'All we can do is watch': Huge jump in humpback whale numbers

This weekend Shona Lorigan will be on a coastal headland, joining thousands of others around the country scanning the horizon for whales.

Sunday marks the annual national humpback migration census day run by Ms Lorigan's marine mammal rescue group, ORCCA and conducted by hundreds of eager volunteers. Every indication points to another record year.

As of  4pm on Saturday, June 24, 2209 humpback whales had been sighted passing Cape Solander near the entrance to Botany Bay since May 24, almost 50 per cent more than a year ago, according to the National Parks and Wildlife Service.

"All of us love to be around them, they are truly majestic creatures," Ms Lorigan said. "We're so fortunate to be able to experience them literally off every headland."

Humpbacks tend to be the early movers ahead of minke, southern rights and rarer species such as false killer whales.

It helps too that they tend to track the coast closely, aggregating in particular near North Stradbroke Island, south east of Brisbane.

There, regular scientific surveys since the 1980s have shown a surprisingly rapid and consistent increase in humpback numbers, said Michael Noad, an associate professor at the University of Queensland.

Humpback boom

"In the early1980s, they'd think it was a big day if they saw six or seven whales" in a 10-hour day of watching, he said. "These days, the average number is about 150 whales and some days up to 200."

Professor Noad estimates more than 30,000 humpbacks alone will migrate northwards up the coast this year, roughly matching peak historical numbers.

The 10-11 per cent annual increase, though, means the population is doubling about every seven years. That raises concerns about whether the animals will have a "soft landing or a relatively nasty oscillation", he said.

For reasons yet unclear, southern right numbers are growing only about half as fast. Antarctic blue whales – the largest creatures that have every lived – may not be increasing at all even with curbs on whaling.

"We've driven [blue whales] down to such low numbers that they are having trouble finding mates – that's one possibility," Professor Noad said.

Shark myth

Researchers are more confident about another issue of public concern – the apparently unfounded fear that rising whale numbers are bringing more sharks to places such as the northern NSW coast.

A spike in shark bites there prompted the state government to introduce sharks net last summer. These have now been removed to avoid snagging whales.

"There's no evidence at all that whales coming up the coast increase the shark risk to people," Professor Noad said.

A study for WA Fisheries last year came to a similar conclusion.

The research did, though, find dead whales can be a shark magnet. One beached whale near Albany in 2010 lured sharks to the area for as long as 17 days afterwards.

While people should be careful, the predator feeding on a dead whale "is a happy shark" that would be unlikely to hunt alternative food, Professor Noad said. "It's the shark risk, not shark numbers, you need to worry about."

New hazard

If the population growth rates continue – and there is no sign humpbacks are going hungry because of krill shortages – governments had better start planning for the risk of more whale collisions with boats.

"There's a real navigational hazard and safety issue ... that's coming to a head very rapidly," he said. "I just wonder how long our love affair with whales will go on for if people start losing their lives running into humpbacks."

Professor Noad doubts, however, that anybody will advocate resuming whaling. Still it could be time to consider improving safety especially for recreational vessels such as yachts that whales may not detect and avoid.

"We've got no control over really what happens with humpbacks," he said. "All we can do is watch."