The Whale Unit of the University of Pretoria’s Mammal Research Institute (MRI) will be conducting their annual aerial survey of southern right whales from 30 September through to mid-October. This year celebrates the 50th anniversary of the aerial surveys, and the 40th year of consecutive photo-identification data collection. It is therefore one of the longest running datasets on any marine mammal worldwide.
The survey is flown annually between Nature’s Valley and Muizenberg at an altitude of approximately 300 m and within 1 km offshore. Flying is usually only carried out under adequate survey/weather conditions between 08:00 and 16:00, as light and glare outside of these times compromise 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 female southern right whales with calves, as well as all individuals with distinctive brindle colouration or markings, will be photographed in order to allow for 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 m to 200 m above the whales.
After the survey, the collected photographs and associated data are analysed. The best images of each individual will be selected from each encounter and compared to all other selected images from the 2019 survey, as well as to the Whale Unit’s catalogue of identification photographs of just over 2 300 recognisable adults from the previous 39 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. This 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 which a female has her first calf), which allows researchers to accurately model the population demographic parameters over the long term.
Despite a large number of calves present on our shores last year, this year the numbers appear to be lower again. A preliminary count survey conducted in mid-August indicated the presence of 131 females with calves and 26 unaccompanied adults, leading to a total of 288 southern right whales between Hawston and Witsand. This is considerably less than last year, and less than what would be expected.
In fact, sightings of southern right whales in their breeding ground haven’t been normal in the last couple of years. In South Africa, sightings of females with calves decreased dramatically in 2015, 2016 and 2017 and increased above normal levels in 2018. Sightings of unaccompanied adults (males and non-calving females) have decreased drastically in 2010 and have not yet returned to normal levels.
The exact reason for these enormous fluctuations in numbers is currently under investigation. Preliminary data strongly suggest that non-optimal feeding conditions in the Southern Ocean are resulting in poor energy levels, which limits them in following normal migration patterns and also leads to an increase in calving intervals (a female giving birth every 4 to 5 years instead of every 3 years).
In this regard, the MRI Whale Unit is currently investigating the whales’ nutritional condition using overhead drone images, as well as the effect of climate change on the productivity of their feeding grounds. Similar trends have been observed in the breeding grounds of Argentina and Brazil, as well as Australia.
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 to 80 000 individuals to a mere 60 reproductive females at the termination of southern 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 6.5% per annum. Currently, the regional (southern African) abundance is estimated at just over 6 000 individuals, with a global population of just under 15 000 individuals. Thus, one of the main objectives of the annual aerial survey is to monitor this recovery and the new challenges these whales face.
As this year celebrates the 50th anniversary of the aerial surveys, and the 40th year of consecutive photo-identification data collection, MRI Whale Unit invites everyone to a celebration on 24 October between 17:00 and 19:00 in the Municipal Auditorium. Prof Ken Findlay, Research Chair of Oceans Economy (CPUT) and previous head of the Whale Unit will speak on the history of whale research in South Africa, and Dr Els Vermeulen, Research Manager of the Whale Unit, will provide information on the current research projects and results related to South Africa’s southern right whales.
You can also help and stay up to date on the status of southern right whale research by joining the adopt-a-whale programme. All funds raised are used to cover the costs of fieldwork. For more information, please visit www.adoptawhale.co.za. You can also follow the whale counting activities on their Facebook page, MRIWhaleUnit.
For further enquiries please contact Dr Els Vermeulen, research manager, on 060 9714301 or Chris Wilkinson, Technical Manager, on 083 580 8247.