(DRAFT) - Taxonomy
Species crab, brown rock
Species Id M070015
Date 26 AUG 96
TAXONOMY
NAME - crab, brown rock
OTHER COMMON NAMES - rock crab, brown crab, red rock crab and spot-bellied crab
ELEMENT CODE -
CATEGORY - Aquatic Crustaceans
PHYLUM AND SUBPHYLUM - Arthropod,
CLASS AND SUBCLASS - Crustacea,
ORDER AND SUBORDER - Decapoda, Brachyura
FAMILY AND SUBFAMILY - Cancridae,
GENUS AND SUBGENUS - Cancer,
SPECIES AND SSP - antennarius,
SCIENTIFIC NAME - Cancer antennarius
AUTHORITY - Stimpson
TAXONOMY REFERENCES - 261 and 231
Taxonomy - 1 (DRAFT) - Status
Species crab, brown rock
Species Id M070015
Date 26 AUG 96
STATUS
Coded Status
Commercial
Sport Fish
Existing, FMP exists
REFERENCES FOR STATUS - 261
COMMENTS ON STATUS -
Rock crabs had been fished previously at a low level of effort since at
least 1930. Commercial fishery landings statistics of CDFG showed that
annual landings in the mid-1980's approached 2 million lb with an ex-vessel
value exceeding $1.6 million. Declines in the stocks of other commercially
important nearshore species have stimulated interest in further use of rock
crab species; continued growth of the fishery is expected. The species also
supports small recreational fishery.*261*
In California, the sport catch limit on all Cancer species in combination
(excluding the Dungeness crab) is 35 crabs per day, and the minimum legal
carapace width is 4 inches.*261*
Rock crabs occupy a variety of coastal habitats and are an ecologically
important component of the nearshore environment. As juveniles, they are
important prey of numerous invertebrates and many commercially and
recreationally important fishes. Adult rock crabs are a major food of the
threatened southern sea otter (Enhydra lutris) along the central California
coast.*261*
Status - 1 (DRAFT) - Distribution
Species crab, brown rock
Species Id M070015
Date 26 AUG 96
DISTRIBUTION
Distribution - 1 HABITAT ASSOCIATIONS
HABITAT - AQUATIC
REFERENCES FOR HABITAT - 261
LAND USE -
Water
REFERENCES FOR LAND USE - 261
NATIONAL WETLAND INVENTORY CODES
NWI NWICLS NWIMOD NWISPEC
Marine, intertidal RS.
Marine, intertidal UB2
REFERENCES FOR NWI - 261
COMMENTS ON HABITAT ASSOCIATIONS -
Brown rock crab ranges from Sequim, Washington, to Baja California, Mexico,
including Islas de Todos Santos. Its habitat extends from the low
intertidal zone to depths greater than 100 m, and includes substrates of
rocky shores, subtidal reefs, and coarse to silty sands.*261*
Habitat Associations - 1 (DRAFT) - Food Habits
Species crab, brown rock
Species Id M070015
Date 26 AUG 96
FOOD HABITS
TROPHIC LEVEL -
CARNIVORE
SCAVENGER
REFERENCES FOR TROPHIC LEVEL - 261
LIFESTAGE FOOD FOOD PART
General Bivalve Molluscs Not Specified
General Snails Not Specified
General Echinoderms Not Specified
General Crustaceans Not Specified
REFERENCES FOR GENERAL FOOD - 261
COMMENTS ON FOOD -
Rock crabs as a group are both scavengers and predators, feeding on a wide
variety of snails, clams, echinoderms, and crustaceans. Powerful crusher
claws enable adult crabs to eat thick-shelled snails; cockles, Protothaca
staminea; barnacles and hermit crabs; abalone, Haliotis spp.; and a variety
of thin-shelled infaunal and epifaunal species. Rock crabs are extremely
sensitive to the scent of potential food in the water and can detect amino
acid concentrations as low as 10 (to the -11 exponential) moles/l.*261*
Food Habits - 1 (DRAFT) - Environment Associations
Species crab, brown rock
Species Id M070015
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
J Estuarine habitat zone: offshore
G Currents: tidal
G Coastal Features: Rocky beaches
G Substrate: Mud or silt
G Substrate: Sand
G Substrate: Plants
E Bottom Type [Aquatic]: Sand
E Aquatic Habitat Zonation: Shallows with emergent vegetation [littoral zone]
L Aquatic Habitat Zonation: Open water [pelagic zone]
J Relation to Substrate: Occurs in substrate [penetrating]
J Bottom Type [Aquatic]: Sand
A Substrate: Sand
A Substrate: Rocks
J Bottom Type [Aquatic]: Rooted aquatic vegetation
J Aquatic Vegetation [specified type]: Specified in comments
L Bottom Type [Aquatic]: Sand
L Substrate: Rocks
REFERENCES FOR ENVIRONMENTAL ASSOC_ - 261
