(DRAFT) - Taxonomy
Species crab, dungeness
Species Id M070001
Date 26 AUG 96
TAXONOMY
NAME - crab, dungeness
OTHER COMMON NAMES - Pacific edible crab, edible crab, market crab and commercial crab
ELEMENT CODE -
CATEGORY - Aquatic Crustaceans
PHYLUM AND SUBPHYLUM - Arthropoda, Crustacea
CLASS AND SUBCLASS - Malacostraca, Eumalacostraca
ORDER AND SUBORDER - Decapoda, Dendrobranchiata
FAMILY AND SUBFAMILY - Cancridae,
GENUS AND SUBGENUS - Cancer,
SPECIES AND SSP - magister,
SCIENTIFIC NAME - Cancer magister
AUTHORITY - Dana, 1852
TAXONOMY REFERENCES - 197, 86, 260 and 231
COMMENTS ON TAXONOMY -
Other common names include Pacific edible crab, edible crab, market crab,
commercial crab *86*.
Taxonomy - 1 (DRAFT) - Status
Species crab, dungeness
Species Id M070001
Date 26 AUG 96
STATUS
Coded Status
Commercial/consumption
Sport Fish
See Comments
REFERENCES FOR STATUS - 11323, 86 and 260
COMMENTS ON STATUS -
The Dungeness crab supports a valuable commercial and sport fishery along
the west coast of the US. It occupies ecological niches in both marine and
estuarine waters and is important as both predator and prey at all life
stages. Recent studies on the environmental consequences of dredging in
estuaries have established a strong probability that the Dungeness crab
population is likely to be seriously reduced by habitat alteration from
dredging unless proper precautions are taken to reduce losses *11323. The
loss of vital estuarine habitat could significantly reduce recruitment to
the offshore fishery *86*.
An important predator (on crangon shrimp and bivalves) and prey (includes
all age classes) in nearshore and estuarine habitats. Estuaries are
important in early life stages.*255*
Status - 1 (DRAFT) - Distribution
Species crab, dungeness
Species Id M070001
Date 26 AUG 96
DISTRIBUTION
Distribution - 1 HABITAT ASSOCIATIONS
NATIONAL WETLAND INVENTORY CODES
NWI NWICLS NWIMOD NWISPEC
Marine, intertidal FL2 L 5
Marine, intertidal FL2 L 5
Marine, intertidal FL2 L 5
Estuarine AB2 L 5
Marine, intertidal FL3 L 5
Estuarine AB.
Marine, subtidal UB2 L
Marine, subtidal UB3 L
REFERENCES FOR NWI - 86
COMMENTS ON HABITAT ASSOCIATIONS -
Eggs occur on pleopods of female crabs in euhaline (30-40 ppt) waters.
Females with eggs can be found intertidally and out to deeper nearshore
waters. Larvae initially occur in nearshore euhaline waters (5-16 kn from
shore), with offshore movement and distribution influenced by depth,
latitude, temperature, salinity, and currents. Larvae are found near the
surface at night and 15-25 meters deep during daylight. Megalopae are in
the upper 15 meters both day and night, but they also have diel migrations
and are found primarily in shallow water nearshore areas. Juveniles occur
primarily in shallow coastal waters and estuaries. Adults are found
primarily intertidally to 90 meters in marine (euhaline) waters, but
sizable numbers occur in the lower reaches of estuaries.*255*
Habitat Associations - 1 (DRAFT) - Food Habits
Species crab, dungeness
Species Id M070001
Date 26 AUG 96
FOOD HABITS
TROPHIC LEVEL -
CARNIVORE
REFERENCES FOR TROPHIC LEVEL - 86 and 260
LIFESTAGE FOOD FOOD PART
Larva Zooplankton Not Applicable
Juvenile Crustaceans Not Specified
Juvenile Molluscs Not Specified
Juvenile Fish Not Specified
Adult Malacostraca Not Specified
Adult Fish Not Specified
Adult Molluscs Not Specified
REFERENCES FOR ADULT FOOD - 86 and 260
REFERENCES FOR JUVENILE FOOD - 86 and 260
REFERENCES FOR LARVAE FOOD - 86 and 260
COMMENTS ON FOOD -
Larvae eat both zooplankton and phytoplankton, but zooplankton is most
important. The larvae capture food items with the natatory hairs of their
maxillipeds, and size of food is a selection factor. The diet of juvenile
crabs consists largely of fish, mollusks, and crustaceans. Crabs progress
from eating bivalves their first year, to eating shrimp (Crangon spp.) their
second year, and finally to eating juvenile teleost fish in their third
year. Cannibalism is common among adults *86*.
