Gulf dolphin numbers astonish researchers

By PHILIP ENGLISH

The Hauraki Gulf is "teeming" with dolphins and whales, according to the results of aerial surveys made public for the first time.

Up to 20 species of whales and dolphins (cetaceans) can be seen in the Hauraki Gulf Marine Park, some of them year-round.

The number of common dolphins in the area from just north of Cape Rodney across to the northern tips of Great Barrier Island and the Coromandel Peninsula has been put at up to 1000 at any time.

But the most surprising survey result is that the gulf could be home to a permanent population of between 50 and 100 Bryde's (pronounced Broodah's) whales, which can grow up to 15m and weigh 20 tonnes or more.

The survey results were revealed by a Department of Conservation cetacean expert, Dr Alan Baker, giving evidence at the hearing of a Ports of Auckland application to dredge the Rangitoto Channel. The dredging could involve underwater blasting, which could harm the sensitive hearing mechanisms of whales and dolphins.

"The risk to cetaceans should be zero and there should be no underwater blasting," Dr Baker told the hearing before the consent authority, the Auckland Regional Council.

"Should the consenting authority grant blasting approval, however, then in my opinion the precautionary principle should prevail and conditions be made to avoid any potential adverse effects of explosions."

On Tuesday, Dr Baker was in the air continuing his surveillance flights over the gulf. He saw 18 Bryde's in two locations north of the Noises islands and east of Kawau Island, the most he has spotted in one day.

"I think it's terrific that the Hauraki Gulf is such a productive place," he said. "I have been astounded flying around it at the activity that is there.

"More often than not it is teeming with dolphins. Then there are the Bryde's whales and other whale species from time to time and thousands of gannets and thousands of shearwaters and thousands of petrels ... I bet most Aucklanders don't know about it.

"The Bryde's are quite active whales. A lot of big whales just keep cruising along and ignore boats or people, but Bryde's whales are very lively. They are what you call evasive. They dart here and there. They are hard to get up close to."

Dr Baker said the evasive nature of the whales was one reason whalers once based on Great Barrier Island did not hunt Bryde's, although they are now hunted by Japanese whalers in the north Pacific.

He said Bryde's were baleen whales, meaning they filtered food from seawater through plates at the back of their mouths.

"Mostly when I see them feeding they are feeding with gannets, dolphins, shearwaters and sometimes Orca," he said.

"I am pretty sure they are feeding on small fish because gannets have a particular diet. They can't eat big fish.

"On Tuesday, we found a number of Bryde's whales feeding in the traditional baleen whale style of lying on their sides and gulping in huge amounts of water, so there must have been krill they were feeding on."

Another development this week is the start of a University of Auckland research project on the Hauraki Gulf Bryde's by a PhD student, former Shetland Islander Kirsten Tompson.

She will attempt to discover the number of whales present and photo-identify individuals.

She will also try to discover through DNA analysis if the Hauraki Gulf Bryde's are a genetically distinct species.