Blue whales Balaenoptera musculus off Angola: recent sightings and evaluation of whaling data

Abstract

The population of blue whales Balaenoptera musculus inhabiting the South-East Atlantic (Gabon to South Africa) was heavily depleted by commercial whaling. We report four photographically-verified sightings, and one probable sighting, of blue whales in deep waters (>1 000 m) off central Angola (11° S to 12°30′S) during 2012. International Whaling Commission catch data from south-western Africa between 1908 and 1967 included an estimated 2 071 blue whales taken off Angola between 1909 and 1934. The highest combined catches at any one station during this period (n = 833) occurred at Elephant Bay (13°13′S), located just south of the recent sightings. Despite year-round survey effort the sightings had strong seasonality and occurred only between July and October. Similarly, whaling catches peaked during July and August. Body lengths and seasonality indicate that at least some captured animals comprised the Antarctic blue whale B. m. intermedia subspecies. The sightings included at least one cow–calf pair. Catches comprised a high proportion (63.3%) of immature animals and at least five Antarctic blue whale cow–calf pairs. Food (zooplankton) was present in 85% of captured individuals, indicating feeding in Angolan waters. Further survey work is required to better clarify the status of blue whales in Angolan waters, particularly with regard to population structure and potential calving grounds.

Keywords: Antarctic blue whale, calving, catch data, pygmy blue whale, South-East Atlantic, stomach contents

African Journal of Marine Science 2014, 36(2): 269–278