Cetacean observations during the RESILIENCE cruise aboard the RV Marion Dufresne (19 April – 22 May 2022)
The RESILIENCE cruise was a multidisciplinary cruise aimed at investigating the links between oceanographic features, such as eddies, and marine life, ranging from phytoplankton to megafauna. This was an international collaborative cruise, involving scientists from France and South Africa, to build on the existing knowledge and understanding of the biological and oceanographic features of the Mozambique Channel and Agulhas current.
The cruise departed Reunion Island on the 19 April 2022, transiting south of Madagascar and up into the Mozambique Channel, where fine scale sampling of a large eddy took place over 4 days. The ship then headed south to the KwaZulu Natal coast of South Africa in pursuit of more eddies, before transiting back to Reunion Island and docking on the 22 May 2022. This presented a valuable opportunity for marine mammal observations in otherwise hard-to-reach places for the average MM scientist’s budget.
Fortunately, the cruise leaders and partner organisations welcomed the opportunity to collect megafauna data and provided space for a marine mammal team. This included Bernard Rota, from Globice (Reunion Island), Dr Gwenith Penry, marine mammal scientist (CMR Nelson Mandela University), Prof Amanda Lombard (SA Research Chair in Marine Spatial Planning, CMR NMU), as well as two drone operators from the NMU Autonomous Operations Unit. Prof Lorien Pichegru (NMU) and Prof Peter Ryan (UCT) were also on board to record seabirds and document macroplastics.
For the MMO team, the primary aim was to record species occurrence along the track line. The survey design did not lend itself to data collection for abundance estimates and owing to the fine scale ‘radiators’ needed for eddy-sampling, we spent several days in one area. During the cruise planning phase I was in touch with Violaine Dulau from Globice to find out how the observations made could best serve the wider SWIO database. Violaine informed me of the opportunistic large-scale surveys in the SWIO that Globice had started to coordinate, and therefore to standardize the data, it seemed sensible to use the same datasheets as previously used on the opportunistic surveys, and to send Bernard on the cruise as a second experienced observer.
Overall, the number of cetacean sightings was low, possibly due to a combination of unfavorable sea conditions and because the cruise took place before the main northward migration of humpback whales. A total of 35 marine mammal sightings, comprising 9 different species, were made. The team conducted observations between sunrise and sunset and on-effort observations totalled over 260 hours.
The species recorded included Risso’s dolphins (Grampus griseus ), short-finned pilot whales (Globicephala macrorhynchus ), Sperm whales (Physeter macrocephalus ), Common bottlenose dolphins (Tursiops truncatus ), Common dolphins (Delphinus sp ), Spinner (Stenella longirostrus ), Striped (Stenella coeruleoalba ), and Spotted dolphins (Stenella attenuata ), and Indo-Pacific bottlenose dolphins (Tursiops aduncus ). Unidentifiable cetaceans included a single beaked whale (surfing the swell < 5m from the ship but never surfaced), a small group of blackfish (possibly false killer whales), and 3 baleen whales.
The sightings will be overlaid with environmental data collected by the oceanographic teams and contribute to further understanding of the importance of ocean fronts to marine megafauna.
The team would like to thank the PI’s (Jean-Francois Ternon, Pierrick Penven, and Margaux Noyon) for inviting us to participate in the cruise; Conservation International, the Belmont Forum, and Prof Lombard’s Research Chair (SARChI) for funding support; the captain and crew of the Marion Dufresne for supporting our work in any way they could; students of the Floating University for help with observations; and the South African authorities (DFFE and Ezemvelo KZN Wildlife) for issuing permits at short notice.