How Slow Is a Greenland Shark? The Ocean's Slowest Shark

How fast does a Greenland shark swim?

The best measurements come from a 2012 study by Yuuki Watanabe and colleagues, who attached data loggers to wild Greenland sharks in the cold fjord waters of Svalbard, Norway. The tags recorded swimming speed and the movements of the tail.

On average, the sharks swam at about 0.34 m (1.1 ft) per second, roughly 1.2 km/h (0.76 mph). Their fastest cruising speed was about 0.74 m (2.4 ft) per second, or around 2.7 km/h (1.7 mph). Their tails swept from side to side only about once every seven seconds, the slowest tail-beat rate recorded for a fish of their size. The researchers titled their paper “The slowest fish.”

Why are Greenland sharks so slow?

The main reason is temperature. Greenland sharks live in water that is usually between about −1 and 7 °C (30–45 °F), and like most fish they are cold-blooded, so their body is about the same temperature as the water. At near-freezing temperatures, the chemical reactions that power muscles run several times more slowly than in warm water. Their muscles also appear suited to slow, steady swimming rather than sprinting.

Swimming slowly also saves energy. In the cold, dark waters of the Arctic and the deep North Atlantic, food can be scarce and unpredictable. A large shark with a low metabolism can cruise steadily for long periods, wait for a meal and survive long gaps between big feeds, such as a seal or a whale carcass.

The same slow pace of life shows up in everything the Greenland shark does. It grows about 1 cm (0.4 in) a year or less, appears to mature only at around 150 years of age, and may live for centuries, as explained in How long do Greenland sharks live?

How does such a slow shark catch seals and fish?

This is one of the great puzzles about Greenland sharks. Their stomachs often contain fast-swimming fish such as cod and redfish, and in Svalbard the remains of ringed and bearded seals are common. Seals swim several times faster than the sharks’ measured cruising speed, so a shark could never win an open chase.

Scientists have several explanations:

• Ambushing sleeping seals. Seals often rest and sleep in the water. A dark, slow, silent shark rising from below may be able to approach a sleeping seal unnoticed.
• Stealth and suction. Greenland sharks can expand their mouths quickly to suck in prey at close range, which may work on fish resting near the seabed.
• Scavenging. They have an excellent sense of smell and readily eat carcasses of seals, whales and fish, including discarded catch from fishing boats.
• Short bursts. The tags may have missed rare moments of faster swimming, although no burst speeds have yet been measured.

Many sharks are found with whole prey in their stomachs, which supports the idea that they suck in prey or catch animals that are asleep or already dead.

Is the Greenland shark the slowest fish in the world?

It depends how you measure. Relative to its size, the Greenland shark is the slowest fish known: bigger fish normally swim faster, and no other fish of its size has been recorded swimming so slowly. In absolute terms, though, small fish such as the dwarf seahorse are far slower, moving only about 1.5 m (5 ft) per hour. Both feature among the slowest animals in the world.

Among sharks, the Greenland shark sits at the opposite extreme from the shortfin mako, generally considered the fastest shark, which uses warm muscles and a streamlined body to chase fast prey such as tuna and swordfish.

Slow but not idle

A slow swimming speed does not mean the Greenland shark stays in one place. Tagging studies show that individuals can cover long distances over months, traveling along coasts and between fjords. Many also move up and down through the water column, rising toward the surface and descending to depths of hundreds of meters.

The species ranges from the surface under Arctic sea ice to depths of more than 2,000 m (6,600 ft) farther south. In the deep, cold water where it lives, steady, economical swimming is far more useful than speed, and it has served this ancient-looking shark well for a very long time.