(DRAFT) - Taxonomy
Species pollock, walleye
Species Id M010602
Date 26 AUG 96
TAXONOMY
NAME - pollock, walleye
OTHER COMMON NAMES -
ELEMENT CODE -
CATEGORY - Fish
PHYLUM AND SUBPHYLUM - ,
CLASS AND SUBCLASS - ,
ORDER AND SUBORDER - ,
FAMILY AND SUBFAMILY - ,
GENUS AND SUBGENUS - Theragra,
SPECIES AND SSP - chalcogramma,
SCIENTIFIC NAME - Theragra chalcogramma
AUTHORITY -
TAXONOMY REFERENCES - 232
Taxonomy - 1 (DRAFT) - Status
Species pollock, walleye
Species Id M010602
Date 26 AUG 96
STATUS
Coded Status
Migrant
Existing, FMP exists
See Comments
REFERENCES FOR STATUS - 232
COMMENTS ON STATUS -
In the Bering Sea, pollock follow a circular pattern of migration, moving
inshore to the shallow (90 to 140 m) waters of the continental shelf to
breed and feed in the spring (March) and moving to warmer, deeper areas of
the shelf (160 to 300 m) in the winter months (December-February). A similar
movement of pollock is noted in the Gulf of Alaska *232*.
Pollock within the 200-mi limit are managed by the North Pacific Fishery
Management Council (NPFMC) within their groundfish fishery management plan
*232*.
Status - 1 (DRAFT) - Distribution
Species pollock, walleye
Species Id M010602
Date 26 AUG 96
DISTRIBUTION
Distribution - 1 HABITAT ASSOCIATIONS
HABITAT - MARINE
REFERENCES FOR HABITAT - 232
LAND USE -
Water
REFERENCES FOR LAND USE - 232
NATIONAL WETLAND INVENTORY CODES
NWI NWICLS NWIMOD NWISPEC
Marine
REFERENCES FOR NWI - 232
COMMENTS ON HABITAT ASSOCIATIONS -
Walleye pollock are schooling fish, found on or near the sea bottom as well
as at mid-water and near-surface depths. Juvenile pollock in their first
months of life are found above the thermocline. Pollock feed mainly in the
shallow (90 to 140 m) waters of the outer continental shelf, where tidal
mixing occurs in the spring *232*.
ANIMAL/PLANT SPECIES ASSOCIATIONS -
Fur seal
Seabirds
Pacific salmon (Oncorhunchus spp.)
Walleye pollock ( Theragra chalcogramma)
REFERENCES FOR SPECIES ASSOCIATIONS - 232
COMMENTS ON SPECIES ASSOCIATIONS -
Pollock are a major prey item for several animals, including fur seals,
seabirds, and other fish. Estimates have indicated that in the eastern
Bering Sea marine mammals consume about 1.13 million tons of pollock
annually. In Southeast Alaska, juvenile walleye pollock are one of the most
common foods of troll-caught Pacific salmon (Oncorhynchus spp.). In the
Bering Sea, juvenile pollock have been identified as a major prey item of
adult pollock *232*.
Habitat Associations - 1 (DRAFT) - Food Habits
Species pollock, walleye
Species Id M010602
Date 26 AUG 96
FOOD HABITS
TROPHIC LEVEL -
CARNIVORE
REFERENCES FOR TROPHIC LEVEL - 232
LIFESTAGE FOOD FOOD PART
General Osteichthyes Not Specified
General Gadiformes Not Specified
Important Crustaceans Not Specified
Adult Osteichthyes Not Specified
Larva Crustaceans Not Specified
Larva Copepods Not Specified
Larva Copepods Adult stage
Larva Copepods Egg/Fetus stage
Adult Gadiformes Juvenile stage
Juvenile Crustaceans Not Specified
Juvenile Copepods Not Specified
Adult Crustaceans Not Specified
Adult Malacostraca Not Specified
Juvenile Zooplankton Not Specified
Important See Comments; Food See Comments
Adult See Comments; Food See Comments
Larva See Comments; Food See Comments
Juvenile See Comments; Food See Comments
Important Osteichthyes Not Specified
REFERENCES FOR GENERAL FOOD - 232
REFERENCES FOR IMPORTANT FOOD - 232
REFERENCES FOR ADULT FOOD - 232
REFERENCES FOR JUVENILE FOOD - 232
REFERENCES FOR LARVAE FOOD - 232
COMMENTS ON FOOD -
Cannibalism was observed in only 1 % of the stomachs; however, few pollock
greater than 450 mm were examined *232*.
