A female elephant seal equipped with two data-logging tags.

A female southern elephant seal wears tags that collect data on light levels, sound, movement and more. Credit: Martín Ignacio Brogger

Animal behaviour

Mighty seals humbled by prey that flickers and flashes

Enormous predators of the deep are forced to invest extra time to chase luminous prey.

Glowing and flashing bioluminescent creatures brighten the sea’s dark depths — and might even be able to dazzle the massive elephant seal.

Southern elephant seals (Mirounga leonina), which can weigh as much as 4,000 kilograms, often hunt in the dark waters more than 500 metres beneath the ocean’s surface. To piece together the seals’ interactions with prey, Pauline Goulet and Mark Johnson at the University of St Andrews, UK, and their team outfitted seven seals with a fast-sampling light sensor together with location and movement sensors.

The team hypothesized that anti-predator flashes recorded before and during fast ‘attack’ motions by a seal would probably be coming from prey rather than bioluminescent bystanders. The researchers recovered tags from four seals and found that two, both from the Kerguelen Islands in the southern Indian Ocean, ate substantial amounts of bioluminescent prey.

When the two seals chased flashing prey, the pursuit took longer than did attempts to capture non-flashing prey. This suggests that flashing prey are tougher to capture, possibly because the bursts of light dazzle the seals.