Food Habits - 1 (DRAFT) - Environment Associations
Species crab, dungeness
Species Id M070001
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 Water Temperature: Specified in Comments
G Turbidity: Specified in Comments
G Nutrient [Phosphorus and Nitrogen]: Specified in comments
G Substrate: Specified in Comments
G Relation to Substrate: Unattached - normally free living
G Estuarine habitat zone: offshore
J Water Temperature: Between 21-27 degrees C
J Water Temperature: Between 15-21 degrees C
J Water Temperature: Specified in Comments
A Water Temperature: Between 15-21 degrees C
A Water Temperature: Below 15 degrees C
A Water Temperature: Specified in Comments
BA Water Temperature: Below 15 degrees C
BA Water Temperature: Specified in Comments
L Water Temperature: Below 15 degrees C
L Water Temperature: Specified in Comments
E
E
E
E
L
L
G Bottom Type [Aquatic]: Sand
REFERENCES FOR ENVIRONMENTAL ASSOC_ - 86 and 260
REFERENCES FOR LIMITING ENVIRONMENTAL ASSOC_ - 86
REFERENCES FOR ADULT ENVIRONMENTAL ASSOC_ - 260
REFERENCES FOR FEEDING ADULT ENVIRONMENTAL ASSOC_ - 86
REFERENCES FOR RESTING ADULT ENVIRONMENTAL ASSOC_ - 86
REFERENCES FOR BREEDING ADULT ENVIRONMENTAL ASSOC_ - 86 and 260
REFERENCES FOR JUVENILE ENVIRONMENTAL ASSOC_ - 260
REFERENCES FOR FEEDING JUVENILE ENVIRONMENTAL ASSOC_ - 86
Environment Associations - 1 (DRAFT) - Environment Associations
Species crab, dungeness
Species Id M070001
Date 26 AUG 96
REFERENCES FOR RESTING JUVENILE ENVIRONMENTAL ASSOC_ - 86
REFERENCES FOR LARVAE ENVIRONMENTAL ASSOC_ - 260
REFERENCES FOR FEEDING LARVAE ENVIRONMENTAL ASSOC_ - 86
REFERENCES FOR RESTING LARVAE ENVIRONMENTAL ASSOC_ - 86
REFERENCES FOR PUPAE ENVIRONMENTAL ASSOC_ - 86
REFERENCES FOR EGG ENVIRONMENTAL ASSOC_ - 86
COMMENTS ON ENVIRONMENTAL ASSOCIATIONS -
The temperature preferences of adult crabs are different among seasons.
They are somewhat tolerant of abrupt temperature and salinity fluctuations,
and water temperatures from 3 to 19 degrees C were listed as normal for the
Dungeness crab.
Dungeness crabs have different optimal water temperatures at different
stages. In the laboratory, it has been reported that optimal water
temperatures for mating ranged from 12 to 16 degrees C during long
photoperiods. An apparent trend toward crabs mating later in colder water
was noted in the laboratory. In Washington coastal waters, where Dungeness
crabs usually mate in early spring, the bottom temperatures are between 8
and 10 degrees C. The egg brooding periods varied inversely with seawater
temperatures of 9 to 17 degrees C. Prolonged egg brooding periods in
colder water are consistant with prolonged occurrences of ovigerous crabs
and cooler ocean temperatures with progressively northward movement along the
Pacific coast. Hatching success, considered as the number of larvae that
hatch from an egg mass, decreased as the temperature increased from 10 to
17 degrees C. A similar correlation was found between egg mortality and
temperature with 20% mortality at 10 degrees C and 100% mortality at 20
degrees C.
Optimal temperatures for larvae are 10 to 14 degrees C. Juvenile
crabs, 80 mm wide and acclimated to 10 degrees C, have been exposed to
water temperatures up to 25 degrees C for 7 days with little or no
mortality; however, an increase of 2.5 degrees C above 25 degrees C was
fatal to all crabs tested. In the laboratory, adult crabs had a maximum
tolerable temperature of 25 degrees C during long photoperiods, which
decreased to 20 degrees C when exposed to short photoperiods. With adults
crabs held for 8 months, mortality increased with temperature from 17% at
10 degrees C to 58% at 13 degrees C and to 80% at 17 degrees C, although
laboratory stress probably exacerbated the effect of high temperatures.
