How elephant seals use body fat to navigate a lightscape of fear

Science · Published 7 October 2026 Swipe more like this →

In short: Every May, female elephant seals embark on a 6,000-mile journey across the North Pacific. To survive, they must master a high-stakes calculation: when to hunt for calories and when to hide from the visual predators lurking in the surface waters.

A recent study led by UC Santa Cruz's Roxanne Beltran, published March 17 in Science Advances, reveals how northern elephant seals balance the need to feed against the threat of predation. By tracking 71 adult females with satellite tags and time-depth recorders, researchers discovered that the seals' strategies shift dramatically based on their physical condition. This study provides a rare, continuous look at how wild animals weigh risks and rewards.

The researchers utilized a unique biological trick: buoyancy. Because the seals' weight changes as they eat, their ability to sink or float changes. At the start of their seven-month migration, the seals are extremely thin and sink through the water column. As they consume fish and squid to regain lost weight, they become more buoyant. Eventually, they reach a point of positive buoyancy that they maintain for the remainder of the trip.

This physical change dictates their exposure to 'lightscapes of fear.' Surface waters are dangerous, as visual predators like sharks and killer whales hunt there. To minimize vulnerability, seals perform deep foraging dives, averaging 23 minutes per dive with only two minutes at the surface to breathe. While skinny seals prioritize feeding—often taking more risks—fatter seals prioritize safety. This shift is evident in their rest patterns; seals in poor condition begin drift dives just after sunrise, whereas those in good condition begin just before sunrise to avoid the light.

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