The ama are Japan’s fisherwomen, free divers who retrieve abalone, sea snails and other ocean products (they’re best known for their pearl fishing) out of the shallows without using oxygen tanks. Portuguese documentarian Cláudia Varejão immerses herself in the daily rhythms and rituals of one group, filming them at home and at work as they go about raising kids, singing karaoke and swimming to the bottom of the sea.

Made in the low-key, vérité style associated with directors such as Fred Wiseman (Titicut Follies, National Gallery), Varejao favours an austere approach that relies on long, unblinking takes, uses no music that doesn’t occur within the action itself and no subtitles that clarify who’s who. Indeed, there are no explanations at all, leaving the viewer to work out why, for instance, the women wear both modern diving suits and traditional linen headscarves over their waterproof balaclavas. Much screen time is devoted to watching the subjects wrapping, folding and tucking these bits of white cloth, a kind of origami that’s seemingly both symbolic and practical, like the tying up of the laces on a ballet slipper. Out of the water, they favour dress that similarly mixes modern and traditional, with regular trousers and blouses below the neck and white bonnets with deep brims on their heads, like in the The Handmaid’s Tale.

This kind of unfiltered anthropological study can be mesmerising and there are some lovely sequences here, not just of the women diving in the olive-green depths but also moments where they’re just hanging out with their families, playing with fireflies or making supper. But some viewers may find it frustrating that we never hear them discuss their lives or even learn their names properly, as if we are just ghosts, weaving among them while they go about their business. It’s a style of film-making that’s as traditional and in its way mannered as the head wraps and diving techniques that are being observed.