Dungeness Crab

Dungeness Crab

Cancer magister

Importance to Oregon

Dungeness crab is an important part of the Northwest’s seafood heritage, and has been commercially harvested since the 1800’s. Dungeness crab are salt water, ocean creatures. Their range extends from central California to the Gulf of Alaska. The Dungeness crab fishery is Oregon’s most valuable ‘single species’ fishery. In 2013, Oregon harvested, or landed, 26.1 million pounds of Dungeness crab. Oregon named Dungeness crab the state crustacean in 2009.

Main Ports

Dungeness crab can be found all along the Oregon coast. The top five Oregon ports for Dungeness crab are Newport, Charleston, Astoria, Brookings, and Port Orford. Newport is often called the Dungeness Crab Capital of the World.

Dungeness Crab 101

Below you will find everything you need to know about Dungeness crab. From anatomy, to how they walk, and what they eat, you will be a crab expert once you are finished.

Life Cycle

Crab hatch out as tiny larvae that mostly live among other tiny animals in the sea, swimming near the surface and feeding on even smaller organisms.

The first stage after hatching is called zoea larva. The larva has a long spine behind its head to help prevent predators eating it.

The second stage is called a megalops larva. This looks a bit more like a crab, but the abdomen is large and stretched out, not folded beneath the rest of the body.

Crab stays in its larval stage for up to 12 months and are free floating, vulnerable to the ocean and predators.

Before the last stage in development crabs are ¼ inch to dime size. They settle on the bottom of the ocean floor. During their first two years, crabs shed their shells many times. Each time the crab and its shell get bigger. They are mature adults after about 10 molts or about 2 years.

The life cycle of crabs

Zoea larva, the first stage for crab

Megalops larva, second stage for crab

Anatomy

Dungeness crab belong to a group of animals called crustaceans meaning they have an exoskeleton or shell that protects their bodies. This shell is called the carapace. A crab’s body is made up of a head, thorax, and abdomen. The head and thorax are merged together under the carapace.

The Dungeness crab is a ten-footed crustacean, or decapod. The crab have five pair of legs attached to the thorax. The two front legs are called chelipeds. They have a pair of claws on them that the crab uses for defense and to tear apart food. Behind these are four pairs of walking legs, each with a pointed foot. At the rear of the thorax is the crab’s abdomen, which is no more than a small flap in most crab.

Photo source: Oregon Department of
Fish & Wildlife

Tall Eyes

Crabs have two black eyes which sit above its head on stalks. The eyes can fold into sockets in the shell for protection. Having eyes on stalks means crabs have a better field of vision. Crab also have compound eyes just like insects. Each eye is made up of thousands of tiny units, each with its own lens. Though compound eyes do not focus well, they are very sensitive to movement and can see colors.

Sense of Smell

The antennae on crab are called chemoreceptors. They allow the crab to taste and smell, to find food and mates. Crab smell things they eat underwater by detecting chemicals from food with the tufts of hairs on the tips of their antennas. When a crab detects these chemicals, it starts to search for food. Between the eyes are two pair of feelers. Taste-sensitive hairs are located on the mouth parts, along the pincers, and on the crab’s feet.

Mouth

Below a crab’s feelers is its mouth. The mouth of the crab is made up of hard pairs of mouth parts which have different uses. One pair of jaws holds the food; other mouth parts break the food into small bits and put them into the crab’s mouth. A flap on one pair of these mouth parts pumps water over the crab’s gills, so the crab can breathe while eating.

Sense of Touch

In spite of their hard shell, crab have a good sense of touch. This is because growing through the cuticle are tiny, but very sensitive bristles. These bristles are scattered all over a crab’s body, legs and feet. Other types of hair on crab are sensitive to vibrations traveling through the water. These hairs are found mostly along the pincers.

Growing New Legs

A crab can grow new legs to replace the ones it loses. Limbs may be bitten off in a fight with a rival crab, or while a crab is trying to escape from a predator. Some crab may actually shed a limb if it is being grasped. When a limb is lost or shed, a new one starts to grow as a tiny bud almost immediately. As it re-grows it triggers molting. After two molts, the new limb will be as large as the original.

Molting

Just as we outgrow our clothes, crabs outgrow their shells. Crabs have a hard outer shell that does not grow as the rest of its body does. As the crab grows larger, they must shed their shells, in a process called molting.

