Giant boat-knives and other bad decisions: The tale of the basking shark.

Article originally appeared on Sketchy Science.

The ocean is full of sea monsters. That is a pretty well established fact. Any parent who has ever told an insomniac child, awake and trembling at 3AM, that there is no such thing has clearly never seen a picture of a giant squid or an angler fish. Sea monsters range from the very small (jellies) to the unfathomably enormous, but few are as impressive as the basking shark (known to science by the delightfully gladiatorial name of Certorhinus maximus).

Basking sharks fall into the “sea monsters” camp because of their size. They are the second largest fish in the ocean, reaching lengths of up to 33 feet and weighing as much as 8,000 pounds (3,600 kilograms). They also look unmistakably ferocious in their classic sharky way. They have dorsal fins that stick out of the surface of the water, streamlined bodies, and (scariest of all) enormous mouths. You could swim into a basking sharks mouth pretty easily without ever touching the edges.

The good news about basking sharks is that they aren’t ferocious at all. Like so many of the biggest things in the ocean, they are almost comically gentle. They cruise around at around 5 kilometers per hour with their mouths agape, swallowing tiny plankton and filtering out massive amounts of water. They love to hang out in the sun right at the surface of the water, hence their name.

Unfortunately, this affinity for sunshine and their ridiculous size has caused some trouble between us and them, but not for the reasons you might think. Whereas humans normally hunt things as impressive as basking sharks for trophies or meat, these lumbering beasts are actually pretty useless as a commodity (unless you’re one of the 3 people alive who enjoy hakarl).

The problem with basking sharks is that back in the 1940’s and 50’s, they routinely got caught in fishermen’s gillnets by mistake. You may think that a basking shark would make a good catch for a humble fisherman, but the only sellable part of the great fish is its liver. I say “sellable” instead of “valuable” because in the mid 20th century, basking shark livers sold for 3 cents a pound (about $35 per shark) whereas the nets they destroyed with their massive bodies cost roughly ten times that much.

This inevitably led to fishermen hating basking sharks and complaining to the government. In 1949, the Canadian government gave in and labeled basking sharks marine pests and set to work at killing them. The method of choice was either ramming them with boats or slicing them in half with a huge makeshift blade mounted on the bow of a boat. In the 1950’s a giant boat-knife was an impressive thing, at least impressive enough to be featured in the November 1956 issue of Popular Mechanics magazine.

The giant knives proved remarkably effective and in a matter of decades, basking sharks were nowhere to be found. Nowadays there is about one siting per year of the coast of British Columbia. Ask someone at the Department of Fisheries and Oceans where they went and you will likely get a sheepish, embarrassed look in return.

In 2010, Canada followed the lead of countries like Ireland and Great Britain and declared the basking shark endangered. A recovery strategy was finalized in July 2011 and the people who once drove the knife-boats have since been at work mashing the ocean’s CTRL+Z key. Only time will tell if they’ve changed their minds in time.