South East African Coastal Migration Corridor IMMA

Criterion C: Key Life Cycle Activities

Sub-criterion C3: Migration Routes

The East Coast of South Africa is utilised by humpback whales (Megaptera novaeangliae) of the IWC-recognised C sub-stock (IWC, 1998) as a migration corridor for both the northward (June to August) and southward (October to November) migration (Findlay and Best, 1996; Best et al., 1998; Findlay et al., 2011). The orientation of the coast funnels whales into the inshore zone (and inshore of the southward flowing Agulhas Current) during the northward migration, while the southward migration appears to remain within the Agulhas Current, rather than as a direct migration to the south. The corridor extends from the south Cape coast to the South African – Mozambique border (Best and Ross, 1996) and appears limited to within 15 km of the coast (Findlay and Best, 1996; Findlay et al., 2011), although more offshore records were found by aerial spotters in the Durban whaling grounds (Findlay and Best, 2016). Migratory destinations have been identified as the coastal waters of Mozambique (through photo-identification returns (Banks, 2013) and returns of lost harpoons (Olsen, 1914)) and to a limited extent (a single individual) to Antongil Bay, Madagascar. Catch histories of the migration stream (at Durban) are markedly different to those of Madagascar (Findlay, 2001).

Shore-based surveys from Cape Vidal at 27˚ S between 1988 and 2002 show this sub-stock to be increasing at 9% per annum (Findlay et al., 2011). Preliminary results of recent surveys in 2018 suggest a slight decrease in this rate. Results of these surveys describe both the temporal aspects of this migration and the spatial distribution offshore. The northward migration (on which these surveys have concentrated) show a marked inter-annual consistency in migration timing of a number of migration waves. Such waves possibly comprise different age or sex class cohorts of the population as identified by Dawbin (1966) from whaling catch data. Olsen (1914) reported on the seasonality of humpback whale catches on the Durban whaling grounds over the period 1910 to 1912, and although Best et al. (1998) suggests that the 1912 data may be compromised, the seasonality of catches in both 1910 and 1911 show bimodal peaks during July and in mid- to late September over the last 10 days. Further bimodal seasonality of catches and sightings off Durban were reported by Matthews (1938) and Bannister and Gambell (1965), respectively, with similar seasonality. Sightings of humpback whales made by the Union Whaling Company’s spotter aircraft on the Durban whaling grounds between 1972 and 1975 were too few to describe any seasonal abundance patterns (Findlay and Best, 2016).

This area therefore contains important habitat used for the annual northward and southward migration corridors of humpback whales, migrating between summer Antarctic feeding grounds and winter breeding grounds in low latitude waters of the Western Indian Ocean on the east coast of South Africa (Findlay and Best, 1996; Findlay et al., 2011). The orientation of the African coast to the northward migration and the presence of the southerly strong Agulhas Current funnels the northward corridors inshore (within 10 – 15 km from the coast), while during the southward migration the corridor still appears to be coastal as animals utilise the southward flowing Agulhas Current as far west as Knysna (Best and Ross, 1996). The linking of this migration with the Mozambique C1 Breeding Ground is well established through photo-identified individuals, however the relationship with other Breeding Grounds (C2, C3 and C4) is not well understood, but believed from genetic (Rosenbaum et al., 2009), sparse unpublished photo-identification (Banks, 2013) and catch timing data (Findlay, 2001), to be limited.