UP Whale Unit conducts annual aerial survey of southern right whales

Posted on October 17, 2022

The Mammal Research Institute (MRI) Whale Unit at the University of Pretoria (UP) recently conducted its 43rd annual aerial survey to monitor the South African population of southern right whales.

During the survey, 658 southern right whales were sighted between Nature’s Valley on the Garden Route and Muizenberg in Cape Town. The researchers also noted a slight increase in the number of calving females and an exceptionally low number of unaccompanied adults, indicating a low rate of migration to the South African coast.

The findings will allow the team to monitor the recovery of the South African population of southern right whales and investigate possible causes and consequences of the decrease in sightings along our shores in recent years.

During the four-day aerial survey, which made use of an AS350 (Squirrel) under charter from Silvercross Helicopters, all cetaceans were recorded with a special focus on southern right whales. Photographs were taken of southern right calving females (those with associated calves) and of whales with a brindle, grey or white blaze colouration.

“Just under 21 hours of flying time was needed to complete the survey,” says Dr Els Vermeulen, research manager at the MRI Whale Unit. “During that time, 304 calving females (equating to 608 whales) and 50 adult whales without a calf (so-called “unaccompanied adults”) were counted and photographed, bringing the total of southern right whales spotted to 658.”

As Figure 1 shows, the vast majority of southern right whales were observed between De Hoop Nature Reserve and Hermanus New Harbour, as is usually the case. Other than southern right whales, the team observed four humpback whales, several groups of humpback dolphins and bottlenose dolphins, and 32 large sharks.

Figure 1. Flight path of the 2022 southern right whale aerial survey (blue line) and sightings of all southern right whales (red points).

The number of calving females (represented by the blue line in Figure 2) is slightly higher than the number recorded in 2015 (249 calving females), but is still well below what is expected under “normal conditions”. “This data demonstrates that females are still calving at lengthier and non-regular calving intervals, which we will corroborate with the photo identification data,” Dr Vermeulen says.

As in the past decade, the number of unaccompanied adults (males and non-calving females), represented by the red line in Figure 2, continues to remain extremely low, indicating that they are still not migrating to the South African coast at the same rate as they used to.

Figure 2. Number of calving females (cows) and unaccompanied adults (UA) counted along the coastal stretch between Nature’s Valley and Muizenberg during the annual southern right whale aerial surveys since 1979.

 

A total of 15 116 photographs were taken during the survey for photo identification purposes, and will be analysed to identify individual whales. Such photo identification analyses makes use of a computer-assisted image recognition system; the whales are then matched by eye. The process usually takes about two months to complete.

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, which has been increasing at a rate of 6.5% per year since international protection of the population against whaling,” Dr Vermeulen says. “These 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 continue to support the survey, such as Silvercross Helicopters, De Hoop Collection, Grootbos, Orms, Canon South Africa, Denel Overberg Test Range and private citizens along the route, she adds. “The survey was 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. This year’s survey was funded by TotalEnergies, to whom we are thankful for their continued support.”

A whale cow and her calf in clear blue sea water

If you wish to support this important research and conservation programme and stay up to date on the status of the unit’s southern right whale research, please contact the MRI Whale Unit to find out more about its exciting and informative adoption programme run in collaboration with WWF South Africa. Symbolic whale adoptions make unique and exciting gifts, and are an authentic opportunity for corporate environmental responsibility. All funds raised in this way directly support the unit’s fieldwork.

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Published by Hlengiwe Mnguni

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