(DRAFT) - Taxonomy
Species halibut, Pacific
Species Id M010015
Date 27 AUG 96

TAXONOMY

NAME - halibut, Pacific

OTHER COMMON NAMES -

ELEMENT CODE -

CATEGORY - Fish

PHYLUM AND SUBPHYLUM - ,

CLASS AND SUBCLASS - Osteichthyes,

ORDER AND SUBORDER - Pleuronectiformes,

FAMILY AND SUBFAMILY - Pleuronectidae,

GENUS AND SUBGENUS - Hippoglossus,

SPECIES AND SSP - stenolepis,

SCIENTIFIC NAME - Hippoglossus stenolepis

AUTHORITY -

TAXONOMY REFERENCES - 232, 209 and 211

Taxonomy - 1 (DRAFT) - Status
Species halibut, Pacific
Species Id M010015
Date 27 AUG 96

STATUS

Coded Status
Commercial
Migrant
Existing, FMP exists
Commercial/consumption
International treaty
See Comments

REFERENCES FOR STATUS - 209 and 232

COMMENTS ON STATUS -
Pacific halibut in the Gulf of Alaska undergo extensive migrations in an
easterly and southerly direction *209*.
The Pacific halibut fishery is one of the most valuable luxury food
fisheries in North America *209*.
The International Pacific Halibut Commission (IPHC) was established between
Canada and the United States in 1923 as the first international convention
for the joint management of a marine fishery, the Pacific halibut *209*.
After a severe depletion during the 1960s attributable to trawling fleets,
strict catch restrictions were levied and the fishery is slowly recovering
*209*.
Halibut stocks are approaching historical highs above maximum sustainable
yield (MSY) in the northeastern, central and western Gulf of Alaska. MSY,
however, is below average off British Columbia and in the Bering Sea, but
improving *209*.

Halibut move from deep water (up to 1,097 m) along the edge of continental
shelf to shallower (27 to 274 m) banks and caostal waters to feed during
the summer. The halibut return to deep water in the winter to spawn. These
movements and coastwide migrations may encompass hundreds of miles *232*.

The International Pacific Halibut Commission manages the Pacific halibut
fishery. The commission monitors catch and effort, restricts gear and size
of fish landed, and defines fishing areas. The North Pacific Fishery
Management Council includes Pacific halibut in their list of unallocated
species that must be avoided by groundfish fleets and includes in their Gulf
of Alaska and Bering Sea Groundfish Management Plans time-area closures
designed to minimize incidental catch of halibut *232*.

Status - 1 (DRAFT) - Distribution
Species halibut, Pacific
Species Id M010015
Date 27 AUG 96

DISTRIBUTION

Distribution - 1 HABITAT ASSOCIATIONS

HABITAT - MARINE
AQUATIC

REFERENCES FOR HABITAT - 209

LAND USE -
Water

REFERENCES FOR LAND USE - 209

NATIONAL WETLAND INVENTORY CODES

NWI NWICLS NWIMOD NWISPEC

Marine
Marine
Marine

REFERENCES FOR NWI - 209

COMMENTS ON HABITAT ASSOCIATIONS -
Adult halibut are primarily benthic apex predators of widely varied
epibenthic prey types but often leave bottom to feed on bathypelagic or
even pelagic fishes, such as herring *209*.
Halibut eggs are bathypelagic *209*.
Larvae develop through a variable and protracted 5-7 month pelagic phase
*209*.
Juvenile halibut settle to the bottom in shallow inshore nursery areas.
In general, juveniles tend to remain closer inshore than adults *209*.

Pacific halibut are distributed on the continental shelf of the North
Pacific Ocean. Adult halibut feed both on benthic and pelagic organisms as
they move on and off the continental shelf. Halibut spawning occurs all
along the coast in the northeast Pacific but is concentrated near the edge
of the continental shelf *232*.

ANIMAL/PLANT SPECIES ASSOCIATIONS -
Sea lion

REFERENCES FOR SPECIES ASSOCIATIONS - 232

COMMENTS ON SPECIES ASSOCIATIONS -
Sea lions often prey upon halibut hooked on longline gear, but it is
unlikely that they are any threat to free-swimming halibut. Eggs, larvae,
and juvenile halibut probably fall prey to many fish species, but older
halibut, because of their size, must be safe from predation by most animals,
except possibly large marine mammals *232*.