REFERENCES FOR ADULT ENVIRONMENTAL ASSOC_ - 261
REFERENCES FOR JUVENILE ENVIRONMENTAL ASSOC_ - 261
REFERENCES FOR LARVAE ENVIRONMENTAL ASSOC_ - 261
REFERENCES FOR EGG ENVIRONMENTAL ASSOC_ - 261
COMMENTS ON ENVIRONMENTAL ASSOCIATIONS -
Its habitat extends from the low intertidal zone to depths greater than 100
m, and includes substrates of rocky shores, subtidal reefs, and coarse to
silty sands.*261*
No tolerance levels have been established for the larval life history
stages of rock crabs, but researchers found that low salinities impaired
the molting process in larvae of the closely related Dungeness crab.*261*
Environment Associations - 1 (DRAFT) - Environment Associations
Species crab, brown rock
Species Id M070015
Date 26 AUG 96
COMMENTS ON ADULT ENVIRONMENTAL ASSOC_ -
The brown rock crab ranked second in abundance in southern California and
was most abundant in traps set on sand adjacent to rocky habitats, or on
extensive rocky reefs at depths less than 55 m. In samples taken along a
depth gradient between 8 and 18 m, relative abundances decreased,
proceeding seaward, for brown rock crabs.*261*
In laboratory thermal tolerance studies on brown rock crabs, mortality was
100% in adult crabs exposed for 1 h to acute temperatures above 31.1
degrees C, and nil in crabs similarly exposed to 29.2 degrees C. Chronic
exposure (96 h) of crabs to several test temperatures yielded a median
effective 50% mortality at a theoretical value of 25.4 degrees C. Although
such temperatures are unlikely along the open coast in California, they
sometimes occur near the cooling water discharges of coastal power
plants.*261*
COMMENTS ON JUVENILE ENVIRONMENTAL ASSOC_ -
Juvenile brown rock crabs are common in the intertidal zone, where they may
be exposed to the air daily for several hours. Mortality is unlikely,
however, provided they are shaded from direct sunlight beneath algae, or
protected in rock crevices.*261*
COMMENTS ON LARVAE ENVIRONMENTAL ASSOC_ -
During their planktonic existence, crab larvae become widely distributed
over the continental shelf. Researchers found that, in central California,
estuarine runoff and upwelling probably dispersed Dungeness crab zoeae
offshore, and the northward flowing Davidson current dispersed larvae
upcoast in winter. Researchers presented evidence that early stage larvae
of rock crabs generally occurred on the bottom, or in depths up to 80 m,
during the day; late stage larvae, however, were more abundant near the
surface. The researchers suggested that a combination of physical factors,
primarily wind-generated surface currents and tidally forced internal
waves, caused megalopae to be transported shoreward. Late stage larvae
generally begin to recruit to the nearshore habitat in spring, a season of
strong onshore sea breezes along the California coast.*261*
Researchers who conducted field experiments to determine preferred sustrate
types of newly settling rock crab larvae in southern California, observed
that brown rock crabs were equally abundant on sand and rock
substrates.*261*
COMMENTS ON EGG ENVIRONMENTAL ASSOC_ -
Ovigerous brown rock crabs have been observed buried in sand at the base of
rocks in shallow water, and are found more commonly in water less than 18 m
deep in southern California.*261*
Environment Associations - 2 (DRAFT) - Life History
Species crab, brown rock
Species Id M070015
Date 26 AUG 96
LIFE HISTORY
PHYSICAL DESCRIPTION:
All Cancer species are recognized by their broad, oval, uneven but not
highly sculptured carapace which has numerous anterolateral teeth. Males
are distinguished by a slender abdomen and mature females by a broad abdomen
that is often hirsute on the margin. Researchers, who studied the
morphological relationships of 10 northern temperate Cancer species,
considered the brown rock crab, red rock crab, and yellow crab closely
related primarily on the basis of similarities in claw shape.
The brown rock crab is mottled dark brown dorsally (rarely uniformly orange
or gray), and has red spotting over a white background ventrally. There are
nine anterolateral teeth, and the carapace is widest at the eighth tooth.
