Giant Japanese Spider Crabs and Red King Crabs | Sea Life, Islands and Oceania

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GIANT JAPANESE SPIDER CRABS

giant Japanese spider crab

Japan's giant spider crabs duel with Alaska's red king crabs for the honor of being the world's largest crustacean. According to the Guinness Book of Records, one giant spider crab weighed 18.6 kilograms (41 pounds) and had a claw span of 3.7 meters (12 feet 1 inch). They are sometimes called the 'dead man's crab' for their habit of feeding on drowned bodies. Males have two penises like male sharks. Some sources report that Japanese spider crabs can live for up to 100 years!

Even though they look scary Japanese spider are more or less harmless. If you happen to go swimming or diving in the deep, cold water where they live and get pinched by one, the pain is probably less than being pinched by a crab at the beach. National Geographic writer and scientist Eugene Clark was snagged on the legs of a group of them. Each time she pried one leg loose another grabbed her, she said. But she never felt in danger and said it was like wrestling a giant sloth.

Japanese Spider Crab(Scientific name: Macrocheira Kaempferi) measure up to 3.8 meters (12.5 feet) from claw to claw. Most of their size is in their legs. The carapace (central shell) can measure 40 centimeters (16 in) across while the longest legs can reach almost two meters in length. Residing in northeast Pacific Ocean around Japan and places further north, Japanese spider crabs are categorized a omnivores, consuming a large variety of things, including mollusks, plant matter, other crustaceans and detritus such as dead and decaying animals. They are generally found at depths of 150–300 meters (500–1,000 feet) on the sandy bottom of continental shelves but migrate to shallow water once a year to spawn.

Japanese Spider Crab are profitable fishing catches. They are considered a delicacy in Japan, where they are eaten in the winter, and elsewhere. Some people pay bog money to eat them. There are bans on catching and hunting them during the springtime, when the crabs move to shallow waters to reproduce. [Source: Chris Sergeant, Listverse, October 18, 2014]

Websites and Resources: Animal Diversity Web (ADW) animaldiversity.org; National Oceanic and Atmospheric Administration (NOAA) noaa.gov; Fishbase fishbase.se ; Encyclopedia of Life eol.org ; Smithsonian Oceans Portal ocean.si.edu/ocean-life-ecosystems

Red King Crab

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a big red king crab caught by a
Japanese fisherman
Red King crabs (Scientific name: Paralithodes camtschaticus) are regarded by some as the largest of the commercially harvested crabs. Also known as Alaska king crabs and king crabs, they range in color from brownish to bluish red and are covered in sharp spines. They have three pairs of walking legs and one pair of claws. Their claws are different shapes. One is a large, heavy-duty claw that is used for crushing prey, and the other smaller claw is used for more delicate handling of food items. They have sharp spines all over their body. [Source: NOAA]

Red king crabs can be found as far south as the Sea of Japan, and as far north as the Kamchatka Peninsula of Russia in the northwestern Pacific Ocean. In North American waters, red king crabs are found in the Bering Sea as far north as Barrow, Alaska. and Aleutian Islands, along the coast of the Gulf of Alaska, and as far south as the Queen Charlotte Islands in British Columbia, Canada. While not native to the Atlantic Ocean, Red king crabs have been commercially introduced in the Barents Sea, north of Russia. [Source: Michael Kluce, Animal Diversity Web (ADW) /=]

Determining the sex of red king crabs is easy. Males have a triangular abdominal flap and females have a rounded one. The expected lifespan of red king crabs is 15 to 20 years. They may live as long as 30 years. The main limit on their life span is fishing. Adults migrate between deeper water, typically less than 200 meters (650 feet) along the continental shelf) to feed, and shallow waters, where they mate and females hatch their eggs.

Adults are found in the intertidal zone at depths of more than 200 meters (660 feet) in places with sandy or muddy substrates. They migrate annually from these deep waters to shallow waters of 50 meters (165 feet) or shallower in the late winter or early spring. Juveniles less than two years old live in shallow waters in complex habitats, such as shell hash, cobble, algae, and bryozoans (branching, coral-like invertebrates) to avoid being preyed upon by fish and other crabs. Older juveniles form pods that travel together, mounding up during the day and feeding at night.

