On the trip in early February, the scientists were joined by 148 passengers and a flock of naturalists. For those paying hefty sums to see Antarctica, the 10-day voyage was like a floating science classroom. In the lounge, naturalists lectured on such pertinent topics as “Know Your Penguins,” “What Does Ice Tell Us About Climate Change?” and a Belgian expedition’s epic discovery of the Gerlache Strait.

Durban and Fearnbach gave several talks about their work in Antarctica, and how the health of killer whales is a barometer of the continent’s rapidly changing environment. Their research has been especially revelatory. Until as little as 20 years ago, scientists used to believe that Antarctic killer whales were all alike. But Durban, his colleague Bob Pitman and others took small skin samples of whales, analyzed their DNA, and ended up discovering that there are five distinct types, each with its own prey preferences, hunting techniques, and habitats. Durban and his colleagues are proposing that they may be separate species. This means that each type of killer whale will adapt to climate change in different ways—some likely better than others—largely depending on their food supply.

The enormous Type A’s, which are a striking black and white, feed on minke whales and perhaps elephant seals. The B2’s, which are the smallest and most plentiful, typically frequent the Gerlache Strait, munching on gentoo and chinstrap penguins and probably fish. The B1s, which are a dazzling gray and white, dine on seals. When they hunt, the clever whales band together and literally make waves to wash seals off ice floes. “They are my favorite animals,” said Durban during their talk.

It’s not exactly easy to spot killer whales in the Antarctic seas, where the horizon can be an endless expanse of whites and grays and mesmerizing teal-blue ice sculptures. The creatures are mostly underwater, and race through the seas at a brisk 55 miles per hour. When Durban and Fearnbach do spy them, or get a tip from the sharp-eyed crew on the bridge that whales are in sight, the scientists chase after them in a Zodiac—a small, black rubber motorboat—taking photographs and collecting data. The photos help them identify individual whales and keep close track of their health from year to year. They can also pinpoint where in the vast Antarctic waters the whales are most likely to be, and how stable the various populations are. Although they already know a lot, they want to learn more about what the insatiable animals eat. That will tell them if the warming environment is threatening their food sources.

There’s abundant enthusiasm for their research on the ship. Passengers and naturalists have contributed thousands of photographs of killer whales to the scientists. Counting their own photographs snapped from the Zodiac and from the Explorer’s decks and bow, they’ve amassed nearly 80,000 images of the little-observed animals.