Latin name

Hippoglossus stenolepis

Other names

Giant halibut, northern halibut, hali (Canada), barn door; Japanese: ohyô; Portuguese: alabote do Pacifico; Spanish: fletán del Pacifico.

Identification

Halibut are usually dextral, meaning both eyes are on the right side of the head. Its coloration ranges from olive to dark brown or black with lighter irregular spots. More elongated than other flatfish, the body of the Pacific halibut is medium wide, being about a third of its length. The mouth is large, extending to the lower eye. The fine, smooth scales are well recessed in the skin, and the lateral line has a pronounced arc over the pectoral fin. The tail is crescent-shaped, longer at the tips than in the middle, which distinguishes it from most other flounders.

Distribution

Pacific halibut inhabit the continental shelf of the North Pacific and have also been recorded along the coast of North America from central California to Nome, Alaska. They live on or near the bottom and have been caught at depths of up to 3,600 feet, although most are caught in the summer when they are 75 to 750 feet deep. In the fall and winter, they usually return to deeper water.

Habitat

Preferring cool water (37° to 46 °F), halibut are most often found where the bottom consists of cobble, gravel, and sand, especially near the edges of underwater plateaus and breakaway lines.

Size

Typical halibut range in length from 28 to 50 inches and weigh from 10 to 60 pounds. Record catches on rod and reel include several halibut weighing over 400 pounds (the all-tackle record is 459 pounds), and 500-pound specimens have been caught commercially. The largest specimens are females, as males rarely weigh more than 90 pounds.

Life history and Behavior

Spawning occurs in the North Pacific and Bering Sea during the winter. Eggs and larvae swim freely in the ocean current for 6 months, settling to the bottom in shallow coastal waters, and migrate counterclockwise across the Pacific Ocean, reaching their spawning grounds by mature age.

Food and feeding habits

Halibut lie on the bottom and wait for tidal currents to wash food within reach. They are good swimmers and may leave the bottom to feed on pelagic fish such as herring and sand lance. They also inhabit almost anywhere crab, squid, octopus, cod, pollock, or other food is abundant.

Reproduction

Pacific halibut mature quite late, and the timing differs significantly between males and females. Males on average become sexually mature at about 8 years of age. Females mature later, on average at about 12 years, although this age can range from 6 to 14 years. Spawning occurs annually during the winter months, from November to March. For spawning, halibut gather on spawning grounds at the outer edge of the continental shelf and on the continental slope. They form aggregations. Studies have shown that about 42% of adults in some areas may skip a breeding season (so-called "skip spawning"). They are batch spawners. Their ovaries develop in a group-synchronous pattern, where there is one main group of fast-growing eggs that will be spawned in the current season. The number of eggs directly depends on the size of the female. A female weighing about 23 kg (51 lbs) can spawn about 500,000 eggs, and a large individual weighing over 113 kg (249 lbs) — up to 4 million.

Offspring development occurs in the pelagic zone, far from the shore. The eggs are about 3 mm (0.12 inches) in diameter. They are fertilized externally and drift in the water column at depths of 100–450 meters (328–1,476 feet). Incubation lasts 15 to 20 days at temperatures of 5–6 °C (41–43 °F). The hatched larvae lead a pelagic lifestyle. They initially feed on the yolk sac reserves, and after about 55 days, they transition to feeding on zooplankton. When the larva reaches a length of about 2.5 cm (1 inch) (after about 6 months), it begins metamorphosis: the left eye migrates to the right side, and it acquires the typical flatfish shape. Juveniles settle to the bottom in shallow coastal areas.

Interesting facts

The Pacific halibut spawns at a depth of 200–300 meters (656–984 feet). The eggs are buoyant and are slowly carried by the current. Far from the shore, larvae hatch from the eggs, which initially lead a pelagic lifestyle. But as soon as the left eye begins to migrate to the right side and the small fish become similar to adults, they descend to the bottom and migrate to the shores. Development lasts 4–5 months, and during this time, the eggs and newly hatched halibut, driven by currents and their own movement, complete a thousand-kilometer journey.