(CNN) A bottlenose dolphin was found dead with a deep head wound on a southwest Florida beach in May. Marine officials are offering a $38,000 reward for help track down its attackers.

Officials found the impaled dolphin stranded along Captiva Island, near Fort Myers. The fatal injury was probably from a spear-like weapon, the National Oceanic and Atmospheric Administration said Thursday.

The wound was 6 inches deep and ended at the dolphin's skull. It "completely punctured" the tissue in its path, NOAA bottlenose dolphin conservation coordinator Stacey Horstman said.

A necropsy revealed that the dolphin was alive when it was impaled, evident by hemorrhaging at the site of the wound, she said.

The dolphin was found in a "begging position," which isn't natural for wild dolphins, Horstman said. It's a learned behavior enforced when people feed or interact with the animals.

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