Feeding Locations: Pollock feed mainly in the shallow (90 to 140 m) waters
of the outer continental shelf, where tidal mixing occurs in the spring.
Juveniles follow a diel vertical movement, rising to feed on zooplankton
near the surface at night *232*.
Feeding Behavior: In the Bering Sea, pollock feeding activity is
concentrated in the summer months (June-August). Pollock feed very little
or not at all during the spawning period (April-mid May) *232*.
Food Habits - 1 (DRAFT) - Food Habits
Species pollock, walleye
Species Id M010602
Date 26 AUG 96
COMMENTS ON ADULT FOOD -
Fish make an important contribution to the diet of adult Bering Sea pollock,
making up 70 % of stomach contents by volume. Studies in the Bering Sea
have shown that small (young-of-the-year and one-year-old) pollock comprise
at least 44 % by weight of the total stomach contents of adult pollock.
Large pollock (larger than 349 mm) generally ate larger prey, such as shrimp
and fish *232*.
COMMENTS ON JUVENILE FOOD -
In the Southeastern Gulf of Alaska, small (less than 250 mm) walleye pollock
ate mostly planktonic crustaceans, particularly euphausiids, mysids, and
copepods *232*.
Juveniles follow a diel vertical movement, rising to feed on zooplankton
near the surface at night *232*.
COMMENTS ON LARVAE FOOD -
Pollock larvae (4.8 to 17.7 mm standard length) from the Bering Sea consume
mainly copepod nauplii and eggs and adult copepods (especially Oithona
similis). Copepods are consumed only by small (less than 200 mm) pollock
*232*.
Food Habits - 2 (DRAFT) - Environment Associations
Species pollock, walleye
Species Id M010602
Date 26 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 Aquatic Habitat Zonation: 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
J Water Depth Preference: Specified in Comments
J Water Temperature: Specified in Comments
A Water Temperature: Below 15 degrees C
A Water Temperature: Specified in Comments
FA Water Depth Preference: Specified in Comments
FA Water Depth Preference: 200-500 ft.
BA Water Depth Preference: 200-500 ft.
BA Water Depth Preference: 500-1000 ft.
BA Water Depth Preference: Specified in Comments
BA Water Temperature: Specified in Comments
BA Water Temperature: Below 15 degrees C
E Water Depth Preference: 50-100 ft.
E Water Depth Preference: Specified in Comments
FJ Water Depth Preference: Specified in Comments
REFERENCES FOR ENVIRONMENTAL ASSOC_ - 232
REFERENCES FOR ADULT ENVIRONMENTAL ASSOC_ - 232
REFERENCES FOR FEEDING ADULT ENVIRONMENTAL ASSOC_ - 232
REFERENCES FOR BREEDING ADULT ENVIRONMENTAL ASSOC_ - 232
REFERENCES FOR JUVENILE ENVIRONMENTAL ASSOC_ - 232
REFERENCES FOR FEEDING JUVENILE ENVIRONMENTAL ASSOC_ - 232
REFERENCES FOR EGG ENVIRONMENTAL ASSOC_ - 232
COMMENTS ON ENVIRONMENTAL ASSOCIATIONS -
Walleye pollock are schooling fish, found on or near the sea bottom as well
as at mid-water and near-surface depths, although most catches are found
between 50 and 300 m *232*.
Environment Associations - 1 (DRAFT) - Environment Associations
Species pollock, walleye
Species Id M010602
Date 26 AUG 96
COMMENTS ON ADULT ENVIRONMENTAL ASSOC_ -
Concentrations of adult walleye pollock in the Bering Sea are usually found
in water temperatures between 2 and 4 oC *232*.
