Pacific halibut (Hippoglossus stenolepis) can be found throughout most of the marine waters of the North Pacific. Halibut are the largest of all the flatfishes and are distributed along the continental shelf of the North Pacific from Southern California to Nome, Alaska and along the coasts of Japan and Russia. Halibut are demersal fish, being found on or near the bottom over mud, sand, or gravel banks. While halibut have been recorded at depths of 3,600 feet, most are caught at depths of 90 to 900 feet. Halibut generally are in deeper waters during the winter where they spawn at depths of 600 to 1,500 feet during the period from November through March. Following spawning, halibut begin to migrate to shallower coastal summer feeding areas.
Male halibut become sexually mature at approximately eight years old while females typically are not mature until age 12. A female can release from 1/2 to 4 million eggs depending on the size of the fish. After spawning, the eggs float near the bottom and hatch into larvae after approximately 15 days. These larvae are free floating and are subject to movements by deep ocean currents. As the larvae mature, they move higher in the water column where surface currents move them to shallower coastal waters.
These currents generally carry the eggs and larvae in a northwesterly direction.Halibut larvae begin life in an upright position similar to other fish with an eye on each side of the head. However, when the larvae are approximately one inch long, they undergo an amazing transformation in which the left eye moves over the snout to the right side of the head and the pigmentation on the left side of the fish fades. The young halibut take on the features of adult fish approximately six months after hatching and settle to the bottom in shallow, nearshore areas.
The halibut now have both eyes on the pigmented (olive to dark brown) side of the body while the underside of the fish is white.
During their first year of life, they feed on plankton. Young halibut (1-3 years old) feed on small shrimp-like organisms and small fish. As halibut increase in size, fish make up a larger part of the diet. Besides pollock, sablefish, cod, and rockfish, large halibut also eat octopus, herring, crabs, clams, and smaller halibut.While halibut can live to be up to 40 years old, grow to over eight feet long, and weigh over 500 pounds, most halibut caught in the sport fishery will be 8-15 years old and weigh between 10 and 100 pounds. Female halibut live longer and grow faster and larger than do males. Few males exceed 80 pounds and generally all halibut over 100 pounds are females. The oldest halibut on record was a 42 year old female while the oldest male observed was 27 years old. The age of halibut is determined by a bony structure in the inner ear called an otolith. As the fish grows, annual growth rings are formed on the otolith, similar to rings on a tree.
Halibut typically move to deeper waters as they grow older. Besides the seasonal movement from deeper waters in the winter to shallower waters in the summer, halibut may also undergo intensive geographic migrations. Halibut tagged in the Bering Sea have been caught as far south as the coast of Oregon, a migration of over 2,000 miles. This migration is generally in an easterly and southerly direction, counter balancing the northeasterly drift of the eggs and larvae.