Nature & living things

Warm-blooded, seemingly playful, and fished to collapse twice

The porbeagle is a stocky, cold-water shark related to the great white's family, found across the North Atlantic and in a broad band of the Southern Hemisphere, with the closely related salmon shark filling its niche in the North Pacific. It's built for speed and endurance rather than agility, with a spindle-shaped body, crescent tail and lateral keels, and it's one of the few sharks that can keep its body, brain and eyes noticeably warmer than the surrounding water thanks to special heat-exchanging blood vessels. It hunts opportunistically up and down the water column for fish and squid, migrates long distances between shallow feeding grounds and deeper overwintering or pupping areas, and has even been seen apparently playing with kelp fronds or floating debris. Unlike most sharks, pregnant females feed their few embryos on a steady supply of unfertilized eggs over an eight-to-nine month pregnancy, usually producing just four pups a year, with the strongest embryo sometimes outcompeting a sibling for food in the womb.

That slow reproductive rate has made the species extraordinarily vulnerable to fishing, and its history is a textbook case of boom and bust. Norwegian longliners built up an intense fishery in the northeast Atlantic from the 1930s that collapsed the stock there by the 1950s, after which the fleet moved to the northwest Atlantic and did the same to that population within about six years during the 1960s. Prized for its meat, especially in Italy, and for its fins, the porbeagle kept being fished even as numbers fell, with Canada later becoming the main fisher in the region before tightening quotas in response to further depletion. In the Mediterranean the population has crashed by more than 99.99 percent since the mid-twentieth century and is now confined to waters around Italy, despite decades of supposed protective listings that were never backed by real management.

Today the species is rarely dangerous to people, with only a handful of ambiguous or minor bites ever recorded, and it's prized instead as a hard-fighting game fish often mistaken by novices for the mako. Conservation status varies sharply by region: the IUCN rates it vulnerable worldwide but endangered in the western North Atlantic and critically endangered in the eastern North Atlantic and Mediterranean. It has gained some international protections, including a 2013 listing that allows tighter trade controls, and outright fishing bans in European Union and Norwegian waters since 2011 and 2012, while New Zealand and Canada apply catch limits rather than full protection. Even where fishing has stopped, scientists expect recovery to take decades because the shark simply cannot reproduce fast enough to bounce back quickly.

Porbeagle embryos develop inside the mother and feed on unfertilised eggs while still in the uterus — a reproductive strategy that yields roughly four pups a year.

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