TOKYO — Elevated levels of cesium still detected in fish off the Fukushima coast of Japan suggest that radioactive particles from last year’s nuclear disaster have accumulated on the seafloor and could contaminate sea life for decades, according to new research.

The findings published in Friday’s issue of the journal Science highlight the challenges facing Japan as it seeks to protect its food supply and rebuild the local fisheries industry.

More than 18 months after the nuclear disaster, Japan bans the sale of 36 species of fish caught off Fukushima, rendering the bulk of its fishing boats idle and denying the region one of its mainstay industries.

Some local fishermen are trying to return to work. Since July, a handful of them have resumed small-scale commercial fishing for species, like octopus, that have cleared government radiation tests. Radiation readings in waters off Fukushima and beyond have returned to near-normal levels.