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Species at Risk Act- Legal Listing Consultation Workbook, Porbeagle Shark (Lamna nasus)
Species specific information
The porbeagle, Lamna nasus, is a large, strong swimming shark representing the only member of the genus Lamna known across the North Atlantic Ocean. They have a spindle shaped body which changes from dark bluish-grey above to white along the sides and belly. Although they have been recorded at lengths over 3 meters, specimens over 2 meters are uncommon.
Porbeagle sharks are found on both sides of the Atlantic, but tagging studies have concluded that the northwest population is separate from the northeast population. In the northwest Atlantic, porbeagle sharks are widely distributed from Greenland to Bermuda, with the highest numbers found between Newfoundland and the Gulf of Maine. They are a mid-water species commonly found on continental shelves but are known to inhabit inshore and offshore waters from the surface to at least 700 m in depth. Porbeagle sharks prefer water temperatures less than 18 °C and evidence from Canadian commercial fisheries suggests that they travel to maintain their preferred temperature range throughout the year.
Based on observations of mature individuals, mating is thought to occur from August to November on the Grand Banks, off southern Newfoundland and at the entrance to the Gulf of St. Lawrence. Analyses of catch data indicate that adult males begin migrating to these spawning grounds in spring in advance of the females.
Porbeagle sharks exhibit rapid growth in their first year when, at a mean length of 85 cm, they start to be caught in the fishery. The growth rate begins to slow at maturity which for males is an age of 8 years at a length between 162 and 185 cm and for females is an age of 13 years at a length between 210 and 230 cm. Females bear an average of 4 young per year after a gestation period of 8 to 9 months.
The porbeagle is a voracious fish-eater. Diet studies have identified over 21 prey items including redfish, gaspereau, herring, cod, mackerel and squid. They are not known to feed on marine mammals.
COSEWIC Assessment COSEWIC provides the following rationale for designating the porbeagle shark as endangered:
This wide-ranging oceanic shark is the only representative of its genus in the North Atlantic. The abundance has declined greatly since Canada entered the fishery in the 1990s after an earlier collapse and partial recovery. Fishery quotas have been greatly reduced, and the fishery has been closed in some areas where mature sharks occur. The landings now are comprised mostly of juveniles. Its life history characteristics, including late maturity and low fecundity, render this species particularly vulnerable to overexploitation.
Threats to Porbeagle Shark
Although porbeagle sharks have no identified predators other than humans, the superior quality of their meat makes them highly sought after. But their low number of offspring and late maturity make them extremely sensitive to over-fishing, so when commercial fishing for porbeagle sharks began in the early 1960's, the population crashed only 6 years later. It had only recovered to 30 % of its original abundance when fishing pressure increased in the 1990's plunging the population once again into a decline.
Current quota levels are substantially reduced from those of the mid 1990's and bycatch in other fisheries is limited. However, due to porbeagle shark's low population numbers, even this level of fishing pressure may still affect its recovery.
There is a concern that limited food availability, due to dwindling groundfish stocks, could be contributing to the decline of the porbeagle shark. However, this is not likely to be a significant factor because of the varied diet of this species.
The COSEWIC status report states that there is no evidence to support other reasons for the decline in population numbers of porbeagle sharks.
Protecting Porbeagle DFO developed Fisheries Management Plans for porbeagle in 1994 and 1995 that prohibited finning, and allowed for limited exploratory licences along with restrictions on gears, areas and seasons. A collaborative porbeagle research program between DFO and the shark industry has resulted in the quota being reduced from 1000t in 1997 to 250t for 2002 to 2007 at which time a detailed stock assessment is planned.
Potential Impacts on Stakeholders Once added to the List of Wildlife Species at Risk, porbeagle shark will be protected. If particular activities are assessed to be a threat to the survival and recovery of a listed species, management measures will be put in place to restrict those activities and ensure the protection of species at risk.
These measures may lead to a variety of impacts on stakeholders, including additional costs. The following list is not exhaustive; please use this consultation as an opportunity to list omissions.
Aboriginal Groups or People
Prohibitions could affect aboriginal people directly fishing for porbeagle shark if the conservation of the species is at risk. Some bycatch may be allowed in fisheries taking porbeagle incidentally if measures are taken to reduce the impacts on porbeagle and the conservation of the species is not compromised.
It is important to fully determine the extent of potential threats to porbeagle shark by any fishing activities. Once this species is listed, prohibitions will apply to fishing activities identified to be a threat to the survival and recovery of porbeagle shark. A directed fishery would not likely continue. Some level of bycatch may be allowed for fishing activities that take porbeagle shark incidentally, but only if measures are taken to minimize the impact of the activity on this shark and the bycatch level will not cause a further decline in the status of the species.
Those wishing to carry out research on porbeagle sharks or in areas of their habitat may be required to comply with strict guidelines. This may limit the types and/or durations of research permitted on porbeagle shark and may lengthen the preparation time required for planning research projects.
Shipping, Oil and Gas exploration and other activities may be impacted by the listing of porbeagle shark. No specific threats from these or other activities have been identified. However, if porbeagle shark is listed as suggested by COSEWIC, prohibitions will apply to ALL activities affecting this species. Proposed oil and gas activities that fall under the Canadian Environmental Assessment Act (CEAA) will need to address the impacts on SARA listed species in accordance with this legislation.
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