Fisheries and Oceans Canada
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Underwater World
Atlantic Halibut
Estuary and Gulf of St. Lawrence (Canadian East Coast)
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The Atlantic halibut is distinguished by its flat shape and its strange appearance due to the position of both its eyes on the right side. When the Atlantic halibut changes from a larva to a fish, its eyes are initially located on each side of its head. However, during its first year of life, its body morphology undergoes a major change whereby its left eye migrates towards the right side of its head. It then swims with its blind (eyeless) side facing the sea bottom.
Closeup
Despite being recognized as one of the largest flatfishes in the world, the Atlantic halibut was considered for many years as undesirable and even a nuisance fish. It was only in the 19th century that a market developed in Boston for this powerful swimmer. Growing to a length of 2.5 m and weighing in excess of 300 kg, the species now represents a seafood delicacy thanks to its firm and tasty flesh.
Like its relatives in the Pleuronectidae family, Atlantic halibut have both their eyes on the right side of their bodies and swim with the right side facing the surface. This side varies in colour from greenish brown to very dark chestnut brown whereas the blind (left) side is usually white in young fish and generally mottled with grey or even cherry red in older, larger fish. The blind side of some halibut occasionally takes on a bicoloured appearance.
With its huge mouth sporting very sharp curved teeth, the Atlantic halibut is distinguished from other flatfish by its powerful concave tail and the strongly curved lateral line above the pectoral fin.
A very close relative of the Atlantic halibut, the Pacific halibut (Hippoglossus stenolepis) lives in the northern half of the Pacific Ocean from southern California to the Bering Sea, as well as northeast of Sakhalin Island (Russia) in the Okhotsk Sea and northeast of Japan.
In the northwest Atlantic, Atlantic halibut live along the eastern coast of North America from Virginia and New Jersey (USA) north to Greenland, several degrees inside the Arctic Circle. Atlantic halibut are also found in the northeast Atlantic. In the south, major concentrations are found in the Gulf of Gascony, while in the north, they are found near the Faroe Islands (in the frigid waters off the west coast of Norway) as well as along the southwest coast of Iceland.
There are two stocks of Atlantic halibut on the Canadian east coast: the first stock, commonly called the Gulf of St. Lawrence stock, is concentrated in two sectors - the northern sector in the Esquiman Channel, the Laurentian Channel and north of Anticosti Island, and the southern sector around the Magdalen Shallows and the Magdalen Islands. The second stock, the Nova Scotia and southern Grand Banks stock, is found mostly in the waters along the edges of Georges Bank, Sable Island Bank, Banquereau Bank, the Grand Banks and the Flemish Cap.
The information provided under the following headings deal with the Atlantic halibut stock in the Gulf of St. Lawrence. When the information concerns both Canadian east coast stocks or the species in general, the terms "halibut" or "Atlantic halibut" are used.
Lifecycle and reproduction
The spawning season of Gulf of St. Lawrence Atlantic halibut takes place between December and June. The female spawns at between 10 and 14 years of age. Older and larger females can lay several million eggs during the season. The male reaches sexual maturity at 8 to 10 years old.
We currently know little about the exact Atlantic halibut spawning sites on the Canadian east coast. Certain indicators in the Gulf of St. Lawrence point to the Magdalen Shallows as a favourable spot for Atlantic halibut reproduction.
The spherical and pink unfertilized eggs are 3 to 4 mm in diameter. After fertilization in the sea, they float freely in the water. The eggs hatch in approximately 16 days at a temperature of 6°C giving birth to larvae measuring approximately 7 mm long. At hatching, the larvae possess a large yolk sac that provides them with a source of food for four to five weeks until they can start feeding on plankton.
Halibut larvae resemble the larvae of most other marine fish inasmuch as they swim with their bellies towards the sea bottom and their eyes are positioned on each side of their heads. When halibut grow to between 16 and 20 mm in length, the left eye begins to migrate over the top of their heads towards the right side. This migration process continues for several months until the eye is completely relocated on the right side at a time when the larvae are about 44 mm long.
During this period, the pigmentation intensifies and becomes increasingly restricted to the right side of the body. When juveniles reach lengths of 50 mm or more, they start to swim like adults, i.e., with their unpigmented left side facing the bottom and the eyed right side facing the surface. After a period of adaptation, the young halibut begin a slow migration down the water column to the deeper waters in the channels.
