South East African Coastal Migration Corridor IMMA

Size in Square Kilometres

47 060 km2

Qualifying Species and Criteria

Humpback whale – Megaptera novaeangliae

Criterion C (iii)

Marine Mammal Diversity 

Megaptera novaeangliae, Eubalaena australis, Stenella longirostris, Orcinus orca, Tursiops aduncus, Sousa plumbea, Delphinus delphis

 

Summary

The Southern Hemisphere humpback whale (Megaptera novaeangliae) C1 stock utilises the east coast waters of South Africa as northward (June to August) and southward (September to November) corridors during their annual migrations from high latitude summer feeding grounds to low latitude winter breeding grounds. Seasonality of these migrations has been determined from both historic whaling catches and more recent shore-based surveys. The orientation of the coast to the northward migration and the southerly strong Agulhas Current funnels the northward corridors inshore, 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. The inter-relationship of this migration with the Mozambique Breeding Ground is well established through the photo-identification of individuals. The relationship with other Breeding Grounds (C2, C3 and C4) is not well understood but believed to be limited from genetic, photo-identification and past catch timing data.

Description of Qualifying Criteria

Criterion C: Key Life Cycle Activities

Sub-criterion Ciii: 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.

Supporting Information

Banks, A.M. 2013. The seasonal movements and dynamics of migrating humpback whales off the east coast of Africa. Thesis submitted for the Degree of PhD at the University of St Andrews, Scotland.

Bannister, J.L. and Gambell, R. 1965. ‘The succession and abundance of fin, sei and other whales off Durban.’ Norsk Hvalfangst-tidende 54: 45–60.

Best, P. B. and Ross, G. J. B. 1996. ‘Whale observations from the Knysna Heads, 1903–1906.’ South African Journal of Marine Science, 17:1, 305-308.

Best, P.B., Findlay, K.P., Sekiguchi, K., Peddemors, V.M., Rakotonirina, B., Rossouw, A., and Gove, D. 1998. ‘Winter distribution and possible migration routes of humpback whales Megaptera novaeangliae in the southwest Indian Ocean.’ Marine Ecology Progress Series,162: 287-299.

Findlay, K. P., Best, P. B., and Meÿer, M. A. 2011. ‘Migrations of humpback whales past Cape Vidal, South Africa, and an estimate of the population increase rate (1988–2002).’ African Journal of Marine Science 33(3): 375–392.

Findlay, K.P. 2001. ‘A review of humpback whale catches by modern whaling operations in the Southern Hemisphere.’ Memoirs of the Queensland Museum. 47(2): 411-420.

Findlay, K.P. and Best, P.B. 1996. ‘Preliminary population estimates of humpback whales migrating past Cape Vidal, South Africa, 1988‑1991.’ Marine Mammal Science. 12(3): 354-370.

Findlay, K.P. and Best, P.B. 2016. ‘Distribution and seasonal abundance of large cetaceans in the Durban whaling grounds off KwaZuluNatal, South Africa, 1972–1975.’ African Journal of Marine Science 38(2): 249–262.

IWC. 1998. ‘Report of the Scientific Committee. Annex G. Report of the sub-committee on Comprehensive Assessment of Southern Hemisphere humpback whales’. Reports of the International Whaling Commission, 48, 170-182.

Lea, E. 1919. Studies on the modern whale fishery in the Southern Hemisphere. (unpublished), Bergen, Norway. 95 + tables and mapspp. Unpublished manuscript in British Museum (Nat. Hist.) files. Handwritten note on cover says `received by the Falklands Islands Committee’.

Matthews, L. 1937. The humpback whale, Megaptera nodosa. Discovery Reports, 17, 7-92.

Olsen, O. 1914. ‘Hvaler og hvalfangst I Sydafrika’. Bergens Museum. Aarbok, 1914-1915, 1-56.

Rosenbaum, H.C., Pomilla, C.C., Mendez, M.C., Leslie, M., Best, P., Findlay, K., Minton, G., Ersts, P., Collins, T., Engel, M., Bonatto, S., Kotze, D., Meÿer, M., Barendse, J., Thornton, M., Razafindrakoto, Y., Ngouessono, S., Vely, M., and Kiszka, J. 2009. ‘Population structure of humpback whales from their breeding grounds in the South Atlantic and Indian oceans.’ PLoS ONE 4: e7318.

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