Blue shark (Atlantic and Pacific populations) COSEWIC assessment and status report: chapter 6

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Distribution

• Global Range
• Canadian Range

Global Range

Blue sharks are found worldwide in temperate and tropical oceans primarily in surface waters and offshore (epipelagic) (Figure 2). There is no evidence of either a reduction or expansion in the global range.

Figure 2: Global Distribution of Blue Shark

Map source: FAO 2004

Canadian Range

Atlantic

Blue sharks are encountered along the shelf break from northeastern Newfoundland southward including the Gulf of St. Lawrence and the Bay of Fundy (Figure 3). Abundance in Canadian waters varies seasonally with higher catches occurring in the third and fourth quarters. Catch is very low in the first quarter and moderate in the second quarter (Figure 4). Extent of occurrence is approximately 1.2 million km² based on the distribution of catch records. Area of occupancy is 0.8 million m² based on the area with the most frequent sightings.

Figure 3: Distribution of Blue Sharks in Canada’s Atlantic Region Based on All Known Commercial Catch Records Between 1986-2004

Figure 4: Blue Shark Catch Location by Season Observed by the International Observer Program on Canadian Vessels Fishing Swordfish or Tuna Between 1986-2001

From Campana et al. 2004. Note that most blue sharks are caught in the 3^rd and 4^th quarters.

Pacific

Blue sharks are encountered in trawl and hook and line fisheries along the west coast of Vancouver Island and the Queen Charlotte Islands, as well as in Hecate Strait (Figure 5). Surveys conducted throughout most of the continental shelf by the International Pacific Halibut Commission (IPHC) from 1998-2004 using longline gear show a similar encounter pattern as the commercial fishery (Figure 6). There is also an increase in hook and line commercial catches of blue sharks during summer which reflects a seasonal increase in blue shark abundance (Figure 7) as catch per unit effort in the third and fourth quarters is nearly fifty times that in the first and second quarters (Appendix 1).

Figure 5: Distribution of Blue Shark Catch off British Columbia Based on Records from All Commercial Fisheries Between 1996-2004

(23.5 t visible). Source: DFO PacHarvHL and PacHarvTrawl databases.

Figure 6: Catch Location of Blue Sharks (n=170) in the International Pacific Halibut Commission Set Surveys in Area 2B Between 1998-2004

Data from International Pacific Halibut Commission (IPHC).

Figure 7: Distribution of Blue Shark Caught by British Columbia’s Commercial Hook and Line Fleet by Season Between 1998-2004

Source: DFO, PacHarHL database.

Based on known movement patterns (Nakano and Seki 2002), it is unlikely that blue sharks have extended residency in Pacific Canadian waters and at any time only a small portion of the overall North Pacific population is likely utilizing Canada’s waters. There are few data available to detect changes in range in Canadian waters. The extent of occurrence is approximately 117 000 km² based on the area within polygons encompassing catch records (Appendix 2). Being a pelagic species, their distribution likely extends from depths of 200 m offshore to the limits of Canada’s international boundary, an area of 450 000 km².