Characteristic long and stout paired antennae (from which the species name
is derived) arise between the retractable stalked eyes. Legs are generally
rough along the edges and may be hairy, especially in females and juveniles.
The claws are black tipped with a single tooth or spine on the wrist.*261*
REPRODUCTION:
The female mates in the soft-shell condition, after molting. Soft-shell
female rock crabs are most common in spring and fall, though they may be
found throughout the year. A pheromone released in the urine of females
before they molt attracts males and stimulates mating behavior. Brown rock
crabs are stimulated to pre-copulatory position and activity by pheromone
concentrations as low as 10(to the -10) moles/l. The male carries the
female, before her ecdysis, through insemination, and until initial
hardening of her shell occurs. Mating involves insertion of the male
gonopod into the spermatheca of the female and deposition of a
spermatophore. Spermatophores contain sperm that is potentially viable for
a year or longer, for multiple spawnings. Mated females (in the "plugged"
condition) may be identified by the presence of the hardened spermatophore
deposited in the spermatheca by the male, which presumably blocks further
mating and prevents loss of sperm. The plug is ejected during the first
oviposition; multiple ovipositions may occur but no record of them has been
published.*261*
Eggs and Fecundity. The eggs are fertilized internally as they are extruded,
about 11 weeks after the mating, and are carried by the female during
development. They appear as a bright orange mass ("sponge") attached to
setae on the endopodites of the pleopods, beneath the abdominal flap.
Egg-bearing ("berried" or ovigerous") female brown rock crabs are most
common in central California in winter. Ovigerous brown rock crabs have
been observed buried in sand at the base of rocks in shallow water, and are
found more commonly in water less than 18 m deep in southern California.
The color of the eggs progressively darkens from orange to dark brown as
embryos absorb the yolk during development.*261*
Larvae. Larvae hatch as prezoeae and molt to first stage zoeae in less than
1 h. They advance through six stages of successive increases in size-five
zoeal and one megalopal. During their planktonic existence, crab larvae
become widely distributed over the continental shelf. Researchers found
that, in central California, estuarine runoff and upwelling probably
dispersed Dungeness crab zoeae offshore, and the northward flowing Davidson
current dispersed larvae upcoast in winter. Researchers presented evidence
that early stage larvae of rock crabs generlly occurred on the bottom, or in
Life History - 1 (DRAFT) - Life History
Species crab, brown rock
Species Id M070015
Date 26 AUG 96
depths up to 80 m, during the day; late stage larvae, however, were more
abundant near the surface. It was suggested that a combination of physical
factors, primarily wind-generated surface currents and tidally forced
interanl waves, caused megalopae to be transported shoreward.*261*
Juveniles. Most megalopae molt into juveniles (first crab instars) in late
spring or summer months. Despite a widespread spatial and temporal overlap
of larval distribution in coastal waters, certain species-specific patterns
of recruitment vary with depth and substrate. Juvenile brown rock crabs,
which had the more generalized pattern of the rock crabs on substrate and
depth preference, settled on both rock and sand substrata; among the two
substrate types and various depths, however, their densities were greatest
on rock substrata that were at 13 m. In central California
juvenile brown rock crabs and red rock crabs are commonly found from the
intertidal zone to depths exceeding 30 m, and in summer may be especially
common in shallow stands of surfgrass along the open coast, or partly buried
in sand beneath rocks.*261*
BEHAVIOR:
Movements. The few tag-and-recapture data available indicate that adult
rock crabs remain fairly close inshore; localized movements rarely exceed
several kilometers from their release sites. From a total of over 17,000
tagged crabs released and nearly 2,000 recaptured during a 10-year study in
central California, the greatest distances traveled by brown rock crabs were
less than 8 km over an 8-month period. Although the few studies
thus far do not permit verification of seasonal migration patterns,
the occurrence of larger numbers of female brown crabs in traps during fall
than in other seasons suggests that onshore-offshore movements in some areas
may be related to annual cycles of molting and mating. Trap placement and
fishing success may strongly bias the interpretation of recapture or
movement data. Crabs were more likely to enter a trap if the opening
was perpendicular to prevailing currents.*261*.
