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Shark Working Group

Blue Shark (Prionace glauca) --- North Pacific

◊ Biological Profile

Blue shark is an epi- and mesopelagic shark species with a circumglobal distribution in the major oceans. It is the most widely distributed and most abundant oceanic pelagic shark. Blue shark ranges from about 50°S to 60°N.

Blue shark abundance increases with latitude in both hemispheres, reflecting preference for temperatures around 12-20°C. As a result, blue sharks are abundant near-surface in temperate waters but deeper-dwelling and less abundant in the tropics.

North Pacific blue sharks are highly migratory with complex movement patterns and spatial structure related to reproduction and the distribution of prey. Seasonal shifts to higher latitudes associated with oceanic convergence or highly productive boundary zones also occur. Their diet consists primarily of squids and small pelagic fishes.

Distribution for blue shark
in the North Pacific Ocean.
  • Life span: About 16 years
  • Maximum size: About 380 cm total length (TL)
  • Start of maturity: Age 4-7 years
  • Reproductive cycle: 1-2 years
  • Reproductive mode: Placental viviparity; gestation period 9-12 months
  • Parturition season:Variable, spring to fall
  • Litter size: averages about 25-30 pups
  • Size at birth: 35-50 cm TL

◊ Fisheries for Blue Shark in the North Pacific Ocean

Blue sharks are caught in large numbers in the North Pacific Ocean by longline, gillnet, recreational, and artisanal fisheries. Although considered bycatch and discarded at sea by many pelagic fleets, they are retained for human consumption, fish oil, leather and animal feed in several countries.

◊ Stock Status (From ISC13)

Based on the base case and most alternative model scenarios, the blue shark biomass level in 2011 in the North Pacific is estimated to be near the highest levels seen in the time series, and the current fishing mortality rates and catch levels are below those expected to produce MSY. Stock status in relation to maximum sustainable yield (MSY) demonstrates that the stock is not overfished and that overfishing is not occurring.

A single scenario using CPUE data for the Hawaii-based deep longline fleet for 1995-2011 in place of the Japan shallow longline index for 1994-2010 showed a continual decline in stock biomass from 1971 to 2011, which could lead to a different conclusion regarding stock status. The Hawaii index was not considered to be representative of the Pacific-wide stock due to the relatively small amount of catch, limited spatial coverage, and the potential impact of regulatory changes in the fishery.

Kobe plot for the base-case in the North Pacific blue shark (Prionace glauca) stock assessment. The solid blue circle indicates the median estimate in 1971 (the start-year of stock assessment calculation); the solid gray circle and horizontal and vertical solid gray lines indicate the median and 90% confidence limits in 2011, respectively.

◊ Conservation Advice (From ISC13)

Based on the base-case and most alternative model scenarios, the North Pacific blue shark stock is not overfished and overfishing is not occurring. Future projections of the base case model show that median blue shark biomass in the North Pacific will remain above BMSY under the catch harvest policies examined (status quo, +20%, -20%). Similarly, future projections under different fishing mortality (F) harvest policies (status quo, +20%, -20%) show that median blue shark biomass in the North Pacific will remain above BMSY.