A ship is repairing or replacing 10 ocean buoys in the Pacific Tsunami Warning System after an environmental group called attention to the "large dead zones" in the ocean.

Jeff Ruch, executive director of the Public Employees for Environmental Responsibility, says the group's scientists worry that the tsunami warning system is like a fire alarm that can't ring.

But Charles "Chip" McCreery at the Pacific Tsunami Warning Center in Ewa Beach says he can still monitor data from adjacent buoys and other sources to compensate.

National Oceanic and Atmospheric Administration officials say they needed to wait until rough winter seas passed before starting repairs.

One buoy has already been fixed, and a NOAA ship is heading west to replace five more.