Habitat Associations - 1 (DRAFT) - Food Habits
Species halibut, Pacific
Species Id M010015
Date 27 AUG 96

FOOD HABITS

TROPHIC LEVEL -
CARNIVORE

REFERENCES FOR TROPHIC LEVEL - 209

LIFESTAGE FOOD FOOD PART
Adult Squid, Octopus Not Specified
Adult Crustaceans Not Specified
Adult Fish Not Specified
Adult Osteichthyes Not Specified
Adult Clupeiformes Not Specified
Adult Pleuronectiformes Not Specified
Adult Malacostraca Not Specified
Adult Gadiformes Not Specified
Adult See Comments; Food Not Applicable
Larva Crustaceans Larva stage
Larva Crustaceans Juvenile stage
Larva Crustaceans Not Specified
Larva Copepods Not Specified
Larva Malacostraca Not Specified
Larva See Comments; Food Not Applicable
Juvenile Molluscs Not Specified
Juvenile Bivalve Molluscs Not Specified
Juvenile Crustaceans Not Specified
Juvenile Malacostraca Not Specified
Juvenile Fish Not Specified
Juvenile Osteichthyes Not Specified
Juvenile Clupeiformes Not Specified
Juvenile Salmoniformes Not Specified
Juvenile Pleuronectiformes Not Specified
General Crustaceans Not Specified
General Malacostraca Not Specified
Juvenile Malacostraca Not Specified
Important Malacostraca Not Specified
Juvenile Perciformes Not Specified
Important Perciformes Not Specified
Juvenile Gadiformes Not Specified
Important Gadiformes Not Specified
Adult Malacostraca Not Specified
Adult Osteichthyes Not Specified
Adult Perciformes Not Specified
General Molluscs Not Specified
General Squid, Octopus Not Specified
General Gadiformes Not Specified
General Pleuronectiformes Not Specified

REFERENCES FOR GENERAL FOOD - 232

REFERENCES FOR IMPORTANT FOOD - 232

Food Habits - 1 (DRAFT) - Food Habits
Species halibut, Pacific
Species Id M010015
Date 27 AUG 96

REFERENCES FOR ADULT FOOD - 209 and 232

REFERENCES FOR JUVENILE FOOD - 209 and 232

REFERENCES FOR LARVAE FOOD - 209

COMMENTS ON FOOD -
Halibut are opportunistic feeders, using whatever food is available.
Halibut less than 10 cm in length feed primarily on small crustaceans,
mainly shrimp and small crabs. As the size of the halibut increases, the
frequency and size of fish in the diet also increases. In a survey of
stomach contents of young halibut mainly between 10 and 80 cm in length,
that species important in the diet were Tanner crab (Chionoecetes bairdi),
hermit crab (Paguridae), sandfish (Trichodon trichodon), sand lance
(Ammodytes hexapterus), and walleye pollock (Theragra chalcogramma). Larger
halibut feed on shrimps, crabs, and fish (especially sand lances). In the
Gulf of Alaska, halibut feed largely on Tanner crab (Chionoecetes spp.),
octopus, Pacific cod (Gadus macrocephalus), and arrowtooth flounder
(Atheresthes stomias) *232*.

Type of Feeding Areas Used: Adult halibut feed both on benthic and pelagic
organisms as they move on and off the continental shelf *232*.

Factors Limiting Availability of Food: Growth rate information indicates
that food may be a limiting factor when halibut abundance is high.
Apparently, large numbers of halibut can cause a significant reduction of
their food supply *232*.

Feeding Behavior: Halibut feed year-round, but large halibut feed less in
winter than in summer *232*.

