A night out catching crabs

When we first arrived on the island we all accepted responsibility for a variety of additional tasks. For example, Neil is our fire chief and undertakes monthly inspections of all the hydrants, hoses and extinguishers, Bas collects the CO2 readings and insect samples and I’m in charge of maintaining our evacuation food and water supplies.

Another role that fell to Neil and I is the co-ordinatation of the annual land crab survey. This is a research project initiated by Kala Sivaguru and Alison Botha, which aims to find out more about the recovery rate of land crabs following the eradication of rats here, along with their population density, sex ratio and other bits and pieces.

The nocturnal land crab (Geograpsus grayi) is endemic to Raoul and our island is the only place in New Zealand where they can be found. The crabs live in burrows and are 30-40mm in carapace length.

During daylight hours we went to the designated research areas, marked out our plots and familiarised ourselves with our areas (it always looks very different at night). The search areas usually involve the floor and sides of ravines, which makes for an interesting time in the dark with torches covered in red cellophane so as not to frighten the little creatures.

The Crab Crew

Our work began at 7.00pm and each plot took about 40 minutes to search. We recorded the number of crabs we saw out and about as well as the number in each burrow, along with any other interesting observations. We caught any we could, determined their sex and let them go again. The information is then collated at base and emailed back to NZ.

The nocturnal land crab (Geograpsus grayi)

It sounds like a sad and sorry sort of observation, but this was a great night out on Raoul island.