Salmon Shark (Lamna ditropis) scratching behaviour using floating anthropogenic debris

Abstract

Observations of animal behaviour in the open ocean are relatively rare. However, while conducting surveys in the Northeast Pacific in the summers of 2019 and 2021, we encountered two Salmon Shark (Lamna ditropis) using floating anthropogenic debris to scratch their bodies. We captured the activity with aerial (drone) and underwater cameras. We document and describe this novel behaviour as high energy, high impact, repetitive, fast, and long lasting (e.g., every ~15 s for >20 minutes). We explore these observations in light of traditional ecological knowledge and scientific literature.