When I took the ferry to northern Spain this summer, I didn't expect to enjoy a little whale-watching on the side. OK, so I didn't see the whale – my nose was deep in a book when the cry went up – but I did catch sight of several dolphins, a far more exciting diversion than my holiday bonkbuster.

I was sailing from Portsmouth to Santander with Brittany Ferries on its ship Pont-Aven, which criss-crosses the waters between Britain and northern Spain, a stretch of sea which, while not so far from home, offers some of the best dolphin- and whale-watching in Europe, I'm told.

Indeed, alongside ferrying holidaymakers to Spain – cars chock full of buckets and spades – the company runs a nice little sideline welcoming passengers who come just to sail from Britain to the Iberian peninsula and back, spotting the marine life along the way (with a little turn around Santander thrown in).

The gaggle of binocular-clutching passengers who alerted me to the performance out at sea were on a two-night whale and dolphin cruise, one of seven such excursions that were laid on through the summer by Brittany Ferries and a specialist operator called Planet Whales. More are promised for next year.

Porpoises, Bottlenose and Common dolphins, pilot and sperm whales are among the thrilling sights that you can catch on camera from the decks of the ships. Yet Brittany Ferries' interest in marine life isn't just about swelling passenger numbers. For the past few years, it has been working with one of the leading whale and dolphin conservation charities, Orca, hosting its research scientists on board ships from March to October.

The charity's work is serious stuff. For example, one project it has just concluded has focused on how fin whales – at up to 26m, the world's second-largest species of whale – behave around ships, so that it could draw up guidelines on how large vessels can avoid collisions with the animals.

Up on deck, Orca has also posted wildlife officers to raise passengers' awareness of the whales. If you're lucky enough to meet one when you're aboard, don't be shy of asking a few questions. They're there to reveal more to the likes of you and me (and the kids, too) about the creatures of the deep: increased knowledge helps conservation efforts, they say.

And you can even keep up with the wildlife officers' work when you're back on dry land by reading their blog at brittanywildlife officer.wordpress.com.

The director of Orca, Sally Hamilton, told me: "By allowing Orca research teams on board their ships, Brittany Ferries is making a real contribution to marine conservation. Brittany Ferries has played an important role in helping the United Kingdom's government to meet its obligations under the EU Habitats Directive as part of the development of a European network of marine protected areas."

Who knew a ride on a ferry could be so educational?

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