A powerfully built shark with a pointed, conical snout. First dorsal fin origin over or anterior to pectoral fin insertion. First dorsal apex somewhat rounded. Second dorsal fin about 1/4 height of first dorsal. Second dorsal origin opposite anal fin origin. Prominent lateral keels on caudal peduncle support a large, powerful falcate, caudal fin. Shorter secondary caudal keel positioned below main keel. Upper caudal lobe slightly longer than lower.
Dorsal coloration metallic grey, bluish-brown, or almost black. Ventral surface white without any obvious spots or blotches. White free rear tip on first dorsal fin.
Maximum length at least 280cm. Anecdotal records of larger animals (up to 360cm) are probably exaggerations. Size at birth 60-80cm.
Cold to warm-temperate oceanic and inshore environments. Surface to 1809m but usually 0-200m.
Found throughout the Southern Ocean and in the temperate/arctic latitudes of the North Atlantic.
The porbeagle shark has low biological productivity with small litters, late age-at-maturity, and a shorter life span of 26 years in the North Atlantic compared to 60 years in the Southern Hemisphere. Globally, the species is targeted and caught incidentally in coastal and pelagic commercial and small-scale longline, purse seine, and gillnet fisheries, as well as by rod and reel, and is often retained for the high-value meat as well as its fins. Steep declines have occurred in the North Atlantic; with declines also evident, though not as steep, in the Southern Hemisphere. The North Atlantic subpopulation reduction was 50–79% over three generations (58.5 years) and the Southern Hemisphere subpopulation reduction was <20% over three generations (114.9 years). The overall estimated median reduction was 26.5%, with a 41.5% probability of <20% reduction and 45.5% probability of >30% reduction over three generations. Expert judgement elicitation was used to estimate that globally, the reduction is 30–49% over three generations (58.5 and 114.9 years) and therefore, the Porbeagle is assessed globally as Vulnerable A2bd.
Citations and References
Rigby, C.L., Barreto, R., Carlson, J., Fernando, D., Fordham, S., Francis, M.P., Herman, K., Jabado, R.W., Liu, K.M., Marshall, A., Pacoureau, N., Romanov, E., Sherley, R.B. & Winker, H. 2019. Lamna nasus. The IUCN Red List of Threatened Species 2019: e.T11200A500969. https://dx.doi.org/10.2305/IUCN.UK.2019-3.RLTS.T11200A500969.en. Downloaded on 15 December 2020.
An aplacental viviparous species with oophagous (egg eating) embryos. 1-6 embryos per litter, but usually 3-4.
Porbeagle sharks in the North Atlantic consume a wide range of fishes, squids, and crustaceans, including butterfish, menhaden, cods, capelins, mackerel, herring, pilchards, hake, cusk, flounders, alewifes, loligo squids, and crabs.
Migratory. In the North Atlantic, porbeagles move inshore and northward during the summer.
Reaction to divers
Extremely shy. Difficult to approach on scuba or snorkel unless fixated on bait.
The porbeagle is a difficult shark to swim with. Blue shark chumming trips off the south/west coast of the UK, occasionally attract porbeagle sharks but encounters are few and far between.
I have photographed porbeagles in the Bay of Fundy in Canada while accompanying researchers from the University of New Brunswick. However, I have not heard of any porbeagles being encountered by sport divers anywhere on the west side of the North Atlantic.
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