Topic: Greenland shark

The Greenland shark can be up to 7 m long. Whereas other large predatory sharks are rapid and have a robust appearance, such as its distant cousins the white shark and porbeagle, the Greenland shark appears somewhat more sluggish. This is reflected in its Latin name: Somniosus, the ‘sleepy one’. The name is somewhat misguided for this top predator, which is known to consume large cod, oceanic birds and seals (it has been hypothesized that they can sneak up on and attack sleeping seals). Remains of whale, reindeer and horse have also been found in Greenland shark digestive tracts, presumably scavenged after drowning. There are no known harmful interactions with humans, including from divers who have observed these animals under water.

Biology

Greenland sharks have an extremely slow growth rate and can live well over 100 years, possibly several hundred years. Studies indicate that females might not be reproductively mature until they are around 100 years old. These characteristics mean that any recovery in population numbers after overfishing would take many years.

Greenland sharks swim very slowly in deep and shallow waters. They often have a characteristic parasitic copepod attached to their corneas. This likely renders the sharks blind, but this does not seem to affect them too much. All sharks, including the Greenland shark, have a highly developed set of other senses, such as electroreception and smell, allowing them to effectively home in on prey from many kilometres away.

Fishery

There is a long tradition of hunting Greenland shark in Norway. A small-scale fishery near the coast took place in the 1700s and 1800s, but from the beginning of the 1900s fishermen needed to venture further offshore to find Greenland shark. Catches were often plentiful in the early days, but strong fishing pressure drove population numbers down quite rapidly. Many fishermen even decided to venture as far as Greenland to sustain the fishery. By the 1950s, the fishery had more or less ended, although some localized fishing continued into the 1970s. This story is a classic example of ‘serial overfishing’, where fishing effort moves on to deplete stocks further afield after first depleting the local stock. Although we do not know the size of the Greenland shark population, it appears very probable that the population was depleted as a direct result of overfishing.

After 50 years without a targeted fishery for Greenland shark, it now appears to be returning to our shores. Experimental fishing, performed as part of research efforts, have demonstrated improved catch rates. However, this does not necessarily signify the presence of a sustainably harvestable resource.

Initially, the Greenland shark was valued for its enormous oily liver, which was harvested for the production of liver oil (tran) and oil lamps. Its meat is considered poisonous and is not considered safe to eat unless properly treated. Icelanders have an old and unique tradition of fermenting and drying Greenland shark meat, a process that renders it safe for consumption as a local delicacy. There is currently little or no interest to reinstate the fishery. In fact, Greenland shark is often considered a nuisance to fishermen. It is a notorious thief, consuming halibut caught by hook-and-line fishermen and damaging their gear in the process.

Historically, the Greenland shark fishery was incentivised to reduce their numbers. Today, they are mostly caught by sports fishers as catch-and-release. Some of these sports fishermen collaborate with the Institute of Marine Research, registering their catches and providing us with valuable data to assess the growth and distribution of this mysterious shark.