What a wonderful way to get distracted from computer work . . getting a request to ID a live shark at the surface.
The video came from Scott Turton (below). The shark’s behaviour with the log helped with IDing the species. We have seen similar interactions with Salmon Sharks and logs while doing offshore surveys with Fisheries and Oceans Canada (DFO).
Note that Salmon Sharks belong in the ocean near British Columbia.
Other scientists have also thought this behaviour may be about Salmon Sharks removing parasites. See this news article “Salmon shark treats scientists to ‘surprising’ behaviour off B.C. coast.” It includes another video of a Salmon Shark / log interaction and Dr. Cherisse Du Preez’s interpretation including: “We noticed it started brushing itself along this log over and over again,” Watts said in a video released by Fisheries and Oceans Canada. “It looked like it was aiming for this big clump of barnacles,” Du Preez said. “It would heave its body out of the water and slide at the log.” The shark had parasites visible on its dorsal fin. “It’s really interesting to see these logs out at sea may be scratching posts for them to rid themselves of parasites”.
Du Preez et al have published their observations of two such interactions in Canadian Field- Naturalist (2023) “Salmon Shark (Lamna ditropis) scratching behaviour using floating anthropogenic debris“.
See below for DFO’s “Sharks of British Columbia“.