(DRAFT) - Taxonomy
Species tomcod, Atlantic
Species Id M010019
Date 26 AUG 96
TAXONOMY
NAME - tomcod, Atlantic
OTHER COMMON NAMES - frostfish and Atlantic tomcod
ELEMENT CODE -
CATEGORY - Fish
PHYLUM AND SUBPHYLUM - Chordata,
CLASS AND SUBCLASS - Osteichthyes,
ORDER AND SUBORDER - Gadiformes,
FAMILY AND SUBFAMILY - Gadidae,
GENUS AND SUBGENUS - Microgadus,
SPECIES AND SSP - tomcod,
SCIENTIFIC NAME - Microgadus tomcod
AUTHORITY - Walbaum
TAXONOMY REFERENCES - 32
COMMENTS ON TAXONOMY -
Preferred common name is Atlantic tomcod. Other common name is
Frostfish.*32*
Taxonomy - 1 (DRAFT) - Status
Species tomcod, Atlantic
Species Id M010019
Date 26 AUG 96
STATUS
Coded Status
See Comments
Sport Fish
REFERENCES FOR STATUS - 32
COMMENTS ON STATUS -
Atlantic tomcod are widespread along coastal regions of the northeastern
coast of the U.S. They are abundant in estuarine habitats such as river
mouths and salt marshes. These same habitats are subject to a wide variety
of human sources of disturbance.*32*
Status - 1 (DRAFT) - Distribution
Species tomcod, Atlantic
Species Id M010019
Date 26 AUG 96
DISTRIBUTION
Distribution - 1 HABITAT ASSOCIATIONS
HABITAT - AQUATIC
REFERENCES FOR HABITAT - 32
NATIONAL WETLAND INVENTORY CODES
NWI NWICLS NWIMOD NWISPEC
Estuarine AB2
REFERENCES FOR NWI - 32
Habitat Associations - 1 (DRAFT) - Food Habits
Species tomcod, Atlantic
Species Id M010019
Date 26 AUG 96
FOOD HABITS
TROPHIC LEVEL -
CARNIVORE
REFERENCES FOR TROPHIC LEVEL - 32
LIFESTAGE FOOD FOOD PART
Juvenile Copepods Not Specified
Juvenile Crustaceans Not Specified
General Crustaceans Not Specified
General Molluscs Not Specified
General Polychaetes Not Specified
General Fish Not Specified
Adult Crustaceans Not Specified
REFERENCES FOR GENERAL FOOD - 32
REFERENCES FOR ADULT FOOD - 32
REFERENCES FOR JUVENILE FOOD - 32
COMMENTS ON FOOD -
It was found that tomcod in the Weweantic River Estuary preyed on
species in direct proportion to their availability. They fed principally on
crustaceans, primarily the shrimp Crangon septemspinosa (68% of total items)
and amphipods. Other prey included polychaete worms, small molluscs, and
fish.*32*
COMMENTS ON JUVENILE FOOD -
The diet of juvenile tomcod in the Hudson River, New York, shifted as size
increased. Primary prey items of young-of-the-year in May and June
were copepods and small amphipods. As total length reached 80-90 mm,
prey shifted toward larger individuals and species of amphipods and mysids.
The shift was probably not due to shifts in densities of prey species, as
the copepod population increased and amphipod population decreased during
this period.*32*
Food Habits - 1 (DRAFT) - Environment Associations
Species tomcod, Atlantic
Species Id M010019
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
E Water Temperature: Specified in Comments
G Water Temperature: Specified in Comments
J
L
A
REFERENCES FOR ENVIRONMENTAL ASSOC_ - 32
REFERENCES FOR FEEDING JUVENILE ENVIRONMENTAL ASSOC_ - 32
REFERENCES FOR FEEDING LARVAE ENVIRONMENTAL ASSOC_ - 32
REFERENCES FOR EGG ENVIRONMENTAL ASSOC_ - 32
COMMENTS ON ENVIRONMENTAL ASSOCIATIONS -
No fish were found at water temperatures higher than 26 degrees C.
Tomcod have been found at temperatures as low as -1.2 degrees C;
glycoproteins that depress the freezing point enable the fish to
avoid freezing.*32*
COMMENTS ON RESTING ADULT ENVIRONMENTAL ASSOC_ -
Adults have been found at all salinities from full-strength seawater to
freshwater, in bays and estuaries *32*.
