Spotting the right whale with annual survey

Posted on September 26, 2017

The Whale Unit of the University of Pretoria’s Mammal Research Institute will be conducting their annual aerial survey of southern right whales from the 2nd of October through to mid-October. Having commenced in 1979, this is the 39th consecutive annual survey and the resulting dataset is one of the longest running datasets on any marine mammal worldwide.

The survey is flown annually between Nature’s Valley and Muizenberg (although may extend further westwards if conditions allow) at an altitude of approximately 300m and some 500 to 800m offshore using an Airbus H120B helicopter. Flying will only be carried out under adequate survey / weather conditions between 08h00 and 16h00 as light and glare outside of these times compromises survey photography. During the survey, all encountered whale species will be recorded, but special focus will be given to encounters of southern right whales. As such, all southern right whale females with calves, as well as all individuals with distinctive brindle colouration or markings, will be photographed in order to allow individual identification. Vertical images of both the heads and the backs of the animals will be taken, which will allow recognition of the pattern formed by the wart-like callosities on their heads, and in some cases of the white and grey pigmentation patterns on their backs. Photography of each group usually takes less than five minutes, during which time the helicopter decreases in altitude to hover some 150-200m above the whales. When photographs are obtained, the helicopter returns to the 300m altitude to continue searching for whales, although in areas of high whale densities the aircraft may move directly from group to group at the lower altitude. 

After the survey, the collected photographs and associated data will be analysed. The best images of each individual will be selected from each encounter and compared to all other selected images from the 2017 survey as well as to the Whale Unit’s catalogue of identification photographs of just over 2300 recognisable adults from the previous 38 annual surveys. Sorting of images is initially done using a computer-assisted image recognition system, followed by final matching of the whales by eye. These analyses allow for sighting histories of known individuals to be compiled and a subsequent investigation of individual movement and distribution patterns as well as the reproductive / calving histories of females. These data will then be used to further investigate the vital parameters of the population, including abundance estimation, population growth rate, survival, calving intervals, and age at first parturition (age at when a female has her first calf ), which will and over the longer term allow researchers to accurately model the population demographic parameters.

Southern right whales received their name from the historic whalers who believed them to be the “right whale” to hunt, as they are were predictable in distribution, generally slow swimming, and most importantly float when killed. Indeed, the species was heavily whaled in the past (particularly by the Moby Dick style foreign open-boat whaling fleets between about 1780 and 1835), and it reduced the global population from an estimated 70,000 - 80,000 individuals to a mere 60 reproductive females at the termination of right whaling in 1935. However, since their international protection in 1935, the three breeding populations (in coastal waters of Australia, Argentina and South Africa) have been increasing at about 7% per annum. Currently, the regional (southern African) abundance is estimated at 5,000 to 6,000 individuals, with a global population size of just under 15,000 individuals. Thus, one of the main objectives of the annual aerial survey is to monitor this remarkable recovery! Despite this increase in local and global population size, in the last 2 years a decrease in southern right whale sightings was noticed along the South African coast. A similar trend has been recently recognized in the breeding grounds of Argentina & Brazil, as well as in Australia, although there the changing trend seemed to be a year off. Reasons for this decline are currently being investigated but remain speculative. Luckily, this year the whales are back with hundreds of sightings over the last three months!

The MRI Whale Unit’s 2017 survey is being flown in association with Silvercross Aviation and is being generously funded by the International Whaling Commission and will be run with the assistance of the Dyer Island Conservation Trust, and support of De Hoop Collection, Denel Overberg Test Range, CapeNature, and private citizens along the route. The survey is carried out under a permit from the Department of Environmental Affairs to approach whales and under specific Marine Protected Area permits from the relevant conservation authorities. Weather plays an important part in achieving the full survey coverage and flying will be required over weekends.

For further enquiries please contact Dr Els Vermeulen (Research Manager at the Whale Unit ) on 060 9714301 or Chris Wilkinson (Technical Manager at the Whale Unit) on 083 580 8247

- Author Els Vermeulen
Published by Christopher Weldon

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