Blue king crab facts for kids
Quick facts for kids Blue king crab |
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Lithodes platypus J.F. Brandt in von Middendorf, 1851 |
The blue king crab, known scientifically as Paralithodes platypus, is a large type of king crab found in the North Pacific Ocean. These crabs live near places like St. Matthew Island, the Pribilof Islands, and the Diomede Islands in Alaska. You can also find them along the coasts of Japan and Russia. Blue king crabs are among the biggest crabs in the world. They can weigh more than 18 pounds (8.2 kg), but they are usually a bit smaller than red king crabs.
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Catching Blue King Crabs
People started fishing for blue king crabs in the eastern Bering Sea in the mid-1960s. The biggest catch happened in 1981, with 13,228,000 pounds (6,000 t) of crabs caught.
Fishing in the Pribilof Islands
The fishing in the Pribilof Islands by the United States reached its peak in 1980. About 10,935,000 lb (4,960 t) of crabs were caught then. However, fishing was stopped in 1988 because there were not enough crabs left. It opened again for three years but closed once more in 1999.
Fishing in St. Matthew Island
The St. Matthew Island fishery had its biggest catch in 1983, with 9,453,500 lb (4,288.0 t) of crabs. This fishery also saw a big drop in crab numbers and closed in 1999. It reopened in 2009 and was even shown on the TV show Deadliest Catch. The crab population in St. Matthew is slowly getting better, but fishing there is still closed. The Pribilof Islands crab population has not improved much.
Diomede Island Crabs
Blue king crabs near the Diomede Islands have never been fished for money. However, the Native Village of Diomede, Alaska, which has about 170 people, fishes for them to feed themselves. This is called a subsistence fishery.
Crab Size Limits
Colder water makes crabs grow more slowly. Crabs living in northern areas are often smaller than those in southern areas. For commercial fishing, blue king crabs caught near the Pribilof Islands must have a carapace (shell) width of over 6.5 in (17 cm). For St. Matthew Island, crabs must have a shell width greater than 5.5 in (14 cm). This means their shell length is over 4.7 in (12 cm). Diomede blue king crabs are similar in size to those from St. Matthew Island.
Where Blue King Crabs Live
Blue king crabs are found in the Bering Sea, but not in huge numbers compared to red king crabs. The main groups of blue king crabs near Alaska live near the Diomede Islands, Point Hope, St. Matthew Island, and the Pribilof Islands. You can also find smaller groups in the Norton Sound all the way to St. Lawrence Island.
There are also smaller populations off the eastern coast of Asia, near northern Japan and Siberia. Blue king crabs prefer colder waters, so they live further north than red king crabs. The special places where blue king crabs live are because of how glaciers affected the Bering Sea's water temperature a long time ago. When the water got warmer, cold-water species like the blue king crab had to move further north into the deeper parts of the Bering Sea. This period of warming and glaciers might have also made their populations smaller.
How Blue King Crabs Move
Female blue king crabs move with the seasons. In winter, they live in deeper waters, from about 400–600 feet (120–180 m) deep. When it's time to lay eggs, females with eggs move to shallower waters, about 20–35 ft (6.1–10.7 m) deep. Females without eggs go to depths of 150–250 ft (46–76 m). Male crabs that are big enough to be fished usually live around 230 ft (70 m) deep. However, you can often find them in shallower waters during winter.
How Blue King Crabs Reproduce
Blue king crabs near the Pribilof Islands mate and lay eggs from late March to early May. Female crabs carry their eggs on the outside of their bodies for 12 to 14 months. Since it takes more than a year to carry their eggs, female blue king crabs usually skip a breeding cycle. This means they only lay eggs every other year. However, crabs laying eggs for the first time might lay eggs in the next year too.
Female crabs release their tiny larvae (baby crabs) around the middle of April in the Pribilof Islands. If kept in warmer water in a lab, they might release larvae as early as February.
Egg Production
Female blue king crabs in the Pribilof Islands grow to be the largest before they can reproduce. About half of these crabs are ready to reproduce when their shell length is about 5 in (130 mm). Female crabs from St. Matthew Island can start reproducing when their shell length is about 3 in (76 mm). Diomede crabs are similar.
Larger female crabs from the Pribilof Islands produce the most eggs. They can produce about 162,360 eggs or 110,033 larvae per crab. About 33% of the eggs are lost before they hatch into larvae. In Japan, blue king crabs release about 120,000 larvae each. Diomede blue king crabs release about 60,000 larvae per female.
Larval Release
Things like tides, temperature, saltiness of the water, light, and how much food (phytoplankton) is available can affect when larvae are released. Releasing larvae over a longer time might give the female a better chance for her babies to hatch when conditions are best. This is like "bet-hedging" – spreading out the risk. In the lab, Pribilof larvae hatch over about one month, and Diomede larvae hatch over 2 to 3 weeks. These differences might be due to the water temperature in the lab, which affects how fast the eggs and larvae develop. This might be a bit different from how they hatch in their natural home.
See also
In Spanish: Cangrejo azul gigante para niños