COMMENTS ON RESTING JUVENILE ENVIRONMENTAL ASSOC_ -
Juveniles have been found at all salinities from full-strength seawater to
freshwater, in bays and estuaries.*32*
COMMENTS ON RESTING LARVAE ENVIRONMENTAL ASSOC_ -
In the Hudson River, it was found that the densities of larvae and
juveniles to be highest within a salinity range of 4.5 to 8.7 ppt; the
total range was 1.5 to 10.0 ppt.*32*
COMMENTS ON EGG ENVIRONMENTAL ASSOC_ -
It was determined that the upper lethal temperature of tomcod eggs was 6.6
degrees C.*32*
Environment Associations - 1 (DRAFT) - Life History
Species tomcod, Atlantic
Species Id M010019
Date 26 AUG 96
LIFE HISTORY
Morphology and Identification Aids:
Atlantic tomcod generally have the same body plan as the much larger
Atlantic cod (Gadus morhua). The body is elongated, and the upper jaw
projects past the lower jaw. There is a barbel on the chin. Differences in
several key external characters allow easy differentiation. The second rays
of the ventral fins of the tomcod are long, narrow, and tapering (the
tapered portion is as long as the rest of the fin). The caudal fin of the
tomcod is rounded; coloration is olive, olive-brown, or muddy green, with
some yellow on the dorsal surface; lower lateral surfaces have a more
yellowish cast, especially in larger fish; dorsal fins are mottled with dark
spots or blotches; and the belly is gray or yellow-white. The margin of the
anal fin is olive.*32*
Spawning:
Although the range of the tomcod extends south to Virginia, no spawning has
been reported in estuaries south of the Hudson River; however, spawning
occurs in many estuaries in the northern part of the range. North of the
Hudson River, tomcod spawn from November to February with a peak in January.
Spawning occurs in shallow waters of estuaries or stream mouths, in salt,
brackish, or freshwater.*32*
Fecundity and Eggs:
Females 170 to 340 mm long produce an average of 20,000 eggs within a range
of 6,000 to 30,000; average fecundity was 25,000 eggs (maximum 44,000). The
eggs of Atlantic tomcod are large, approximately 1.5 mm in diameter, and
have a large oil globule. They sink to the bottom after spawning and adhere
in masses to available substrate.
Salinity affects fertilization, development, and subsequent hatching
success. Sperm motility is greatest at low salinities; hence
fertilization success is also highest at low salinity. Eggs generally occur
and develop mostly in freshwater, due to stream flow characteristics at the
heads of estuaries; seawater intrusion occurs only at extreme high tides.
Normal development does not occur when eggs are continuously exposed to
salinities of 30 ppt or higher. It was found that the percentage of eggs
that developed to the blastula stage was highest when salinities ranged from
0 to 15 ppt.
Incubation time is approximately 30 days at 6.1 degrees C and 24 days at 4.4
degrees C, time to hatching decreases as salinity increases (up to 30 ppt).
For example, at temperatures between approximately 4 and 9 degrees C, median
times of hatching were reduced from 53 days at 0 ppt to 38 days at 30 ppt
(at 30 ppt development was abnormal).*32*
Larvae:
Atlantic tomcod larvae became photopositive within 24 h after hatching, and
swim to the surface to inflate the swim bladder by gulping air. Larvae are
transported seaward as water temperatures begin to increase.
Larvae are most abundant in the water column in early March in southern New
England. They are generally found near bottom in the (low salinity) upper
reaches of estuaries. This distribution pattern would facilitate retention
of larvae in the estuary, since downstream movement is reduced near bottom
and upstream tidal movement is enhanced in this area. No pelagic larvae
Life History - 1 (DRAFT) - Life History
Species tomcod, Atlantic
Species Id M010019
Date 26 AUG 96
more than 12 mm in total length (TL) have been collected, reflecting
the change to benthic habits. All fins are formed when the larvae reach
about 10 mm TL; the resulting greater motility allows increased
directional movement.*32*
Juveniles and Adults:
Young-of-the-year remain in the estuary where they were hatched during the
succeeding summer months, and are restricted by water of relatively low
salinity. For example, no juveniles were found in water of less than
10 ppt salinity or at temperatures above 26 degrees C in the Weweantic River
Estuary, MA.
Age of tomcod is determined from both scales and otoliths. Growth of
young-of-the-year is rapid from June to mid-July then decreases. Fish are
about 90 mm by their first September, and the larger juveniles are more than
100 mm long by early fall.
Researchers reported young-of-the-year tomcod in southern New England
to be 63-77 mm long in fall. These values agree with the growth
found in the more northern populations in MA.
Tomcod may grow larger during their first year in southern New England than
those in the Canadian Maritimes.
Growth rates of tomcod are highest from January, February, or March
(according to region) through July. Feeding is heaviest after the fish
spawn, as water temperatures increase.*32*
REFERENCES FOR LIFE HISTORY- 32
Life History - 2 (DRAFT) - Management Practices
Species tomcod, Atlantic
Species Id M010019
Date 26 AUG 96
MANAGEMENT PRACTICES
RESULT MANAGEMENT PRACTICE
Beneficial Restricting/regulating human use of habitats
Beneficial Restricting/regulating human disturbance of populations
REFERENCES FOR BENEFICIAL MANAGEMENT PRACTICES - 32
COMMENTS ON MANAGEMENT PRACTICES -
Tomcod are abundant in estuarine habitats such as river mouths and salt
marshes. These same habitats are subject to a wide variety of human sources
of disturbance.*32*
Management Practices - 1 (DRAFT) - References
Species tomcod, Atlantic
Species Id M010019
Date 26 AUG 96
References
32* Stewart, L., P. Auster. 1987. Species Profiles: Life Histories
and Environmental Requirements of Coastal Fishes and
Invertebrates (North Atlantic) -- Atlantic Tomcod. U.S. Fish and
Wildlife Service Biol. Rep. 82(11.76) pp 8.
References - 1