North "Straddie" Humpbacks

Here is a little history about the population of humpbacks I'll be studying and some background on the research. Note: I didn't write this. Also the photo depicts humpbacks seen in Monterey Bay (whales that I'm familiar with), which have less white than humpbacks in the southern hemisphere.


Every year, a large population of humpback whales migrate along the east Australian coast between their breeding grounds inside the Great Barrier Reef and their feeding grounds in the Southern Ocean. At the latitude of southeastern Queensland, the northward migration occurs May – August while the southward migration occurs August – November. This population is part of what, historically, was called the Southern Hemisphere Group V, i.e. whales that feed in Area V of the Southern Ocean, between 130E and 170W (longitudinally from about the middle of Australia across to just east of New Zealand). While whalers thought of this a one amorphous population, we now know that this is overly simplistic and there is really a meta-population that stretches across much of the South Pacific. Distinct populations migrate to breeding grounds off east Australia, New Caledonia, Fiji, Tonga, and Samoa all within the old boundaries of ‘Group V’, and French Polynesia and the Cook Islands that historically were in ‘Group VI’. While these populations are distinct, there appears to be low levels of interchange among them. East Australian whales are now referred to as Breeding Stock E1 with New Caledonia being E2 and Tonga being E3. French Polynesia is group F.

In the 1950s and early 1960s humpbacks were hunted from several shore stations along the Australian east coast during their migration. The largest of these was at Tangalooma near Brisbane which took 600 - 660 whales per year. By the early 1960s, however, whale numbers were badly depleted and whaling ceased in 1962. Although it was originally assumed that the shore stations had overfished the whales causing their population to collapse, the real problem was high levels of illegal, unreported pelagic whaling by Soviet fleets in the Southern Ocean in the early 1960s. Either way, the population, originally numbering around 30,000, was reduced to only a couple of hundred whales at the most.

Despite this tremendous depletion, the humpbacks are staging a remarkable comeback with around 14,000 in the population currently and an annual rate of growth of around 11%. We know this as the result of a series of surveys of the whales that began in the late 1970s. Every year or two since then there has been a survey by one or both of two different teams at Pt Lookout, North Stradbroke Is, just off Brisbane, which juts out into the migratory path of the whales. The surveys were run by Dr Robert Paterson, a Brisbane radiologist, and Prof. Michael Bryden of the University of Queensland and later the University of Sydney. Together, these surveys form one of the longest, most rigorous and most comprehensive series of surveys of any population of whales in the world with the possible exception of the Californian gray whales.

We took over the surveys in 2004 when we conducted a long 14 week survey of nearly the entire northward migration (late May to late August). This was designed as an absolute abundance survey where we wanted to estimate the size of the migratory population. We estimated that there were around 7,090 in the population then and confirmed that the whales were still increasing rapidly (10.6% per anuum).
The next survey was in 2007. This was designed as a relative abundance survey where we wanted to get a count of the numbers of whales passing per 10h during the peak 4 weeks of migration to compare with a similar index developed originally by Paterson, Paterson and Cato. We ran the survey for 6 weeks thinking that that would allow us to capture the peak 4 weeks even if it was a week early or late. Unfortunately the migration peak was even earlier than anticipated and so we started off with very high number straight away. Despite this, the results sat close to the levels predicted by previous surveys and allowed us revise the long term rate of growth to 11.1%.

The 2007 survey also involved aerial surveys. We did a series of aerial surveys north and south of Pt Lookout to determine the true distribution of the whales off Pt Lookout. Doing land-based surveys, you expect to see lots of whales close to land and fewer off shore, but it’s not until you do aerials that you can see the true distribution. Anyway it demonstrated that this is not an illusion, with about 80% of the whales seen within 5km of Pt Lookout and only about 5% beyond 10km of the Point. This helps validate our absolute abundance estimates.

The other thing the aerial surveys allowed us to do was to estimate the numbers of whales we were missing from the land. Land-based double counts (where we had two land stations independently observing the whales) suggested we were missing around 10% of the passing whales. The aerials, however, showed this to be much higher, around 30%. If this was true then our absolute abundance estimates would be underestimating the size of the population by around 18%. We are currently undertaking a revision of all the data from these surveys and using a more sophisticated modelling approach to try to resolve this discrepancy.