When Australian director Sean Byrne got Nick Lepard’s script for “Dangerous Animals,” it appealed to him because it’s the kind of concept you could write on a napkin and sell. It’s about a serial killer who feeds people to sharks, and given that “Jaws” defined the high-concept blockbuster in 1975, it’s astonishing that it took half a century for a movie like this to materialize.

If that sounds fun to you, “Dangerous Animals” is the sum of its parts. It could’ve been something more, but it’s not really trying to be; it’s a fun 90 minutes in the water, far from enamored-with-its-own-badness fare like “Sharknado” but not nearly as artful as “Jaws.”

The best thing in the movie is the killer, Tucker (Jai Courtney). Scarred physically and mentally by a shark attack, he makes a living on Australia’s Gold Coast by taking tourists out to sea for caged shark dives that end with a closer encounter with the creatures than his clients expect. How he’s been able to dodge questions about all the missing tourists for so long is unanswered by the movie, though a goblin-like supplies man (Rob Carlton) acts as a sort of familiar.

Tucker kidnaps a surfer girl named Zephyr (Hassie Harrison), a foster kid with sound common sense and a fierce survival instinct. As she uses all her resources to wriggle loose from Tucker’s traps, we feel his excitement grow as he senses he might have found someone who’s a match for his sharks.

Meanwhile, Zephyr’s boyfriend Moses (Josh Heuston) waits dutifully at the shore like a widow waiting for her husband to return from sea until an opportunity for heroism arises, and he ends up stuck on the boat with Tucker. There are so many emergency dockings, aborted murders and false alarms that even Tucker’s intended victims look tired of it after a while.

Byrne has a good eye for the vagabond culture of Australia’s Gold Coast. The soundtrack is full of songs by garage rockers like the Regrettes and the Donnas, exactly the kind of bands an edgy alternative surfer born circa Y2K would blast from their hippie van.

Meanwhile, Tucker flexes a different and scarier kind of Aussie jollity. There are a lot of scenes of him rocking out to antipodean classics like Crowded House’s “Mean to Me” or Stevie Wright’s “Evie,” but these scenes don’t really work. He’s such a jovial guy’s guy we almost get the sense the filmmakers want to hang out with him in spite of his murderous intentions.

He’s more compelling when he gets wide-eyed and waxes poetic about the shark and its nature as an apex predator, a keeper of order amid the chaos of the ocean (“God’s down there,” he whispers, pointing to the water). He has a poet’s soul. Too bad he directed his creative energy toward ritualistic murder ceremonies rather than something more productive.

Zephyr doesn’t have much patience for poetry, not least when she’s at the end of a harness dangling 5 feet above a pool of chum, and she counters Tucker’s high-minded pretensions with barbs aimed at his manhood. At one point, she kicks Tucker’s camera into the water, something I suspect a lot of people reviewing this movie would have trouble doing.

The two-hander between a shrewd, working-class young woman and a killer who fancies himself an artiste brought to mind 2022’s “The Menu,” a movie that will be referenced in the annals of film history for decades to come as shorthand for a certain era of class-conscious horror movies.

There’s a subtext that Zephyr, not coming from money, will be missed a lot less than wealthy tourists like the English Heather (Ella Newton), whose scene in the harness is truly pitiful. Yet though there’s a well-observed bit of dialogue where one character says something shockingly insensitive to the other out of pure moneyed ignorance, the movie never really delivers on that theme.

There’s a more incisive version of the movie floating out there in theoretical space, as well as a more atmospheric one that shares Tucker’s wonder about the vastness of the ocean and the leviathans it contains, but these approaches might get in the way of the escapism “Dangerous Animals” delivers. If it has anything in common with the creatures of its title, it’s by being lean, efficient and good at its job.