The center must dispatch ships to service the buoys, whose mooring lines often get tangled in fishing lines or are severed by collisions with boats.

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The activists travelled by inflatable speedboats from a nearby Greenpeace vessel and used ropes and ladders to climb up mooring lines, the group said in a statement.

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As daybreak approached, the Mobile Fire-Rescue Department's fireboat Phoenix was moving toward the barges, checking to make sure their mooring lines were secured, the fire department said in a statement.

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