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Beaked whales may frequent a seabed spot marked for mining

A series of seafloor grooves look a lot like those made by the deep-diving marine mammals

DEEP DIVER Beaked whales, such as this Cuvier's beaked whale (Ziphius cavirostris), may have made the shallow seafloor depressions seen near a region designated for seabed mining.

Rogue nations that want to hide nuclear weapons tests may one day be thwarted by antineutrinos. Whales may have made their mark on the seafloor in a part of the Pacific Ocean designated for future deep-sea mining. Thousands of grooves found carved into the seabed could be the first evidence that large marine mammals visit this little-explored region, researchers report August 22 in Royal Society Open Science. If deep-diving whales are indeed using the region for foraging or other activities, scientists say, authorities must take that into account when planning how to manage future mining activities.

The Clarion-Clipperton Fracture Zone, or CCZ, is a vast plain on the deep seafloor that spans about 4.5 million square kilometers between Hawaii and Mexico. The region is littered with trillions of small but potentially valuable rocky nodules containing manganese, copper, cobalt and rare earth elements. Little is known of the seafloor ecosystems in this region that might be disturbed by mining of the nodules. So several research cruises have visited the area since 2013 to conduct baseline assessments of what creatures might live on or near the seafloor.

A 2015 cruise led by Daniel Jones of the National Oceanography Centre Southampton in England is the first to find evidence that suggests that live whales may have dived down to visit the seafloor in the region. Using an autonomous underwater vehicle to scan the seafloor at depths from 3,999 meters to 4,258 meters, Jones' team found 3,539 grooves in all. These depressions tended to be arranged into sequences of as many as 21 grooves, spaced six to 13 meters apart. It's difficult to determine exactly when the marks were made, because sediment settles very slowly through the deep water to fill in seafloor depressions. The oldest marks were made within the last 28,000 years, the team estimates. But some newer tracks appear to overlap older tracks. No known geologic mechanism could produce the grooves, report Jones and his National Oceanography Centre colleagues, deep-sea ecologist Leigh Marsh and marine geoscientist Veerle Huvenne. But living creatures might: Some scientists, including biologist Les Watling of the University of Hawaii at Manoa and marine ecologist Peter Auster of the University of Connecticut at Avery Point, previously suggested that certain deep-diving whales, known as beaked whales, can make such markings as they use their beaks to forage for food hiding in the seafloor.

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