What Whales Do at Night

On a Saturday night in April Scott Kraus is getting ready to take out his boat from Sandwich, Mass., to spend the evening on Cape Cod Bay’s calm waters. Kraus, vice president of research at the New England Aquarium, and his two-member crew are not out for a leisure sunset cruise but are on a mission—they want to find out what North Atlantic right whales are doing at night. “It is like pulling an all-nighter in college, without the beer,” says Kraus, who has loaded an arsenal of militarylike night vision tools on the boat, including a high-resolution infrared camera, a light intensifying scope and a mirrorless, low-light digital camera. Kraus has been studying right whales for more than 35 years.

The whales come to this region in late winter and early spring to feed on copepods. Scientists have studied the whales for years but most of what they know about the behavior of these large mammals is derived from daylight observations. “Being out in a small boat amongst whales during the day is a lovely experience,” says Mark Baumgartner, an associate scientist at Woods Hole Oceanographic Institution. “Being out in a small boat trying to track a whale in darkness is slightly terrifying.”

With only 500 remaining worldwide, the North Atlantic right whale population is considered endangered and faces multiple threats. Nearly 83 percent of the whales have become entangled with fixed fishing equipment such as lobster gear at least once. Kraus has been experimenting with colored fishing rope that whales could potentially better see at night. “My concern is what these animals are seeing at night and what they are capable of avoiding,” he says.

The lack of technology and the practical challenges explain why whales’ nightlife largely remains a mystery. Thermal-imaging technology may hold the answer, however, at least when it comes to certain aspects of a whale’s life such as their behavior at the surface. Thermal sensors can detect the blow from a whale as it surfaces to breathe. “A whale is this big engine that is well insulated on the outside,” says Wayne Perryman, a biologist with the National Oceanic and Atmospheric Administration's Southwest Fisheries Science Center. “As it is swimming along and generating heat, it takes in a breath of air and holds it in for a long time,” he says. “When it blows that air out, it is much warmer than the background, and we can see the difference.”

The military has used infrared cameras for years, and in the early 1990s Perryman got the U.S. Navy to loan his team a thermal-imaging system to help count migrating gray whales day and night off the California coast. Perryman found the whales’ nocturnal migration rate was higher than the diurnal rate during the second half of the migration and suggested that males and females without calves spent more time socializing during the day and were slower in their migration. Because visual observers can only count migrating whales during the daytime, the overall population estimate may change if thermal-imaging systems count more whales during the night.

The early military instruments were expensive, unreliable and required a refrigeration unit. Today, as the technology is advancing, infrared cameras are commercially available at a fraction of the cost, offer higher resolution and are better adapted to field work. Researchers can now take the cameras from land stations to boats and helicopters. In 2014 Martin Stanley, a marine science consultant from Ocean Life Survey, tested a thermal-imaging technique to detect surfacing whales in real time from a vessel platform at distances that would allow large ships to avoid strikes day and night. The study was carried out in the Hauraki Gulf off the east coast of New Zealand’s North Island, where 15 Bryde’s whales had been killed by vessel strikes between 2006 and 2012. Stanley is investigating how these instruments can be installed on vessels to reduce collisions.

Scientists have also used digital acoustic recording tags on different whale species to understand underwater movements. These small suction-cup tags typically stay on the whales for a few hours during the day. Over the years some scientists managed to leave a few tags on whales overnight and were met with surprising results. In waters off the West Antarctic Peninsula, Ari Friedlaender, an ecologist with Oregon State University’s Marine Mammal Institute, found that humpback whales fed exclusively at night when the krill migrated vertically into shallower water and became an easier catch. During the day, when krill were deeper and harder to access, the humpbacks spent more time resting at the surface.

In the Gulf of Maine a team led by Susan Parks, a biologist at Syracuse University, found that humpback whales made a special noise similar to the ticking of a clock when they were bottom-feeding on sand lance in darkness. Researchers believe this sound may act as a "dinner bell" for nearby whales listening for signs of a successful hunt.

Off the coast of California Friedlaender and his colleagues found that unlike the humpbacks, blue whales feed during the day and rest at night, probably because the krill they eat becomes too dispersed for the whales to efficiently catch them. Unsurprisingly, blue whales are also vulnerable to ship strikes. “It is probable that these animals are being struck when they are up near the surface, as they are in harm’s way at night and ships can’t see them,” Friedlaender says.

Because tags stay on the whales for just a few hours and are expensive, scientists can only follow a limited number of individual whales at a time. “If you were able to go out at night and collect data the same way you do during the day on a boat, you could get a lot more data about a lot more different animals,” says Parks, who has been tagging right whales since 1998.

In Cape Cod Bay Kraus’s efforts are paying off. The infrared camera revealed temperature differences between healing and surrounding tissues in some of the right whales. The hot spots, located on the mammals’ heads, possibly indicated an infection, but those lesions were not visible to the eye in daylight. “That might mean that infrared cameras could be used as a health assessment diagnostic tool,” Kraus says.

Kraus made his most surprising finding when he took the camera to look at the whales from the air in a helicopter. As the whales were skim-feeding, they left a trail of cool spots on the ocean surface that the camera detected because of the temperature difference. After dark, those thermal footprints disappeared. “The conventional wisdom is that copepods migrate to the surface at nighttime and we believed that the right whales do a great deal of skim-feeding at night because it would be easy for them to get the copepods at the surface,” Kraus says.

Instead he found the whales stopped skim-feeding after dark. Copepods’ vertical movements can vary, and the whales may follow the food at depths that infrared cameras can no longer detect. This may make conservation measures even more difficult to implement. “Ships are at the surface and fishing gear tends to be close to the bottom,” Baumgartner says. “We want to know how long the whales stay in these two danger zones.”

This spring Baumgartner will test a brand-new tag on right whales in the Gulf of Maine that can stay on the animals for a longer period of time. “All whales are largely unknowable by us,” Kraus says. “What we are going to learn about whales at night is an extension of the kind of mystery that we are confronted with every day.”