Amity has been covering up shark attacks for years.It seems a strange coincidence that the first summer Brody serves as chief of police in Amity would see a rogue shark just happen to wander into Amity's waters. And when Brody's being pressured to report Chrissie's death as a boating accident, the phrase "It's happened before" seems ominous. Also, that tiger shark they catch is a man eater and "extremely rare for these waters"; another coincidence that there were two rare maneating rogues in those waters and they caught the wrong one. Or was the tiger shark planted to get caught and calm people back down? Perhaps when the shark first appeared, the town lost a fortune and a number of lives trying to kill it; eventually, to protect tourist dollars, they just developed a cycle of keeping deaths mysterious and then, when that eventually fails, "killing" the shark. It was just the unfortunate combination of a series of unusually high-profile attacks and a meddlesome new chief of police that finally made the system fail.
The shark was mutated by the Hiroshima bomb.Exposure to the massive radiation not only gave the shark a prolonged lifespan, but also made it bigger, faster, and definitely stronger (strong enough to drag flotation barrels underwater). Also, Quint was the only surviving crew member of the USS Indianapolis. Seeing as how the crew were responsible for delivering the Hiroshima bomb, Steven Spielberg wanted to give Quint a Karmic Death by having the shark kill him during the climax.
The shark and all the sharks in the sequels are suffering from a type of slow-acting "fish-rabies".While it's true that sharks have gone on month-long maneating sprees in the past, it's unlikely that so many sharks would be like this. It's possible that, in the Jaws Universe, a disease somewhat similar to rabies is going through the Great White population, causing them to become highly aggressive.
The shark is an escaped minion of a James Bond villain.James Bond thought the shark died when he destroyed the island fortress of the shark's master.
Martin Brody, the Sheriff of Amity Island, is the nephew of Marcus Brody, the main patron for Indiana Jones in Raiders of the Lost Ark and The Last CrusadeNo reason other than that it'd be cool.
The shark is a zombie sharkTo be precise, it's the shark from Lucio FulciÂ's Zombi 2. This fight led to the infection.
The shark doesn't exist. Jaws was an In-Universe propaganda film.The purpose of the film was to scare the residents of Amity Island into avoiding the beaches, where an old man lives who remembered life before the government takeover and is willing to tell anyone...
Bruce is the juvenile form of a shark-based Kaiju.See the Hiroshima thing above.
The shark is a baby Megalodon, an enormous but supposedly extinct species of shark.Which would explain why it's both so large and so strong. In the book Meg, a baby Megalodon is mistaken for a great white shark. They aren't extinct. They just usually spend their time too deep for humans to find. There's a breeding population nearby, and juveniles are taking advantage of the shallower waters near the town until they're big enough to hold their own against the adults. That's why there's enough sharks for the sequels.
The fifth movie, titled "Jaws 4", will star a Planet Eater sized shark!"How the heck are we going to revive the Jaws series?" "We're gonna need a bigger shark."
The sharks are part of an extortion racket run by the Deep OnesThey've heard that the island has fallen on hard times, and they are looking to start an outpost there. They organize the shark attacks as part of a ploy to drive the townsfolk into desperation so that they'll agree to their terms while carrying on a blood feud with the Brody family. Their latest plan will involve the aforementioned "bigger shark". This also makes sense, as the film is set in New England.
It will be retconned that the sharks are being sent by a clan of shark-people, some of which live amongst humans.They're ticked off, and so they use their non-voodoo Shark Powers to get the humans to keep away from the oceans. Only they
The shark is actually a robot.From the future.
Brody is actually Buddy Rosso from The French ConnectionBrody tells he used to be a cop in New York and how people got killed all the time. He got fed up with it, but being an undercover cop, he wanted to keep his identy secret and thus changed his name and moved far away to Amity.
The entire movie is the shark having a dream.It was hurt by a fisherman once, and so it imagines a nice little revenge fantasy against the land-dwellers. Then it drifts off, starts to sleep-swim, and whangs its mouth painfully on a drainpipe, leading to the "exploding metal tank in the teeth" image just before it wakes up. And yes, contrary to Urban Legend, sharks do sleep.
Only the first film occurred: All the sequels are Brody having increasingly surreal nightmares from the events of the first film.That's why the sequels got progressively stupider, the edge to Brody's PTSD is wearing off.
The shark was a Time Lord.Somebody had to say it. Explains how it kept coming back for the Brodys.
The Shark is an ancient god that Amity Worshipped before it became modern.The Shark is really just an ancient islander god, that Amity worshipped. It provided wealth and resources for them in exchange for sacrifices, specifically ones that would swim in the beach. When Amity became modern, the Island started to disbelieve said god and deny it sacrifices. In revenge, the shark would ruin their July 4th summerfest every year and rather than take responsibility for their actions, the Islanders decided to cover it up like it never happened. Then Martin Brody defeated it, so in addition to it's traditional ruining, the shark goes after the Brodys as well.