COMMENTS ON ADULT FOOD -
Adult halibut are strong swimmers and vigorous carnivores. They are
opportunistic feeders and, as they grow beyond 80 cm, their preferences
shift from small to larger crustaceans and especially to fish and octupus.
Recent examination of the stomach contents of over 300 halibut indicated
that the principal prey are Pacific sand lance, walleye pollock and Tanner
crab. Pacific cod was the third most important fish prey species; other prey
were sable fish, rockfish, sculpins, arrowtooth flounder, and other
flatfish, Pacific herring and various clams and shrimp. There is evidence of
occasional cannibalism on juveniles by adults. The influence of cannibalism
on recruitment remains unknown but is likely to be insignificant *209*.

Larger halibut feed on shrimps, crabs, and fish (especially sand lances)
*232*.

COMMENTS ON JUVENILE FOOD -
Feeding is primarily within the benthic realm, but bathypelagic prey species
and even some pelagic fishes such as herring and salmon have been identified
*209*.

Smallest juveniles have been reported to eat small crustaceans (mainly
shrimp and crabs). Prey in the stomach contents of larger juveniles in
Food Habits - 2 (DRAFT) - Food Habits
Species halibut, Pacific
Species Id M010015
Date 27 AUG 96

decreasing order of occurrence have been Tanner crab, hermit crab, Pacific
sand lance, sand fish, and walleye pollock. Diet of juveniles of similar
size vary considerably, indicating their highly opportunistic feeding
behavior. In some areas, a large number of 0-age rock sole are consumed.
Other studies have reported clams, shrimps, hermit crabs and Tanner crabs in
stomach contents of young halibut from otter trawls in summer. Another
study reported harpacticoid copepods, amphipods and shrimp *209*.

Halibut less than 10 cm in length feed primarily on small crustaceans,
mainly shrimp and small crabs. As the size of the halibut increases, the
frequency and size of fish in the diet also increases. In a survey of
stomach contents of young halibut mainly between 10 and 80 cm in length,
that species important in the diet were Tanner crab (Chionoecetes bairdi),
hermit crab (Paguridae), sandfish (Trichodon trichodon), sand lance
(Ammodytes hexapterus), and walleye pollock (Theragra chalcogramma) *232*.

COMMENTS ON LARVAE FOOD -
No quantitative stomach analyses have been carried out, but qualitative
examinations and generalized relative proportions by depth and location have
been made. A high proportion of euphausiids have been identified in hauls
containing halibut larvae, followed by, in decreasing order: copepods,
decapod larvae, mainly megalops; crab zoeae and megalops; a carnivorous
copepod; and amphipods. A few of these cohabitants were found in the
stomachs of halibut larvae; one contained six megalops and a copepod,
another contained euphausiids, unidentified zoea and megalops, and juvenile
amphipod remnants. Others had pieces of euphausiid and megalops *209*.

Food Habits - 3 (DRAFT) - Environment Associations
Species halibut, Pacific
Species Id M010015
Date 27 AUG 96

ENVIRONMENTAL ASSOCIATIONS

G = General A = Adult
LIM = Limiting RA = Resting Adult
J = Juvenile FA = Feeding Adult
RJ = Resting Juvenile BA = Breeding Adult
FJ = Feeding Juvenile P = Pupae
L = Larvae E = Egg
RL = Resting Larvae
FL = Feeding Larvae

LIFESTAGE ENVIRONMENTAL ASSOCIATIONS
G Water Temperature: Below 15 degrees C
G Water Temperature: Specified in Comments
G Relation to Substrate: Occurs on substrate [not penetrating]
G Relation to Substrate: Specified in Comments
G Water Depth Preference: 100-200 ft.
G Water Depth Preference: 200-500 ft.
G Water Depth Preference: 500-1000 ft.
G Water Depth Preference: Specified in Comments
BA Water Depth Preference: 200-500 ft.
BA Water Depth Preference: 500-1000 ft.
BA Water Depth Preference: 1000-1500 ft.
BA Water Depth Preference: Greater than 1500 ft.
BA Water Depth Preference: Specified in Comments
E Water Temperature: Below 15 degrees C
E Water Temperature: Specified in Comments
E Water Depth Preference: 200-500 ft.
E Water Depth Preference: 500-1000 ft.
E Water Depth Preference: Specified in Comments
E Currents: upwelling
E Currents: specified in comments
L Currents: upwelling
L Currents: specified in comments
J Water Depth Preference: Specified in Comments
G Water Temperature: Specified in Comments
G Water Depth Preference: 100-200 ft.
G Water Depth Preference: 200-500 ft.
G Water Depth Preference: Specified in Comments
G Water Temperature: Below 15 degrees C
J Water Temperature: Below 15 degrees C
J Water Temperature: Specified in Comments
A Water Depth Preference: 50-100 ft.
A Water Depth Preference: 100-200 ft.
A Water Depth Preference: 200-500 ft.
A Water Depth Preference: 500-1000 ft.
A Water Depth Preference: 1000-1500 ft.
A Water Depth Preference: Greater than 1500 ft.
A Water Depth Preference: Specified in Comments
BA Water Depth Preference: 500-1000 ft.
BA Water Depth Preference: 1000-1500 ft.
BA Water Depth Preference: Greater than 1500 ft.
Environment Associations - 1 (DRAFT) - Environment Associations
Species halibut, Pacific
Species Id M010015
Date 27 AUG 96