Tolerance to salinity varies among the life stages of the Dungeness
crab. In general, salinity is not as important as temperature to egg
development and hatching, but the larvae are highly sensitive to changes in
salinity. The percentage of eggs hatching was optimal at 15 ppt, but
hatching occurred to some degree over a wide range of salinities between 10
ppt and 32 ppt. When salinity was increased from 15 ppt to 32 ppt, the
average prezoeal period was reduced from about 60 min to less than 11 min.
At a salinity of 10 ppt, no prezoeae molted to zoeaea, but 100% molted at
30 ppt. The highest survival for larvae was between salinities from 25 ppt
to 30 ppt. Survival decreased with salinity and was poorest at salinities
of 15 ppt. No juvenile or adult tolerance levels are available in the
Environment Associations - 2 (DRAFT) - Environment Associations
Species crab, dungeness
Species Id M070001
Date 26 AUG 96
literature at this time.
Salinity and temperature are both related to larval survival.
Significant interaction exists between these two factors with salinity
buffering temperature. At favorable temperatures, unfavorable salinities
resulted in complete mortality, but favorable salinities at unfavorable
temperatures allowed some survival.
Adult crabs are found living over several substrate types, but they
prefer sandy-mud bottoms. This preference may stem from an abundance of
food organisms on such substrates or perhaps the crabs find shelter from
predation there. Older crabs seem less dependent on epibenthic cover and
can be found over more exposed substrates. Most crabs remain in the
subtidal environment, but may venture into littoral areas at high tide.
This behavior is enhanced by the presence of preferred food items and
decreased during low salinities following heavy rains.
COMMENTS ON RESTING ADULT ENVIRONMENTAL ASSOC_ -
Dungeness crabs have different optimal water temperatures at different
stages. In the laboratory, it has been reported that optimal water
temperatures for mating ranged from 12 to 16 degrees C during long
photoperiods. An apparent trend toward crabs mating later in colder water
was noted in the laboratory. In Washington coastal waters, where Dungeness
crabs usually mate in early spring, the bottom temperatures are between 8
and 10 degrees C. The egg brooding periods varied inversely with seawater
temperatures of 9 to 17 degrees C. Prolonged egg brooding periods in
colder water are consistant with prolonged occurrences of ovigerous crabs
and cooler ocean temperatures as you move progressively northward along the
Pacific coast.
COMMENTS ON FEEDING ADULT ENVIRONTAL ASSOC_ -
Adult crabs are found living over several substrate types, but they
prefer sandy-mud bottoms. This preference may stem from an abundance of
food organisms on such substrates or perhaps the crabs find shelter from
predation there. Older crabs seem less dependent on epibenthic cover and
can be found over more exposed substrates. Most crabs remain in the
subtidal environment, but may venture into littoral areas at high tide.
This behavior is enhanced by the presence of preferred food items and
decreased during low salinities following heavy rains.
Environment Associations - 3 (DRAFT) - Environment Associations
Species crab, dungeness
Species Id M070001
Date 26 AUG 96
COMMENTS ON BREEDING ADULT ENVIRONMENTAL ASSOC_ -
Dungeness crabs have different optimal water temperatures at different
stages. In the laboratory, it has been reported that optimal water
temperatures for mating ranged from 12 to 16 degrees C during long
photoperiods. An apparent trend toward crabs mating later in colder water
was noted in the laboratory. In Washington coastal waters, where Dungeness
crabs usually mate in early spring, the bottom temperatures are between 8
and 10 degrees C. The egg brooding periods varied inversely with seawater
temperatures of 9 to 17 degrees C. Prolonged egg brooding periods in
colder water are consistant with prolonged occurrences of ovigerous crabs
and cooler ocean temperatures as you move progressively northward along the
Pacific coast. Hatching success, considered as the number of larvae that
hatch from an egg mass, decreased as the temperature increased from 10 to
17 degrees C. A similar correlation was found between egg mortality and
temperature with 20% mortality at 10 degrees C and 100% mortality at 20
degrees C.
COMMENTS ON RESTING JUVENILE ENVIRONMENTAL ASSOC_ -
Juvenile crabs, 80 mm wide and acclimated to 10.0 degrees C, have been
exposed to water temperatures up to 25.0 degrees C for 7 days with little
or no mortality; however, an increase of 2.5 degrees C above 25 degrees C
was fatal to all crabs tested.
COMMENTS ON FEEDING JUVENILE ENVIRONMENTAL ASSOC_ -
Juvenile crabs, 80 mm wide and acclimated to 10.0 degrees C, have been
exposed to water temperatures up to 25.0 degrees C for 7 days with little
or no mortality; however, an increase of 2.5 degrees C above 25 degrees C
was fatal to all crabs tested.
