Migratory movement of photo-identified humpback whales Megaptera novaeangliae along the southeastern coast of Africa

Abstract

The global conservation of humpback whales Megaptera novaeangliae relies on continuous assessments of the populations’ post-whaling status, which in turn require information on population mixing and movements. One of the seven breeding stocks in the Southern Hemisphere, breeding stock C and its associated four substocks (C1–C4), utilises the western Indian Ocean in several discrete breeding grounds. However, information on the mixing of stocks across breeding grounds is limited. This study utilises photo-identification methods applied to the first multi-regional catalogue of fluke images available for substock C1S (the southern component of substock C1) which uses the southern portion of the breeding ground, developed as part of this study, to investigate the whales’ movements along the southeastern coast of southern Africa. The identification of 1 746 unique individuals, including 11 withinyear matches and 48 between-year matches of 45 individuals, provides new insight into the intra-regional migration patterns, fidelity and structure of substock C1S. The within-year match results confirmed that individual humpback whales are broadly seasonally present for extended periods and visit multiple subregions along this coast, while the between-year matches revealed long-term fidelity to this coastline. Moreover, five of the between-year matches between subregions in South Africa and Mozambique linked the South African migration corridor to the breeding ground in southern and central Mozambique. These findings provide valuable insights into the movement patterns of substock C1S and significantly address the challenges of effective population management, which includes difficulties associated with the whale-watching industry on the east coast of South Africa.