Population structure and migration links of Southern African East Coast Humpback Whales (Megaptera Novaeangliae) using photographic identification techniques

Abstract

The conservation of humpback whales is of global concern, particularly due to their extensive exploitation during the 19th and 20th centuries. For such conservation to be effective, continuous assessments of the post-whaling status of the populations are essential, which requires detailed information on population structure and migration patterns. Seven Southern Hemisphere humpback whale Breeding Stocks have been identified (named Breeding Stocks A to G). Some of these are further divided into sub-stock, with limited information available on their structure and inter-relationship, as in the case of the Western Indian Ocean (WIO) C Breeding Stock, particularly the C1 sub-stock migrating past the south-eastern coast of Southern Africa. Photo-identification has proven to be a valuable non-invasive method to obtain key information on migration patterns, as well as to provide information on the structure of stocks and levels of connectivity that occur between stocks and sub-stocks. The unique black and white pigmentation patterns on the ventral surface of humpback whales’ tail fluke is amongst the most important characteristics used for the photo-identification of these animals. Preceding this study, no single photo-identification catalogue was available for the humpback whales associated with the C1 sub-stock. The development of such a catalogue was one of the key objectives of this Masters’ project, where an extensive collection of historic fluke images (collected by several sources since 1988) and new fluke images (collected as part of this Study) were included. The collection of the new fluke images was carried out during dedicated scientific research surveys off Bazaruto, Mozambique, and Durban, South Africa, as well as during opportunistic surveys on commercial BBWW platforms. The development of such an identification catalogue representing 1,746 unique individuals, has the capability to provide novel information on the intra-regional migration patterns and connectivity, migration fidelity and structure of the C1 sub-stock. Photo-identification matching analyses applied to this catalogue’s images revealed 11 within-year matches of individuals, and 48 between-year matches representing 45 individuals. The within-year match results confirmed that humpback whales from the C1 sub-stock are broadly seasonally present for extensive periods. Furthermore, the within-year match results confirmed that multiple regions along the south-eastern African coast, including the south coast and north-eastern regions are visited by individuals from this sub-stock. From the between-year matches, long-term fidelity to this coastline was demonstrated. Moreover, five between-year matches obtained between South Africa and Mozambique regions, links the C1 sub-stock migration corridor to the southern and central Mozambique breeding ground. Evaluation of the phenotypic characteristics pertaining to the individual humpback whales identified within the C1 sub-stock provided valuable insight into the geographic structure of the population and suggest strong intra-regional connectivity along the South African coastline, as well as between the migration corridor and breeding region. Overall, the results obtained from this study emphasise the value of using photo-identification as research method and highlights the importance of continuous research to obtain more accurate population parameters of the C1 sub-stock. Furthermore, the findings of this research can play a key part in addressing the challenges of effective marine management (including of the South African east coast whale watching industry).