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Wednesday, May 23, 2007

ANIMAL TRACKER

Mitten crab


* Japanese name: Mokuzu gani
* Scientific name: Eriocheir japonica
* Description: A curious-looking crustacean, colored light brown or olive green, the mitten crab does indeed appear to be wearing a furry pair of gloves, with dense tufts growing on the claws, which have white tips. Adults and large juveniles have these fuzzy patches, but they do not reappear on claws that have regenerated. The carapace (shell) grows up to 8 cm across, but more usually 5 cm, and the legs reach out about twice as long as the shell is wide, giving the crab something of a spider-crab appearance. There are four spines on each side of the shell.
* Where to find them: Mitten crabs are catadromous, which means that they live mainly in fresh water, and breed in salt water. As larvae they live in estuaries, and as they grow they move into freshwater streams where they stay for up to three years before returning to coastal waters to reproduce. Inland, look for them in the mud and stones at the bottom of freshwater rivers and estuaries, and also in the mud along the banks. They live in burrows, sometimes at high densities, and their digging can destabilize river banks. They can be seen in freshwater areas throughout the year, but they stay in saltwater coastal areas only from September to January and from March to May.
* Food: Mitten crabs are not fussy eaters, and being omnivorous they will take both plants and pretty much any animal they can catch in their claws: clams, worms, insect larvae, shrimps or fish.
* Special features: Two things: their taste and their invasive nature. Mitten crabs are considered delicacies in East Asia, and over the years they have been illegally imported live into the United States to be sold as food. When they escape, however, they survive. Their long legs allow the crabs to walk well on land, which means they can get round barriers and invade new areas. Also, they are very tolerant of altered and polluted habitats. Combined with their non-fussy diet, this allows mitten crabs to aggressively invade new areas and displace existing species. It is thought that males wanting to mate do not approach females using smell, but only by sight. This means that they are unable to determine if the targeted female has mature ovaries, and so they just try any female. If she is not mature, she will reject the male. This is a primitive form of mating, but it hasn't prevented the mitten crab from prospering.



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