LIMITING FACTORS:
Predation. Benthic fishes are major predators on juvenile rock crabs; among
the many that are known are scorpionfish (Scorpaena guttata), cabezon
(Scorpaenichthys marmoratus), barred sand bass, and severl species of
rockfishes. Larger crabs eventually attain a size large enough to
preclude predation by most fishes, except when the shell
is soft, just after molting. Rock crabs may fall prey to southern
sea otters. Rock crabs are also the preferred prey of octopuses
in southern California, and have been found in the gut of bottom-foraging
sharks in Elkhorn Slough, central California.*261*
The polychaete worm Iphitime holobranchiata infests the gills of brown rock
crabs and can be potentially detrimental to its host. The nemertean
egg predator Carcinonemertes epialti often occurs in the egg
masses of rock crabs.*261*
POPULATION ATTRIBUTES:
Growth. Growth in rock crabs, as in all crustaceans, progresses as a step
function through a series of molts. In brown rock crabs the maximum
carapace width is at least 155 mm in males (measured at the widest point on
carapace, excluding the anterolateral spines) but does not exceed 145 mm in
females. Longevity has been estimated to be about 5-6 years for brown rock
Life History - 2 (DRAFT) - Life History
Species crab, brown rock
Species Id M070015
Date 26 AUG 96
crabs. Size increases are slightly greater in males than in females. In
brown rock crabs, size difference in claws is a sexually dimorphic
characteristic that occurs at the pubescent molt, males attaining larger
claws than females. Unsexed juveniles has a constant ratio of claw height
to carapace width up to a width of 65 mm. Beyond this size, the ratios in
males and females diverged from juvenile proportions. Discontinuities in
growth rates of appendages were more distinct in males than in females.
Molting appears to occur most frequently in rock crabs during fall and early
winter, although it may occur throughout the year.*261*
Commercial Harvest. Rock crabs have historically supported only a
relatively minor fishery in California, particularly when compared with the
fishery of the Dungeness crab. The rock crab fishery has grown steadily
since landings of about 20,000 lb were reported in 1950. Annual landings
exceeded 1.2 million lb in 1976 and approached 2 million lb in 1986.
Commercial landings show no well-defined trends in seasonal crab abundance.
Monthly landing totals may be a misleading indicator of seasonal abundance
because total fishing effort varies and marketable crab size may fluctuate
with consumer demand. Experimental trapping studies, however, indicate a
trend toward the catches being highest in fall and lowest in summer. This
pattern of increased seasonal abundance has been noted for brown rock crabs
in central California. Higher catches in central California were positively
correlated with annual maximum water temperatures and an increased
proportion of female crabs in the catches.*261*
The variability in the harvest of crabs in southern California has been
historically linked to the changing success of other commercial fisheries.
In particular, the rock crab fishery is closely associated with the
California commercial fishery for spiny lobsters, in terms of seasonal
effort, gear, and methods. Fishermen can easily switch to trapping crabs in
the "off-season" or when catches of lobsters are low. Lobster gear has been
widely used for harvesting crabs.*261*
Recreational Harvest. The crabs are taken mainly in small numbers with
baited hoop nets near piers and jetties, and by hand by sport divers. This
harvest is insignificant compared with the total commercial harvest. In
California, the sport catch limit on all Cancer species in combination
(excluding the Dungeness crab) is 35 per day, and the minimum legal carapace
width is 4 inches.*261*
REFERENCES FOR LIFE HISTORY- 261
Life History - 3 (DRAFT) - Management Practices
Species crab, brown rock
Species Id M070015
Date 26 AUG 96
MANAGEMENT PRACTICES
RESULT MANAGEMENT PRACTICE
Adverse Drilling
REFERENCES FOR ADVERSE MANAGEMENT PRACTICES - 261
COMMENTS ON MANAGEMENT PRACTICES -
Toxicities of 11 metals found in drilling muds to embryos and prezoeae of
the yellow crab have been measured. The distribution of this crab overlaps
significantly with current and planned offshore oil drilling and production
platforms. Lethal concentrations to embryos after 7 days were 1 g/l of iron
or barium (sulfate), two of the most common contaminants. Increased
mortality of embryos resulted from longer exposure. Exposure of embryos to
chromium VI, copper, or zinc actually protected zoeae from those metals,
possibly as a result of induction of biochemical pathways of metal
inactivation.*261*
Management Practices - 1 (DRAFT) - References
Species crab, brown rock
Species Id M070015
Date 26 AUG 96
References
261 * Carrol, Jay C. 1989. Species Profiles: Life Histories and
Environmental Requirements of Coastal Fishes and Invertebrates
(Pacific Southwest)--Brown Rock Crab, Red Rock Crab and Yellow
Crab. Species Profile Series 82(11.117) (ed.). U.S. Army Corps
of Engineers Report Washington D.C:16.
References - 1