Aerial portraits help whale conservation efforts

Posted on September 13, 2021

On the 1st of October 2021, the Mammal Research Institute (MRI) Whale Unit of the University of Pretoria will be commencing their annual aerial survey of southern right whales. This is the 42nd annual southern right whale photo-identification aerial survey, making this one of the longest uninterrupted datasets on any marine mammal worldwide.

The survey is flown between Nature’s Valley and Muizenberg with a standard methodology. As in previous years, an Airbus H120B helicopter will be used to survey the coastal stretch (within 1km from shore) at an altitude of approximately 300m. Flying is only 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, with a special focus on 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. Once sufficient 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 are analysed. The best images of each individual will be selected from each encounter and compared to all other selected images from this survey to search for within-year duplicates, as well as to the Whale Unit’s catalogue of identification photographs of just over 2,400 recognisable adults from the previous 41 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 allows researchers to accurately model the population demographic parameters over the long term.

Preliminary count surveys conducted at the beginning of August indicated the number of right whales between Hermanus and Witsand is better than what it has been in 2019 and 2020, with a 158 females with calves (316 individuals) and 52 unaccompanied adults counted, leading to a total of 368 southern right whales on this stretch of coastline at that time. This is about double of what was seen last year around the same time, but still well below the number of southern right whales we would expect on our coastline this time of year under “normal conditions”.

Sightings of females with calves decreased dramatically in 2015, 2016 and 2017, increased above normal-levels in 2018 and dropped again substantially in 2019 and 2020. Sightings of unaccompanied adults (males and non-calving females) have decreased drastically in 2010 and have not yet returned to normal levels. This suggests that only pregnant females, which are about to give birth, complete their migration to the South African coast to increase their calf’s survival chances, whereas most of the others are not undertaking their migration to the full extent. Additionally, data continues to show that females are giving birth to a calf every 4 to 5 years instead of every 3 years.

Successful migration and calving in southern right whales relies heavily on having an adequate body condition (blubber thickness or “fatness”), which is directly influenced the amount of food they can consume during their foraging season in the Southern Ocean. Results from our ongoing research confirm that our whales have changed the location at which they feed as well as the prey they target in the past decades, indicating that they are responding to environmental changes in their Southern Ocean feeding grounds. Additionally, a study we recently completed indicated that our right whale mothers decreased 24% in body condition (or “fatness”) since the late 1980s, indicating clearly that their feeding is less successful. We strongly believe this lack of energy reserves lies at the basis of the increased calving interval (from 3 years to 4 years) and a reduced migration towards our shores.

Southern right whales received their name from the historic whalers who believed them to be the “right whale” to hunt, as they are predictable in distribution, generally slow swimming, and most importantly float when killed. As a consequence, 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 main 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 just over 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 recovery and the new challenges these whales face.

The MRI Whale Unit’s 2021 survey will be flown in association with SilverCross Aviation, and with the support of the De Hoop Collection, Denel Overberg Test Range, and private citizens along the route. The survey is carried out under a permit from the Department of Forestry, Fisheries and the Environment to approach whales, and under specific Marine Protected Area permits from the relevant conservation authorities.

Stay up-to-date on the status of our southern right whale research through our adopt-a-whale programme, in which everyone can join our community by symbolically adopting a whale, this way supporting whale research and conservation in South Africa. All raised funds go integrally to cover the costs of our fieldwork. For more information, please check www.adoptawhale.co.za You can also follow our activities through our FB page https://web.facebook.com/MRIWhaleUnit

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

Published by Christopher Weldon

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