout, so that future generations of Albertans will also be able to enjoy this remarkable species.
