Amongst the debris exposed by an extreme low tide, were several crab carapaces dotted about. Surprisingly, perhaps there were only very few disarticulated legs and pincers, certainly not enough for the carapaces. They belonged to paddle crabs Ovalipes catharus which are common on open sandy beaches. Distributed round New Zealand, including Stewart Island and the Chathams. They are also found in Tasmania though there they tend to be smaller.
This 'smiling face' carapace is about 5-6cm wide which is typical. During the day paddle crabs spend their time in temporary burrows emerging at night to hunt. They are most often found at depths of 10m, but can be found in much deeper offshore waters, up to 100m and are more abundant now than in the 1970s, possibly because their predators have been heavliy fished.
According to the National Aquatic Biodiversity Information System website 'paddle crabs are migratory,these movements being related to breeding, moulting, and feeding. Males and females aggregate and mate in sheltered inshore waters during winter, and it is thought that the females then migrate offshore to deeper waters, generally during September to March.'
