Formation and healing of pectoral fin bite marks in a female whale shark Rhincodon typus

Biting behavior by males during mating has been widely documented in elasmobranchs; however, its characteristics in the whale shark, Rhincodon typus , remain poorly understood. In this study, we recorded a pectoral fin biting event by a male directed toward a female at Okinawa Churaumi Aquarium on May 12, 2020, using surveillance cameras. Subsequently, we monitored the healing process of the resulting scars through underwater observations and post-mortem tissue analyses over 13 months. The bite marks initially appeared as open wounds, which closed within approximately 4 weeks, and were followed by the regeneration of dermal denticles and progressive melanization that persisted for more than 13 months. Additionally, 523 bite marks (233 dorsal and 290 ventral) were digitized and analyzed using orientation-based analysis and Gaussian mixture model clustering. Three distinct clusters were identified among bite marks attributed to this single documented interaction event, suggesting that variation in jaw orientation or repositioning may have occurred during the event. In this individual, wound closure occurred within approximately 4 weeks, providing a preliminary reference for the temporal interpretation of recent injuries, while melanized scars remained externally visible for more than 13 months. These observations provide a preliminary framework for evaluating pectoral fin bite marks as potential indicators of male–female interaction history in whale sharks, although validation across additional individuals is required. These findings provide a foundation for future studies integrating behavioral observations and scar-based assessments in both ex situ and in situ contexts.