Basking Sharks Don’t Just Skim the Surface — They’re Diving Nearly a Kilometer Down to Eat

Did you know the second-biggest fish in the ocean has been hiding a secret feeding habit right under everyone’s nose?

Basking sharks are usually pictured cruising near the surface, mouths wide open, filtering plankton out of the water. That image isn’t wrong — it’s just incomplete. New research from the Woods Hole Oceanographic Institution shows that during their long winter migrations, these endangered sharks dive far deeper than anyone expected: down to nearly 1,000 meters, into a zone of the ocean that gets almost no sunlight at all.

Here’s how scientists found out. Researchers analyzed more than 8,000 days of tracking data from 37 basking sharks tagged near Cape Cod, following their journeys south to the Sargasso Sea and Caribbean each winter. Instead of fasting along the way, as scientists had long assumed migratory sharks did, the data showed something different: these sharks were repeatedly diving to the lower edge of the ocean’s “twilight zone,” a stretch of water between 200 and 1,000 meters down that’s cold, dark, and low in oxygen.

“Reaching depths of 800 to 1,000 meters is physiologically demanding,” said Jaida Elcock, a doctoral candidate in the MIT-WHOI Joint Program and the study’s lead author. “Yet these sharks repeatedly dive into the secondary deep scattering layer, a resource that most large pelagic predators cannot exploit.”

Why they’re doing it: Researchers believe basking sharks are hunting small fish and squid that live in that deep layer — food that’s simply too small or too deep for most other big ocean predators to bother with. It suggests these sharks aren’t just riding out their migration on stored energy; they’re actively feeding the whole way, tapping into a food source almost nobody else can reach.

Why it matters: Basking sharks were hunted heavily for their oil-rich livers for centuries and still haven’t fully recovered, landing them on the IUCN’s endangered list. Understanding exactly where and how they feed is critical groundwork — especially as commercial interest grows in fishing the twilight zone itself for the small fish and squid that live there.

A creature this big, doing something this demanding, in a part of the ocean most of us will never see. That’s worth a little more wonder next time you spot one near the surface.

Sources: Woods Hole Oceanographic Institution