Science Advisory Report  2015/048

Recovery Potential Assessment for Porbeagle (Lamna nasus) in Atlantic Canada

Summary

• Porbeagle (Lamna nasus) is a species of mackerel shark in the family Lamnidae. This species is widely distributed in the Northwest (NW) Atlantic, occurring in Canadian waters; the Gulf of St. Lawrence, around Newfoundland and Labrador, on the Scotian Shelf, and in the Bay of Fundy. 
• Porbeagle was originally assessed by the Committee on the Status of Endangered Wildlife in Canada (COSEWIC) as Endangered in 2004. As per section 24 of Species at Risk Act (SARA), COSEWIC reviewed the classification of Porbeagle in May 2014. The status of Porbeagle was confirmed as Endangered.
• The life span of Porbeagle is estimated to be between 25 and 46 years and generation time is about 18 years. The species has low fecundity (approximately 4 pups per year) and a late age of sexual maturation.
• All modeled runs indicated that abundance of Porbeagle in the NW Atlantic declined during the 1960s, increased slightly during the late 1970s and early 1980s, and decreased again during the late 1990s. Estimates of the population size in 2009 ranged from 196,911 to 206,956 sharks or approximately 22% to 27% of its size in 1961. Female spawner abundance was estimated to be approximately 16% of what it was in 1961.
• Porbeagle appear to occupy relatively cool water temperatures throughout the year, with 50% being caught between 5-10°C (gear depth). Temperature at depth is a significant predictor of catch rate, while sea surface temperature is not. Results from Pop-up Satellite Archival Tags indicate that Porbeagle can reside in slightly warmer temperatures than those suggested by fishery captures, with 50% of their time being spent between 8-13°C.
• Fishing is the only known source of human-induced mortality on Porbeagle in Atlantic Canada. With closure of the Canadian Porbeagle directed fishery in 2013, the only remaining source of fishing mortality in Canada’s exclusive economic zone (EEZ) is bycatch. There are unknown and unregulated catches outside of Canadian waters.
• In Canadian waters, Porbeagle bycatch mortality from all sources (capture + post release + landing) has averaged 110 metric tonnes (mt) annually since 2010.
• The swordfish and other tuna longline, offshore tuna longline, groundfish longline, groundfish gillnet and otter trawl are considered the greatest current threats based on landings records and discard estimates. Although the threat risk of each fishery independently is considered low/medium, the cumulative impacts of all fishing-related mortality would represent a higher threat risk.
• Anthropogenic activities that could pose a potential threat to Porbeagle habitat necessary for population viability (e.g. mating grounds and areas of high population density) include: noise associated with offshore petroleum exploratory seismic surveys, marine pollution associated with a catastrophic offshore petroleum exploration or development spills, and large scale marine development projects such as pipelines and submarine cables.
• A recovery target for the Northwest Atlantic Porbeagle population is proposed as achieving 80% of female spawning stock numbers (SSN) at Maximum Sustainable Yield (MSY), or SSN80%, within three generations (or approximately 54 years). Across the four productivity models examined, this would equate to 24,000 to 32,000 mature females.
• Under what is considered the most realistic of the four productivity models that were examined (Model 3), recovery to SSN80% in the absence of fishing would occur around 2033, while recovery under recent fishing mortality rates (approximately 110 mt or 2%) would occur around 2042.
• The current 2% mortality rate from all sources (based on 110 mt bycatch mortality since 2010) would allow the population to recover under all scenarios and at a faster rate than the 4% total allowable catch (185 mt) mortality rate. Total harm to the population (from all sources, including capture mortality, post release mortality, and landings) should not exceed a 4% mortality rate to allow the population to continue to increase and move towards the recovery targets.

This Science Advisory Report is from the 19-20 February 2015, zonal peer review on “Recovery Potential Assessment – Porbeagle (Lamna nasus)” to update and support specific processes with regards to recovery targets, allowable harm, and other related aspects of SARA. Additional publications from this process will be posted on the Fisheries and Oceans Canada (DFO) Science Advisory Schedule as they become available.

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