Blue shark

In open water, a slender silhouette appears: a deep-blue back, pale belly and long pectoral fins. Tagging studies show that blue sharks may remain near the surface at night and dive far deeper by day; one tracked individual in the central Mediterranean descended beyond 1,100 metres.

Telemetry data from 39 sharks identified the Gulf of Lion as a major mating, birthing and nursery area in the western Mediterranean. The silhouette passing beneath a diver therefore completes a crucial part of its life cycle close to our coasts before returning offshore.