Page 58 - University of Pretoria RESEARCH REVIEW 2018

Whales – sentinels of ocean health Els Vermeulen, Mammal Research Institute (MRI)
The South African right whale population is estimated
to be just over 6 000 individuals, or 30% of its pre- exploitation levels. In the last few years, there has been a slow yet continuous decline in their population growth, most likely a consequence of reproductive failure.
The survey UP’s Mammal Research Institute Whale Unit undertakes of the South African right whales (Eubalaena australis) is one of the longest running research projects
on any marine mammal in the world. Annual aerial surveys are conducted along the southern Cape coast which, since 1979, have included the photo identification of all females with calves. These photographic surveys make possible the tracking of individual females over time, from which population parameters are derived.
Dr Els Vermeulen, lead researcher and manager of the Whale Unit,
has collaborated in an international comparative study on right whales, published in Royal Society Open Science in 2018, and on the movement patterns of humpback dolphins in South Africa, published in Aquatic Conservation: Marine and Freshwater Ecosystems.
Her research team’s analyses of the latest data on South African right whales show that the numbers of whales along the southern Cape shore have fluctuated enormously in the
last few years. The number of males and non-calving females migrating to the southern Cape coast plummeted from over 400 in 2013 to a mere nine individuals in 2016, and remain
extremely low. Similarly, the number of females calving have varied from over 300 in 2014, to 55 in 2016, with an all-time record of over 500 in 2018. From the analyses undertaken, these fluctuations seem to be related to an increase in the calving intervals, which is indicative of calving failure.
The reproductive success of many species is known to be affected by foraging success and body condition. This is no different for whales. Indeed, the first results of a new project, initiated in 2018, have shown a strong correlation between the number
of right whale calves, and climate conditions and productivity in their Southern Ocean feeding grounds. The next step will be to collect skin samples for stable isotopes analysis, in order to gain insight into where exactly the whales are feeding, and information on their diet in the different locations.
Due to its annual migration to
the coast of South Africa, and the availability of a unique 40-year long dataset, these whales seem to be the ‘right sentinel’ to assess, from mainland Africa, the health condition of a wide region in the Southern Ocean, while monitoring the population dynamics of these recovering baleen whales.
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