COMMENTS ON RESTING LARVAE ENVIRONMENTAL ASSOC_ -
Optimal temperatures for larvae are 10 to 14 degrees C.
COMMENTS ON FEEDING LARVAE ENVIRONMENTAL ASSOC_ -
Dungeness crabs have different optimal water temperatures at different
stages. In the laboratory, it has been reported that optimal water
temperatures for mating ranged from 12 to 16 degrees C during long
photoperiods. An apparent trend toward crabs mating later in colder water
was noted in the laboratory. In Washington coastal waters, where Dungeness
crabs usually mate in early spring, the bottom temperatures are between 8
and 10 degrees C. The egg brooding periods varied inversely with seawater
temperatures of 9 to 17 degrees C. Prolonged egg brooding periods in
colder water are consistant with prolonged occurrences of ovigerous crabs
and cooler ocean temperatures as you move progressively northward along the
COMMENTS ON EGG ENVIRONMENTAL ASSOC_ -
Dungeness crabs have different optimal water temperatures at different
stages. In the laboratory, it has been reported that optimal water
temperatures for mating ranged from 12 to 16 degrees C during long
photoperiods. An apparent trend toward crabs mating later in colder water
was noted in the laboratory. In Washington coastal waters, where Dungeness
crabs usually mate in early spring, the bottom temperatures are between 8
and 10 degrees C. The egg brooding periods varied inversely with seawater
temperatures of 9 to 17 degrees C. Prolonged egg brooding periods in
Environment Associations - 4 (DRAFT) - Environment Associations
Species crab, dungeness
Species Id M070001
Date 26 AUG 96
colder water are consistant with prolonged occurrences of ovigerous crabs
and cooler ocean temperatures as you move progressively northward along the
Hatching success, considered as the number of larvae that hatch from an egg
mass, decreased as the temperature increased from 10 to 17 degrees C. A
similar correlation was found between egg mortality and temperature with
20% mortality at 10 degrees C and 100% mortality at 20 degrees C.
Environment Associations - 5 (DRAFT) - Life History
Species crab, dungeness
Species Id M070001
Date 26 AUG 96
LIFE HISTORY
Morphology and Identification Aids
Color: Beige to light brown with blue trim and hue, darkest anteriorly,
often light orange below, sometimes light gray-purple below; inner sides of
anterior feet and claws crimson, tips not dark. Short eyestalks with small
orbits. Frontal area: narrow with five unequal teeth, not markedly
produced beyond the outer orbital angles; middle tooth largest, more
advanced than outer pair; outer pair form inner angles of orbit. Teeth:
(antero-lateral) ten, counting orbital tooth; widest at 10th tooth, which
is large and projecting; all teeth pointed, with anterior separations.
Postero-lateral margins: unbroken, entire, without teeth, meets
antero-lateral margin with distinct angle. Abdomen: narrow in male, broad
in female.
Juveniles: antero-lateral and postero-lateral margins meet at a distinct
angle; carapace widest at 10th tooth; posterio-lateral margin entire;
carpus of cheliped with single spine above, fingers light colored, carapace
not as broad as the adult.
Mating
Dungeness crabs mate from April to September in British Columbia, mostly in
March and April, but sometimes in May and June in Washington, and March to
July in California. Mating usually occurs in offshore locations. Premolt
females are located by adult males for mating, possibly through a
pheromonal homing system similar to those used by other crab species. The
female is held by the male in a premating embrace up to 7 days prior to her
molting. Approximately 1h after molting of the female is completed, mating
between the hardshell male and softshell female occurs. Mating involves
the insertion of the male gonopods into the spermathecae of the female and
the deposition of spermatophores. Following copulation, the female may be
embraced again by the male for a period of up to 2 days. Both pre- and
postmating embraces may serve to protect the female from predation, while
insuring the maing success of the male by guarding the female against other
males. The spermatorphores deposited by the male in the spermathecae
contain sperm that are viable for many months and which remain viable
through molting until a second egg extrusion. Eggs are not fertilized
until extrusion, at which time they are attached to the female pleopod
setae and are carried beneath the abdominal flap. Eggs hatch in 60 to 120
days.*86*
Eggs and Fecundity
Eggs are extruded from September to February in British Columbia, October
to December in Washington, October to March in Oregon, and September to
November in California. An egg mass may contain from one to two million
eggs and a female may produce up to five million eggs in three or four
broods during her lifetime. Eggs are pale white to orange at extrusion,
becoming progressively darker in color as they develop.
