Bull Trout

Salvelinus Confluentis

Diet, Habitat, and Reproduction

The bull trout is the largest stream-dwelling char in Alberta. They can weigh up to 12 kg (26 lbs.) and have been known to reach lengths of 70 cm (28 inches) but sizes smaller than this are more common in Waterton Park. It was once found in large numbers in most eastern slopes drainages of Alberta, including the Waterton and Belly River drainages of Waterton Lakes and Glacier National Parks. In the 1920's, the bull trout was chosen as a symbol of Waterton Lakes National Park and used on the park entry license plate. The bull trout is commonly referred to by anglers as the Dolly Varden (an ocean and freshwater species occurring west of the continental divide) but it is a separate species native to Alberta and various western US states.

Being a native species, the bull trout is ideally adapted to its south-western Alberta home. They usually spawn in small, spring-fed headwater streams. Depending on where they live as adults, bull trout use on of 3 life history strategies. They may live in either streams, larger streams and rivers or lakes and reservoirs. Fish that stay in headwater streams are called resident stream-dwellers. These fish don't grow very big due to cold water temperatures and lack of food.

Juvenile fish may later migrate downstream to reside in rivers and larger streams or lakes and reservoirs. The abundant food and warmer water temperatures in these areas allow these bull trout to grow very large. However, in mid-August to the end of September, older fish still make the trip back to the headwater streams to spawn.

The large size of the spawning female allows her to dig her redd (nest) deeper in the stream channel and in larger gravel to protect it from spring flooding, common in mountain streams in southern Alberta. However, long term drought conditions on the prairies are also common in southern Alberta. The bull trout has hedged its bets by maintaining populations of smaller, resident stream-dwelling fish that are vulnerable to spring flooding but less affected by drought and conversely, populations of larger river and lake- dwelling fish that are vulnerable to low water caused by drought but more tolerant of spring flooding. At least one of the populations should remain in good health if water conditions change.

The bull trout is also known for its appetite. The cold water in which it lives limits food sources so the bull trout has been known to eat anything it can get its mouth around, including the odd mouse, frog, or snake. The normal diet of the bull trout is insects and fish.

The adaptations that help bull trout survive in healthy streams undamaged by human activities may have contributed to its disappearance from most of its previous range in Alberta. Its voracious appetite makes it vulnerable to over fishing, and in the past, more bull trout have been caught than produced. Adding to this problem was its slow reproductive rate. Many female fish were caught before having reproduced. Many female fish were caught before having reproduced. They don't usually produce offspring until their fifth or sixth year, about twice as long as other trout species. Brook and bull trout have also interbred, producing sterile offspring, further impacting population numbers. Rapidly reproducing, introduced species such as brown, brook, and rainbow trout can also overwhelm bull trout populations in the competition for food and habitat. However, it is the currently low populations of bull trout, due to over fishing, that make them more susceptible to this competition from other species. Healthy bull trout populations can compete with other species.

The places where bull trout live are also being affected. The spawning habitat requirements of the bull trout are not commonly found and many areas have been damaged or destroyed by industrial activity. The most common impacts are siltation, interrupted spring flows, and loss of streamside vegetation which is important for cover and providing shade. The bull trout also encounters problems in getting where it wants to go. Dams and improperly designed culverts block migration routes to spawning grounds.

"No Black, Put it Back!"

It's not too late for the bull trout though! Waterton Lakes National Park and the Province of Alberta are taking steps to aid its recovery. In 1995, a complete ban was implemented on the possession of bull trout by anglers. The slogan developed to aid anglers in identification was "No Black, Put it Back!" referring to the lack of black spots or lines on the back or dorsal fin of the bull trout. A bait ban was also introduced in the Belly and Waterton Rivers and their tributaries to reduce hooking mortality. Bull trout tend to swallow bait deeply and it is often difficult to remove the hook without hurting or killing the fish. Additionally, the North Fork of the Belly River, known bull trout spawning habitat, was closed to all fishing. Work is also being done to reduce the impacts of on stream structures like culverts, dams, and weirs on bull trout.

Parks Canada policies prioritize protection and management of native species such as bull trout. This fish contributes to biodiversity since it is suspected every bull trout in the Province is a pure native with its original gene pool intact. This genetic diversity should contribute to recovery efforts by providing healthy, hardy breeding fish and offspring. It's fortunate that some headwater areas are protected in Waterton Lakes and Glacier, but outside the parks habitat is often degraded or migration routes blocked. Continued cooperation with outside agencies and individuals will be needed to address these issues. It is very possible that bull trout populations can be brought back to levels approaching their historic numbers.

References:

2000, "Bull Trout", Canadian Heritage Parks Canada