Research Document - 2015/026
Current Status and Threats to the North Atlantic Blue Shark (Prionace glauca) Population in Atlantic Canada
By Steven E. Campana, Mark Fowler, Dan Houlihan, Warren Joyce, Mark Showell, Carolyn Miri and Mark Simpson
Abstract
Both conventional and satellite tagging studies indicate that blue sharks are widely distributed and highly migratory across both Atlantic Canada and the North Atlantic waters, with no evidence of year-round residency in Canadian waters.
There is no fishery-independent index of abundance for blue sharks in Canadian waters. Standardized catch rates from observers on pelagic longline vessels provide an index of local, short-term abundance, but do not appear to reflect population abundance.
Population abundance in the North Atlantic appears to have decreased modestly since 1994.
The reported catch of blue sharks grossly underestimates both the actual catch (sum of landed catch and discards) and the catch mortality. In recent years, almost all catch mortality can be attributed to hooking and post-release mortality in pelagic longlines. Bycatch appears persistently along the edge of the continental shelf and in basins on the Scotian Shelf. Mortality from derbies and recreational shark fishing accounts for less than 3% of overall fishing-related mortality in Canadian waters.
Blue sharks have negligible commercial value in Canada and large quantities (approximately 1400 mt annually) are discarded by commercial pelagic fisheries. Their persistence to this point is partly attributable to their productivity relative to other sharks species, the fact that few mature females are caught either in Canadian or American waters, and the relatively low overall Canadian contribution to overall population mortality. At present, fishing-related sources of mortality in Canadian waters appear to be sustainable, although large quantities of discards remain unutilized.
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