The Japanese spider crab, a creature of remarkable appearance and immense proportions, inhabits the deep waters surrounding Japan. Its striking long legs and considerable size distinguish it from other marine life, drawing both scientific interest and public fascination.
The Enigmatic Japanese Spider Crab
The Japanese spider crab (Macrocheira kaempferi) is the largest living arthropod, with a leg span reaching up to 12 feet (3.7 meters). Its body, or carapace, measures up to 15 inches (38 cm) across and weighs up to 44 pounds (20 kg). It displays a reddish-orange coloration with white spots on its legs, and its carapace is pear-shaped. Males have longer chelipeds than females.
These crabs inhabit deep-sea environments off the southern coasts of Honshu, Japan, including Sagami Bay and Suruga Bay. They are found at depths ranging from 160 to 1,970 feet (50 to 600 meters), preferring rocky substrates and undersea ridges. Despite their imposing size, Japanese spider crabs are docile scavengers, moving slowly along the seafloor to consume decaying fish, invertebrates, algae, and mollusks. During the spring mating season, they migrate to shallower waters, 160 feet (50 meters) deep, for reproduction.
Its Conservation Status
The conservation status of the Japanese spider crab is “Not Evaluated” by the International Union for Conservation of Nature (IUCN) Red List. This designation means the species has not been assessed against the criteria used by the IUCN to determine extinction risk. A “Not Evaluated” status does not imply the species is endangered or threatened; it indicates a lack of sufficient data for an assessment.
“Not Evaluated” differs from other IUCN categories like “Least Concern,” which applies to species assessed as widespread and abundant. For a species to be categorized as “Least Concern,” adequate information on its population status and distribution is necessary. While the Japanese spider crab is not currently listed as endangered, its “Not Evaluated” status suggests more research is needed to understand its population trends and potential vulnerabilities.
Factors Affecting Its Population
Although the Japanese spider crab is “Not Evaluated” by the IUCN, various factors influence its population, leading to public concern about its future. Overfishing is a primary consideration, as these crabs are sought after for their meat and are a delicacy in Japan. Historical data shows a significant decline in catches, from 24.7 tonnes in 1976 to 3.2 tonnes in 1985, indicating past pressures on the population.
Fishing practices, such as deep-sea trawling, can pose threats through habitat destruction and bycatch, even if not directly targeting the species. To manage these impacts, Japanese law prohibits fishing during its mating season, typically from January to April, when crabs move to shallower, more vulnerable waters. Conservation efforts also involve restocking artificially cultured juvenile crabs into fisheries to help maintain natural populations. Beyond fishing, climate change can also impact the species by altering ocean temperatures and food availability, potentially affecting larval survival and seaweed beds that contribute to their diet.