LIFESTAGE ENVIRONMENTAL ASSOCIATIONS
BA Water Depth Preference: Specified in Comments
E Water Temperature: Specified in Comments
E Aquatic Habitat Zonation: Specified in Comments
E Water Depth Preference: 200-500 ft.
E Water Depth Preference: 500-1000 ft.
E Water Depth Preference: Specified in Comments
E Water Depth Preference: Greater than 1500 ft.
L Water Depth Preference: 200-500 ft.
L Water Depth Preference: Specified in Comments
J Aquatic Habitat Zonation: Specified in Comments
G Water Depth Preference: 50-100 ft.
G Water Depth Preference: 500-1000 ft.
G Water Depth Preference: 1000-1500 ft.
G Water Depth Preference: Greater than 1500 ft.
FA Water Depth Preference: 50-100 ft.
FA Water Depth Preference: 100-200 ft.
FA Water Depth Preference: 200-500 ft.
FA Water Depth Preference: 500-1000 ft.
FA Water Depth Preference: Specified in Comments

REFERENCES FOR ENVIRONMENTAL ASSOC_ - 209 and 232

REFERENCES FOR ADULT ENVIRONMENTAL ASSOC_ - 232

REFERENCES FOR FEEDING ADULT ENVIRONMENTAL ASSOC_ - 232

REFERENCES FOR BREEDING ADULT ENVIRONMENTAL ASSOC_ - 209 and 232

REFERENCES FOR JUVENILE ENVIRONMENTAL ASSOC_ - 232

REFERENCES FOR LARVAE ENVIRONMENTAL ASSOC_ - 232

REFERENCES FOR EGG ENVIRONMENTAL ASSOC_ - 209 and 232

COMMENTS ON ENVIRONMENTAL ASSOCIATIONS -
Halibut are demersal, living on or near bottom in 3-8 degrees C water.
Most are caught in summer in depths of 30-300m as they move from deep slope
areas to shallower banks and coastal waters *209*.

Halibut are concentrated in areas with bottom water temperatures ranging
from 3 to 8oC. The bathymetric range for adult halibut is between 27 and
1,100 m *232*.

The seasonal distribution of halibut is directly affected by bottom
temperature. During winter the bottom temperature in the shallow, shelf
area of the Bering Sea drops to 0oC and halibut concentrate in warmer,
deeper waters along the edge of the shelf. By June, the halibut migrate
into water from 50 to 150 m deep and halibut are distributed over a broad
region of the shelf as far north as St. Larwence Island during summer and
fall *232*.

Environment Associations - 2 (DRAFT) - Environment Associations
Species halibut, Pacific
Species Id M010015
Date 27 AUG 96

Halibut move from deep water (up to 1,097 m) along the edge of the
continental shelf to shallower (27 to 274 m) banks and coastal waters to
feed during the summer. The halibut return to deep water in the winter to
spawn *232*.

COMMENTS ON ADULT ENVIRONMENTAL ASSOC_ -
The bathymetric range for adult halibut is between 27 and 1,100 m *232*.

