Blue shark (Atlantic and Pacific populations) COSEWIC assessment and status report: chapter 14
Technical Summary
Range of Occurrence in Canada: Atlantic Ocean
Extent and Area Information
Extent of occurrence (EO)(km2)
Sum across the annual distributional range determined from catches.
1 200 000 km2
Specify trend in EO
Unknown
Are there extreme fluctuations in EO?
Unlikely
Area of occupancy (AO) (km2)
Represents area of frequent and regular sightings (catches).
800 000 km2
Specify trend in AO
Unknown
Are there extreme fluctuations in AO?
Unlikely
Number of known or inferred current locations
Widespread, non localized.
Specify trend in #
Not Applicable
Are there extreme fluctuations in number of locations?
Not Applicable
Specify trend in area, extent or quality of habitat
Habitat not considered to have changed.
Population Information
Generation time (average age of parents in the population)
8 years (approximate)
Number of mature individuals
Unknown
Total population trend
Possible decline
% decline over the last/next 10 years or 3 generations
Northwest Atlantic longline CPUE (Baum)(1986-2000): 60% decline
ICCAT longline CPUE (ICCAT)(1971-2000): No overall trend
Scotian shelf longline CPUE (Baum)(1986-2000): 64% decline
Grand Banks longline (Baum) (1986-2000 ): No overall trend
Canadian bigeye swordfish fleet CPUE (Campana)(1995-2003): 50% decline
Canadian bluefin fleet longline CPUE (Campana)(1995-2003): No overall trend
Are there extreme fluctuations in number of mature individuals?
No
Is the total population severely fragmented?
No
Specify trend in number of populations
Considered a single ocean basin-wide population
Are there extreme fluctuations in number of populations?
N/A
List populations with number of mature individuals in each
Not Available
Threats (actual or imminent threats to populations or habitats)
The primary threat is fishing, especially mortality from pelagic longline fishing operations where blue sharks are regularly caught as bycatch. Fishing in Canada’s Atlantic waters contributes a small fraction of the overall removals in the North Atlantic
Rescue Effect (immigration from an outside source)
Status of outside population(s)?
Blue sharks are highly migratory and status in Canada is a reflection of the population as a whole.
Is immigration known or possible?
Yes (seasonal)
Would immigrants be adapted to survive in Canada?
Yes (seasonal)
Is there sufficient habitat for immigrants in Canada?
Yes
Is rescue from outside populations likely?
Yes
Quantitative Analysis
[provide details on calculation, source(s) of data, models, etc] : Not undertaken
Current Status
COSEWIC: Special Concern, April 2006
IUCN: lower risk/ near threatened
Status and Reasons for Designation
Status: Special Concern
Alpha-numeric code: Not applicable
Reasons for Designation: This species is a relatively productive shark (maximum age 16-20 years, mature at 4-6 years, generation time 8 years, 25-50 pups every two years) but as an elasmobranch, populations are susceptible to increased mortality from all sources including from human activities. The species is considered to have a single highly migratory population in the North Atlantic, of which a portion is present in Canadian waters seasonally. The abundance index which is considered to best represent the whole population has declined 60% 1986-2000 but another index shows no long-term trend for the whole population 1971-2003. Indices of abundance in and near the Canadian waters show variable trends from no decline to 60% decline from the 1980s to early 2000s. There is evidence for a decline in mean length in longline fisheries in Canadian waters 1986-2003. The primary threat is bycatch in pelagic longline fisheries; although the threat is understood and is reversible, it is not being effectively reduced through management. Assessing the impact of bycatch on the population would benefit from better information on proportion of individuals discarded which survive. It appears that recent fishery removals from the North Atlantic have been several tens of thousands of tons annually. Estimated Canadian removals, a small proportion of the total, have been declining since the early 1990s and recently have averaged around 600 t/yr.
Applicability of Criteria
Criterion A (Declining Total Population):
Not applicable.
Criterion B (Small Distribution, and Decline or Fluctuation):
Not applicable.
Criterion C (Small Total Population Size and Decline):
Not applicable.
Criterion D (Very Small Population or Restricted Distribution):
Not applicable.
Criterion E (Quantitative Analysis):
Not applicable.
Range of Occurrence in Canada: Pacific Ocean
Extent and Area Information
Extent of occurrence (EO)(km2)
Sum across the annual distributional range determined from catches.
117 000 km2
Specify trend in EO
Unknown
Are there extreme fluctuations in EO?
Unlikely
Area of occupancy (AO) (km2)
Unknown
Specify trend in AO
Unknown
Are there extreme fluctuations in AO?
Unlikely
Number of known or inferred current locations
Widespread, non localized.
Specify trend in #
Not Applicable
Are there extreme fluctuations in number of locations?
Not Applicable
Specify trend in area, extent or quality of habitat
Habitat not considered to have changed.
Population Information
Generation time (average age of parents in the population)
8 years (approximate)
Number of mature individuals
Unknown
Total population trend
Unknown
% decline over the last/next 10 years or 3 generations
Unknown
Are there extreme fluctuations in number of mature individuals?
Unlikely
Is the total population severely fragmented?
No
Specify trend in number of populations
Considered a single ocean basin-wide population
Are there extreme fluctuations in number of populations?
No
List populations with number of mature individuals in each
Not Applicable
Threats (actual or imminent threats to populations or habitats)
The primary threat is fishing - blue sharks are caught as bycatch. Fishing in Canada’s Pacific waters accounts for an insignificant proportion of the total annual catch in the North Pacific (20-40 t of the estimated total 39 000 t/yr.)
Rescue Effect (immigration from an outside source)
Status of outside population(s)?
Blue sharks are highly migratory and status in Canada is a reflection of the population as a whole. The overall status in the Pacific is unknown.
Is immigration known or possible?
Yes (seasonal)
Would immigrants be adapted to survive in Canada?
Yes (seasonal)
Is there sufficient habitat for immigrants in Canada?
Yes
Is rescue from outside populations likely?
Yes
Quantitative Analysis
[provide details on calculation, source(s) of data, models, etc] : Not undertaken
Current Status
COSEWIC: Data deficient, April 2006
IUCN: lower risk/ near threatened
Status and Reasons for Designation
Status: Data deficient
Alpha-numeric code: Not applicable
Reasons for Designation: The species is apparently present regularly in Canada’s Pacific waters, probably as part of a wider North Pacific population. Catch information and data from the International Pacific Halibut Commission longline survey (1998-2004) suggest the species is widespread on the continental shelf with a concentration at the shelf break. It has also been taken, at times in large numbers, in oceanic waters. No information is available to assess status in Canada, as there have been few records in existing surveys. Pacific-wide indices are of low reliability because of historical misidentification issues, but one recent assessment from United States National Marine Fisheries Service suggests that fishing mortality on this species in the North Pacific is well below the level of maximum sustainable yield. Level of fishery removals (bycatch) in the Canadian Pacific are low, of the order of 20-40 t/yr.
Applicability of Criteria
Criterion A (Declining Total Population):
Not applicable.
Criterion B (Small Distribution, and Decline or Fluctuation):
Not applicable.
Criterion C (Small Total Population Size and Decline):
Not applicable.
Criterion D (Very Small Population or Restricted Distribution):
Not applicable.
Criterion E (Quantitative Analysis):
Not applicable.
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