Water temperatures and changes in water temperatures have considerable
influence on the rate of egg development and mortality after fertilization
and spawning. When temperatures rise, the rate of egg development also
rises, but so does the rate of mortality. Eggs mature in about 2-3 weeks.
The hatching season commonly shortens from north to south along the
Pacific coast. Eggs hatch in coastal waters from December to June in
Life History - 1 (DRAFT) - Life History
Species crab, dungeness
Species Id M070001
Date 26 AUG 96
British Columbia, January to April in Washington, December to April in
Oregon, January to early March in northern California and late December to
early February in central California.
Larvae
Larvae emerge as prezoeae and molt to zoeae within 1h. The duration of the
prezoeal period and the transformation to zoeae vary with salinity. The
larvae progress through five zoeal stages before molting into megalopae.
Zoeae first appear within a distance of 5-16 km from shore. Offshore
movement and distribution of larvae probably is regulated by a variety of
factors including depth, latitude, temperature, salinity, and ocean
currents. Distribution is dependent upon the larval stage and the larvae
shore a diel pattern of vertical distribution; they are near the surface at
night. There is considerable offshore movement of larvae that occurs
during the zoeal stages; the larvae appear to be transported seaward from
the onset of hatching. The trend of abundance of megalops proceeds from
south to north. Megalope are often abundant on the hydrozoan Velella
velella, when they are scarce or absent elsewhere in the water column. It
is thought the Velella act as a transport mechanism or possibly a food
source or protection from predation.
Juveniles
Most megalope molt into juveniles in August off the coast of British
Columbia and in April-May off the coasts of both Oregon and Washington.
After molting, the juveniles are found in shallow coastal waters and
estuaries, and large numbers live among eelgrass or other aquatic
vegetation that provides protection and substrate, and harbors food
organisms for early instars. Recently, shells of bivalves such as Mya
arenaria and Crassostrea gigas have been documented as very important
habitat for young crabs. In cental California, there is evidence that
movement of postlarval Dungeness crabs into the estuaries takes place in
May and June via bottom currents, where they stay for 11-15 months.
Juveniles are common in estuaries, while subadults and adults are common
offshore. Juveniles most 11 or 12 times prior to sexual maturity.
Carpace width at the first instar varies from about 5 mm to greater than
8.5 mm. After 1 year of growth beyond hatching, most crabs (in
California) are in their 8th, 9th, or 10th instar. By comparison, crabs
in Washington attain only the sixth or seventh instar by the end of their
first year of life. Crabs mature after about 2 years at carpace widths of
about 116 mm for males and 100 mm for females.
Adults
At about 4 years old, most adult Dungeness males in the coastal waters of
Washington are of marketable size (>159 mm). Marketable crabs usually
only most once a year. The maximum lifespan of Dungeness crabs is 8 to 10
years. The maximum size attained is about 218 mm CW in males and 160 mm
CW in females at the 16th instar. Along the coast of northern California,
legal-sized male crabs probably move offshore (often to the south or
north) in late summer, sometimes through early winter; sometime in winter
the direction of movement is probably reversed and the crabs return
inshore. Crabs display a definite diel activity; they are more abundant
by day in the subtidal area and more abundant at night in the intertidal
area; the response is positively correlated with food availability.
Life History - 2 (DRAFT) - Life History
Species crab, dungeness
Species Id M070001
Date 26 AUG 96
Cannibalism is common among adults, but no correlations have been made
between the rate of cannibalism and abundance.
Growth
In Dungeness crabs, like other crustaceans, growth proceeds in steps
through a series of molts. The number of molts that a crab undergoes
before becoming mature depends upon the increment at each most and the
frequency of molting, both of which vary among crabs at different
locations. Dungeness crabs grow in carapace size at molt and gain weight
between molts. Populations of 0+ crabs that settle directly offshore, as
well as 1+ nearshore crabs, grow significantly slower than those in the
estuary. Dungeness crab growth is quite variable along the Pacific
coast. However, in general, it is somewhat slower in the northern part
of the range (Washington and British Columbia) when compared to the
southern part of the range.*86*
The red rock crab, Cancer productus, also has 10 antero-lateral teeth;
frontal teeth are unequal. However, this species differs from C. magister
in that the frontal area is markedly pronounced beyond outer orbital angles,
cheliped fingers are black, and the carapace is widest at eighth
antero-lateral tooth. It attains a width of 7 inches.*260*
The rock crab, Cancer antennarius, like C. productus, is dark red with
black-tipped chelae, is widest at the eighth tooth, but red-spotted on its
ventral surface. It attains a width of about 13 cm. Cancer oregonensis
(Oregon Cancer crab) is a small, oval crab with 12 antero-lateral teeth.