Red King Crab Physical Characteristics and Behavior

Red king crabs can reach a weight of 12.7 kilograms (28 pounds), with their average weight being 10 kilograms (22 pounds). They can have a leg span of 1.5 meters (5 feet), with their average carapace length being 220 centimeters (8.66 inches). Males grow faster and larger than females. Both sexes are roughly equal in size and look similar. [Source: NOAA]

Red king crabs have a dark red body and a fan shaped tail. They have five sets of appendages, the first two are pincers, the right is usually larger then the left. The last appendages are used for mating. Among males the last two appendages are used to spread sperm over the genital opening of a female. Among females they are used to spread the sperm. [Source: Michael Kluce, Animal Diversity Web (ADW) /=]

spiny king crab

Red king crabs are motile (move around as opposed to being stationary), social (associates with others of its species; forms social groups) and colonial (living together in groups or in close proximity to each other). Pods can consist of tens of thousands of individual crabs sometimes form; it has been theorized that this is an an anti-predator strategy, similar to schooling in fish.

Alaskan king crabs tend to be segregated by sex when at deeper waters. Social and colonial activity is most often seen in juveniles between the ages of one to four years old. This podding occurs mostly in shallow depths. Alaskan king crabs are active swimmers when they are in their pelagic (open ocean) stage of development as free-swimming zoea. /=\

Alaskan king crabs communicate with touch, chemicals usually detected by smelling and pheromones (chemicals released into water that are detected by and responded to by other animals of the same species) and sense using vision, touch and chemicals usually detected with smell. During mating the female communicates by releasing a chemical that signals a male that she is ready to ovulate.

Red King Crab Feeding and Predation

Red king crabs eat almost anything they can find and crush with their claws. Larger crabs eat a much wider range of items including worms, clams, mussels, crustaceans, barnacles, crabs, fish, echinoderms (star fish), zooplankton, sand dollars, and brittle stars. Smaller crabs eat algae, small worms, small clams, and other small animals. Larval king crabs are planktivores.

Large red king crabs have few predators except right after molting.. Molting itself can be stressful and cause death. The days after a molt has taken place is the most dangerous time for Red king crabs, when the soft shell is vulnerable to predation. Smaller crabs are eaten by a variety of groundfish, octopi, sea otters, and crabs, including other red king crabs.

The adult Alaskan king crabs have few predators because of their heavily armored and bumpy carapace and leg exoskeletons. According to Animal Diversity Web: During the first year Alaskan king crabs hide in crevices formed by rocks or kelp forests to avoid predation. From the ages of one to four they form clusters of up to 500,000 individuals called pods. The pods disperse only for feeding.

Red King Crab Mating, Reproduction and Offspring

Red king crabs engage in external reproduction in which sperm from the male fertilizes the female’s egg outside her body. They are polygynous (males having more than one female as a mate at one time). Female red king crabs reproduce once a year and release between 50,000 and 500,000 eggs when they spawn. Males can mate with as many 11 females during the breeding season. Alaskan King Crabs breed in the spring after migrating to water depths of 50 meters or less. Female and male king crabs reach sexual maturity at five to six years. Females incubate eggs for one year, providing protection. Within days of hatching, the female begins incubating next group of eggs. [Source: Michael Kluce, Animal Diversity Web (ADW) /=]

According to Animal Diversity Web: Females attract males with a chemical that is released after eggs have hatched. The male then clasps onto the female and they remain connected until the female molts, and produces new eggs. The female and male may remain connected for up to seven days. After molting the male uses his fifth pair of legs to spread spermatophores over the females opening. The females eggs are then released and pass over the spermatophores and become fertilized. These fertilized eggs are attached by the female to her pleopods under the abdomen and are incubated for approximately a year before hatching.

Larvae hatch from eggs looking like tiny shrimp. The larvae feed on phytoplankton and zooplankton for 2 to 3 months before metamorphosing into tiny crabs and settling on the ocean bottom. Red king crabs can only grow by molting (shedding their old shell and growing a new one). After molting they are soft and vulnerable to predators until their new shell hardens.

