When the captain of a whale and dolphin-watching boat based in Tenerife promises a sighting on every outing, it's tempting to raise an eyebrow. How can they be so sure?

The answer is intriguing: many of the whales and dolphins plying the waters around the Canaries throughout the year, though totally wild, limit their roamings to a surprisingly narrow home range. It's common for a particular pod to be seen time and again in the same patch of water close to the coast.

Scientific studies of Canarian bottlenose dolphins seem to confirm their home-loving tendencies. The Canarian whale and dolphin research foundation Secac (Sociedad para el Estudio de los Cetáceos en el Archipélago Canario) has discovered significant genetic differences between family groups from different parts of the archipelago. To a pod of dolphins, an island is a glittering oasis in the vast underwater desert that is the ocean. Once it has found a spot with plenty of fish, it stays put and doesn't mingle.

To date, more than a third of the world's cetacean species – some resident, some migrant – have been spotted in this pocket of the Atlantic. It's an impressive count for a region that is barely 300 nautical miles wide. As well as several types of dolphin, there are regular sightings of pilot and Bryde's whales. Of particular interest to Secac are the rare and little-studied beaked whales found in the more remote extremes of the archipelago. A recent survey near El Hierro revealed that these can dive to depths of 2km and spend more than two hours underwater.

A good range of specialist boat trips caters for those keen to catch a glimpse of a fluke or a fin. Tenerife has the lion's share; there are also a few on Gran Canaria – try Spirit of the Sea ( dolphin-whale.com ), which operates from Puerto Rico, in the south-west of the island. La Palma and La Gomera also have options.

Guidelines designed to minimise disturbance are in place; all boats are required to keep a respectful distance away from the wildlife, so photographers should come prepared with a good zoom lens.

Los Gigantes on Tenerife's west coast is a great place to board. