An update on the occurrence of humpback whale (Megaptera novaeangliae) super-groups on the West Coast of South Africa

Abstract

Humpback whale (Megaptera novaeangliae) super-groups, comprising 20+, tightly aggregated, feeding individuals, form during the austral summer in the southern Benguela ecosystem off the west coast of South Africa. This phenomenon, observed since 2011, is thought to be linked to increased productivity from positive chlorophyll-a anomalies associated with reduced water export in the area, and possible changes in associated trophic structures. Oceanographic conditions vary over time and space, so that super-groups occurrence can also be highly spatially variable. In this study, we investigate the spatiotemporal patterns of super-groups by compiling records from scientific surveys, whale-watching operators, and citizen science reports between July 2015 and June 2022. In total, sightings of 239 humpback whale super-groups were collated for this period, considering sighting with best estimate group size of 20 individuals or more. Super-groups appeared from August to April, peaking between October and January, and the seasonality of their occurrence seems to have expanded in comparison to previously published data. Although the effect of inconsistent effort throughout the study is unknown, results identify the overall regularity and spatiotemporal patterns of super-group formations, while highlighting the need for improved, collaborative and systematic data collection to gain deeper insights into this mid-latitude feeding phenomenon.