Atlantic halibut

What it is

This fish is a right-eyed flounder belonging to the family Pleuronectidae. It lies on its left side with both eyes on the right head side. Adults display dark chocolate, olive or slate colours on top, while the underside is white. Younger specimens appear paler and mottled. The tail fin ends in a concave shape. Males typically weigh between 10 and 25 kilograms, whereas females can reach 250 kilograms. It ranks as the largest flatfish globally, with maximum recorded lengths hitting 4.7 metres and weights of 320 kilograms.

Where it lives

Its native waters span the temperate and arctic zones of the northern Atlantic. In the west, it ranges from southwestern Greenland and Labrador down to Virginia. Eastern populations inhabit areas around Iceland, the United Kingdom, Ireland, and northern Europe extending to Russia. These demersal creatures rest on ocean floors composed of sand, gravel or clay. They dwell at depths ranging from 50 to 2,000 metres, though they occasionally venture closer to the surface.

How it lives

Larvae drift pelagically before settling on the bottom at roughly four centimetres in length. Juveniles aged two to four years stay near shorelines, moving deeper as they mature. This species occupies a high trophic level. Diets shift from plankton in the first year to krill and small fish until age three. Adults consume cod, haddock, herring, sand eels, capelin, cephalopods and large crustaceans. Seals, Greenland sharks and killer whales hunt them. They are strong swimmers capable of long migrations.

Breeding and life cycle

Sexual maturity arrives late, with males maturing at seven to eight years and females at ten to eleven. Spawning takes place between December and April near the seabed in water temperatures of 5 to 7 degrees Celsius. Females act as batch spawners, releasing anywhere from a few thousand to four million eggs depending on size and age. The eggs measure approximately 3.0 to 3.8 millimetres. Hatched larvae are about 6.5 millimetres long. Growth rates depend on food availability and competition.

Fish and people

Historically a vital food source, demand surged in the 19th century. Overfishing has caused wild stocks to collapse because the species grows slowly. Most wild halibut sold today is actually Pacific halibut. Anglers use circle hooks baited with herring and heavy weights. Catch-and-release survival rates are high at 95 per cent due to the lack of a swim bladder. Aquaculture efforts began in countries like Canada, Norway, the UK, Iceland and Chile by 2006 to meet market demand.

Status and threats

The International Union for Conservation of Nature listed it as Endangered in 1996. Slow population growth prevents quick recovery from fishing pressure. The US National Marine Fisheries Service marks it as a Species of Concern. The American Fisheries Society classifies it as Vulnerable. Greenpeace International added it to its seafood red list in 2010 due to unsustainable sourcing risks. Insufficient data currently prevents listing under the US Endangered Species Act.

Questions people ask about Atlantic halibut

Good reading and sources

• Atlantic halibut on WikipediaEncyclopedia
• More photos on Wikimedia CommonsPhotos
• Wikidata recordOpen data