Bull trout (Salvelinus confluentus) COSEWIC assessment and status report 2012: chapter 2

Assessment Summary – November 2012

Common name
Bull Trout - South Coast British Columbia populations

Scientific name
Salvelinus confluentus

Status
Special Concern

Reason for designation
This freshwater fish exists in five large river systems in this area. The population sizes are unknown for three of the rivers but are likely not large. This is a slow-growing and late-maturing species that thrives in cold, pristine waters, and many populations require long unimpeded migratory routes joining spawning to adult habitat. Therefore the species is particularly vulnerable to habitat degradation, fragmentation of river networks by dams, negative effects from the invasion of non-native Eastern Brook Trout, and overharvest. The anadromous life history form found in these populations is unique within this species.

Occurrence
British Columbia

Status history
Designated Special Concern in November 2012.

Assessment Summary – November 2012

Common name
Bull Trout - Western Arctic populations

Scientific name
Salvelinus confluentus

Status
Special Concern

Reason for designation
This freshwater fish is broadly distributed throughout the Western Arctic drainage although populations are never abundant. There are areas with evidence of decline in numbers and distribution but quantitative estimates for the whole range are lacking. This is a slow-growing and late-maturing species that thrives in cold, pristine waters, and many populations require long unimpeded migratory routes joining spawning to adult habitat. Therefore the species is particularly vulnerable to habitat degradation, fragmentation of river networks by dams, negative effects from the invasion of the non-native Eastern Brook Trout, and overharvest, but these threats are localized within its range.

Occurrence
Yukon, Northwest Territories, British Columbia, Alberta

Status history
Designated Special Concern in November 2012.

Assessment Summary – November 2012

Common name
Bull Trout - Upper Yukon Watershed populations

Scientific name
Salvelinus confluentus

Status
Data Deficient

Reason for designation
This freshwater fish is believed to be distributed in the upper Yukon River drainage but information on population sizes and trends is not available. This is a slow-growing and late-maturing species that thrives in cold, pristine waters, and many populations require long unimpeded migratory routes joining spawning to adult habitat. In general, the species is vulnerable to habitat degradation, fragmentation of river networks by dams, and overharvest, but specific threats in these populations are largely unknown and likely minor in this remote watershed.

Occurrence
Yukon, British Columbia

Status history
Species considered in November 2012 and placed in the Data Deficient category.

Assessment Summary – November 2012

Common name
Bull Trout - Saskatchewan - Nelson Rivers populations

Scientific name
Salvelinus confluentus

Status
Threatened

Reason for designation
This freshwater fish is broadly distributed east of the Rocky Mountains. It is a slow-growing and late-maturing species that thrives in cold, pristine waters and often requires long unimpeded migratory routes joining spawning to adult habitat. Historical range contractions now limit the populations to the foothills and east slopes of the Rocky Mountains, likely in response to habitat deterioration and reduced habitat connectivity through damming of the larger rivers. No populations are abundant and more than half show evidence of decline. The primary and persistent threats to these populations include competition and hybridization with introduced Eastern Brook Trout and climate-induced increases in water temperature. Although legal harvest has been eliminated, this species is highly catchable and is therefore likely susceptible to catch and release mortality in many areas that are accessible to recreational anglers. Consequently, an aggregate decline in abundance of > 30% over the next three generations is projected.

Occurrence
Alberta

Status history
Designated Threatened in November 2012.

Assessment Summary – November 2012

Common name
Bull Trout - Pacific populations

Scientific name
Salvelinus confluentus

Status
Not at Risk

Reason for designation
This freshwater fish is broadly distributed throughout Pacific drainages. Although populations are never abundant, there are many dispersed populations across this area. There is no overall evidence of declines in abundance of mature adults and distribution. Although this is a slow-growing and late-maturing species that thrives in cold, pristine waters, and requires unimpeded migratory routes joining spawning to adult habitat, the risk level is assessed as low in these populations.

Occurrence
British Columbia

Status history
Designated Not at Risk in November 2012.