COMMENTS ON FEEDING ADULT ENVIRONTAL ASSOC_ -
Halibut move from deep water (up to 1,097 m) along the edge of the
continental shelf to shallower (27 to 274 m) banks and coastal waters to
feed during the summer. *232*.

COMMENTS ON BREEDING ADULT ENVIRONMENTAL ASSOC_ -
Known spawning grounds in the Gulf are in deep waters (200-500 m) just
beyond the continental shelf break. Eggs are released primarily at bottom
depths of 270-405 m and 75-400 m in the Gulf of Alaska and British Columbia
waters, respectively *209*.

The halibut return to deep water in the winter to spawn *232*.

Halibut spawning occurs all along the coast in the northeast Pacific but is
concentrated near the edge of the continental shelf, generally in depths
from 180 to 550 m. In the area from Cape St. Elias to Kodiak Island and in
the Bering Sea spawning takes place along the shelf edge at depths greater
than 180 m in concentrations of varying size *232*.

COMMENTS ON JUVENILE ENVIRONMENTAL ASSOC_ -
Catches in juvenile halibut surveys were usually larger when bottom water
temperatures were near 4oC. Juveniles settle to the bottom at about six
months old and remain in nearshore waters for one to three years *232*.

COMMENTS ON FEEDING JUVENILE ENVIRONMENTAL ASSOC_ -
Juveniles are limited to their benthic habitat during the
temperature-related seasonal interchange between summer feeding and
dispersal over shallower flats to deeper offshore areas in winter. The
surveys indicate a tendency for the greatest abundance to be at depths less
than 110m *209*.

COMMENTS ON LARVAE ENVIRONMENTAL ASSOC_ -
Larvae of halibut are heavier than surface sea water and drift passively in
deep ocean currents, generally at depths of 90 to 180 m but down to 686 m.
In the Gulf of Alaska, larvae are transported great distances by westward
ocean currents. As the larvae grow, their specific gravity decreases. By
the age of three to five months all larvae were in the upper 100 m. Larvae
are moved by prevailing winds to the shallow (about 12 m) sections of the
shelf *232*.

COMMENTS ON RESTING LARVAE ENVIRONMENTAL ASSOC_ -
Temperatures of 3.5-4.5 degrees C increase development times. Unusually
cold conditions, particularly if extended in time, would thus increase the
vulnerable period for predation. Salinity variations also may affect such
vulnerability. For example, if an unusual depression of isohalines
Environment Associations - 3 (DRAFT) - Environment Associations
Species halibut, Pacific
Species Id M010015
Date 27 AUG 96

persisted (excessively high freshwater runoff with a lowered pycnocline),
larvae would remain deeper longer even as their specific gravity decreases,
thus restricting a timely rise to upper layers for feeding and subsequent
development *209*.
Transport of eggs and larvae may present substantial differences from year
to year, with discernable spatial patterns of variation in abundance and
utimately recruitment. Interannual variations in the Alaska Coastal
Current system, particularly vigorous in the western Gulf, greatly affect
the alongshore and cross-shelf drift of larvae as they rise into surface
layers from deeper waters *209*.

COMMENTS ON EGG ENVIRONMENTAL ASSOC_ -
Eggs occur mainly in the deep water (100-200 m) along the shelf break (over
425 m), but also at intermediate depths over the slope *209*.
Ova have been found along the outer shelf and the deep waters outside at
temperatures of 3.5-6.5 degrees C *209*.
Temperature is an important factor in successful egg development. In
laboratory experiments, slowed and aborted development occurred with
decreasing temperatures and considerable mortality at higher temperatures;
7 degrees C was optimal for hatching, and hatching efficiency and time to
hatching varied with temperature. Slowed development may decrease survival
by delaying normal density changes and the resultant rise in the water
column for favorable transport in surface layers *209*.
Transport of eggs and larvae may present substantial differences from year
to year, with discernable spatial patterns of variation in abundance and
utimately recruitment. Interannual variations in the Alaska Coastal
Current system, particularly vigorous in the western Gulf, greatly affect
the alongshore and cross-shelf drift of larvae as they rise into surface
layers from deeper waters *209*.

