From Ocean to Plate: The Life of the Red King Crab

TheresaArticles, Biodiversity, Environmental Awareness Theme, Original

Photo of a young red king crab. Image Credit: Alaska Department of Fish and Game.

Photo of a young red king crab. Image Credit: Alaska Department of Fish and Game.

A young red king crab. Image Credit: Alaska Department of Fish and Game.

The red king crab (Paralithodes camtschaticus) is not your archetypal supper crab species. Red king crabs are vibrant red to deep purple in color, with sharp spines covering the entirety of their shell. They have extremely long legs, full of meat. Reds become enormous with age, overcoming the size of a human infant at times, and weighing up to 24 pounds. They are incredible not only superficially, but also because reds, as they are colloquially known, live immensely deep in the ocean — up to 100 fathoms, or 600 feet deep. A relative, the golden king crab (Lithodes aequispinus), can live up to 400 fathoms, or nearly a half mile beneath the surface. These are quite mysterious depths of ocean, areas that humans know little about. Fortunately, because the red king crab species is commercially important, we have been able to study the life cycle of these deep-sea dwelling crabs. From reproduction to harvest, the reds’ journey can be traced.
The study of shellfish biology is well advanced. All crab species have five pairs of legs. Reds, though, hide one of their leg pairs inside their abdomen. The other four pairs include the chelae, or pincers, and three pairs of walking legs. According to Michael Kluce from the University of Michigan’s Museum of Zoology, the right claw is often larger than the left, making most reds naturally right-chelae dominant. Their walking legs, which can hang up to three feet from their bodies, offer most of the crab meat valuable to humans.
A red king crab’s hidden fifth pair of legs is used in mating and rearing of immature crabs. Females are thought to use these mini-legs to clean fertilized eggs, which remain in their abdomen for 11 months after fertilization. Males, on the other hand, use their tiny fifth leg pair to grab a female before mating. Reds mate once a year, in the springtime, when they migrate to shallower waters. Mating can occur after a female releases her clutch of eggs from the previous year, emitting chemicals to attract males. A male then latches onto a female with his fifth pair of legs.
Photograph of a female crab's abdomen filled with eggs. Image Credit: NOAA

A female crab’s abdomen filled with fertilized eggs. Image Credit: NOAA

With a connected male protector, a female will discard her outer shell for annual growth, a process called molting. A molted female has a soft and delicate carapace that makes her vulnerable to predation. For this reason, a male guard who offers protection is advantageous to her. The male clasps unto the female’s carapace for days, and after molting has occurred, the male can finally fertilize the female’s clutch of 50,000 to 500,000 eggs.
Before the crab larvae hatch, they remain in the female’s abdomen for nearly a year. After this shielding period, crabs will hatch as zoea, and be carried by ocean currents. Due to the force of currents acting upon the crabs, rather than consciously controlled movements, young crabs essentially have no power over where they begin their lives. Each molting event, though, brings the crabs closer to their adult form that includes walking legs, and thus more control over their bodies. In their first year, reds molt about six times, each time gaining more advanced traits.
It is thought that red kings have a lifespan of up to 30 years. A juvenile crab reaches maturity at about five years of age. Red kings forage for food during summer and winter months, eating other bottom-dwellers like mollusks and groundfish. Reds have even been known to feed upon one another, and can be considered a cannibalistic species. For most of the year, reds align themselves with only individuals of the same sex. The crabs only unite with the opposite sex for mating purposes, after long migrations of up to 100 miles from deep to shallower seas.
Once mature, reds will use their long thin legs to maneuver past fantastical corals, enormous flatfish like Pacific halibut, and other creatures of the deep. Crab habitat, at 600 feet beneath the ocean surface, is exceptionally dark. Robust claws prove to be the creatures’ strongest weapon.
Photograph of a deep sea Alaskan bubblegum coral. Image via Live Science.

Deep sea Alaskan bubblegum coral. Image via Live Science.

