Life Cycle: Halibut spawn at depths of 600 to 1,500 feet from November through March. Female halibut release anywhere from a few thousand to 4 million eggs, depending on the size of the fish. About 15 days later, the eggs hatch and the larvae drift with deep ocean currents. In the Gulf of Alaska, the eggs and larvae drift in a counter clockwise direction along the coast.
As the larvae mature, they move higher in the water column and ride the surface currents to shallower, more nourishing coastal waters.
Although age at maturity varies over time, about half of male halibut are sexually mature by 8 years of age, while half of the females are mature by age 11.
Eye Migration: The larvae start life in an upright position like other fish, with an eye on each side of the head. When the larvae are about one inch long, the left eye moves over the snout to the right side of the head. At the same time, the coloration on the left side of the body fades. The halibut end up with both eyes on the pigmented (olive to dark brown) upper side of their body, while their underside is white. By the time they are six months old young halibut settle to the bottom in shallow, nearshore areas.
Diet: Halibut feed on plankton during their first year of life. Young halibut (1-3 years old) feed on euphausiids (small shrimp-like organisms) and small fish. As halibut grow, fish make up a larger part of their diet. Besides pollock, sablefish, cod, and rockfish, large halibut also eat octopus, herring, crabs, clams, and smaller halibut.
Size and Age: Halibut are the largest of all the flatfishes. Some halibut exceed 400 pounds, including the 459 pound state record fish caught during 1996 in Unalaska Bay.
Female halibut grow faster and are typically larger than males of the same age. Males rarely reach 100 pounds.
Halibut age is estimated by counting growth rings laid down in the fish's "otolith", a bony structure in the inner ear. Male and female halibut reach ages in excess of 50 years, but most fish taken in the sport fishery are 5-15 years old.
Where to Find Them: Halibut can be found throughout most of the marine waters of Alaska - as far north as Nome, along the Aleutian Chain, and throughout the waters of the southeastern Alaska panhandle. Halibut can also be found along the continental shelf as far south as southern California, as well as along the coasts of Japan and Russia.
Halibut are usually on or near the bottom over mud, sand, or gravel banks. Most are caught at depths of 90 to 900 feet, but halibut have been recorded at depths up to 3,600 feet. As halibut mature, they migrate in a clockwise direction in the Gulf of Alaska, countering the drift of eggs and larvae. Halibut tagged in the Bering Sea have been caught as far south as the coast of Oregon, a migration of over 2,000 miles.
Halibut also move seasonally between shallow waters and deep waters. Mature fish move to deeper offshore areas in the fall to spawn, and return to nearshore feeding areas in early summer. It's not yet clear if fish return to the same areas to spawn or feed year after year.