Influence of water temperature, body size, condition, and gull-inflicted lesions on heat loss in southern right whales in Península Valdés, Argentina

Southern right whales (Eubalaena australis, SRWs) are well adapted to cold waters due to their large body size and thick blubber. Each year, they migrate from high-latitude feeding grounds to warmer breeding grounds where they give birth. To assess thermal benefits of this migration, we modelled the effects of body size, condition, and water temperature on heat loss. Using unmanned aerial vehicle photogrammetry at the Península Valdés (PV) calving ground in Argentina, we measured body length, volume, condition, and surface area of living SRWs. Blubber thickness was predicted from a blubber-mass model and validated using necropsy/catch data. Sensible heat loss was estimated using a model incorporating blubber thermal conductivity and body temperature, while respiratory heat loss was based on respiration rate and tidal volume models. We compared heat loss in PV to South Georgia/Georgia del Sur (SG/GS), a key feeding ground. Body size had a strong positive effect on both heat loss types, but mass-specific loss decreased as surface-area-to-volume ratio declined. Increased body condition reduced sensible heat loss. Migration from SG/GS to PV reduced calf heat loss by 26% during early lactation. However, total heat loss remained low relative to field metabolic rate (FMR), indicating limited thermoenergetic benefit from migration. Only at poor body condition (<-0.35) did heat loss exceed FMR, threatening survival. Notably, gull-inflicted lesions significantly increased heat loss in small and poorly conditioned calves, but had no effect on larger or better-conditioned calves. These findings highlight body condition as a key regulator of heat loss in baleen whales.