COMMENTS ON FEEDING ADULT ENVIRONTAL ASSOC_ -
Pollock feed mainly in the shallow (90 to 140 m) waters of the outer
continental shelf, where tidal mixing occurs in the spring *232*.
COMMENTS ON BREEDING ADULT ENVIRONMENTAL ASSOC_ -
Pollock spawn in shallow (90 to 200 m) waters of the outer continental
shelf. Oceanic spawning has been reported over waters 640 m deep south of
Seward, Alaska, and in the Aleutian basin. Some spawning may also occur
under the sea ice. Spawning in the Bering Sea occurs at temperatures of 1
to 3 oC. In Asian waters, variability in time of spawning is believed to
be an adaptation to periods when water temperatures are favorable for
production of abundant supplies of the initial food of the larvae and for
larval growth. Temperature at time of spawning is, however, apparently not
as important for the Shelikof Strait spawning population. Pollock
consistently return to Shelikof Strait to spawn, though the temperature
varies from 3.5 to 6.5 oC *232*.
COMMENTS ON JUVENILE ENVIRONMENTAL ASSOC_ -
Juvenile (age 0) pollock in their first months of life are found above the
thermocline (depth at which temperature rapidly decreases) in the Bering
sea. Age 0 pollock avoid depths where water temperature is less than
approximately 2.5 to 3.0 oC. Age 0 pollock begin to settle to the bottom
in the fall months, after which they mainly occupy semidemersal waters
*232*.
COMMENTS ON FEEDING JUVENILE ENVIRONMENTAL ASSOC_ -
Juveniles follow a diel vertical movement, rising to feed on zooplankton
near the surface at night *232*.
COMMENTS ON EGG ENVIRONMENTAL ASSOC_ -
Eggs are planktonic and are found primarily within 30 m of the surface
*232*.
Environment Associations - 2 (DRAFT) - Life History
Species pollock, walleye
Species Id M010602
Date 26 AUG 96
LIFE HISTORY
Reproductive Habitat: Pollock spawn in shallow (90 to 200 m) waters of the
outer continental shelf. There is also evidence that pollock spawn in
oceanic areas off the continental shelf. Oceanic spawning has been reported
over waters 640 m deep south of Seward, Alaska, and in the Aleutian basin.
Some spawning may also occur under the sea ice. Spawning in the Bering Sea
occurs at temperatures of 1 to 3 oC. In Asian waters, variability in time
of spawning is believed to be an adaptation to periods when water
temperatures are favorable for production of abundant supplies of the
initial food of the larvae and for larval growth. Temperature at time of
spawning is, however, apparently not as important for the Shelikof Strait
spawning population. Pollock consistently return to Shelikof Strait to
spawn, though the temperature varies from 3.5 to 6.5 oC *232*.
Reproductive Seasonality: In the Bering Sea, spawning begins in late
February. Fish in the southeastern Bering Sea spawn first. Most spawning
occurs from late March to mid June, with a peak in May. In the western Gulf
of Alaska, more than 85 % of pollock adults had spawned prior to their
earliest sampling in May, indicating that most spawning occurred in March
and April *232*.
Reproductive Behavior: Spawning and prespawning fish move high in the water
column, forming dense schools. Eggs are planktonic and are found primarily
within 30 m of the surface *232*.
Age at Sexual Maturity: Pollock begin to recruit to the spawning population
at age 2, but age classes 4 and 5 contribute most to potential reproduction
of the population *232*.
Fecundity: Estimates of individual female fecundity are difficult to
achieve because ovaries of female pollock contain oocyte populations
composed of two or three size classes. The percentage of each size class
released during spawning is uncertain. Fecundities have been found of
37,000 to 312,000 eggs per female in fish of lengths of 40 to 80 cm in the
Bering Sea and 199,000 to 996,600 for lengths of 32 to 49 cm off the Pacific
coast of Canada *232*.
Frequency of Breeding: Pollock breed yearly *232*.
Incubation Period: Length of incubation is dependent upon temperature.
