Whalewatching venture at risk says marine expert

By SIMON COLLINS science reporter

Kaikoura's whalewatching tourist industry may be threatened by overfishing of the species the whales eat.

Auckland squid expert Dr Steve O'Shea says studies of the contents of sperm whales' stomachs show fish species such as groper and ling have declined from 37 per cent of the whales' diet in the 1960s to virtually zero today.

Instead, sperm whales stranded on New Zealand beaches in recent years have fed almost exclusively on squid.

He says squid populations are now threatened as each sperm whale eats 800 to 1000 squid a day, and trawlers' nets increasingly disturb the squid's deepwater habitat.

"Squid are often the first to go. If the whales are eating the squid, what's going to happen to the whales?" he asked.

"I think we will see further shifts which could force the whales to move away, with implications for Kaikoura."

Whalewatching at Kaikoura has become one of New Zealand's biggest tourist drawcards, attracting more than 80,000 visitors a year.

But an Otago University marine scientist who has studied the Kaikoura whales since 1990, Dr Steve Dawson, said there was no evidence the population was declining despite Dr O'Shea's fears.

"I think he is drawing a long bow, to be honest," he said.

Sperm whales, the world's largest toothed whales, were once common throughout the oceans.

But two centuries of whaling up to the 1980s reduced their population from around 2.8 million to levels put at 570,000 to 1.8 million.

Whaling has been banned since the 1980s until the population of any species recovers to its pre-whaling level.

Dr O'Shea said there was no sign yet of a recovery in sperm whale numbers. He believes that is because they cannot find enough food.

"Back in the 1960s they were eating 37.5 per cent commercial fish species such as orange roughy and southern kingfish. Those species have been driven almost to extinction."

The other 62.5 per cent of the whales' diet was squid, but 21 of the 96 species of squid found around New Zealand were also endangered.

Trawlers fishing for other species were catching squid in their nets and destroying both their habitat and the clumps of eggs which hatch into schools of squid.

"Trawl nets could be not only wiping out whatever is down there, but modifying the environment to such an extent that the squid move on."

Dr O'Shea said New Zealand had more reported whale strandings than any other country, and the Conservation Department sent him the contents of the whales' stomachs.

"I have personally been inside the stomachs of more dead whales than I care to remember."

He has found hundreds of squid beaks and other signs of squid - but no fish.

Forest and Bird Society conservation officer Barry Weeber said deepwater fish species such as orange roughy and oreo dory had been cut to less than 20 per cent of their numbers through the huge expansion of deepwater fishing in the past 25 years.

Dr Dawson said the whales sampled from commercial whaling catches in Cook Strait in the 1960s ate unusually large volumes of fish.

"Almost everywhere else in the world, if you sample the amount of fish eaten by sperm whales, it's mostly squid," he said.

It was still too soon to expect a big recovery in sperm whale numbers since whaling ended in 1964 because the females live an average of 60 to 70 years, take seven to 13 years to reach sexual maturity, spend 14.5 to 16.5 months in each pregnancy, and generally wait three to six years between births.

A co-author of the original 1967 study, Dr Martin Cawthorn, said sperm whales were "opportunistic feeders" and ate fish at Kaikoura simply because they were there.

"There must be very good reasons for the whales to go into Kaikoura," he said. "There are some squid there, and there are a lot of fish there.

"The sperm whale stocks are very healthy. They are not reducing at all. They have been increasing since the whaling stopped, and there has been fairly constant replacement of older animals in Kaikoura."

But Dr O'Shea said Kaikoura was not a major fishing region so there was no reason to expect more fish in whale stomachs there than elsewhere.

He has recruited a doctoral student from India to examine changes in the stomach contents of whales stranded in New Zealand during the past 10 years.

"In a few months, I will not be at all surprised to have found a change in the classes of animals the whales are eating, because the species once common in New Zealand that made up the diet of the whale have gone."

Sperm whales

* Sperm whales are the world's largest toothed whales and were the main target of commercial whaling in New Zealand.

* Worldwide, their numbers dropped from 2.8 million to between 570,000 and 1.8 million during the whaling era.

* Studies of stomach contents show that NZ sperm whales may have switched from a fish-and-squid diet to squid only.

* Trawlers' nets are catching deep-water squid and destroying their habitat - potentially forcing the whales to go elsewhere.