When cuttlefish freeze as enemies approach, they are reducing their bioelectric fields, which predators can detect.

Credit: P. Sutter/Corbis

Christine Bedore at Duke University in Durham, North Carolina, and her colleagues showed videos of approaching predators, including sharks, to Sepia officinalis cuttlefish (pictured) in lab tanks, and analysed their behaviour and the electric fields they emitted. Most cuttlefish froze when they saw the predator, flattening themselves against the tank, reducing their breathing rate and closing their orifices. These behaviours reduced their bioelectric fields, which are generated by ion exchange between respiratory structures and seawater.

Captive sharks that were presented with electric currents mimicking both frozen and resting cuttlefish were more likely to bite at the stronger fields that represented resting creatures. This suggests that the freeze response lowers the electric 'visibility' of cuttlefish.

Proc. R. Soc. B 282, 20151886 (2015)