Eggs of halibut are heavier than surface sea water and drift passively in
deep ocean currents, generally at depths of 90 to 180 m but down to 686 m.
In the Gulf of Alaska, eggs are transported great distances by westward
ocean currents *232*.

Environment Associations - 4 (DRAFT) - Life History
Species halibut, Pacific
Species Id M010015
Date 27 AUG 96

LIFE HISTORY

Identification
The largest flatfish in the area, commonly over 2 1/2 ft. Almost always
right-eyed. Caudal fin slightly indented, more so in larger specimens.
Lateral line arched over pectoral fin. Jaw does not extend past the middle
of the eye. Scales on both sides are small and cycloid. Eyed side is dark
brown to blackish, often with marbling or spots. Blind side is usually
white. Females are 8 3/4 ft (267 cm), about 500 lb. (227 kg), but reported
to 800 lb. (363 kg); males are smaller and average size caught by fishermen
is about 5-10 lb (2.3-4.5 kg).*211*

Similar species
The California Halibut has a larger mouth and is usually left-eyed, and the
caudal fin is rounded at the middle (not indented). The Greenland Halibut
has dark pigment on the blind side, rough (ctenoid) scales and a larger
mouth with little or no arch in the lateral line.*211*

Migration
Migrations often are extensive along the coast; however, distance and
direction differ substantially between seasons, years and fish size or age.
the longest record is 2500 miles (Aleutians to Oregon) *209*.
Gulf of Alaska research data from 1924 show active adult migrations between
winter spawning grounds along the continental slope and summer feeding
grounds on the shelf. Tagging records document the dispersal of the
spawning population, e.g., adults tagged in the Gulf have not been recovered
in the Bering Sea *209*.

Growth and maturation
Size and maturity of Pacific halibut varies with regions in the Gulf of
Alaska and has changed over time. Males usually attain sexual maturity by
about 70 cm body length. Maturity occurs much earlier in males than in
females and is more difficult to discern; 50% are mature by age 8 (60-80
cm). On average, 50% of females are mature by 115-125 cm (ages 11-12) and
90% by 150 cm (age 15); age of females at maturity ranges from 8-16 years
*209*.

Spawning
Only small numbers of ova to be released during spawning periods are ripe at
any one time; thus batch spawning is likely, as it is impossible for an
ovary to hold at one time all the ripe ova it will shed in a season.
There is disagreement on whether mature halibut spawn annually *209*.
Peak spawning occurs from the last week of December to the third week of
January; movements to and from the spawning grounds are predominantly in
November, February and March. Batch spawning extends this stage through a
gradual shedding of ripe ova over an unknown number of weeks. Males always
release milt before the earliest and after the latest spawning females
*209*.

Fecundity
Halibut fecundity is best estimated by size and is high, as are losses due
to prolonged egg and larval drift and the lack of parental care. A 120 cm
female produced 646,000 eggs in 1927 as compared to 573,000 in 1973, and a
Life History - 1 (DRAFT) - Life History
Species halibut, Pacific
Species Id M010015
Date 27 AUG 96

40 kg female produced an estimated 1,575,000 in 1927 but 1,227,000 in 1973
*209*.

Eggs
The bathypelagic halibut eggs are round; the clear glassy outer surface is
punctured by numerous minute holes, giving a honeycombed appearance. The
comparatively large yolk is colorless and without oil globules; the
perivitelline space is very small and there are no markings around the
micropyle. Ova size varies geographically and interannually *209*.

Larvae
Pacific halibut larvae undergo remarkable metamorphic transitions as they
develop through a variable and protracted 5-7 month pelagic phase. Twelve
continuous stages have been described *209*.

Juveniles
After the 6-7 month pelagic larval phase, the young halibut (about 25 mm
length) settle to the bottom in shallow inshore nursery areas. They have
the adult form with fully developed fin rays and differentiated sides, one
colorless and blind and the other with developing adult pigmentation
(initially spotted), and two very large eyes *209*.
Juveniles remain inshore for 1 to 3 years, and therefore are usually
unavailable to the commercial fishery. As they become older, they move
offshore to depths of 100 m and beyond and migrate eastward and southward,
in contrast to the passive drift of eggs and larvae *209*.