Right before molting, a crab reabsorbs some of the calcium carbonate from its old shell, and then secretes enzymes to separate the old shell from its under skin. Next, the skin secretes a new, soft, paper-like shell beneath the old one. This process can take several weeks.

A day before molting, the crab starts to absorb seawater and begins to swell up like a balloon. This helps expand the old shell and causes it to come apart at a special seam which runs around the body. The carapace then opens up like a lid. The crab extracts itself from its old shell by pushing and compressing all of its appendages repeatedly. First it backs out, then pulls out its hind legs, then its front legs, and finally it comes completely out of the old shell. This takes only about 15 minutes.

When a crab molts it removes all its legs, eye stalks, antennae, all its mouthparts, and its gills. It leaves behind the old shell, the esophagus, its entire stomach lining, and even the last half inch of its intestine. Often a large group of crabs will molt at the same time, and their old shells wash up on the beach.

If you find something on the beach that looks like a dead crab, pick it up, open the lid, and look closely inside. If nobody is home, it is a cast-off exoskeleton.

Molting is a very dangerous time for crabs because they are soft and defenseless for days afterward. The crab cannot walk because its legs will not support its weight, and it cannot eat.

While the crab’s new shell is soft it takes in water and expands, stretching its new skin. After 32-60 hours, the crab is able to walk, however it can be three to seven days before it starts eating again. After two to three weeks its new, soft shell fully hardens.

A crab’s shell splits open at a special seam and peels off when it molts

Photo source: Washington Department of Fish & Wildlife

Female crab will molt under the protection of a male crab

Photo source: Oregon Department of
Fish & Wildlife

Juvenile crab exuvia, the castoff crab shell

Photo source: Oregon Department of
Fish & Wildlife

Reproduction

Dungeness crabs can only successfully mate when the female is newly molted.

In the early spring, adult male crab look for female crab likely to molt soon. When a female crab is ready to mate, she sends signals the male crab recognize. Female crabs produce special chemicals that males pick up and follow. When they meet, a male and female may touch each other with their antennae to let each other know they are not going to attack.

The male may carry the female for a few days before mating with her. Crabs will stay in this “pre-mating embrace” until females molt, this can go on as long as two weeks. They mate just after the female has molted. The male continues to carry her around to protect her until her new shell has hardened.

After the female has mated, eggs develop inside her body until they are ready to be laid in one large egg mass. She holds this mass of eggs under her body. The eggs are kept in place by her flap-like abdomen and clasped by the tiny limbs until they are ready to hatch.

The female holds her eggs in a special flap on her abdomen until they
are ready to hatch

Photo source: Oregon Department of
Fish & Wildlife

Crabs in Motion

Crab walk sideways, not forward and backward. The reason for this is the long walking legs are so close together on each side of a crab’s short body that if it were to move forward or backward, the legs would trip over each other.

What they Eat

Most crab will eat almost anything, plant or animal, dead or alive. Animals that have such a wide range of food items in their diet are called omnivores.

Males and Females

In Oregon only the male crab can be harvested. The females must be returned to the ocean. The abdomens of male and female crabs are different. A female has a broader abdomen than the male and it is fringed with eight small limb-like structures. This difference is an easy way for crabbers to tell them apart.

Male crabs have a thin triangular abdominal flap, and female crabs have a rounded shorter abdominal flap

Photo source: Oregon Department of
Fish & Wildlife

Crab Season

Oregon’s commercial crabbing season generally begins December 1 and continues through August 14. The peak harvest occurs during the first eight weeks of the season, with up to 75% of the crab harvested during that time.

Commercial Harvesting

Dungeness crab have been commercially harvested along the Pacific coast for over 150 years. Dungeness crab harvests are cyclical and can fluctuated from a low of 3.2 million pounds of crab to a high of over 33 million pounds of crab in recent years. The typical landing in Oregon is about 10.3 million pounds. The value of Oregon Dungeness crab fishery also fluctuates yearly, based on the size of the harvest and market conditions.

Tough Job

Commercial crabbers catch Dungeness crab in circular steal traps commonly called pots. A full crab pot can weigh 60-125 pounds. The pots are baited with squid or razor-clams. They are allowed to soak or float in the open ocean for one to four days.

Crabbing is an extremely dangerous job. Crabbers go out in boats and drop pots at depths 30 to 600 feet deep. The average boat fishes 300-500 pots at once. Crabbers work in round-the-clock shifts. The vessels used to harvest crabs, range from a small wooden trollers with two-men crews to large steel combination vessels with a four-men crews.

