Whales roam the Hauraki Gulf - that's like saying there are a lot of fish in the sea. We think of whales as migratory or transitory visitors to the gulf, gorging on takeaways before heading on their way.

What will surprise many is that the gulf has a resident whale population and that it may disappear before most of us know what we're missing.

The Bryde's whale is a type of baleen whale which grows to about 15m and 20 tonnes.

"They're a funny little whale," says marine biologist Dr Rochelle Constantine of the Auckland University's school of biological sciences. "Most baleens migrate between polar and warmer seas but the Bryde's [pronounced "Brooders"] likes to stay in temperate waters.

"It's unusual to see them so close to a large city. We have whales in our backyard and I think most Aucklanders are oblivious to that.

"We seem to have an offshore species of Bryde's inshore. They've decided the gulf is a good place to stay where they can reliably get enough food and give birth to their calves."

But the whales that call the Hauraki Gulf home may not be the brightest cetaceans in the sea.

The gulf is relatively shallow and confined; they are competing for space with about 2000 ships that enter and leave the Port of Auckland each year. There are fast ferries and the keels, rudders and propellers of thousands of recreational boats to avoid.

Auckland University researchers have established that collisions with vessels - ship strikes - are the major killers of the Bryde's whale population in the gulf.

Masters student Steph Behrens found ship strike was the probable cause of death of 13 of the 39 Bryde's whales reported dead in the area since 1989.

It's likely that both the number of fatalities and the number caused by ship strikes are much higher.

A lot more research is needed - the scientists would like more funding, please, at a time when conservation agencies are under the thumb.

Better reporting of sightings and strandings and forensic necropsies to determine cause of death are on the wish list. But most of all, researchers and conservationists want Auckland's resident whale to be a secret no more.

The Bryde's whale's status is nationally critical, the Department of Conservation's highest threat ranking. This means they are at high risk of extinction; the New Zealand population is estimated to be less than 250.

The number living in the gulf may be as low as 50, with others coming and going - scientists hope to do more research to establish population size.

"If the population at any one time is only around 50 animals, then two deaths a year is not good," says Behrens.

Constantine says it's important to learn how many whales there are. "There may be more than we think, there may be fewer, but for New Zealand to lose them would be a great shame because they've been here a lot longer than we have."

What they have learned is that the whales tend to hang out in the inner gulf between Whangaparaoa and the Coromandel Peninsula. This puts them in the firing line as container ships move to and fro, sometimes at considerable speed. Cruise ships also represent a potential threat.

The big ships draw up to 12m and the gulf is only about 46m deep. That leaves not a lot of room for a 15m whale to duck and dive. "For the group of around 50 whales that are always in the gulf, the risk of vessel strike is very high," says Constantine.

There may be more around Great Barrier Island and the eastern Coromandel - those areas have yet to be surveyed.

Not much is known about the way the whales behave in the water column, information which could pinpoint ways to avoid collisions. Disconcertingly, the whales responded to tests in which an underwater alarm was sounded by surfacing in panic.

The researchers' next aim is to increase knowledge of the Bryde's movements using satellite monitoring equipment attached with suction cups from trailing boats as the whale surfaces. The Auckland Regional Council is providing $55,000 in funding for the "D-tag" project.

"Once the D-tag work is completed we'll be able to say with a little more certainty how whales are using the gulf because they are not always foraging," says Constantine.

"Sometimes they are just swimming along and there's no clue they are there but if there's a big workup of birds and dolphins and fish that's a pretty good sign. The D-tag work will definitely help with advising recreational vessels and ferries about how best to proceed when they do see whales."

Ferries are much more manoeuvrable than big ships and the skippers of major gulf operator Fuller's Ferries routinely look out for dolphins and whales, as well as other obstacles.

"We get quite excited about seeing dolphins and orca - they are hugely popular with passengers," says Fuller's general manager of support services, Mike Fitchett. "The skippers radio each other to look out for them when they see one."

But ships' captains won't usually look for whales and rarely know when they've hit one.

Globally, the Bryde's whale is not endangered but it's the presence of whales so close to a big city which lured the International Whaling Commission's conservation head to Auckland this week. Alexandre de Lichtervelde attended a seminar which discussed the mortality data and debated options to save the whales.

De Lichtervelde says though up to 3000 whales are killed by hunting each year, up to 300,000 will die by other means including fishing nets, pollution, illness and ship strikes. He says 44 per cent of ship collisions result in death.

Delegates from DoC, the Auckland Regional Council, Maritime NZ and other interested parties saw some disturbing images. When a ship hits a whale side-on, the effect is like punching a feather-down pillow - it leaves a lasting hollow.

