Lifeguards found the male sea lion injured but still alive on Bolsa Chica State Beach on Aug. 7. According to the National Oceanic and Atmospheric Administration's Office of Law Enforcement, an exam revealed that the animal had a fresh gunshot wound in its back.
It was rescued by the Pacific Marine Mammal Center, but the animal died from its injuries the following day.
Law enforcement is now actively seeking information on the person who shot the animal and any other details surrounding its shooting. A $20,000 reward is being offered for any information.
"The Marine Mammal Protection Act prohibits the harassment, hunting, capturing, or killing of sea lions and other marine mammals," officials said. "However, the law allows for non-lethal methods to deter marine mammals from damaging private property, including fishing gear and catch, if it does not injure or kill an animal."
Like all marine mammals, the California sea lion is protected under the Marine Mammal Protection Act which has helped their population to continue increasing since at least 1975, after protections were put in place under the MMPA.
"California sea lions are easy to view in the wild, but this puts them at higher risk of human-related injuries and death. Feeding or trying to feed them is harmful and illegal, because it changes their natural behaviors and makes them less wary of people and vessels," the NOAA said. "They learn to associate humans with an easy meal and change their natural hunting practices-for example, they take bait (and) catch directly off fishing gear. Sometimes they fall victim to retaliation (such as shooting) by frustrated boaters and fishermen."
Anyone with information about the sea lion shooting should call NOAA's 24/7 enforcement hotline at (800) 853-1964.
ABC News contributed to this report.