Most of Oregon’s coastal seafood processors purchase and process Oregon grown Dungeness crab during the course of the season.

A full crab pot

A loaded crab boat ready for sea

Crabbers hauling in a pot

Measuring Crab

Dungeness crab live about eight to ten years and grow to nine-plus inches. Mature males that are 6 ¼ inches across the back of the shell or more are legal to harvest. For recreational harvesting it is legal at 5 ¾ inches across the back, but not including the spines. Undersized male crabs must be returned to the ocean to insure healthy breed stock. It is illegal to harvest female crabs.

A crab gauge is used to determine if a crab is big enough to keep

Photo source: Oregon Department of
Fish & Wildlife

Recreational Crabbing

Recreational crabbing is open in estuaries, beaches, tide pools, piers, and jetties year round. However, fall is typically the best time to crab. Beginning in September, crab will tend to be more filled out, meaning there is a higher percentage of quality meat. Crabbing in the ocean is closed for Dungeness crab from October 16 to November 30.

Best Places to Crab

Dungeness crab prefer sandy bottom habitat. In every Oregon estuary, some crab can be found. According to the Oregon Department of Fish and Wildlife, Coos, Yaquina, Alsea, and Tillamook normally provide the best year round opportunities. Smaller estuaries and those with more freshwater influence may only be good during the driest part of summer when salinity in the bays are at their highest.

Best Time of the Day

Slack tides, the times of peak high or low tide, are the best times to go crabbing. At slack tides, the greatest number of crabs are foraging, since they are not getting pushed around by tidal exchange.

Crab By-Products

Crab meat is a popular northwest favorite and can be eaten fresh, frozen, canned, smoked or dried. A variety of by-products are also made from Dungeness crab, including fertilizers for home gardens and farm, cat food, mink food, aquaculture fish food, nutritional supplements and flavor ingredients.

Preparation for Food

Dungeness crab can be purchased either live or pre-cooked. Live crab are cooked by steaming them for 15–18 minutes, or by boiling for approximately 10 minutes. For ideal freshness, Dungeness crab should be cooked as soon as possible after catching. Many crab boats have steaming pots on board, and will cook and pack the crabs in ice for delivery.
Dungeness crabs will stop eating when removed from the pressure and cold temperatures of their habitat, so keeping them alive in aquaria for even a day will degrade their quality.

Like all crab, the Dungeness crab is high in protein and minerals, and low in fat. Also, crab is rich in Omega-3 fatty acids, which are linked to good heart health. About one quarter of a Dungeness crab’s weight is meat, making it one of the meatiest crabs available. Most of the meat is in the eight legs and two claws, although the body contains plenty as well.

Recipes

Crab Casserole
This crab casserole can be served for breakfast, lunch or dinner. It’s easy to make and kid friendly. Fresh crab meat will give you the best results with this crab casserole, but you can use canned crab.

Ingredients:

  • 2 large eggs
  • 2 cups milk
  • 2-1/2 cups seasoned croutons
  • 1 lb. fresh crab meat
  • 1/2 cup finely-chopped red pepper
  • 8 oz. shredded cheddar cheese
  • 1 tsp. Old Bay seasoning
  • 1/2 tsp. freshly-ground black pepper
  • 1 Tbsp. dried parsley
  • 1/2 cup grated Parmesan cheese

Preparation:

  1. Preheat oven to 325 degrees F. Spray an 1 1/2 quart baking dish with cooking spray.
  2. In a large bowl, beat eggs and milk together. Stir in croutons, crab meat, diced red pepper, cheddar cheese, Old Bay, pepper and parsley.
  3. Pour into prepared baking dish. Sprinkle Parmesan cheese over top.
  4. Bake 50-60 minutes until golden.


Vocabulary

Carapace: name of the crab’s shell
Chelipeds: the two front legs on a crab that have claws
Chemorecptors: antennae on crabs that are used for taste and smell
Crustaceans: an animal that has an exoskeleton or shell that protects the body
Decapod: a ten-footed animal
Exuvia: cast off crab shells as a result from molting
Filled out: when crabs have the highest percentage of quality meat
Landed: the average annual harvested amount
Megalops larva: the second stage in the crab’s life cycle
Omnivores: animals that eat both plants and other animals
Pots: circular steal trap that is used to catch crabs
Slack tides: time of peak high or low tide
Zoea larva: the first stage in a crab’s life cycle after hatching

Additional Resources