Both the slender crab (Cancer gracilis) and Cancer jordani, two rather
uncommon species, have nine antero-lateral teeth; C. gracilis rarely exceeds
a width of 8 cm. The yellow crab, Cancer anthonyi, which is found south of
Humboldt Bay, have large smooth claws with black tips, is yellowish-brown
with a wash of purple anteriorly, has 9 antero-lateral spines and attains a
width of 15 cm.*260*
REPRODUCTION:
Dungeness crabs mate from April to September in British Columbia, mostly in
March and April but sometimes in May and June in Washington; and March to
July in California. Mating occurs in nearshore coastal locations in the
west coastal region of the Pacific Northwest. Premolt female crabs are
located by adult males for mating, possibly through a pheromonal homing
system similar to those used by other crab species. The female is held by
the male in a premating embrace up to 7 days prior to her molting.
Approximately 1 h after molting of the female is completed, the hardshell
male and softshell female mate. The male gonopods are inserted into the
spermathecae of the female and spermatophores are deposted. Following
copulation, the female may be embraced again by the male for a period of up
to 2 days. Both premating and postmating embraces may serve to protect the
female from predation, while insuring the mating success of the male by
guarding the female against other males. The male spermatophores in the
spermathecae contain sperm that may be viable for many months, often through
molting until a second egg extrusion.*260*
Eggs and Fecundity. Actively molting female crabs are more fecund than
non-molting crabs, even though they may be the same size. Eggs are not
fertilized until extrusion, at which time they are attached to the female
pleopod setae and are carried beneath the abdominal flap; they hatch in 60
to 120 days. Eggs are extruded from September to February in British
Life History - 3 (DRAFT) - Life History
Species crab, dungeness
Species Id M070001
Date 26 AUG 96
Columbia, from October to December in Washington, from October to March in
Oregon, and from September to November in California. An egg mass may
contain from one to two million eggs, and a female may produce up to five
million eggs in three or four broods during her lifetime. Eggs are orange
at extrusion, becoming progressively darker in color as they develop. Water
temperatures and changes in water temperatures have considerable influence
on the rate of egg development and mortality after fertilization and
spawning. When temperatures rise, the rate of egg development also rises,
but so does the rate of mortality. In laboratory tests eggs held at 9.4
degrees C hatched in 123 days and at 16.7 degrees C they hatched in 64 days.
At 10 degrees C, 685,000 larvae were produced per egg mass, whereas at 16.7
degrees C, 14,000 larvae were produced per egg mass. Egg mortality for eggs
from Similk Bay, Washington, was 20% after 20 min exposure at 10 degrees C,
30% after 4 min and 90% after 20 min at 15 degrees C, and 100% after 4 min
at 20 degress C.*260*
Epibiotic fouling of Dungeness crab eggs has been linked to increased egg
mortality because of mechanical interference with hatching and oxygen
consumption. Waters with high and rising nutrient levels are suspected to
cause increased fouling. Egg predation by a nemertean worm, Carcinonemertes
errans, is thought to increase the fouling of eggs through the liberation of
yolk during its feeding and defecation. In coastal waters near San
Francisco, the estimated average annual mortality caused by predation of the
worm on Dungeness crab eggs was over 55% in 1974-1979 when worm densities
were about 14 per 1,000 eggs.*260*
Eggs hatch in 2 to 3 months. The hatching season commonly shortens from
north to south along the Pacific coast. Eggs hatch in coastal waters from
December to June in British Columbia, but considerably later in Queen
Charlotte Islands, from January to April in Washington, from December to
April in Oregon, from January to early March in northern California, and
commonly from late December to early February in central California.*260*
LIMITING FACTORS:
Predation. The larvae are preyed upon by numerous fishes. Adults and
juveniles are preyed upon by sea otters, fishes, and octopuses. Cannibalism
is common and probably exercises some control over abundance.*260*
Temperatures. Hatching success, considered as the number of larvae that
hatch from an egg mass, decreased as the temperature increased from 10 to
17 degrees C. Researchers found a similar correlation between egg
mortality and temperature with 20% mortality after 20 min at 10 degrees C
and 100% mortality after 4 min at 20 degrees C.*260*
Temperature-Salinity Interactions. At favorable temperatures, unfavorable
salinities resulted in complete mortality of adults, but favorable
salinities at unfavorable temperatures allowed some survival. The effects
of temperature or salinity alone on C. magister zoeae do not appear to
cause large fluctuations in zoeal survival in the ocean.*260*
POPULATION ATTRIBUTES:
Growth Characteristics. In Dungeness crabs, like other crustaceans, growth
proceeds in steps through a series of molts. The number of molts that a
crab undergoes before becoming mature depends upon the growth increment at
each molt and the frequency of molting, both of which vary among crabs at
different locations. Dungeness crabs grow in carapace size at each molt and
gain biomass between molts. In older crabs the growth, as measured by the
Life History - 4 (DRAFT) - Life History
Species crab, dungeness
Species Id M070001
Date 26 AUG 96
percent change in carapace width, declines as the frequency of molting slows
down, but the rate of weight gain increases over time. The probability of
annual molting in female Dungeness crabs declines from about 1.0 for crabs
of 130-135 mm CW to 0.0 for crabs of 155 mm CW and larger.