Predators
Adult halibut have few predators capable of overtaking them, particularly in
bottom environments *209*.
A wide variety of fish and invertebrate predators consume juvenile halibut
*209*.

Parasites
Halibut appear to have fewer parasites than most marine fish; therefore,
parasitism is unlikely to be a significant problem for survival or spawning
success *209*.

Reproductive Habitat: Halibut spawning occurs all along the coast in the
northeast Pacific but is concentrated near the edge of the continental
shelf, generally in depths from 180 to 550 m. In the area from Cape St.
Elias to Kodiak Island and in the Bering Sea spawning takes place along the
shelf edge at depths greater than 180 m in concentrations of varying size.
Spawning grounds include Portlock Edge, Albatross Gully, Manhattan Ground,
Seward Gully, Cape Cleare Gully and Spit, all situated east of Kodiak
Island. Spawning grounds are also located east and west along the shelf
edge off Middleton Island, Barnabas Gully, and the edges of Albatross Band
located south of Kodiak Island *232*.

Reproductive Seasonality: In the Gulf of Alaska, breeding takes place from
November to March. In the Bering Sea, spawning occurs from October to March
with most of the spawning during December, January, and February.
Environmental conditions could be a factor in determining the time when
Life History - 2 (DRAFT) - Life History
Species halibut, Pacific
Species Id M010015
Date 27 AUG 96

halibut begin to spawn in a given year; thus the peak spawning period could
vary from year to year and from ground to ground *232*.

Age at Sexual Maturity: In the Gulf of Alaska, most males are mature by age
8; average maturity for females is age 12. A study reported age at 50%
maturity for females in the Bering Sea to be 13.8 years at a length of 122
cm. Males in the Bering Sea averaged 7.5 years and 72 cm at 50% maturity
*232*.

Frequency of Breeding: The long (approximately 12 years) immaturity of
female halibut has apparently caused some confusion over the frequency of
spawning. Females have been reported to spawn annually and every two years
*232*..

Fecundity: The number of eggs produced per female is related to size. A
23-kg female produces about 500,000 eggs, whereas a 113-kg female may
produce 4 million eggs *232*.

Incubation Period: Eggs hatch after about 15 days; however, this rate of
development is related to temperature *232*.

Movements Associated with Life Functions: Eggs and larvae of halibut are
heavier than surface sea water and drift passively in deep ocean currents,
generally at depths of 90 to 180 m but down to 686 m. In the Gulf of Alaska,
eggs and larvae are transported great distances by westward ocean currents.
As the larvae grow, their specific gravity decreases. By the age of three to
five months all larvae were in the upper 100 m. Larvae are moved by
prevailing winds to the shallow (about 12 m) sections of the shelf.
Juveniles settle to the bottom at about six months old and remain in
nearshore waters for one to three years. Halibut move from deep water (up to
1,097 m) along the edge of the continental shelf to shallower (27 to 274 m)
banks and coastal waters to feed during the summer. The halibut return to
deep water in the winter to spawn. These movements and coastwide migrations,
which may encompass hundreds of miles, have been documented by extensive
tagging studies *232*.

Natural Factors Influencing Populations: Little is known about predation on
halibut. Sea lions often prey upon halibut hooked on longline gear, but is
unlikely that they are any threat to free-swimming halibut. Eggs, larvae,
and juvenile halibut probably fall prey to many fish species, but older
halibut, because of their size, must be safe from predation by most animals,
except possibly large marine mammals *232*.

Human-related Factors Influencing Populations: A summary of possible impacts
from human-related activities includes: alteration of preferred water
temperature, pH, dissolved oxygen, and chemical composition; introduction of
water soluble substances; increase in suspended organic or mineral material;
alteration of preferred substrate; reduction in food supply; human harvest;
and seismic shock waves *232*.

