Blue shark (Atlantic and Pacific populations) COSEWIC assessment and status report: chapter 11

Limiting Factors and Threats

Fishing mortality is the single largest threat to blue shark populations worldwide. Pelagic fisheries regularly catch blue sharks as bycatch. Campana et al. (2004) examined six pelagic fisheries occurring in Canada’s Atlantic waters and found that, mean blue shark bycatch accounted for 26-152% of the total directed large pelagic catch, with an overall mean of 34%. A review of published catch rates in North Atlantic pelagic fisheries found catch rates ranged from 5.1-40.0 blue sharks per 1000 hooks (Campana et al. 2004). Blue sharks have little value and are therefore released at sea. Campana et al. (2004) estimated that 60% of blue sharks would survive after being captured. Current catch of blue sharks in Canadian waters between 1996 and 2002 has been less than 1000 t/yr which is a decline from the early 1990s when catches were often greater than 1500t. Annual removals in Canadian waters probably represent a small fraction (perhaps 1% or less) of total removals in the North Atlantic.

Longline effort in the entire Atlantic has rapidly increased since 1955 (Figure 11), and fishing mortality is probably increasing in direct proportion to the fishing effort (although this information is not directly relevant to individuals in Canadian waters it is considered a good indication of fishing effort on the wider population). Decreasing fishing mortality on this species is only possible with a decrease in fishing effort for pelagic species worldwide. In 2004, ICCAT adopted the resolution to prohibit shark finning, which is anticipated to decrease fishing mortality. However, the amount of blue shark fins removed on an annual basis is unknown (see next section). The impact on blue shark populations from this change in fishing practice depends on the proportion of blue sharks which are currently being finned and by the compliance rate of the various international fisheries involved.

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