As primal as it is topical, “Buoyancy” is a brutal minimalist thriller about human trafficking in the largely-illegal Thai fishing industry.

The violence is a grim slice of reality, the human suffering shockingly common and well-documented. Australia’s selection for contention in the Best International Feature category in last year’s Oscars is a harrowing story of a handful of men on a rust-bucket fishing boat — some of them the brutish armed and well-fed crew, others the starved, overworked forced labor they’ve “bought” to do the dirty work.

For his debut feature, writer-director Rodd Rathjen uses little dialogue and simple imagery as he patiently tells the story of a 14 year-old Cambodian runaway, Chakra (Sarm Heng) who would rather take his chances in factory work in Thailand that slave away in the family rice paddies back home.

The fact that he has no money to pay the Cambodian equivalent of a “coyote,” the smuggler, means he will “go to a different factory” across the border. When he and a family man (Mony Ros) whom he throws in with are hustled about a boat “to take you to the factory,” the older man smells a rat.

The punches he takes tells us he’s not wrong. The look he gives the kid — helpless and despairing, answers the question he asked the kid when they first spoke.

“Is it worth the risk?”

They’re shuffled onto a 45 foot trawler, barked at and threatened as they dredge up the meager harvest in the over-fished waters of the Golf of Thailand. “What’s this for?” (in Khmer and Thai, with English subtitles) the kid wants to know.

“Dog food.”

The boy is sure they’re just working off their transport into Thailand debt. The man knows better, and grows more bitter by the day. He, like others, looks for ways to escape.

“We will die before we make it back. This is the sea of DEATH!”

The kid? He starts kissing up to the sadistic captain (Thanawut Ketsaro), fetching the pick of the day’s catch for him and his two paid crewmen — well-fed brutes who share a pistol — still hoping and expecting they will do this for a month or so, and be dropped ashore.

The first slave to get sick and give up disabuses the kid of that. Or should. The grinning skipper tosses him overboard. It won’t be the last murder, and yes — Google it. This enslavement and murder at sea of Indochinese and Burmese slave laborers is commonplace in Thailand’s un-regulated and corrupt-cop-protected fishing industry.

Will Chakra adapt? Will there be a mutiny? Will the crew, some of whom don’t speak the same language, figure out the math and a way to defeat the thugs with the gun?

Rathjen gets a lot of movie out of this uncomplicated story, patiently showing Chakra’s evolution, his hardening, the captain’s wary eyes taking in the kid’s increasingly callous turn.

The performances in “Buoyancy” are unfussy, unadorned and spot on, with Heng standing out, embodying a child quick to learn, trusting, headstrong and somebody who learns to not turn his back on anybody else even as they start to figure out they should treat him the same. Ketsaro is every grinning, brawny bully in the flesh, the embodiment of a man capable of anything because he fears no resistance or repercussions.

The detail, the worn-out wooden boat that is the main location, is perfect. And the calming effect of the sea is utterly spoiled by the tension that’s always there. Daily routine aside, every encounter with the pitiless crew is fraught with peril, and the violence when it comes — is shocking, primitive and sadistic.

MPAA Rating: unrated, violence

Cast: Sarm Heng, Thanawut Ketsaro, Mony Ros 

Credits: Written and directed by Rodd Rathjen. A Kino Lorber release.

Running time: 1:32