A SUSPENDED MIGRATION OF HUMPBACK WHALES MEGAPTERA-NOVAEANGLIAE ON THE WEST-COAST OF SOUTH-AFRICA

Between 5 October and 19 November 1993, 62 sightings of 155 humpback whales were made from the lighthouse at Cape Columbine, South Africa, in 3 episodes about 9 d apart. For 59 groups tracked by theodolite, the average distance offshore peaked at 2 to 2.5 km. Independent information on offshore distribution was obtained from 1112 km searched by a ski-boat in the vicinity of Cape Columbine, from which the proportions of humpback whale groups in 2 strata (0 to 5 and > 5 km) from the shore as seen from the lighthouse did not differ from those expected from the boat data. Net directions of movement for 51 groups were distributed equally to all 4 quadrants of the compass, and those groups showing a concerted directionality of movement were headed equally to the north and to the south. Of the same 51 groups, 70% travelled at net speeds of less than 1.5 km h(-1). Migratory indices for individual groups (average speed/net speed) ranged as high as 82, and those with the lowest indices (corresponding to those most likely to be migrating) were distributed equally between northerly and southerly directions. Individual identification photographs taken of 27 humpback whales over 20 d revealed only 10 individuals, 5 of which were resighted on more than 1 occasion and up to 20 d apart. Apparent feeding behaviour by humpback whales was seen on 10 occasions over 38 d, and the production of reddish particulate faeces indicative of recent feeding was seen on 7 occasions, at a defecation rate of 0.22 whale(-1) h(-1). Faecal samples collected contained euphausiid remains (possibly Euphausia lucens) on 2 occasions and amphipods on another. Overall the data indicated that the southward migration of humpback whales expected at this time of year on the west coast of South Africa had been suspended, probably in response to locally abundant prey.