The University of Pretoria’s Mammal Research Institute’s Whale Unit conducted its 42nd annual aerial survey that sought to monitor populations of the southern right whales along the South African coast. The survey was undertaken between 3 to 5 October, with the flight path extending between Nature’s Valley to Muizenberg.
The survey entailed observing and counting the prevalence of southern right whales through aerial photography. Using the photographs, the unique callosity patterns on the heads of females were recorded. The survey was conducted for 17 hours over a span of three days. At the end of the survey, a total of 32 adult whales without accompanying calves and 191 females-calf pairs were recorded, which culminated in a total of 414 southern right whales in the coastal stretches. The area between De Hoop Nature Reserve and Walker Bay showed the highest density of female-calf pairs. The numbers recorded in 2021 showed a marked increase from prior years. However, the lower number of unaccompanied adults pointed to the fact that non-calving southern right whales were not undertaking migration towards the South African coast, as per the norm.
Following the completion of the survey, the photographs are analysed to fine-scale the identification to individual whales. This
consensus is compared against the repository of the Whale Unit’s national southern right whale catalogue compiled through prior surveys. The identification is compiled using a computer assisted image recognition system coupled with a final whale eye match in the photograph. This analysis allows scientists to determine which females have calved in the year, the time of gestation, their movement patterns and reproductive success. This allows close and accurate monitoring of the recovery of the South African population of southern right whales. The Whale Unit confirmed that there has been a 6.5% increase in recovery rate of southern right whales following the international outcry against whaling. The sightings and subsequent analysis help to investigate possible causes and accompanying solutions to dwindling populations along the coastal stretch.
During the week of 18-22 October, researchers from the Whale Unit have deployed satellite transmitters on four adult female
southern right whales. This will facilitate the tracking of the whales’ migration and feeding behaviours. The surveys conducted in prior years showed a marked decrease in reproductive success and body condition, alongside modified foraging and migration behaviours. Such changes have translated to lower prevalence of southern right whales over the past decade. The main food source that southern right whales feed on is located many kilometres away from the location at which they nurse their young. Owing to this, southern right whales are deemed “capital breeders”, as the level at which they undertake adequate feeding dictates the success of their migration and calving.
The Whale Unit has ascertained that there has been decreased food availability for the southern right whales, which necessitates
the importance of identifying these feeding grounds to facilitate oceanographic changes that can alleviate the food shortage.
This identification of the feeding ground was thus undertaken through the tagging of the four female adult whales. The tags provide consensus on the location of the individuals, as well as their feeding and migratory patterns. Based on the success of the pilot study, the Whale Unit hopes to deploy 30 more satellite transmitters over the course of the next two years.
Image: Dr Els Vermeuelen
