Blue shark (Atlantic and Pacific populations) COSEWIC assessment and status report: chapter 1
COSEWIC
Assessment Summary
Assessment Summary – April 2006 (Atlantic Population)
Common name:
Blue shark
Scientific name:
Prionace glauca
Status:
Special Concern
Reason 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.
Occurrence:
Atlantic Ocean
Status history:
Designated Special Concern in April 2006. Assessment based on a new status report.
Assessment Summary – April 2006 (Pacific Population)
Common name:
Blue shark
Scientific name:
Prionace glauca
Status:
Data Deficient
Reason 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.
Occurrence:
Pacific Ocean
Status history:
Species considered in April 2006 and placed in the Data Deficient category. Assessment based on a new status report.