Between 27 and 29 September 2020, the University of Pretoria’s (UP) Mammal Research Institute Whale Unit conducted the 41st annual aerial survey to monitor the South African population of southern right whales. This survey was flown between Nature’s Valley and Muizenberg, using an Airbus EC120B under charter from Silvercross Helicopters. All southern right whales observed along this stretch of coastline were counted, and photographs were taken of the unique callosity pattern on the heads of all individual females with calves as well as all individuals of a brindle grey colouration or white blaze.
A total of 12 hours and 52 minutes of flying time, spread over three days, was required to complete the survey. In total, 136 females and calves (68 pairs) of southern right whales were counted and photographed, as well as 29 adult whales without a calf (so-called ‘unaccompanied adults’), bringing the total to 165 southern right whales between Nature’s Valley and Muizenberg. Most female-calf pairs were observed in De Hoop Nature Reserve and Walker Bay.
These numbers mark the second-lowest number of right whales along our shores in October in the past 32 years, after the extremely low numbers of 2016 (55 pairs). This number is also slightly lower than the 142 females with calves (71 pairs) counted at the end of August of this year between Hermanus and Witsand, re-indicating female southern right whales continue to limit their residency time in the South African breeding ground, with possible negative effects on the chances of calf survival. Also, the number of ‘unaccompanied adults’ (males, resting females and receptive females) remained extremely low, as it has been since 2009, indicating that non-calving right whales are still not migrating to the South African coast as they used to do before 2009.
New data reveal that the South African southern right whales have drastically changed their feeding locations in the past two decades.
In general, successful calving and migration in southern right whales rely on having an adequate body condition (blubber thickness or “fatness”), and thus energy reserves, which is directly influenced by their feeding “success”. It is therefore believed that a decrease in their feeding “success” lies at the heart of these anomalous trends. As the unit’s research continues, this hypothesis is being confirmed by its scientific data, which indicate strong correlations between the southern right whale prevalence along our shores with climate conditions in the Southern Ocean and fluctuations in food availability. In fact, new data reveal that the South African southern right whales have drastically changed their feeding locations in the past two decades, suggesting that their previously productive feeding grounds have changed over time. These findings point toward large-scale ecosystem changes in the Southern Ocean, likely impacting several different oceanic top predators. Data further indicate that while this shift in foraging locations may be an attempt to keep up with a changing ocean, the changes may not be sufficient to ensure an adequate body condition is obtained, negatively impacting the success of their calving and migration. In this regard, the unit is further investigating the whales’ nutritional condition using overhead drone images and analysis of blubber stress hormone levels. These results should be available at the end of this year.
Very similar trends are being recorded in South America and Australia, resulting in the MRI Whale Unit co-leading the Southern Right Whale research Theme under the Southern Ocean Research Partnership of the International Whaling Commission.
Stay up to date on the status of the unit’s southern right whale research through its adopt-a-whale programme. Visit www.adoptawhale.co.za.
Now that the survey has been completed, all photographs taken will be analysed in the coming weeks for individual identification, and compared to the Whale Unit’s southern right whale photo-identification catalogue which contains over 2 300 recognisable adults from the previous 40 annual surveys. This analysis will be done with a computer-assisted image recognition system, followed by final matching of the whales by eye. Through such analyses, the unit will be able to determine which females calved this year, how long it took them to produce a new calf, their individual distribution and movement patterns and, with considerable accuracy, assess their overall reproductive success. These aspects are vital to monitor the recovery of the South African population of right whales, increasing at a rate of 6.5% per year, since their international protection of the population against whaling. The analyses will also allow us to investigate further possible causes and consequences of the concerning decrease in sightings along our shores in recent years.
The MRI Whale Unit wishes to thank all those who support the survey, such as Silvercross Helicopters, De Hoop Collection, Denel Overberg Test Range and private citizens along the route. The survey was 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.
Three of the members of the survey team.
Stay closely up-to-date on the status of the unit’s southern right whale research through its adopt-a-whale programme in which everyone can join the MRI Whale Unit 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 the unit’s fieldwork. For more information, please check www.adoptawhale.co.za
You can also follow the MRI Whale Unit’s activities through its FB page
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