Elevated radiation levels in fish caught near Japan's damaged Fukushima nuclear plant suggest low-level leaks are still occurring, a marine scientist says.

Marine chemist Ken Buesseler of the Woods Hole Oceanographic Institution in Massachusetts said official Japanese data on cesium levels in fish, shellfish and seaweed collected near the crippled nuclear plant showed signs of nuclear contamination, Sky News reported Friday.

That could be due to low-level leaks from the facility damaged in the March 201 earthquake and tsunami or contaminated sediment on the ocean floor, he said.

While radiation levels in most fish caught off Japan's northeast coast are well within safety limits, he said, some fish caught near Fukushima are considered unfit for consumption under Japanese regulations.

The highest cesium counts from the damaged plant are consistently being detected in bottom-dwelling fish such as cod and skate.

"To predict how the patterns of contamination will change over time will take more than just studies of fish," Buesseler said.

"What we really need is a better understanding of the sources and sinks of cesium and other radionuclides that continue to drive what we're seeing in the ocean off Fukushima."