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.
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