Incubation time from fertilization to 50 % hatching is 10 days at 10 oC but
up to 27.4 days at 2 oC. Newly hatched larvae are 3.5 to 4.4 mm in length
and apparently float upside down at the water surface. The yolk sac is
absorbed at about 7.0 to 7.5 mm (22 days at 2 oC) *232*.
Timing of Movements and Use of Areas: In the Bering Sea, winter
concentrations have been found between Unimak Island and the Pribilof
Islands, with some concentrations east of the Pribilofs and northwest of the
Pribilofs along the continental slope. Summer feeding concentrations in
the Bering Sea are found north of the Pribilofs and to the west and
northwest of St. Matthew Island. A major spawning concentration of pollock
is found in the spring in Shelikof Strait. This concentration disperses
Life History - 1 (DRAFT) - Life History
Species pollock, walleye
Species Id M010602
Date 26 AUG 96
before summer, and it is not known where that population resides at other
times of the year *232*.
Migration Routes: In the Bering Sea, pollock follow a circular pattern of
migration, moving inshore to the shallow (90 to 140 m) waters of the
continental shelf to breed and feed in the spring (March) and moving to
warmer, deeper areas of the shelf (160 to 300 m) in the winter months
(December-February). A similar movement of pollock is noted in the Gulf of
Alaska *232*.
Natural Factors Influencing Populations: Water temperature affects the
length of incubation, rate of growth, and survival of juvenile pollock.
Pollock are a major prey item for several animals, including fur seals,
seabirds, and other fish. Estimates have indicated that in the eastern
Bering Sea marine mammals consume about 1.13 million tons of pollock
annually, an amount approximating the commercial pollock catch in that
region. In Southeast Alaska, juvenile walleye pollock are one of the most
common foods of troll-caught Pacific salmon (Oncorhynchus spp.). In the
Bering Sea, juvenile pollock have been identified as a major prey item of
adult pollock. Because of this, cannibalism may have an important effect on
the dynamics of the population. Weather conditions at the time of first
feeding of larval pollock may be very important for their survival.
Conditions resulting in a reduction of water surface turbulence allow
plankton to become concentrated and may lead to an increased feeding
efficiency (and therefore increased survival) of the pollock larvae *232*.
Human-related Factors Influencing Populations: A summary of possible
impacts from human-related activities includes: alteration of preferred
water temperatures, pH, dissolved oxygen, and chemical composition;
introduction of water soluble substances; increase in suspended organic or
mineral material; reduction in food supply; human harvest; and seismic shock
waves *232*.
LIFE HISTORY CODES -
Dispersion: Clumped
Periodicity: Most active in early summer
Periodicity: Most active in late summer
Breeding/Spawning Season: February
Breeding/Spawning Season: March
Breeding Spawning Season: April
Breeding/Spawning Season: May
Breeding/Spawning Season: June
Average Number of Offspring/Reproductive Effort: Grea
Gestation/Incubation Period: 1-2 weeks
Gestation/Incubation Period: 3-4 weeks
REFERENCES FOR LIFE HISTORY- 232
Life History - 2 (DRAFT) - Management Practices
Species pollock, walleye
Species Id M010602
Date 26 AUG 96
MANAGEMENT PRACTICES
RESULT MANAGEMENT PRACTICE
Beneficial Developing/maintaining suitable pH
Beneficial Developing/maintaining suitable salinity
Adverse Salinity alteration
Beneficial Regulating harvest of species being described
Adverse Underwater explosions
Adverse Other management practices [specified in comments]
Beneficial Other management practices [specified in comments]
REFERENCES FOR BENEFICIAL MANAGEMENT PRACTICES - 232
REFERENCES FOR ADVERSE MANAGEMENT PRACTICES - 232
COMMENTS ON MANAGEMENT PRACTICES -
Human-related Factors Influencing Populations: A summary of possible
impacts from human-related activities includes: alteration of preferred
water temperatures, pH, dissolved oxygen, and chemical composition;
introduction of water soluble substances; increase in suspended organic or
mineral material; reduction in food supply; human harvest; and seismic shock
waves *232*.
Management Practices - 1 (DRAFT) - References
Species pollock, walleye
Species Id M010602
Date 26 AUG 96
References
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