LIFE HISTORY CODES -
Breeding/Spawning Season: January
Breeding/Spawning Season: February
Life History - 3 (DRAFT) - Life History
Species halibut, Pacific
Species Id M010015
Date 27 AUG 96

LIFE HISTORY CODES -
Breeding/Spawning Season: March
Breeding/Spawning Season: December
Breeding/Spawning Season: November
Breeding/Spawning Season: October
Average Number of Offspring/Reproductive Effort: Grea
Gestation/Incubation Period: 1-2 weeks
Gestation/Incubation Period: 3-4 weeks

REFERENCES FOR LIFE HISTORY- 211, 209 and 232

Life History - 4 (DRAFT) - Management Practices
Species halibut, Pacific
Species Id M010015
Date 27 AUG 96

MANAGEMENT PRACTICES

RESULT MANAGEMENT PRACTICE

Beneficial Regulating harvest of species being described
Beneficial Regulating harvest - setting size limits
Beneficial Other management practices [specified in comments]
Adverse Harvest of species using non-selective gear
Adverse Other management practices [specified in comments]
Existing Regulating harvest of species being described
Existing Regulating harvest - setting size limits
Existing Other management practices [specified in comments]
Beneficial Developing/maintaining suitable pH
Existing Regulating harvest - restricting weapons/gear use

REFERENCES FOR BENEFICIAL MANAGEMENT PRACTICES - 209 and 232

REFERENCES FOR ADVERSE MANAGEMENT PRACTICES - 209

REFERENCES FOR EXISTING MANAGEMENT PRACTICES - 209 and 232

COMMENTS ON MANAGEMENT PRACTICES -
After a severe depletion during the 1960s attributable to trawling fleets,
strict catch restrictions were levied and the fishery is slowly recovering
*209*.
The fishery is limited by an 81 cm length minimum *209*.
The technique employed commercially includes fixed-hook setlines or
longlines, and snap-on gear widely introduced in the 1970s. The gear unit
of standard effort is a "skate", with 100 short baited hook lines (gangions)
attached to a ground at 18 ft intervals. Traditional setline craft include
the characteristic halibut schooners, while other ships such as seiners and
trollers are also used *209*.
For the most part, the commercial fleet operates from Oregon to the Bering
Sea in specific areas or grounds where halibut tend to concentrate during
spring and summer. Catches take place along shelfbottom areas wholly within
the 200-mile Fisheries Conservation Zones of the U.S. and Canada *209*.
Since 1975, the commercial catch has been held at the lowest level in its
history and is below ASP (annual surplus production). This action, together
with reduction of incidental catch mortality that has long been a serious
problem, is the strategy of the International Pacific Halibut Commission to
rebuild the stock so that population biomass and fishery yield will be
increased *209*.
Predation on hooked halibut is a consistent problem with setline gear, e.g.,
by Pacific sleeper sharks and particularly by marine mammals, such as
Stellar sea lions who mutilate so much of the local catch that fishermen
often have to change grounds. Actual predation of free halibut by marine
mammals appears exceedingly rare, as analyses of sea lion, harbor seal and
fur seal stomachs from the Gulf of Alaska and Bering Sea attest *209*.
Many juveniles are taken incidentally in trawls for other groundfish,
constituting a serious problem for management, e.g., a sharp decline of the
larger juveniles resulted from the Japanese sablefish setline fishery *209*.

Management Practices - 1 (DRAFT) - Management Practices
Species halibut, Pacific
Species Id M010015
Date 27 AUG 96

Management Practices - 2 (DRAFT) - References
Species halibut, Pacific
Species Id M010015
Date 27 AUG 96

References

209 * Maupin, Sara. 1988. Species Synopses: Life Histories of
Selected Fish and Shellfish of the Northeast Pacific and Bering
Sea. Wilimovsky, N. J., L. S. Incze, S. J. Westrheim (eds.).
University of Washington:8311.

211 * Eschmeyer, W. N., E. S. Herald. 1983. A Field Guide to
Pacific Coast Fishes of North America: from the Gulf of Alaska
to Baja California. The Peterson Field Guide Series (ed.).
Houghton Mifflin Company Boston, MA:288336.

232 * State of Alaska Department of Fish, and Game. 1986. Alaska
Habitat Management Guide: Life Histories and Habitat
Requirements of Fish and Wildlife. (ed.). Alaska Department of
Fish and Game Juneau, Alaska:763.

References - 1