Blue king crab facts for kids

Quick facts for kids Blue king crab
Scientific classification
Kingdom:	Animalia
Phylum:	Arthropoda
Subphylum:	Crustacea
Class:	Malacostraca
Order:	Decapoda
Family:	Lithodidae
Genus:	Paralithodes
Species:	P. platypus
Binomial name
Paralithodes platypus (Brandt, 1851)
Distribution in the Bering Sea region (not showing population further south off northeast Asia)
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Synonyms
Lithodes platypus J.F. Brandt in von Middendorf, 1851

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The blue king crab, known scientifically as Paralithodes platypus, is a fascinating type of king crab. These crabs live in the very cold parts of the North Pacific Ocean and nearby seas. Blue king crabs are usually a bit smaller than their cousins, the red king crabs.

Where Blue King Crabs Live

Blue king crabs love cold water! You can find them in the chilly Bering Sea, which is between Alaska and Russia. They also live in parts of the Chukchi Sea, near the Kamchatka Peninsula in Russia, and off the coast of Hokkaido, Japan. Another home for them is the Sea of Okhotsk.

In the Bering Sea, blue king crabs are not as common as red king crabs. The biggest groups of blue king crabs near Alaska live around the Diomede Islands, Point Hope, St. Matthew Island, and the Pribilof Islands. There's also another group living in the Norton Sound area, stretching to St. Lawrence Island.

Blue king crabs prefer colder areas than red king crabs. Scientists think that after the last ice age, when the Earth got warmer, these crabs moved to deeper, colder waters. This might be why their populations are now found in separate, specific places.

How Blue King Crabs Travel

Blue king crabs are always on the move! Female crabs travel with the seasons. In winter, they live deep down, about 130 to 180 meters (426 to 590 feet) below the surface. When it's time to lay eggs, females with eggs move to much shallower waters, only about 6 to 10 meters (20 to 33 feet) deep. Females without eggs go to depths of 50 to 80 meters (164 to 262 feet).

Male crabs that are big enough for fishing usually stay around 70 meters (230 feet) deep. However, you can sometimes find them in shallower waters during the winter months.

The Blue King Crab Life Cycle

Reproduction

Blue king crabs from the Pribilof Islands usually mate and produce eggs between late March and early May. Female crabs carry their eggs on the outside of their bodies for a long time, about 12 to 14 months! Because it takes so long, they usually only produce eggs every other year. However, young females laying eggs for the first time might lay eggs in the next year too.

The size at which female crabs are ready to reproduce can vary. Pribilof Island females grow quite large before they are mature. About half of them are mature when their carapace length (the length of their shell) is about 5 inches (12.7 cm). Females from St. Matthew Island and Diomede crabs can become mature when their carapace length is around 3 inches (7.6 cm).

Larger female crabs from the Pribilof Islands can produce many eggs. They might carry over 160,000 eggs! However, not all eggs survive to become larvae. About a third of them are lost before hatching. In Japan, blue king crabs release about 120,000 larvae on average. Diomede blue king crabs release around 60,000 larvae per female.

Hatching and Growth

Female crabs release their tiny larvae (baby crabs) around mid-April in the Pribilof Islands. If crabs are kept in warmer water in a lab, their larvae might hatch earlier, sometimes as early as February.

Many things in the environment can tell the crabs when to release their larvae. These include tides, water temperature, how salty the water is, light, and even the growth of tiny ocean plants called phytoplankton. Releasing larvae over a longer time might give the babies a better chance to find good conditions to survive. This strategy is sometimes called "bet-hedging" in biology.

In labs, Pribilof larvae hatch over the course of about one month, and Diomede larvae hatch over the course of 2 to 3 weeks. These differences might be because of the water temperature in the lab. Water temperature clearly affects how fast the eggs and larvae develop. This means the hatching time in a lab might be a bit different from what happens in the ocean.

Diet

Blue king crabs are primarily scavengers and predators of slow-moving or sessile (non-moving) organisms. Their diet includes:

• Bivalves: Clams, mussels, and cockles are a staple.

• Polychaete Worms: Abundant on the seafloor, these are a common and nutritious prey.

• Other Crustaceans: They will prey on smaller crabs, hermit crabs, barnacles, and even brittle stars.

• Sea Stars and Sea Urchins: An important part of their diet, especially in some locations.

• Sponges and Tunicates: Sessile filter-feeders that are easily consumed.

As opportunistic scavengers, they readily consume dead fish, other dead crabs, and any other decaying organic matter they find on the seafloor. This makes them important "clean-up crew" members of the ecosystem.

While not a primary food source for adults, they will consume macroalgae and likely ingest significant amounts of phytoplankton and organic film while feeding on detritus.

Fishing for Blue King Crabs

History of Crab Fishing

People started fishing for blue king crabs for sale (commercial fishing) in the eastern Bering Sea in the mid-1960s. The biggest year for blue king crab fishing was 1981, when over 13.2 million pounds (6,000 metric tons) of crabs were caught! This was just after the red king crab fishing also reached its highest point.

The fishing around the Pribilof Islands, managed by the United States, caught the most crabs in 1980. About 10.9 million pounds (4,960 metric tons) were harvested that year. However, the number of crabs started to drop, so fishing was stopped in 1988. It opened again for three years but closed once more in 1999 because the crab population was still too low.

The St. Matthew Island fishery also had its biggest catch in 1983, with about 9.4 million pounds (4,280 metric tons) of crabs. It also saw a decline and was closed in 1999. It reopened in 2009 and was even shown on the TV show Deadliest Catch.

Protecting Crab Populations

Today, the crab population near St. Matthew Island is slowly getting better, but fishing there is still closed to help them recover. The Pribilof Island crab population has not improved much.

The blue king crabs near the Diomede Islands have never been fished commercially. However, the local Native Village of Diomede, Alaska (which has about 170 people) fishes for them to feed their community. This is called a subsistence fishery.

Colder water makes crabs grow slower. This means crabs living further north are often smaller than those in warmer, more southern waters. To protect the crabs, commercial fishing rules limit the size of crabs that can be caught. For example, around the Pribilof Islands, only male crabs with a carapace width (the width of their shell) over 6.5 inches (16.5 cm) can be caught. Near St. Matthew Island, the limit is crabs with a carapace width greater than 5.5 inches (14 cm). This is about a 4.7-inch (12 cm) carapace length. Diomede blue king crabs are similar in size to those from St. Matthew Island.

See also

In Spanish: Cangrejo azul gigante para niños