Among possible attributes of estuarine residence suggested by researchers is
an enhanced growth rate compared to that of siblings of a year class that
settle offshore. Size attained by juvenile crabs within certain periods
after metamorphosis seems to be somewhat dependent on latitude and on time
of settlement. Upper estimates of age at sexual maturity range from 4-5
years in British Columbia to 1 year in San Francisco Bay, where the crabs
reach by this time a carapace width (100 mm) usually associated with sexual
maturity. More generally, crabs are predicted to reach maturity at the end
of their second year after metamorphosis or in their third growing season
over much of the coast. While age and size at sexual maturity may not
differ substantially along the coast, estimates of growth rates of newly
settled age 0+ crabs do.
Several studies of juveniles indicate that growth rate is accelerated in
estuaries or within nearshore coastal embayments where water temperatures
are relatively high. This difference in growth raye may be due to a
temperature difference which is approximately 6 degrees C higher in the
estuary than the ocean.
Growth of young-of-the-year crabs is substantially slower offshore from San
Francisco Bay, in the Gulf of the Farallons, than in estuaries, where the
offshore crabs are about 28-30 mm and those in the estuary are about 60 mm
in width. Gulf-reared crabs require about 2 years after metamorphosis to
reach the first postlarval instar width of 100 mm, while the average
bay-reared crab reaches this size one year after metamorphosis.
Growth of California Dungeness crabs is somewhat faster in males than
females, but varies from year to year and among geographic regions. In
northern California, age and growth are similar to that observed in
Washington, where crabs become fully recruited into the fishery at 4 years
of age, having reached a carapace width of about 159 mm. Dungeness crab
growth is variable along the Pacific coast. However, in general, it is
somewhat slower in the northern part of the range when compared to the
southern part of the range (California).*260*
Commercial Fishery. Commercial landings of Dungeness crab on the Pacific
coast have fluctuated widely, almost cyclically, over the past 30 years.
Several hypotheses have been proposed to explain the cyclic nature of
Dungeness crab population size. According to researchers, commercial
landings were highest 1.5 years after a period of strong upwelling in
California and Oregon, and 6 months following a strong upwelling in
Washington, although the biological sense of such a relation is much in
doubt. Researchers challenged this conclusion by using auto-correlation to
show that commercial landings are cyclic but that strong upwelling is not.
Another hyposthesis to explain catch fluctuations suggests that periods of
high levels of cannibalism and interspecific competition may cause a decline
in the fishery 3 or 4 years later. In a model predicting recruitment,
researchers discounted cannibalism as a factor and contended that changes in
egg and larval survival regulate population success. Larval survival may be
seriously reduced by a combination of environmental factors that can cause
increased mortality if unfavorable for even short periods of time.
Researchers indicated that diseases caused by various organisms (bacteria,
Life History - 5 (DRAFT) - Life History
Species crab, dungeness
Species Id M070001
Date 26 AUG 96
Protozoa, or fungi) may be reponsible for mass mortalities of adult crabs.
Predation may have a profound impact on the Dungeness crab commercial
fishery in certain geographic areas. Researchers hypothesized that
extensive predation by hatchery-released coho salmon from the Columbia River
continually suppressed the Dungeness crab fishery. There is an apparent
cyclic covariance between abundances of salmon and Dungeness crabs.
