Usually found along the coastlines of Japan, Korea, and Malaysia, Asian paddle crabs were first detected in New Zealand in 2000. An aggressive defender of its territory, this species poses a real threat to our native crabs, commercially important shellfish, and the health of our harbours. It can also give humans a nasty nip.
Where are they from?
Native to the coastal waters of East and Southeast Asia, Asian paddle crabs have established themselves in a number of North Island harbours since their arrival here over two decades ago.
Why are they a pest?
- They prey on commercially and culturally important shellfish species.
- They can carry diseases that affect commercial shellfish fisheries.
- They compete with native crabs for food and space.
- Females can produce up to 85,000 eggs per year, allowing populations to grow rapidly.
Where are they found?
Asian paddle crabs have been detected in several North Island harbours, from Waikare Inlet in Northland, to Whangarei, Waitemata, Tauranga, and as far south as Ohiwa Harbour.
In 2018, two Asian paddle crabs were caught in Tauranga Harbour near the Matapihi rail bridge. An ongoing trapping programme is now in place across both Tauranga and Ohiwa Harbours to monitor for their presence.
They are typically found in tidal and sub-tidal zones down to 15 metres deep, preferring estuaries with firm or fine muddy sand. Their larvae can drift in the water column for three to four weeks, travelling large distances on tides and currents. They can also spread through ballast water or as hull fouling on vessels.
What do they look like?
- Shell width up to 12cm, making them much larger than most native crab species.
- Distinctive black-tipped pincers.
- Six spines on each side of the shell below the eyes, and five prominent spines on the upper surface of each claw.
- Flattened swimming paddles on the back legs, with colouring ranging from pale green and dark green to brown and purple.
What are the rules?
Asian paddle crab is classified as a Progressive Containment pest. This means the aim is to prevent spread, reduce distribution, and work toward eradication within parts of the region over time. Landowners and occupiers are responsible for controlling Progressive Containment species on their property.
To help stop the spread of marine pests like Asian paddle crab, all vessel owners should:
- Keep your boat bottom and any niche areas clean with no more than light slime at all times.
- Keep your anti-fouling paint fresh. Manufacturers generally recommend replacing it every one to two years.
- Check your hull before travelling to a new area, every time.
- If your boat is heavily fouled, haul it out. Cleaning underwater will spread any pests hiding on the hull.
What to do if you spot one
It is important that vessels are clean before entering the Bay of Plenty. If you spot an Asian paddle crab in the Bay of Plenty, please kill it, keep the sample, and contact the Bay of Plenty Regional Council on 0800 STOP PESTS (0800 786 773).