Abundance of the east Australian humpback whale population
Humpbacks along the east coast of Australia
Population Background - Every year, a large population of humpback whales migrates along the east Australian coast between their breeding grounds inside the Great Barrier Reef and their feeding grounds in the Southern Ocean. Off south eastern 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 130E and 170W. In the 1950s and early 1960s these 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 over 600 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 at this time. Either way, the population, originally numbering around 30,000, was reduced to only a couple of hundred whales at the most.
Survey Background - Despite this tremendous depletion in the population size, the east Australian humpbacks are staging a remarkable comeback with around 20,000 in the population currently and an annual rate of growth of around 10-11%. We know this as the result of a series of surveys of the whales that began in the late 1970s. From the late 1970s to the early 2000s, a survey was conducted every year or two at Pt Lookout, North Stradbroke Island. These surveys were run by Dr Robert Paterson, a Brisbane radiologist, and Prof. Michael Bryden, initially of the University of Queensland and later of 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.
The CEAL Lab 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 7000 in the population then and confirmed that the whales were still increasing rapidly (10.6% per annum). The next survey was in 2007 and was designed as a relative abundance survey and was carried out over 6 weeks. We wanted to get a count of the numbers of whales passing per 10h during the peak 4 weeks of migration. The 2007 survey also involved aerial surveys to help validate our absolute abundance estimates.
In 2010 we completed another relative abundance survey which was carried out over 8 weeks. One big change that we made in the 2010 survey was changing the observation site. The main observation site for all surveys up to 2010 was Norm’s Seat, a lookout platform with a north-easterly view at Pt Lookout. In 2010 the survey site was moved to a purpose built tower over looking Frenchman’s beach. The new platform gave us greater height and therefore greater ability to detect whales, as well as a perpendicular view of the whales migratory pathway. We also found a reduced effect of glare at this platform. We conducted 2 weeks of overlap in observations comparing the Frenchman’s and Norm’s seat platforms in order to calculate any potential difference in sight ability of whales from each platform, which could lead to changes in whale numbers counted. We found no significant difference in the numbers of whale sighted from either platforms.
Current Survey 2015 - The main aim of this years survey is to count, as accurately as possible, the number of whales swimming past Pt Lookout during their northward migration. Observers will work in teams of six and will note the time and composition of passing pods. The survey will be 8 weeks long from early June to late July. As in the 2007 and 2010 surveys, the primary aim is to calculate the average number of whales passing every 10h during the peak 4 weeks of the migration. This year we will return to our purpose built whale viewing platform above Frenchman’s Beach. The platform is approximately 55m high and has been funded by the Redland City Council.The 2015 survey is funded by the Australian Marine Mammal Ceter (AMMC) which is part of the Australian Antartic Division (AAD).
To keep up to date with this year’s survey please "Like" and "Follow" Straddie Humpbacks on Facebook for daily updates on the 2015 whale count www.facebook.com/Straddiehumpbacks