The porbeagle is a wide-ranging coastal and oceanic shark feeding on fish and cephalopods. It is streamlined and robust with large black eyes and a smoothly rounded snout. It is highly valued for game fishing and human consumption.

In brief

• Rarely observed in the waters off Northern Ireland, however sighted off Rathlin Island and occasionally caught in fishing gear.
• More likely to be seen in summer or autumn when smaller species come close enough inshore to be caught.
• Is a priority species as the population is in decline.
• Vulnerable to overfishing due to its late age at maturity and low fecundity.
• Threatened due to high commercial value, accidental capture in fishing nets and driftnets.

Species description: The porbeagle is dark metallic blue in colour on top, white on the bottom and can reach up to 350 cm in length. It has five large conspicuous gill slits and the tail fin is large and crescent-shaped. The first dorsal fin is located above the base of the pectoral fins and the second is above the anal fin. Its teeth are large and triangular in shape and it can weigh up to 180 kg. It is described as active and strong when swimming to purse prey but sluggish and inactive when hooked.
Porbeagles feed on a wide range of shoaling and demersal fish including herring, mackerel and whiting. They also feed on cephalopods such as octopus, squid and cuttlefish. It is mostly found over deep water from 10 to 15 miles offshore.

Life cycle: The age of maturity for females is 13 years and 8 years for males. They live for approximately 25-46 years. The reproductive period is annual and the time between conception and birth is 8-9 months with a litter size of 1-5 pups (average 4). There are no recorded spawning or nursery grounds in Irish waters. Pupping and nursery areas may be in continental waters but are little documented.

Similar species: The porbeagle has previously been confused with the Mako shark (Isurus oxyrinchus). However the second dorsal fin of the Mako is located in front of the anal fin, the first dorsal fin is behind the pectoral base and the teeth are long and pointed.

How to see this species: Porbeagle sharks are found in Northern Ireland coastal waters, the actual population is not known. This species has been sighted off the north side of Rathlin Island, around Malin Head and over the many World War II wrecks off Culdaff, Ireland.

Current status: Data deficient. Critically Endangered in NE Atlantic and Mediterranean. Endangered in NW Atlantic. Population has been depleted.

Why is this species a priority in Northern Ireland?

• Criterion 1: Internationally listed species.
• Criterion 2: Decline based on available data and expert judgement.
• Criterion 4: NI stronghold or endemic – both stronghold range/population and designation as ‘endemic’ subject to expert judgement.

Threats: The main threat is fisheries (target and bycatch) utilising its very high value meat. There is no direct fishery in Northern Irish waters however incidences of bycatch do occur. Like many sharks porbeagle produce a fairly low number of young every year making this species highly vulnerable to over exploitation.
Porbeagle is a highly migratory and schooling species. The eastern and western North Atlantic populations have both been seriously overexploited by direct longline fisheries. The North East Atlantic population had been subject to unrestricted fishing pressure since its earlier crash in the 1960s. Driftnets are also known to be a threat to this species.

Action: Records of new sites for this species, with details of habitat and population are always valuable. Observations with a photograph can be recorded using iNaturalist, find the MBDP-NI iNaturalist project here.

Alternatively, records can be sent to CEDaR, National Museums Northern Ireland, 153 Bangor Road, Cultra, Holywood, County Down, BT18 0EU. Tel 028 9039 5257, e-mail cedar.records@nationalmuseumsni.org, or via the online portal.

Objectives:

• Undertake studies on population structure.
• Examine discard survival from commercial longline fisheries in relation to soak time, hook type, etc.
• Undertake studies on the movements and habitat utilisation using pop-up electronic tags.
• Develop a recovery plan.
• Avoid capture of porbeagle.

Conservation:

• In 2010, EC Regulation 23/2010 prohibited fishing for porbeagle in EU waters and, for EU vessels, to fish for, to retain on board, to tranship and to land porbeagle in international waters
• Rathlin Island is a Marine Protected Area with multiple designations.
• Listed as Critically Endangered on European Red List.
• The global status of this species is listed as Vulnerable on the IUCN Red List.
• Listed on Appendix II of CITES.
• On OSPAR List of Threatened and/or Declining Species and Habitats.
• NERC Act 2006 Species of Principal Importance in England and Wales.
• Listed on Annex 1 (Highly Migratory Species) of the UN Convention on the Law of the Sea (UNCLOS).
• Rathlin Island is a Marine Protected Area with multiple designations.

Distribution Map from NBN: Lamna nasus at National Biodiversity Network mapping facility, data for UK.

iNaturalist: Lamna nasus at iNaturalist World Species Observations database.

WoRMS: Lamna nasus at World Register of Marine Species. Accepted name: Lamna nasus (Bonnaterre, 1788). AphiaID: 105841.

Classification: Biota; Animalia; Chordata; Vertebrata; Gnathostomata; Chondrichthyes; Elasmobranchii; Neoselachii; Selachii; Galeomorphi; Lamniformes; Lamnidae; Lamna