Chinese mitten crab
Varunidae - Eriocheir sinensis
BioSecurity

What does it look like?

Chinese mitten crabs are usualy light-brown to olive green shell, which reaches up to 10 cm across. Hairy 'mittens' on its front claws, which is a feature not shared by any native New Zealand crab or other introduced species of crab. These caws have white pincer tips. There are four spines or serrations present on each side of the shell and a distinct raised  notch between eyes.

 Chinese mitten crabs burrow into sand, mud or clay banks. Adult specimens inhabit the bottom and banks of freshwater rivers and tidal creeks, before migrating to brackish and saltwater to reproduce. Their larvae develop into juveniles in marine coastal areas, which  then migrate back to rivers and creeks. Chinese mitten crabs are able to survive in highly polluted habitats.

Why is it a problem?

Burrowing by this species weakens banks and causes accelerated erosion. Damage to fishing nets and catch is also common. Where there are high densities of the species, water blockages can be an issue. This species also hosts liver fluke (Paragonimus sp.) that is harmful to human health. 

The Chinese mitten crab is also a generalist feeder, having impacts on the freshwater and brackish environment where in high densities due to it's tendency to cause an imbalance in the local ecosystem.

Control Methods

You can help prevent the spread of marine pests by:

• Regularly cleaning your boat’s hull – ideally keep fouling growth to no more than a light slime layer.

• Applying good thorough coatings of antifouling paint and keep it in good condition

• Ensuring your hull is clean and free of fouling before you go travel to a new region

• Cleaning and drying any marine equipment (e.g. ropes, lines, pots) before using in a new location.

• Inspecting areas on your boat that retain water in case they’re harbouring marine life.

• Checking anchors, trailers and other equipment for tangled weeds.

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