The main orcas used for filming were trained animals from Marineland of the Pacific and Marine World Africa USA (Six Flags Discovery Kingdom), though artificial whales of rubber were used also. These models were so lifelike, animal rights activists blocked trucks delivering the animatronic whales to the set, thinking real whales were in them.
According to website Wikipedia, "producer Luciano Vincenzoni was first assigned to give the film a head start after being called by Dino De Laurentiis in the middle of the night in 1975. Upon admitting that he had watched Les dents de la mer (1975), Vincenzoni was instructed by de Laurentiis to 'find a fish tougher and more terrible than the great white'. Having had little interest in sea life beforehand, Vincenzoni was directed to killer whales by his brother Adriano, who had a personal interest in zoology. Filming took place largely in Newfoundland during the fishing season. Most filming took place in the town of Petty Harbour, about fifteen kilometers south of the capital city, St. John's."
Many movie posters for the film featured a long text preamble that read: "THE KILLER WHALE! The killer whale, is one of the most intelligent creatures in the universe. Incredibly, he is the only animal other than man who kills for revenge. He has one mate, and if she is harmed by man, he will hunt down that person with a relentless, terrible vengeance, across seas, across time, across all obstacles."
The Killer Whale was portrayed by an animatronic whale, filmed off the coasts of Malta and Newfoundland, and stock footage taken at Marine World in Redwood City, California. The stock footage Killer Whales were named Yaka (a female) and Nepo (a male). They had both been captured in 1969. Nepo died in 1980, while Yaka died in 1997.