Migrations of humpback whales past Cape Vidal, South Africa, and an estimate of the population increase rate (1988–2002)

Abstract

Shore-based surveys of migrating humpback whales Megaptera novaeangliae were undertaken from Cape Vidal, northern KwaZulu-Natal, South Africa, each year between 1988 and 1991, and in 2002. Daily observations of migrating whale groups were carried out from an approx. 60 m-high platform during all surveys. Whale groups were tracked by position-fixing on surfacing bouts using survey theodolites, to determine swimming speeds and headings and distance offshore, while group size estimation was carried out at each theodolite measurement. Numbers of whales observed or projected (at tracked speeds) to cross the midline of the survey area within the observation period each day were tallied in each of three distance bins. These counts were adjusted to account for daily sighting effort and for proportions that were likely to have been missed on account of their distance offshore or poor sighting conditions to produce daily sighting rates. Such daily tallies were summed over the survey period to estimate the number of whales passing Cape Vidal each year, with counts from days of <2.5 h of observation effort (due to weather or sighting condition restraints) replaced by the mean of the previous and following days. The numbers passing to the north of Cape Vidal during coincident periods of 17 days over the 1988-2002 surveys (6-22 July) and 25 days over the 1990, 1991 and 2002 surveys (6-30 July) provide statistically significant increase rates of 11.5% (SE 2.8) and 9.0% (SE 2.7) per annum respectively.

Reducing the environmental impact of shark-control programs: a case study from KwaZulu-Natal, South Africa

“…The increase in the catches of whales, mainly humpback, despite the use of whale alarms, is likely to be due to the rapid recovery, estimated at ,10% and 7% per annum, respectively, in the populations of humpback (Findlay et al 2011) and southern right whales, Eubalaena australis (Best et al 2001), after decades of whaling. The incidence of whale entanglement was highest between July and November (KZNSB, unpubl.…”

The Use of Data from a Platform of Opportunity (Whale Watching) to Study Coastal Cetaceans On the Southwest Coast of South Africa

“…The encounters of adults without calves (single, pairs, and groups of whales sighted in the study area is uncertain and evidence from genetic, acoustic, or photographic matches is needed. Certainly the low overall number of sightings in the current study (233 individuals over 10 years) suggest that the study area is not part of a main migration route (cf., Findlay, Best, & Meÿer, 2011), and the whales sighted may have miscued their point of arrival at the continent on their northward migration. There were relatively few encounters from September to January during the expected southward migration period.…”

Reviewing evidence of marine ecosystem change off South Africa

“…Conversely, abundance on the South-East Coast of Bryde's whales Baleanoptera edeni, which also prey on small pelagic fish, appears to have decreased since the 1980s (Best 2001, Penry et al 2011, possibly because of small-scale, local fluctuations (Penry et al 2011). Numbers of southern right whales Eubalaena australis have continued to recover at a rate of approximately 7% annually since monitoring began in the 1970s (Best et al 2001, Brandão et al 2010 and there has been an increase in humpback whales Megaptera novaeangliae migrating through the coastal waters of KwaZulu-Natal since the late 1980s (Findlay et al 2011). On the West Coast there are approximately 500 humpback whales that are temporarily resident during spring and summer when they feed (Barendse et al 2011).…”