The critically endangered European eel has a fascinating and mysterious life cycle that can span 20 years and four life stages. Their journey begins in breeding grounds close to Bermuda where they drift on ocean currents before migrating into freshwater habitats. Here they mature prior to returning to the sub-tropical seas to spawn as 1 metre long adults. These young eels, known as elvers, were filmed last week in the Cairngorms National Park as they journeyed past waterfalls upstream. Filming: