Genetic structure and diversity of South Africa's inshore Bryde's whale (Balaenoptera edeni brydei, Olsen 1913) population

Abstract

South Africa’s inshore Bryde’s whale (Balaenoptera edeni brydei) is the largest, resident baleen whale species occurring in our coastal waters. However, due to being one of the most elusive and shy marine mammals, there are significant gaps in knowledge relating to their phylogeny, ecology, and demography. The few studies done on this population provided important, broadscale information but also highlighted the more detailed research needed to improve and develop the understanding of South Africa’s inshore Bryde’s whales. It is generally accepted that these whales form a small population (< 1,000 mature individuals) that shows a restricted coastal distribution along the coastline of South Africa. Their movements along the coast are largely dictated by the movements of their main food sources, sardine (Sardinops sagax) and anchovy (Engraulis capensis). However, their population structure, movement patterns, and habitat use across the diverse oceanic system surrounding South Africa, as well as the level of genetic diversity remained unclear. Within the broader, evolutionary perspective the connectivity of the inshore population to other Bryde’s whale populations worldwide is unknown. ii This dissertation uses conservation genetic approaches combined with photo-identification methods to build our understanding of South Africa’s inshore Bryde’s whale population in two main areas. Microsatellite and mitochondrial DNA (mtDNA) markers were used to detect any evidence of population structure and connectivity while assessing current levels of genetic diversity on both local and global scales. Photo-identification data was then used to assess the movement patterns of individuals and formalize a national catalogue for the population. Genetic results show that these whales form one population with low, but significant, levels of genetic differentiation between the west and south coast of South Africa. Neutral nuclear genetic diversity was high which may be indicative of a larger effective population size whereas mtDNA diversity was low, suggesting potential sex-biased dispersal. Results also indicated genetic distinction between South African, Namibian, and Madagascan individuals but highlighted the need for stronger sampling within these regions. The lack of a stronger population structure was also reflected in photo-identification data, with identified individuals moving across different coastal regions, seemingly forming one population. However, many individuals were also re-sighted in the same general area which may relate to the low levels of genetic differentiation still evident within the population. On a global scale, mtDNA results indicated that South Africa’s offshore and inshore populations show connections to different oceanic regions. In addition, inshore individuals share a haplotype with an individual from the East Indian Ocean. These results provide preliminary insight into the origins of the South African Bryde’s whale populations and highlight the overall need for more representative sampling globally. Overall, the results of this study provide important insights into the demography and ecology of the South African inshore population which is key in the formulation of effective conservation strategies for the species.