The Tuna Herders

Climate change has forced these Galápagos sea lions to turn to a new food source. Since they can't outswim their prey, they use wits and teamwork instead.

The water churns in a chaotic flurry of fins and flippers. Hungry onlookers hover, swoop, and scurry, hoping to get in on at least the final stages of the action. There are deep growls, sprays of blood, and flashes of iridescent blue and yellow scales against black volcanic rock. It’s a scene so wild and unprecedented that when local fishermen first started reporting it a few years ago, their accounts might have been dismissed as unbelievable. But this is the Galápagos, a place where remarkable wildlife sightings are so commonplace that practically anything seems possible. Here, in two different fishhook-shaped coves on the islands of Isabela and Fernandina, Galápagos sea lions (Zalophus wollebaeki) were rumored to be successfully hunting yellowfin tuna (Thunnes albacares)—fish that can easily swim twice as fast as the sea lions, even when the marine mammals are lunging at top speed. When acclaimed wildlife photographer and naturalist Tui De Roy heard from a game warden that the rumors appeared to be true, she immediately started planning her next visit to the islands.

Having grown up in the Galápagos, where she’d spent countless hours watching the islands’ sea lions play beach ball with puffer fish, sink dinghies for fun, and taunt Sally Lightfoot crabs with their whiskers, De Roy knew better than most how intelligent and social these animals are. But even she was floored when she first saw a group of sea lions herd a handful of 50-pound tuna out of the water and onto the forbidding shore. “Even though I’d been told what they were doing,” says De Roy, “when I actually saw it I thought, ‘I can’t believe this is happening. I just can’t believe it.’”

While the sea lions’ ability to execute such a feat may have surprised De Roy, their drive to do so certainly didn’t. Over the past 30 years, the population of Galápagos sea lions has declined precipitously, from at least 40,000 individuals to fewer than 15,000. The charismatic mammals have faced a number of threats in recent decades, but by all accounts the most significant has been food scarcity. Pacific sardines (Sardinops sagax), small-bodied baitfish that need relatively cool water in order to spawn, were once the preferred meal for Galápagos sea lions because of their abundance and high fat content. But as the waters around the volcanic islands have warmed, and the frequency and severity of El Niño events have increased, sardines have become harder and harder to find. Without this rich food source, the sea lions are struggling to survive—especially during El Niño years, when up to 100 percent of the pups, 50 percent of the yearlings, and a substantial number of adults may die. It’s little wonder that some Galápagos sea lions have gotten creative in their quest for food.

Tuna, which are among the fastest fish in the sea, are much harder to catch than sardines. But because of both their heft and their similarly high-fat flesh, they are also a much more valuable prize. “I’ve seen big bull sea lions eat two thirds of a 50-pound tuna in one sitting,” says De Roy. And when the herding goes well, they might repeat that meal three or four times a day. (Perhaps that’s why the older bulls that frequent these two coves are among the biggest De Roy has seen in the Galápagos in recent years.) However, success is far from guaranteed. For these sea lions, pulling off such a high-stakes hunt requires three things: patience, teamwork, and exactly the right volcanic formations.

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