Bluntnose sixgill shark (Hexanchus griseus) COSEWIC assessment and status report: chapter 12
Technical Summary
Hexanchus griseus
Bluntnose sixgill shark – Requin griset
Range of Occurrence in Canada:
Pacific Ocean
Extent and Area Information
Extent of occurrence (EO) (km²)
133,139 km². Based on the area representing the preferred depth interval reported in the literature (20-2000 m).
Specify trend in EO
Unknown
Are there extreme fluctuations in EO?
Unlikely
Area of occupancy (AO) (km²)
Unknown. Not calculated due to insufficient data.
Specify trend in AO
Unknown
Are there extreme fluctuations in AO?
Unlikely
Number of known or inferred current locations
Unknown
Specify trend in #
Unknown
Are there extreme fluctuations in number of locations?
Unknown, unlikely
Specify trend in area, extent or quality of habitat
Unknown
Population Information
Generation time (average age of parents in the population)
Unknown, no reliable age or mortality estimates.
Number of mature individuals
Unknown
Total population trend:
Unknown
% decline over the last/next 10 years or 3 generations.
Note: study occurred over a small geographical extent and short time period (5 years).
Largely unknown, single study shows declines >90%.
Are there extreme fluctuations in number of mature individuals?
Unknown, unlikely
Is the total population severely fragmented?
Unknown, unlikely
Specify trend in number of populations
Unknown
Are there extreme fluctuations in number of populations?
Unknown, unlikely
List populations with number of mature individuals in each:
Threats (actual or imminent threats to populations or habitats)
Bycatch of bluntnose sixgill shark during commercial longline fishing operations for halibut and dogfish appear to be the largest threat in Canada’s Pacific waters. Commercial bottom trawling also captures small numbers of this species each year. Historical directed fishing (1930s and 1940s) may have also impacted the overall abundance.
Rescue Effect (immigration from an outside source)
Status of outside population(s)?
USA: The population status in adjacent US jurisdictions is unknown.
Is immigration known or possible?
Possible, unknown
Would immigrants be adapted to survive in Canada?
Yes
Is there sufficient habitat for immigrants in Canada?
Unknown
Is rescue from outside populations likely?
Unknown
Quantitative Analysis
Quantitative analysis was not undertaken.
Current Status
- Committee on the Status of Endangered Wildlife in Canada: Special Concern 2007
- International Union for Conservation of Nature: lower risk/near threatened (LR/nt)
Status and Reasons for Designation
Status: Special Concern
Alpha-numeric code: NA
Reasons for Designations: This large (maximum reported length 4.8 m), heavy-bodied shark is a benthic species that is widely distributed over continental and insular shelves in temperate and tropical seas throughout the world. In Canadian Pacific waters, it is found in inlets and along the continental shelf and slope typically at depths greater than 91 m (range 0-2500 m). In the absence of information about population structure, it is treated as a single population for assessment purposes. The present population size and abundance trends are not known. The only available abundance index, encounter rates with immature sharks at a shallow site in the Strait of Georgia, has decreased significantly (>90%) in the last five years. This index is not likely representative of the overall abundance trend because only immature sharks are encountered and the site is shallow relative to the preferred depth range. The principal known threat to the species is fishing. This shark has been the focus of at least three directed fisheries in Canadian waters, most recently in the late 1980s and early 1990s. It continues to be caught as bycatch, but survival of released sharks is unknown. Sharks observed by divers sometimes show scars from entanglement in fishing gear. Because of its late age of maturity (18-35 yr for females), it is likely susceptible to overfishing even at low levels of mortality. Little is known about the abundanceand movement patterns of this species elsewhere in the world, so the potential for a rescue effect is unknown.
Applicability of Criteria
- Criterion A: (Declining Total Population): Although trends are not known, a decline is suspected because of the past fisheries, present interactions with fisheries and the late age at maturity.
- Criterion B: (Small Distribution, and Decline or Fluctuation): Not applicable because both the extent of occurrence and the area of occupancy exceed threshold values for ‘Threatened’.
- Criterion C: (Small Total Population Size and Decline): Not applicable because population size is unknown.
- Criterion D: (Very Small Population or Restricted Distribution): Does not apply because the number of mature individuals likely exceeds 1,000 and area of occupancy is greater than 20 km².
- Criterion E: (Quantitative Analysis): Not undertaken.
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