Gulf of St. Lawrence halibut go through a period of rapid and continuous growth (7-8 cm per year), increasing from 40 cm to more than a metre long between the time when they adopt benthic life (i.e., close to the bottom), and the time when they reach sexual maturity. Females tend to grow faster than males.
During this growth period, Gulf Atlantic halibut go through several distinct feeding phases: halibut up to 30 cm long feed on worms and small shrimp whereas those measuring 30-80 cm long feed on a combination of crustaceans and small fish. Adult halibut feed almost exclusively on large fish like redfish, cod, haddock, small halibut and lumpfish.
Atlantic halibut can live up to 50 years, but their typical lifespan is 25-30 years.
The underwater world of Atlantic halibut
Gulf of St. Lawrence halibut spend the winter months in waters as deep as 500 m but usually migrate towards shallower waters during the summer. On both sides of the Atlantic, halibut seem to prefer temperatures of between 3°C and 9°C, as well as sandy soft bottoms in which they can bury themselves.
Atlantic halibut migrations are of two types: vertical and horizontal. At sunset, halibut swim up the water column in pursuit of their prey that also migrate vertically towards the surface, and then return to the bottom at dawn.
Although halibut can migrate long distances, they prefer to remain in the area where they were born. Through fish tagging, it has been determined that Atlantic halibut can travel up to 1,000 km in the Gulf of St. Lawrence. However, the absolute record was established by a halibut initially tagged in 1946 near Anticosti Island that was recaptured seven years later on the west coast of Iceland after swimming more than 2,500 km.
Man represents Atlantic halibut's main predator, but juveniles also represent a favourite prey of cod and other fish. When halibut reach adult size, they can be targeted by sharks, killer whales and seals. However, the halibut's powerful tail and ability to swim fast generally enable it to escape such threats.
The Atlantic halibut fishery
In the 17th and 18th centuries, fishers were not particularly interested in halibut. It was only around 1820 that halibut became popular on the northeast coast of America. Due to growing market demand, local fish stocks were quickly depleted, which led to high-sea fishing on Georges Bank and the Nantucket Shoals until catches began to decline during the 1850s. The fishery was then extended to Canadian waters, particularly the Brown Bank sector, and then gradually to other regions. From the 1860s on, American and Canadian halibut fishers worked on various banks of the Scotian Shelf from Newfoundland to western Greenland before expanding to the Gulf of St. Lawrence.
In the 19th century, halibut were fished using handlines equipped with a single hook baited with fish scraps and weighted with lead so that it could reach the bottom. Later, when halibut fishing became more profitable, this type of line was replaced by the longline that has remained the most effective method of fishing halibut up to the present day. A longline consists of a main groundline equipped with many lighter secondary lines called "gangings" attached several metres apart.
Today 95 percent of the commercial fishing in the Gulf of St. Lawrence is done by longliners equipped with hydraulic winches to drag the fishing gear aboard where the halibut can then be detached from the hooks. In 2008 approximately 500 metric tonnes of Atlantic halibut with a landed value of more than $3.5 million were harvested in the Gulf by Quebec and the four Atlantic provinces.
While Atlantic halibut on the Canadian east coast are generally fished wild, the species is also raised in huge sea enclosures in the fjords of Norway and Iceland. The possibility of farming halibut is currently being studied at St. Andrews (Nova Scotia) and St. John's (Newfoundland).
Atlantic halibut is listed as an endangered species on the Red List of the International Union for Conservation of Nature (IUCN). Various management measures are currently in effect for commercial halibut fishing on Canada's east coast, including the 1997 requirement that any halibut less than 81 cm long must be returned to the water.
A powerful blow of its tail
There is a story about a fisherman who caught a large halibut and eventually managed to pull it close to his boat. Under the impression that the fish was exhausted after such a long struggle, the fisherman then gaffed it only to find the tussle begin anew. The fisherman then tried to lift the fish out of the water using the hooks of his spare anchor, but this time the fish struck the fisherman with a big blow of its tail and escaped. Today, fishers are wiser and now club halibut before hauling them aboard.
Revised: October 2009
