Steven Spielberg considered a surprise twist ending for Jaws that involved multiple sharks - which would have been a mistake. Despite its famously tortured production, which went wildly over budget and schedule, Jaws would become the first true summer blockbuster in 1975. The film adapted the bestselling novel by Peter Benchley and later spawned three sequels of mixed quality.
Jaws also made Steven Spielberg a major director, and he would follow up with the likes of Close Encounters Of The Third Kind and Raiders Of The Lost Ark and much more in the years that followed. The movie dropped a lot of material from the source novel, including a subplot where Hooper had an affair with Chief Brody's wife. The ending of the book was darker too, with Hooper being eaten after the shark attacks his cage, while the Great White itself eventually succumbs to its many wound and dies just before it can eat Brody.
Spielberg considered this too anti-climatic a finale, but eventually decided on the notion of the shark biting down on a scuba tank and Brody shooting it to blow it up. Author Benchley himself was somewhat appalled by the concept, considering it too far-fetched. Instead, Jaws' finale is now seen as a rousing conclusion, capped off with Chief Brody's iconic "Smile you son of a bitch" quote as he fires the fatal round. The director also considered an alternate ending, where after Brody kills the shark, he looks around to see more fins coming his way.
While this might have made for a funny pitch, it would have been way too dark a note to end Jaws on. The story hadn't even hinted at there being more than one shark, so it would have been logically faulty. If more than one shark was stalking Amity, then how come only one - which is confirmed, considering it had three barrels attached to it - attacked Quint's boat throughout the story? It was also implied one such shark in the waters around Amity was slightly implausible, never mind multiple Great Whites.
More than anything, Jaws ends on such a note of triumph for Hooper and Brody, that attaching such a bleak coda would have spoiled the fun. Had Spielberg gone with the multiple sharks ending, it would have spelled death for Brody, since at that point he was stranded at sea with no hope of rescue. Thankfully, Spielberg decided better of the idea, which worked to the movie's benefit.