I climbed the rigging of the old Norwegian fishing boat to watch an orange moon rising over the Alborán Sea. It was midnight in Andalucia, southern Spain.

A motorboat chugged quietly into harbour and moored beside us; the mountains of the Sierra Nevada rose black in the distance. In the morning, we would sail in a south-westerly direction towards the coast of Morocco, to look for dolphins.

I was on board the Toftevaag, a wooden ketch commissioned in 1910 for herring fishing in the Northern Sea. Today, beautifully restored, varnished and equipped as a research vessel with modern navigational and scientific equipment, she belongs to Alnitak, which is a non-governmental agency (NGO).

Alnitak operates as cetacean research organisation run by Spanish marine biologists Ana Cañadas and Ric Sagarminaga van Buiten. They patrol the coastal waters of Andalucia, monitoring the dolphins and whales that remain in the area.

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Since 1991, Earthwatch, the international environmental charity, has funded the work of the Toftevaag, largely through the placement of volunteers, who pay for the unique experience of working with biologists in the field to protect cetacean life. The volunteers’ expenses contribute towards the high daily running costs of the Toftevaag, which sails between 40 and 50 nautical miles a day.

The BBC’s “Blue Planet” series filmed aboard the Toftevaag and, inspired, I joined a team from the UK, France, US, Denmark and Germany in the boat’s home port of Almerimar.

Among the brash gin palaces and identical white yachts on the moorings, the Toftevaag, with her wide oak deck, wooden hull, and towering masts had the 19th century feel of a pirate’s ship, a boat built for romance and adventure on the high seas.

We were greeted by skipper Ric and his two young daughters, who spend every school holiday afloat, looking after the ship’s dog and shinning up and down the ropes like bronzed acrobats. He outlined the potential hazards of life on board (sunstroke; dehyradtion; falling down the galley stairs), before taking us for tapas and sherry on the quayside.

The Alborán Sea is one of the most important regions of the entire Mediterannean. The only gateway between the Mediterranean and the Atlantic seas, it is referred to as a “hydrological engine” because the difference in conditions between the two seas (the Atlantic is cooler and less salty) creates a clash of waters that lift up rich nutrients.

These “upwellings”, as they are known, attract an abundance of fish, and thus the cetaceans that feed on them. The Alborán Sea is also an important migration route for many marine species, including pilot whales, sea turtles, and bottlenose and common dolphins, and yet 20 per cent of the world’s maritime traffic passes through it.

Ana and Ricardo’s mission is to document how many dolphins and whales remain in the Alboran Sea, and what factors are affecting their survival. Unsurprisingly, many of these factors stem from human activities.

Over-fishing, toxic pollution from rivers that empty into the sea, pesticide run-off from intensive farming and sewage from tourist sites are all taking their toll on cetacean and marine life. In studying the group structures, abundance, social behaviour and home range, Ana and Rick hope to use the information not only for its own sake, but also as indicators of the health of the ecoystem.

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