Interchange of Southern Hemisphere humpback whales across the South Atlantic Ocean.

The cosmopolitan distribution of humpback whales (Megaptera novaeangliae) is largely driven by migrations between winter low-latitude breeding grounds and summer high-latitude feeding grounds. Southern Hemisphere humpback whales faced intensive exploitation during the whaling eras and recently show evidence of population recovery. Gene flow and shared song indicate overlap between the western (A) and eastern (B1, B2) Breeding Stocks in the South Atlantic and Indian Oceans (C1). Here, we investigated photo-identification evidence of population interchange using images of individuals photographed during boat-based tourism and research in Brazil and South Africa from 1989 to 2022. Fluke images were uploaded to Happywhale, a global digital database for marine mammal identification. Six whales were recaptured between countries from 2002 to 2021 with resighting intervals ranging from 0.76 to 12.92 years. Four whales originally photographed off Abrolhos Bank, Brazil were photographed off the Western Cape, South Africa (feeding grounds for B2). Two whales originally photographed off the Western Cape were photographed off Brazil, one traveling to the Eastern Cape in the Southwestern Indian Ocean (a migration corridor for C1) before migrating westward to Brazil. These findings photographically confirm interchange of humpback whales across the South Atlantic and Indian Oceans and the importance of international collaboration to understand population boundaries.

Seascapes of fear and competition shape regional seabird movement ecology.

Fear effects of predators on prey distributions are seldom considered in marine environments, especially over large spatial scales and in conservation contexts. To fill these major gaps, we tested the Seascape of Fear Hypothesis in the Benguela marine ecosystem off South Africa. Using electronic tracking data, we showed that Cape gannets and their predator, the Cape fur seal, co-occurred in daytime and competed with fisheries within coastal areas. At night, gannets are particularly vulnerable to seals, and 28% of the birds returned to the safety of their breeding colony. The remaining 72% slept at the sea surface, but shifted to offshore areas with lower seal attendance, reducing predation risk by 25%. Overall, our integrative study demonstrates how fear and competition shape the seascape of threatened Cape gannets within a marine environment perturbed by climate change and overfishing. Such knowledge has strong implications for the design of marine protected areas.

Disentanglement of Cape fur seals (Arctocephalus pusillus pusillus) with reversible medetomidine-midazolam-butorphanol.

Anaesthesia in pinnipeds is considered a much higher risk than in most terrestrial mammals because of their frequent proximity to water and physiological and anatomical adaptations related to diving, which also influence their anaesthesia management. Anaesthetising and immobilising entangled seals does not allow for selection of animals that are at a safe distance from the water's edge. Medetomidine-midazolam-butorphanol (MMB) sedation was trialled on eight entangled Cape fur seals (CFS) (Arctocephalus pusillus pusillus) to determine if it was safe to use on animals that entered the water post-darting. The MMB was given at an estimated dose of 0.03 mg/kg, 0.2 mg/kg and 0.2 mg/kg, respectively, via remote darting. Sedation was reversed with intramuscular atipamezole (0.15 mg/kg) and naltrexone (0.4 mg/kg) to antagonise the effects of medetomidine and butorphanol, respectively. Moderate sedation was achieved in six animals. Six of the animals entered the water after being darted. There was a single mortality and a single animal that was too lightly sedated for capture. The preliminary results indicate that MMB produces suitable sedation for disentanglement of CFS. Additionally, MMB might be suitable for application to field-based biological research.

Humpback whale "super-groups" - A novel low-latitude feeding behaviour of Southern Hemisphere humpback whales (Megaptera novaeangliae) in the Benguela Upwelling System.

Southern Hemisphere humpback whales (Megaptera novaeangliae) generally undertake annual migrations from polar summer feeding grounds to winter calving and nursery grounds in subtropical and tropical coastal waters. Evidence for such migrations arises from seasonality of historic whaling catches by latitude, Discovery and natural mark returns, and results of satellite tagging studies. Feeding is generally believed to be limited to the southern polar region, where Antarctic krill (Euphausia superba) has been identified as the primary prey item. Non-migrations and / or suspended migrations to the polar feeding grounds have previously been reported from a summer presence of whales in the Benguela System, where feeding on euphausiids (E. lucens), hyperiid amphipods (Themisto gaudichaudii), mantis shrimp (Pterygosquilla armata capensis) and clupeid fish has been described. Three recent research cruises (in October/November 2011, October/November 2014 and October/November 2015) identified large tightly-spaced groups (20 to 200 individuals) of feeding humpback whales aggregated over at least a one-month period across a 220 nautical mile region of the southern Benguela System. Feeding behaviour was identified by lunges, strong milling and repetitive and consecutive diving behaviours, associated bird and seal feeding, defecations and the pungent "fishy" smell of whale blows. Although no dedicated prey sampling could be carried out within the tightly spaced feeding aggregations, observations of E. lucens in the region of groups and the full stomach contents of mantis shrimp from both a co-occurring predatory fish species (Thyrsites atun) and one entangled humpback whale mortality suggest these may be the primary prey items of at least some of the feeding aggregations. Reasons for this recent novel behaviour pattern remain speculative, but may relate to increasing summer humpback whale abundance in the region. These novel, predictable, inter-annual, low latitude feeding events provide considerable potential for further investigation of Southern Hemisphere humpback feeding behaviours in these relatively accessible low-latitude waters.