The European eel is one of the continent's most enigmatic species. Starting out as larvae in the North American Sargasso Sea, they are swept by the Gulf Stream towards European estuaries and river systems, and after maturing for up to 20 years they make the 6,500-kilometre return journey to the Sargasso to reproduce. However, eel numbers have diminished by 90 per cent over the last 30 years due to overfishing, habitat loss and man-made obstructions to their migratory pathways.

Russell Beard travels to Gloucestershire, England, to meet conservationists and fishermen who are working together to secure the future of the species.

At current rates of decline, scientists predict our seas could be without fish within 40 years. With a billion people eating fish as their primary source of animal protein and 200 million people depending on fishing as their only source of livelihood, that would mean a humanitarian disaster. In 2008, Scotland established its first fully-protected marine reserve, off the coast of the island of Arran.

Oliver Steeds dives to the sea bed, to find out how the marine ecosystem is recovering since the no take zone was introduced.

The Murray-Darling Basin in Australia's southeast is home to the largest river system in the country. But a combination of overgrazing, diversion of water for irrigation and prolonged drought has left agricultural land arid and unusable.

Yaara Bou Melhem heads to the Australian outback to meet farmer Peter Morton, who has created a thriving habitat for wildlife by returning one-fifth of his property to wetlands.

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