Alaskan king crabs have two stages of development. In the first stage of development they are free-swimming zoea. Zoea are very small and do not resemble the adult crab. During a period three to four months, the zoea molt five times. After the fifth molt the larval zoea begin to resemble the adult form, but are they are only about 0.3 centimeters (1/8 of an inch). In any case at this point, they adopt a bottom-dwelling lifestyle. [Source: Michael Kluce, Animal Diversity Web (ADW) /=]

Spider Crab Versus King Crabs

giant spider crab

While their ranges overlap somewhat and look kind of similar king crabs and spider crabs are different species and belong to different crab families. King crabs are brown or red, while the spider crab are bright orange or orangish red. [Source: Jennifer Gaeng, A-Z-Animals.com, April 13, 2022]

Spider crabs have much longer legs than king crabs and their body is noticeably longer than it is wide. King crabs are decapod crustaceans in the “true crab” (Brachyura) infraorder while spider crabs belong to the Majoidea superfamily of crabs. Both crabs are large and routinely harvested and sold as food but king crabs flourish in cold water, while spider crabs are found in warmer temperate seas.

Spider crabs are significantly larger than king crabs and as their name suggests look like spiders. Japanese spider crabs have white spots on their orange legs. Red King crabs have sharp spines on their body and legs. They have one pair of claws and three pairs of walking legs. There are many kinds of spider crab and some are relatively small.

Spider crabs are slow-moving crabs that do not hunt. They subsist primarily on dead animals and plants on the ocean floors, but will also consume live fish and invertebrates, like other crabs if they get their claws on them. King crabs are more aggressive hunters, consuming almost anything and pursing fish, crustaceans and molluscs.

Japanese Giant Spider Crab Fishing

The Japanese love crab and regard it as a wintertime treat. Many places rely on crab to attract tourist in the winter. Japanese eat both Japanese spider crab and king crabs. The crab catch season is from October or November to April or May. It used to be longer but has been shortened as a result of declining catches. One of the best crabbing areas is in the Japan Sea is 50 to 100 kilometers off the coast of Kamicho, Hyogo Prefecture. Typically 38 tons of crabs are caught there per day, with the crabs selling fo ¥25,000 to ¥30,000 per 30 kilogram box at wholesale markets.

These days Japanese spider crab cost $45 to $77 a kilogram ($20 – $35 a pound). They are considered sustainable because they are abundant, easy to catch, and easy to prepare. Spider crabs are commonly marketed as ” Snow crab”.

Northern Japan and eastern Russia are very close to each other and Russians are sometimes accused of crabbing in Japanese waters and Japanese crabbers are sometimes seized in Russian waters. In January 2009, 10 Japanese fishermen in a crab-fishing boat were arrested by Russian authorities waters on charges of poaching in Russia’s exclusive economic zone. The boat apparently drifted into the Russian zone while the fishermen were sleeping. The fishermen were released about a week later after the payment of $140,000 by the firm that employed the fishermen.

Spider crabs fighting
Up until the late 2000s Russian crab fishermen pulled into Japanese ports like Nemuro and Kushiro with forged papers, sold their catch for a huge profit, partied and bought stereos, televisions and other electronics, or maybe even a car, and returned to Russia, hopefully avoiding Russia coast guards boats whose primary duty is catching poachers and who are ordered to shoot at boats the at don’t stop..

Many of the boats involved in the illegal fishing trade were rusting heaps that lacked safety equipment and sometimes working emergency radio. The men that worked the boats were rough and cruel. A few had tattoos on their eyelids. In 1998, Japan imported 70,000 tons of crab from Russia. Only 5,000 tons of that was documented on the books in Russia. In 2000, 86 ,000 tons of crab came from Russia. Only 3,000 tons of that was documented on the books in Russia.

In 2002, the Japanese government began cracking down on crab smuggling. Russian ships fully loaded with crab that lacked proper documents were tuned away from Japanese ports. Afterwards the price of crab soared in Japan by more than 50 percent, which created more incentive for those involved in the illegal crab trade. The Japanese crackdowns gained more traction after Japan and Russia set up a notification system in which Russia provided Japan with prior notification of ports of calls for its fishing boats. The crackdown also hurt the economy in the ports of call. The Russian spent a lot of money in Japan on used cars, electronics and other stuff they took back with them to Russia.

Before the crackdown the fishing boats traveled on their own directly to Japan. Afterwards they tried to outsmart authorities by loading their catch onto cargo freighters at sea and those freighters, which had proper documentation, docked at the ports. In one case the captains of a freighter and trawler were arrested after they were caught transferring a load of crab within Japanese waters.