Only male crabs 6-1/4 inches wide or wider may be taken commercially in
California. Not more than 1% of any catch may be smaller than this size and
no crabs less than 5-3/4 inches may be retained. Most crabs taken in the
California commercial fishery are 4-year-olds, although some 3- and
5-year-old crabs are taken.*260*
REFERENCES FOR LIFE HISTORY- 86 and 260
Life History - 6 (DRAFT) - Management Practices
Species crab, dungeness
Species Id M070001
Date 26 AUG 96
MANAGEMENT PRACTICES
RESULT MANAGEMENT PRACTICE
Existing Other management practices [specified in comments]
Beneficial Controlling pollution [thermal, chemical, physical]
Existing Regulating harvest of species being described
Existing Regulating harvest - setting size limits
REFERENCES FOR BENEFICIAL MANAGEMENT PRACTICES - 255
REFERENCES FOR EXISTING MANAGEMENT PRACTICES - 86 and 260
COMMENTS ON MANAGEMENT PRACTICES -
The State of Oregon has sought to limit the conflict between sport and
commercial crabbers by restricting commercial crabbing to the middle of the
week and to the use of sport gear.*86*
Another theory to explain catch fluctuations suggests that periods of high
levels of cannibalism and/or interspecific competition may cause a decline
in the fishery 3 or 4 years later. Larval survival may be seriously altered
by a combination of environmental factors that can cause increased mortality
if unfavorable for even short periods of time. Disease may also be caused
by various organisms (bacteria, protozoa, or fungi) that may in turn cause
mass mortalitites of adult crabs.
Predation may have a profound impact on the Dungeness crab commercial
fishery in certain geographic area. It is theorized that hatchery released
coho salmon from the Columbia River continue to suppress the Dungeness crab
fishery through extensive predation.*86*
The effect of urban pollution-chlorine residuals, heavy metals, chlorinated
pesticides, PCB's and hydrocarbons-on Dungeness crabs is not clear, but
sublethal effects are indicated for some pollutants at concentrations
presently occurring in San Francisco Bay. Crabs are intolerant of low
dissolved oxygen (optimal >5 ppm). Ammonia is toxic at low concentrations.
The insecticide Sevin (carbaryl) is sometimes used to control ghost shrimp
in Pacific oyster beds but is also very toxic to Dungeness crabs. Zoea of
C. magister are the most sensitive life stages to insecticides and
fungicides.*255*
Recent studies on the environmental consequences of dredging in estuaries
have established a strong probability that the Dungeness crab population will
be seriously reduced by habitat alteration from dredging unless proper
precautions are taken to reduce losses. The loss of vital estuarine habitat
could significantly reduce recruitment to the offshore fishery.*260*
Only male crabs 6-1/4 inches wide or wider may be taken commercially in
California. Not more than 1% of any catch may be smaller than this size and
no crabs less than 5-3/4 inches may be retained. Most crabs taken in the
California commercial fishery are 4-year-olds, although some 3- and
5-year-old crabs are taken.*260*
In California sport fishery the daily catch limit is 10 crabs. Concern
over the excessive take of sublegal sized Dungeness crabs in the sport
fishery prompted the California Fish and Game Commission in 1978 to close
the fishery in San Francisco and San Pablo Bays inside Golden Gate. Sport
fishing for Dungeness crabs is most active in the Crescent City area.
Management Practices - 1 (DRAFT) - Management Practices
Species crab, dungeness
Species Id M070001
Date 26 AUG 96
Nearly 4 times more red crabs (C. productus) than Dungeness crabs are taken
in the sport fishery. Rock crabs, slender crabs, and yellow crabs are also
taken in the sport fishery in limited numbers.*260*
Management Practices - 2 (DRAFT) - References
Species crab, dungeness
Species Id M070001
Date 26 AUG 96
References
86* Pauley, G.B., D.A. Armstrong, T.W. Heun. 1986. Species
profiles: life histories and environmental requirements of
coastal fishes and invertebrates (Pacific Northwest)--Dungeness
Crab. U.S. Fish and Wildl. Serv. Biol. Rep. 82(11.63). U.S. Army
Corps of Engineers, TR EL-82-4:20.
11323* Armstrong, D.A., B.G. Stevens, J.C. Hoeman. 1982.
Distribution and abundance of Dungeness crab and Crangon shrimp,
and dredging-related mortality of invertebrates and fish in
Grays Harbor, Washington, U.S. Army Corps of Engineers, Seattle.
Tech. Rep. Contract No. N-NACW67-80-C0086:349.
255 * Monaco, M.E., R.L. Emmett. 1988. National Estuarine
Inventory: Estuarine Living Marine Resources Project Washington
State Component. Living Marine Resources Program (ed.). National
Oceanic and Atmospheric Administration Rockville, MD:82.
References - 1