NATIONAL NEWS - Marine scientists are investigating the cause of the decrease in sightings of southern right whales along the South African coastline as observed during a recent aerial whale survey.
Between 30 September and 5 October, the whale unit of the University of Pretoria's Mammal Research Institute conducted its 40th annual aerial survey of southern right whales between Nature's Valley in the Garden Route and Muizenberg in Cape Town.
The endeavour was conducted from a helicopter, with many whale and dolphin species being recorded.
During the 14 hours and 18 minutes of flying time over the four days, southern right whales were, however, the focus.
Second-lowest since 1995
According to the researchers, 190 females and calves (95 pairs) of southern right whales were counted and photographed, as well as 10 adult whales without a calf, bringing the total to 200 of these mammals between Nature's Valley and Muizenberg. Most female-and-calf pairs were observed in De Hoop Nature Reserve and Walker Bay.
They said these numbers mark the second-lowest number of right whales along South Africa's shores in October since 1995. This comes after the extreme low numbers of 2016, during which only 55 pairs were observed and a massive decrease from last year's all-time record of 536 cow-calf pairs along the same stretch of coastline.
"At the same time, it is a strong decrease from the 131 cow-calf pairs which were counted between Hermanus and Infanta in August this year. The reason for this apparent shift in peak presence over the past years could be related to female right whales giving birth earlier and therefore leaving the South African breeding ground earlier, or that female right whales are leaving the South African breeding ground earlier, possibly with a calf that is not ready to migrate.
"Also, the number of 'unaccompanied adults' – males, resting females and receptive females – remained extremely low, as it has been since 2009. This tells us that non-calving right whales are still not migrating up to the South African coast as they used to do prior to 2009," the team said.
'Correlation with climate conditions'
They added that whether these are temporary trends or not, remain to be determined. "We are currently busy investigating this matter, with preliminary results indicating strong correlation with climate conditions in the Southern Ocean and fluctuations in food availability and therefore energy reserves. Similar trends are being recorded in South America and Australia."
They added that all photographs taken would be analysed in the coming weeks for individual identification, and compared to the unit's southern right whale photo-identification catalogue that contains more than 2 300 recognisable adults from the previous 39 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, we 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; as well as their overall reproductive success, with considerable accuracy. 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."
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