King Crab Fishing in Alaska

King crab costs around $132 to $154 a kilogram ($60 – $70 a pound). You can understand why those guys on television risk their lives to catch it. In 2021, the commercial landings of all king crab in Alaska totaled 2.7 million kilograms (6 million pounds) and were valued at more than $73 million, according to the NOAA Fisheries commercial fishing landings database.[Source: NOAA]

In the 1960s and 1970s Alaskan king crabs generated hundreds of millions of dollars of revenues. Overfishing can cause populations to crash in a relatively short period of time. During the 2000s, the U.S. got a large portion of its king crab meat from the North Atlantic Ocean north of Russia.

Red king crab are mainly harvested in Bristol Bay. Some catch also comes from fisheries in Norton Sound. Mesh-covered pots that are 7 to 8 square feet are used to catch red king crab. Only male crabs can legally be caught and sold. Crab pots can unintentionally catch female crabs (which may not be harvested), males under the commercial size, and non-targeted crab species as well as a small number of other species including octopus, Pacific cod, Pacific halibut, other flatfish, sponges, coral, and sea stars. Regulations require fishermen to install escape panels and rings on their pots to prevent ghost fishing (when lost pots continue to capture and kill species) and to reduce bycatch.

Habitat impacts from the red king crab fishery are minor because fishing occurs in areas of soft sediment such as silt and mud. Soft sediments are unlikely to be damaged by fishing gear. Crab pots are less damaging than mobile gear because they are stationary and contact a much smaller area of the seafloor. Fishing Rate: The Bristol Bay and Norton Sound stocks are at recommended levels. The Pribilof Islands and Western Aleutian Islands stocks are closed to fishing for red king crab. Habitat impacts from crab pots are minor because fishing occurs in areas of soft sediment, such as silt and mud, which are unlikely to be damaged by fishing gear. Regulations are in place to minimize bycatch.

King Crab Populations in Alaska and Fishing Regulations

There are four stocks of red king crab: 1) Bristol Bay, 2) Pribilof Islands, 3) Norton Sound, and 4) the Western Aleutian Islands. According to the most recent stock assessments: The Bristol Bay, Pribilof Islands and Norton Sound stocks are not overfished (2019, 2021 and 2022 stock assessments) and not subject to overfishing based on 2020 catch data. The Western Aleutian Islands stock is not subject to overfishing based on 2020 catch data, but data are insufficient to determine population status at this time (2017 stock assessment). [Source: NOAA]

Fishing has been closed for red king crab in the Pribilof Islands and Western Aleutian Islands for many years. NOAA Fisheries, the North Pacific Fishery Management Council, and the Alaska Department of Fish and Game manage the red king crab fishery.under the Fishery Management Plan for Bering Sea/Aleutian Islands King and Tanner Crabs, which defers management of crab fisheries to the State of Alaska with federal oversight. State regulations must comply with the fishery management plan, the national standards of the Magnuson-Stevens Act, and other applicable federal laws:

The red king crab fishery is currently managed according to the “three S’s” — size, sex, and season. Only male crabs of a certain size may be harvested, and fishing is not allowed during mating and molting periods. These measures help ensure that crabs are able to reproduce and replace the ones that are harvested. Fishermen must install escape panels and rings on their pots to prevent ghost fishing (when lost pots continue to capture and kill species) and to reduce bycatch.

Every year, managers set the harvest limit for the next fishing season using the most recent estimates of crab abundance. Managers allocate shares of the harvest among harvesters, processors, and coastal communities through the crab rationalization program, which was implemented in 2005 to address economic, safety, and environmental issues in the fishery. This program includes a community development quota, which protects community interests by allowing community groups a percentage of the harvest. They’re given the opportunity to purchase shares in the fishery before the shares are offered for sale outside the community. Vessels carry vessel monitoring systems (satellite communications systems used to monitor fishing activities) and must report their landings electronically. Managers monitor catch in real time and are able to close the fishery when the harvest limit is reached. Observers are required on 20 percent of the vessels in the fishery. They collect data on catch and bycatch and document any violations of fishing regulations.

Image Sources: Wikimedia Commons, NOAA

Text Sources: Animal Diversity Web (ADW) animaldiversity.org; National Oceanic and Atmospheric Administration (NOAA) noaa.gov; Wikipedia, National Geographic, Live Science, BBC, Smithsonian, New York Times, Washington Post, Los Angeles Times, The New Yorker, Reuters, Associated Press, Lonely Planet Guides and various books and other publications.

Last Updated April 2023