A shark killed a man in Hawaii on Monday, as authorities struggle to understand an unusually high streak of attacks in the state this year.

The man, identified as 57-year-old Patrick Briney of Stevenson, Wash., was fishing from a kayak off the island of Maui with his legs dangling from the side when the shark bit one of his feet. A companion paddled over, tied a tourniquet around the wound and flagged down a tour boat that brought him to shore, but Briney died of his injuries, Hawaii News Now reports.

The incident is the 13th shark attack reported in the state so far this year — and the eighth in Maui. Authorities said there has been an average of just four unprovoked shark attacks each year over the past two decades.

“We are not sure why these bites are occurring more frequently than normal, especially around Maui,” the state’s Department of Land and Natural Resources said in a statement, adding that it is conducting a two-year study into shark behavior in the area.

A 20-year-old German tourist was killed in August when a shark severed her arm as she was snorkeling off of Maui.

[Hawaii News Now]