There are now more southern right whales gracing the Western Cape coast than at any time in the past 150 years, and an aerial survey starting next week is expected to confirm the steady population recovery of these gentle giants.
These whales - called "right" whales because they were the right whales to hunt as they floated after being harpooned and yielded substantial amounts of oil - came close to being completely wiped out by whalers during the 18th and 19th centuries.
In just 20 years from 1785 to 1805, an estimated 12 000 were harpooned along the southern African coast, and by 1940, when this species was finally formally protected, there were believed to be just 50 or so adult females left.
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But in recent years, marine scientists from the University of Pretoria's Mammal Research Institute, led by whale expert Peter Best, have found that the southern right population has been reproducing at about seven percent each year - the maximum biologically possible for this species.
This is one of the research findings from the annual aerial whale monitoring programme that has been running for more than a quarter of a century. This year's survey starts on Monday and lasts until October 17.
During this time, the scientists will use a helicopter to count the whales along the coast and to photograph all the cow-calf pairs that they see.
Southern right whales are individually recognisable from the pattern of the wart-like callosities on their head - the characteristic white markings - and the photographs enable the scientists to follow the reproductive history and survival of individual whales over many years.
A female whale usually produces one calf every three years.
"During the survey period, 793 individual adult females have been identified and the birth of 2 298 calves has been recorded, and estimates of survival rate, age at maturity and calving interval obtained," explained post-doctoral fellow Desray Reeb, who will be leading the survey.
"It's been possible to show that the population has been increasing steadily at seven percent a year throughout, based not only on direct census results but also on results from a population model which is independent of possible changes in survey efficiency."
Reeb said there was no certainty about the size of the population before exploitation started in the 18th century. However, they believed it was somewhere between 60 000 and 100 000.
"So the best available evidence suggests that current numbers are about one-sixth of their initial level. Projections also indicate that there are more southern right whales around now than there have been for 150 years!"
Reeb and her colleagues have apologised in advance to whale-watchers for any inconvenience. "To achieve its aims - and particularly to maintain comparability - the survey must cover the entire coastal strip between its eastern and western limits.
"This means covering the Walker Bay whale sanctuary and other marine protected areas along the coast, as well as zones that are otherwise off-limits to boat-based whale-watching operations," she explained.
She assured whale-watchers that she would try to complete the photography of cow-calf pairs as quickly as possible.
"Photography normally takes about three minutes per pair, but some whales are more willing subjects than others."
The survey area is between Nature's Valley near Plettenberg Bay in the east and Lambert's Bay on the West Coast.
This year's survey will again be funded by Nedbank's Green Trust.
- This article was originally published on page 3 of Cape Argus on September 29, 2004
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