Scientists survey basking sharks

Aerial surveys this summer will help scientists determine how many basking sharks, the world's second largest fish, are populating Canterbury waters.

The Department of Conservation (DOC) completed the first of 10 planned flights last week, covering the coast from New Brighton, around Banks Peninsula to the mouth of the Rakaia River.

Each flight involves 16, 10km-long transects from the coast offshore, with surveyors recording all species they observe. The last flight is scheduled for mid-March.

Once schools of basking sharks are seen, their location will be recorded by global positioning system (GPS). Several sharks will then be tagged with satellite transmitters to track their movements.

Basking sharks, second only to whale sharks in size, can grow up to 12m long and weigh more than five tonnes. They are labelled a "vulnerable" species by the International Union for Conservation of Nature. They are harmless to humans, feeding on plankton.

As well as the aerial surveys, DOC is asking beach-goers to keep their eyes peeled.

DOC marine scientist Clinton Duffy said the number of basking sharks around New Zealand was unknown but was likely to be in the low thousands, given several hundred had been caught accidentally by deep-water trawlers in the past decade.

This time of year was the best for the survey and when most sightings had been made.

"When they are in big numbers they are aggregating on a plankton patch. The largest we have documented over Canterbury was more than 100 animals, but we didn't get an accurate count that time," Duffy said.

Basking sharks favoured lower North Island and South Island waters, and Banks Peninsula had fairly regularly sightings, Duffy said. DOC Akaroa biodiversity ranger Wayne Beggs said the research was being carried out with funding from National Geographic. "They have often been seen off Kaitorete Spit. We would love to hear from anyone that spots these magnificent animals."

DOC Canterbury conservancy marine ecologist Laura Allum said basking sharks seemed to be disappearing from New Zealand waters.

"Anecdotally, they are not being reported so much from shore by the public. "

Sightings can be reported to the DOC area office in Christchurch on 03 341 9100 or email wbeggs@doc.govt.nz

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