From the depths to the boat deck
The Alaska Department of Fish and Game authorizes an abundance of red permits for Bristol Bay, but the species occupies waters from British Columbia to Japan and northward. In recent decades, poor regulation has allowed overfishing of reds in much of their range, NOAA Fishwatch suggests. The only two open fisheries in Alaska, Bristol Bay and Norton Sound, are considered recovering populations from the 1990s when stocks hit low numbers just after a harvest boom in the 1980s. Alaska officials carefully manage the fishery, allowing only boats with a permit to retain their specific quota of crab.
According to NOAA, Bristol Bay’s red king crab season opens in mid-October, a time when crabs are still segregated by sex but located in more shallow, fishable waters along their migrations. The time of fishing is intricately selected by the Alaska Department of Fish and Game so that only male king crabs, not females, may be retained and processed for human consumption.
To sustain a healthy population of any animal, of course, there must be an abundance of childbearing females. While males can mate and share their spermatophores with multiple females, females are much more limited in their ability to reproduce and spread their genes unto the next generation of crabs. Even so, only male reds that have reached reproductive size can be kept. This allows males the chance to spread their genes to a wide selection of females before being removed from the ocean and eaten by people. The sex and size restrictions set for the crab fishery by ADF&G allow reds to reproduce and thrive as a species. As a result, the fishing strategy allows persistence of a healthy population of red king crabs into the future, while filling our plates.
Map showing the Red king crab range in Alaskan waters. Image Credit: Alaska Department of Fish and Game.

Red king crab range in Alaskan waters. Image Credit: Alaska Department of Fish and Game.

Processing to your plate
In pursuit of reds, crews of about five strong fishermen begin packing their 100-foot vessels with crab pots around Oct. 12. These pots consist of 7-by-7 foot metal rods, stitched together with twine. Small openings on two sides of the pot allow entrance by six walking legs, attracted by the scent of Pacific cod bait. Once the vessel reaches a location at sea thought to hold a high density of crabs, the boat crew will begin setting pots. The crew will drop the heavy pots over the side of the deck, in strings of up to about 30 pots. After a waiting period of a few days called “soak time,” boats will return to the buoys that mark each pot, and draw them back to the surface. Heavy hauling equipment on board pulls the pots, each weighing up to a ton, to the boat deck. Certain areas yield high crab quantities, whereas others provide bare pots with only a few silent, sliding snails.
The crew dumps all of the pot’s contents onto a revolving table, where crewmen must sort through every organism. Using a crabstick ruler, the crew sifts through crab sizes, making sure only large adult males are kept. All juvenile males, females and other bycatch are thrown back to sea to allow continuation of their lives in the wild. While bycatch is considered to be harmful to third-party species, the direct effect of this stress on organisms, being hauled 600 feet to the surface and thrown back in again, is unknown. In addition to the captain and five crewmembers, an individual employed by the Alaska Department of Fish and Game may be on board, observing regulatory compliance and collecting data.
Photograph of Fisherman sorting through the contents of a full crab pot. Image Credit: Alaska Bering Sea Crabbers

Fisherman sort through the contents of a full crab pot. Image Credit: Alaska Bering Sea Crabbers

The boat deck is a loud, high-energy environment. Work is endless and time is of the essence. The fishermen’s goals are to catch as many crab in as little time possible, because they get paid for their total catch rather than time spent working. Legal reds are put into a holding tank beneath the boat’s deck where they spend the last few days of their lives onboard. Crabs need constant water flow through their gills to respirate, and this keeps them live and fresh until processing.
After the enormous tanks are filled with reds, the vessel will return to shore for crab processing. Here, live crabs are removed from the boat in a net hauled by a crane, and then carried into the fish factory. Legs and claws are removed from the body, these meaty parts boiled, frozen, packaged and shipped to distributors. The majority of Alaskan crab is shipped 3,000 miles to Japan and the rest of the United States. Humans consume the meat in the form of crab cakes, California rolls or by cracking directly through the tough calcite legs.
Theresa Soley is a freelance writer, naturalist and biologist in the state of Alaska. She has worked as an observer on a crab boat, leads a variety of wildlife tours and enjoys spending time on the water with whales.