The carcass of a young humpback whale was found in the Farallone Islands on Sunday by a team of researchers from Point Reyes Bird Observatory Conservation Science (PRBO). The whale displayed large gashes on its side—most likely the result of strikes from a boat propeller. Officials with Gulf of the Farallones National Marine Sanctuary said the cause of the whale’s death is likely to remain a mystery, since the carcass will probably stay at sea. “It’s shark season,” said spokeswoman Mary Jane Schramm. “It’s extremely inadvisable to be doing anything like that in the water. Unless it washes up somewhere, we won’t have any clear idea of what happened.” Since humpback whales float when they die, it is possible that the propeller hit the juvenile after it died. “There are a lot of boats out on the water,” Schramm said. “If it was a large vessel, it may have gone unnoticed—depending on how long the boat was.” An unusual number of whales have been seen in shipping channels near the islands lately due to a large presence of krill. On Tuesday, PRBO reported 93 whales in the sanctuary.