"Nature Guide Journal"
23 August 2001
Water cascaded from the crab ring as we pulled it out of
the water and dropped it onto the dock. The people from my
Elderhostel group gathered around as the scuttling crabs were quickly
examined to determine if we had landed any keepers.
Crabbing is a popular–and rewarding–sport in Oregon's
estuaries. The most popular quarry, Dungeness crab (Cancer
magister), is as fascinating as it is appetizing.
Measuring the largest crab in our ring told us it was large enough to
keep: 5 ¾" across the back (just in front of the longest
spines) for sport-caught. Since only males can be kept, we flipped
the crab over to ascertain its sex. Like most crab, Dungeness have
a jointed flap on the underside: this flap on females is broad and
rounded; on males it's narrow.
Crabs are arthropods (joint-legged invertebrates) that have jointed,
exterior shells rather than interior skeletons for structure and
support. Crabs shed their shells periodically to grow
larger. The old shell splits along a seam around the main part of
the body (the "carapace") and the animal pulls its body out of
the now-too-tight shell.
By the time the crab molts, a new shell has developed under the old
one. The larger shell is quite soft when new, and the crab pumps
up with water to stretch it. A mature animal can gain an inch or
more across the carapace with the molt.
It will take several weeks or a month for the new shell to harden
well. In the meantime, the crab are at greater risk to being eaten
or damaged. Soft-shell crab should be released: From the
crabbers' point of view, soft-shell Dungeness are less valuable since
the meat hasn't yet grown to fill the shell, making it sparse and
Molting is especially significant for mature Dungeness crabs–it is
only when the female molts that she can be fertilized by a male.
Male Dungeness crab seek females that are about ready to molt and trap
them in their legs until the old shell is shed. The male assists
the female in casting off the old shell, then inserts a packet of sperm
under her flap. Mature females usually molt in the spring and
store the live sperm until the eggs are developed in winter.
Up to two million fertilized eggs are carried under the female's wide
jointed flap until hatching. Small enough to float in the water
with other plankton, the microscopic young crab larvae look more like
curled, horned shrimp than like adult Dungeness. The size of a
small pea, the last larval stage of the Dungeness looks like a crab, but
still moves in the water column.
By summer, the young crab metamorphose into thumbnail-sized juveniles
that settle onto the bottom. Dungeness crab will mature in two or
three years, and reach harvestable size in about four. By the time
they're large enough for a legal catch, Dungeness crab will have molted
about 15 times since settling to the bottom.
Mature crab generally molt once a year, with females molting in late
spring and males molting in late summer.
Because molted shells have all the external parts intact–including
legs, mouthparts, antenna, eyes, and gill supports, they look like
whole, dead animals. People often mistake large numbers of molted
shells on the beach as evidence of widespread disease or disaster.
(Visit the Oregon
Department of Fish & Wildlife's informative page on this topic.)
Dungeness crab are predators, not scavengers. Adults feed on
clams, worms, shrimp, smaller crab, and other fresh meat–which is why
fresh bait is more effective than rotten bait. The prey is caught
or snipped off and pulled apart with the claws, then further shredded by
the assemblage of mouthparts before being eaten.
In addition to people, octopus and cabezon are major predators of
Although our group didn't catch our limit of 12 male crab per person,
what we did land was delicious!