COSEWIC Assessment and Status Report on the Bull Trout Salvelinus Confluentus in Canada

COSEWIC Assessment and Status Report on the Bull Trout Salvelinus confluentus South Coast British Columbia populations Western Arctic populations Upper Yukon Watershed populations Saskatchewan - Nelson Rivers populations Pacific populations in Canada South Coast British Columbia populations - SPECIAL CONCERN Western Arctic populations - SPECIAL CONCERN Upper Yukon Watershed populations - DATA DEFICIENT Saskatchewan - Nelson Rivers populations - THREATENED Pacific populations - NOT AT RISK 2012 COSEWIC status reports are working documents used in assigning the status of wildlife species suspected of being at risk. This report may be cited as follows: COSEWIC. 2012. COSEWIC assessment and status report on the Bull Trout Salvelinus confluentus in Canada. Committee on the Status of Endangered Wildlife in Canada. Ottawa. iv + 103 pp. (www.registrelep-sararegistry.gc.ca/default_e.cfm). Production note: COSEWIC would like to acknowledge Jennifer Gow for writing the status report on the Bull Trout, Salvelinus confluentus, in Canada, prepared under contract with Environment Canada. This report was overseen and edited by Dr. John Post, Co-chair of the COSEWIC Freshwater Fishes Specialist Subcommittee. For additional copies contact: COSEWIC Secretariat c/o Canadian Wildlife Service Environment Canada Ottawa, ON K1A 0H3 Tel.: 819-953-3215 Fax: 819-994-3684 E-mail: COSEWIC/[email protected] http://www.cosewic.gc.ca Également disponible en français sous le titre Ếvaluation et Rapport de situation du COSEPAC sur L’omble à tête plate (Salvelinus confluentus) au Canada. Cover illustration/photo: Bull Trout — Picture courtesy of J.D. McPhail and D.L. McPhail. Her Majesty the Queen in Right of Canada, 2013. Catalogue No. CW69-14/659-2013E-PDF ISBN 978-1-100-22290-5 Recycled paper COSEWIC Assessment Summary 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. iii 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. iv 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. v COSEWIC Executive Summary Bull Trout Salvelinus confluentus South Coast British Columbia populations Western Arctic populations Upper Yukon Watershed populations Saskatchewan - Nelson Rivers populations Pacific populations Wildlife Species Description and Significance Bull Trout is a large char. This salmonid derives its name from its large head and jaws. Bull Trout are olive-green to blue-grey in colour and pale round spots on their flanks and back distinguish them from most other similar-looking salmonids. It is difficult to visually distinguish them from Dolly Varden char, however, and detailed measurements or genetic analyses are required for accurate identification where their ranges overlap. Because of its very specific habitat requirements, this sportfish is highly sensitive to habitat changes. Bull Trout are, therefore, viewed as an indicator species of general ecosystem health. Based on genetic analysis, range disjunction and distribution across National Freshwater Biogeographic Zones, five designatable units are recognized; Genetic Lineage 1 (Southcoast BC populations) and Genetic Lineage 2 (Western Arctic, Yukon, Saskatchewan-Nelson and Pacific populations). Distribution Bull Trout is native to western Canada and the U.S. Pacific Northwest. They range north from the Oregon-California border and northern Nevada through British Columbia and Alberta to southern Yukon and southwestern Northwest Territories. The largest portion of their range (about 80%) occurs in western Canada. They are generally restricted to interior drainages but reach the Pacific Coast in southwest British Columbia and northwest Washington. They are concentrated west of the Continental Divide but do extend across it, being found in all of the major eastern slope drainages in Alberta. Their range has become restricted over the last century, particularly in the USA and Alberta, where populations have become more fragmented and isolated. British Columbia, Yukon and the Northwest Territories are the last remaining jurisdictions with wide distributions of Bull Trout. vi Habitat This cold water species’ very strict habitat requirements vary across life history stages. In order to maintain their numbers, Bull Trout require habitat that is cold, clean, complex and connected. Structurally complex habitat provides cover for shelter and the right requirements for breeding and rearing young, while connected habitat allows this migratory species to move between the areas it needs to complete its life cycle. Biology Bull Trout are voracious predators that eat other fish when given the opportunity. They exhibit considerable diversity in life history traits, including four migratory types; a non-migratory stream resident form; a migratory fluvial form that occurs in flowing water; a migratory adfluvial form that matures in lakes; and an anadromous form that migrates to the sea. Each type breeds in headwater or tributary streams at higher elevations but habitat occupied at other

Load more