One of the largest threats to basking sharks is vessel strikes. We recently posted a photograph of a shark that had evidence of propeller damage.
On August 19, 2012 the New England Aquarium spotted a basking shark with a very unusual dorsal fin. At first, we thought it might have suffered propeller damage in the past, but upon closer inspection, we think the marks and grooves might have been caused by an entanglement. These wounds have healed and there was no trace of any lines, but the interaction has left its permanent mark on the shark.