(Image: Jason Edwards/NGS Image Collection)

THE eerie glow emitted by bioluminescent animals in the deep ocean might help seals find their prey. How such deep-diving marine predators manage to locate food without echolocation has previously been a mystery, not least because tracking seals in the gloom isn’t easy.

Jade Vacquié-Garcia at the Chizé Centre for Biological Studies in Villiers-en-Bois, France, and colleagues found a way around the problem. They equipped four southern elephant seals (Mirounga leonina) with recorders that measured the times and depths of the seals’ dives, as well as light levels every 2 seconds. Analysing more than 3300 dives, they found that seals had most hunting success in areas with low-intensity blue light – or a bioluminescent glow (PLoS ONE, doi.org/h8d).

Given that seals have large, round eyes with lots of light-sensitive rods – perfect for seeing in dark underwater conditions – the finding fits nicely with what we already know about how seals hunt, says Jim Harvey, interim director of the Moss Landing Marine Laboratories in California.