15-20 ton Bryde's whale found dead in the Hauraki Gulf, New Zealand

14 Sept, 2011

A 12m whale weighing 15-20 tonnes probably died after being hit by a ship, experts say.

Bryde’s whale 

The death of a Bryde’s whale in the Hauraki Gulf highlights the need for more research and greater vigilance on the water, according to University of Auckland marine mammal scientist Dr Rochelle Constantine.

“Close examination of a whale found floating dead in the Hauraki Gulf last Friday clearly showed that it died as a result of being struck by a ship,” says Dr Constantine, who leads Bryde’s whale research in New Zealand.

One of New Zealand‘s most endangered species, Bryde’s whales are found in the Hauraki Gulf all year round. According to University of Auckland research, 40 Bryde’s whales have been found dead in the region in the last 16 years. “We have evidence of the cause of death for 17 of these whales with 14 whales having died as a result of ship strike,” says Dr Constantine.

The whale found dead last week was reported to the Department of Conservation by a Great Barrier Air pilot. It was retrieved by a fishing boat and towed to the north of the Coromandel Peninsula, where a necropsy was performed on Monday.

“The large areas of external bruising and ruptured intestines required closer examination into the whale’s cause of death’” says Rob Chappell from the Hauraki Area Department of Conservation. “Contact with local iwi supported us in proceeding with this important work,” he says.

The necropsy team, led by Massey University veterinary pathologist Stuart Hunter, found 15 fractured vertebrae and broken ribs as well as a large area with extensive bruising, indicating that the whale was alive when it was struck by the ship.

Historically necropsies have not been conducted on whales but Dr Constantine says that this investigation highlights the value of thorough examination by scientists to determine the cause of death.

The 12-metre animal received injuries along half the length of its body. “It was clear that the whale had severe trauma, running all the way from the rib cage to near the tail of the whale; so it was most likely to be a large vessel that caused these lethal injuries,” says Mr Hunter.

Ship strike poses the greatest threat to Bryde’s whales in the busy Hauraki Gulf waters. Dr Constantine and Dr Natacha Aguilar from The University of Auckland are leading research into why the whales are so vulnerable, using advanced d-tag technology.

The tags, attached by suction cups to the back of the whale, allow the researchers to understand their behaviour and acoustic environment when below the surface of the water. “We have deployed five tags so far and preliminary analysis shows that the whales are spending the majority of their time less than ten metres below the surface. This puts them within the strike depth of many vessels using the Gulf,” say Drs Constantine and Aguilar.

“All vessels using the Hauraki Gulf pose a threat to whales so it is important that everyone using these waters is watching out for these large residents in Auckland’s backyard,” says Dr Constantine.

Bryde’s whales are medium-sized baleen whales of around 13 metres that typically inhabit coastal waters in tropical and temperate regions.

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