Posted on September 28, 2022
On 1 October 2022 the Mammal Research Institute Whale Unit of the University of Pretoria will be commencing its 53rd annual aerial survey of southern right whales to monitor the health of the population.
Since their international protection in 1935, southern right whale population has increased substantially from a mere 60 reproductive females in 1920 to some 15 000 individuals. The South African population, which occupies seasonal calving and nursery grounds in the nearshore and protected waters of the southern Cape coast, is believed to be the largest breeding stock of the global population, comprising some 6 300 individuals.
To monitor the population recovery post-whaling, annual aerial surveys have been initiated in 1969 by the late Professor Peter Best. From 1979, such surveys have incorporated photo-identification, a method by which individual whales are identified through overhead photographs of the callosity pattern on the head. This 53-year long database (including 43 years of individual sighting histories) is one of the longest uninterrupted datasets in the world on any marine mammal, and provides critical information for the estimation of demographic parameters of the population (including, for example, population size and trend, calving intervals, survival rates and age at first calving).
The MRI Whale Unit’s 2022 survey will be flown in association with Silvercross Helicopters, and with the support of the De Hoop Collection, Denel Overberg Test Range, and private citizens along the route.
The 2022 survey will commence on 1 October (weather dependent) and will follow standard survey procedures as described below;
The coastal stretch between Nature’s Valley and Muizenberg will be surveyed using a Eurocopter AS350 (Squirrel) at an altitude of approximately 300 m. Flying is only carried out under adequate survey / weather conditions between 08:00 and 16:00 as light and glare outside of these times compromises survey photography. During the survey, all encountered whale species are recorded. Additionally, and most importantly, 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 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 (but can take up to 15 min), during which time the helicopter decreases in altitude to hover some 150-200 m above the whales. Once sufficient photographs are obtained, the helicopter returns to the 300 m 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 will be 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 2 600 recognisable adults from the previous 42 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 this year indicated the number of right whales between Hermanus and Witsand is better than what it has been in 2019, 2020 and 2021.
Preliminary count surveys conducted at the beginning of August this year indicated the number of right whales between Hermanus and Witsand is better than what it has been in 2019, 2020 and 2021, with 248 females with calves (496 individuals) and 40 unaccompanied adults counted, leading to a total of 536 southern right whales on this stretch of coastline at that time. This is about 50% more than what was seen last year around the same time, but still below the number of southern right whales we would expect on our coastline this time of year under “normal conditions”.
As reported in previous years, sightings of females with calves decreased dramatically in 2015, 2016 and 2017, increased above normal levels in 2018, and then dropped substantially in 2019, 2020 and 2021. Sightings of unaccompanied adults (males and non-calving females) have decreased drastically in 2010 and have not yet returned to normal levels (see Figure 1). This suggests that only pregnant females, which are about to give birth, complete their migration to the South Africa 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 as historically observed. This year’s survey will reveal how these trends continue.
Figure 1. Number of females with calves (CC) and unaccompanied adults (UA) counted on the annual aerial surveys between 1979 and 2021.
The MRI Whale Unit’s 2022 survey will be flown in association with Silvercross Helicopters, 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. Funding for this survey is provided by TotalEnergies.
Following the whales: UP continues satellite tag program to follow southern right whales along their migration
As from 15 October, the Mammal Research Institute Whale Unit of the University of Pretoria will be conducing boat-based surveys in Walker Bay to deploy satellite transmitters on 10 adult southern right whales to study their migration and feeding ecology.
Southern right whales feed in the Southern Ocean, thousands of kilometres away from the South African coast. Because they feed one time of year (summer) and fast another time of year (winter, when they have their calves), scientists call southern right whales “capital breeders”, which means that their successful migration and calving is dependent on them eating enough during their summer feeding season in the Southern Ocean. In other words, they need to have an adequate body condition to be able to migrate and calve successfully. However, a study concluded last year indicated our right whale mothers decreased 24% in body condition (or “fatness”) since the late 1980s, indicating clearly that their feeding has become less successful. Additional research has furthermore indicated that our whales have changed the location at which they feed as well as the prey they target in the past decades. This shows that these whales are responding to environmental changes in their Southern Ocean feeding grounds, which we believe lies at the basis of the above mentioned increased calving interval (from 3 years to 4-5 years) and a reduced migration towards our shores.
In order to better understand these changes in migration patterns and feeding ecology, we will be deploying 10 satellite transmitters (SPOT tags) on adult southern right whales between 15 and 31 October this year. These tags will provide us with information on the location of each individual for up to 1 year maximum. In 2021, satellite transmitters were deployed on 4 adult southern right whales as a pilot study, and results have showed us incredible journeys so far, with one tag still being active to date (see Figure 2). You are able to follow these whales in real time on our website.
Figure 2. Map showing tracks of 4 adult female southern right whales tagged in October 2021 in Walker Bay. The tag on the whale with the light blue track is still active to date. This map can be seen in real time on http://www.mammalresearchinstitute.science/whale-unit.
As the deployment of these tags is of sensitive nature, we will be hosting a scientist specialised in the deployment of these tags (Dr Amy Kennedy) for the duration of the fieldwork. This research project is conducted in collaboration with Dr Alex Zerbini and Dr Amy Kennedy from the National Oceanic and
Atmospheric Administration (NOAA), University of Washington’s Cooperative Institute for Climate, Ocean and Ecosystem Studies (CICOES/UW), and the Marine Ecology and Telemetry Research (MarEcoTel). Funding for this project is provided by the MRI Whale Unit and private donors to whom we are extremely grateful.
Stay closely up-to-date on the status of our southern right whale research through our adopt-a-whale programme which we run in partnership with WWF South Africa:
https://donate.wwf.org.za/adoption/adopt-a-whale
All raised funds go integrally to cover the costs of our fieldwork.
Follow our work via our social media, as we will be posting very regular updates during our surveys in the coming month:
Since their international protection in 1935, southern right whale population has increased substantially.
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