The whale was found emaciated and dying Sept. 24 in Allenhurst. The cause of death was initially unknown but Dr. Julie Engiles, an assistant professor of pathology at the University of Pennsylvania Veterinary School, discovered a bullet lodged in the animal's head during a necropsy, the Philadelphia Daily News reported Thursday.
The .30-caliber bullet had bounced around inside the whale's head without killing it.
"It basically starved to death because it was in too much pain to eat," said Bob Schoelkopf, founder of the Marine Mammal Stranding Center in Brigantine.
Authorities said they believe the incident occurred too far offshore for the shooter to be on a recreational boat. Investigators have handed out fliers at marinas hoping to get someone within the fishing community to come forward with information.
Paul Watson, of "Whale Wars" on the Discovery Channel, has personally donated $10,000 toward the reward, saying he believes the shooter probably viewed the whale as fishing competition.
The punishment for intentionally killing a whale is as much as a year in prison and a $100,000 fine.