The surrounding skin becomes speckled with bruises from internal bleeding. The blubber is discoloured. Ribs may be broken. Even with glancing blows, fins and tails can be broken or sliced off.

The whale may not die immediately but its injuries may leave it vulnerable to illness and eventual death.

Constantine says it doesn't matter that the Bryde's status beyond our shores isn't threatened.

"On an ecosystem level, from algae to plankton and fishes to seabirds and whales, it's important to maintain a healthy productive ecosystem. The Bryde's whales are a really important part of the Hauraki Gulf ecosystem and for that reason alone we should be watching out for them.

"If we're not paying attention to the large animals here there's not a chance of protecting smaller animals."

She says ship strikes are a threat we can do something about. "Accidents do happen and we'll never stop all vessel strikes. But with a bit more awareness and some small changes in how we use the Hauraki Gulf, we can have these whales here and I think that's really important."

The obvious solution is for ships to go slower. International research shows that a whale hit by a ship travelling at 10 knots is three times more likely to survive than if the ship is doing 14 knots. Slowing down to even 12 knots reduces mortality.

But moves in other countries to force ships to go slower in whale areas have met fierce opposition.

Time is obviously money for shipping companies, while Ports of Auckland shipping operations manager Nigel Meek told the meeting the engines on some ships can be damaged at slow speeds.

Fuel economy is affected. He also cites language barriers in telling visiting ships' captains the local rules.

De Lichtervelde says shipping companies can and do comply - years of pressure in the United States eventually saw regulations requiring ships to reduce speed off its eastern seaboard in areas where the highly endangered North Atlantic right whale is present.

He says the plight of the Auckland Bryde's whale is comparable.

"It's a critical situation here and it's very rare to be able to see a whale so close to a big city."

But he believes much can be gained through education and voluntary measures before regulation is considered. Internationally, several major cruise ship companies are on board with measures such as posting observers in the wheelhouse.

Deputy harbour master Jim Dilley favours publicity to change behaviour. "The first step is to make people aware how special these creatures are and how lucky we are to have them here."

Boaties should keep a look-out and be aware of requirements to reduce speed within 300m of whales and dolphins and to keep at least 50m from whales.

Dilley says a brochure may help raise awareness and encourage people to report whale sightings, collisions and deaths. Shipping agents could be encouraged to relay information to ships.

ARC parks deputy chairwoman Christine Rose also backs education. "If people are aware there's a resident population of Bryde's whales out there, they may be more conservative in their boating behaviour," she told the meeting.

"Aucklanders should be taking a higher level of ownership of these whales on their doorstep."

But to really get on top of the problem, researchers need to learn a lot more about how the Bryde's lives and dies. The cause of death of whales washed ashore (often mistaken as strandings) - and even on those collected from ships' bows - is not always obvious.

Was the whale dead before the ship hit it? A forensic necropsy is needed to determine the cause of death but this happens rarely. Ngati Wai, the iwi which cleanses and takes the bones of beached whales under a protocol with DoC, supports the case for more necropsies.

But there's a shortage of veterinary pathologists trained and skilled enough to do the work. Often they are not notified before the whale is carved up and disposed of.

New Zealand could also improve its procedures for notifying ship strikes to the IWC.

The meeting is expected to lead to better co-ordination and communication between agencies, veterinary specialists and researchers. Constantine says many improvements don't cost much money but commitment is needed from DoC senior management to make the Bryde's a priority issue.

"It has the highest ranking for a cetacean in New Zealand waters. We need to be mindful of that and work hard to understand the causes and how to mitigate this mortality.

"No one wants to kill whales and I think the solutions are not too hard. I can actually see an end to this project - I think there's a lot of goodwill."


Key findings from Stephanie Behrens' masters thesis Bryde's Whales in the Hauraki Gulf and the Effects of Vessel Traffic

* Of 39 Bryde's whale mortalities recorded between 1989 and 2009, 13 are either known or suspected to have died due to vessel strike.

* The research is expected to considerably underestimate the true rate of mortality caused by vessel strike. The number of whale deaths is also thought to be much higher.

* The records note significant physical injuries including broken bones, dislocated vertebrae, severed tail flukes and intensive bruising.

* Three whales were stranded alive and died subsequently.

* Entanglement in mussel farm gear was the suspected cause of up to three further fatalities.

* The cause of death was undetermined for most of the other Bryde's whales. Most were buried without a detailed necropsy.

* Five cases were in an advanced state of decay when found.

* The largest whale was 15m and the smallest 7.8m.

* A further seven deaths of other whale species were recorded.