Bluefin Tuna Attacks Basking Shark!!!

That’s not a headline you were expecting to read I bet!

One of our longer term scientific projects is looking at fish piloting with basking sharks. Our records have dated back to 2013 where a variety of species of fish, including some from the sub tropics, have been observed swimming beside basking sharks in the Hebrides. Similar behaviour to say, pilot fish with oceanic white tip sharks in the tropics.

In summer 2022 we had our first basking shark/bluefin tuna interaction, however an interaction between these two fish was taken to a whole new level this year.

We came across a basking shark feeding happily in calm seas, showing normal behaviour as we would expect. The shark was at a distance from us and Shane was filming with the drone. When suddenly the shark spooked, thrashed and dropped from the surface. Initially this was disappointing as we were hoping to watch it for a while.

However on the screen of the drone controller, Shane got excited and announced there was a tuna appearing to chase the basking shark! The shark re-surfaced again, thrashing and swimming round in a close circles. The footage appears to show the tuna repeatedly swimming/rubbing against the basking sharks tail. Of course, the shark isn’t particularly happy about this and is exhibiting a defensive position.

This behaviour carried on for 20min before our guide and swimmers dropped in to investigate the situation. We were able to capture some images of the shark, confirm the size, features & that it was a female. The other discovery was that there was also two piloting fish with the shark. There is discussion about the tuna using the shark to dislodge parasites, predator/prey shape relationship, or even the tuna trying to nibble at something. Tuna have exhibited similar behaviour in the tropics where they are seen to rub against sharks. As you might know sharks have skin which is very abrasive, constructed of dermal denticles, and it’s suggested the tuna us the sharks as a makeshift scratching post to rid themselves of parasites.

These behavioural instances are being reviewed for in-depth scientific study with hopefully full publication in the future. In the meantime, enjoy watching the spectacle. You can find more about our scientific projects here.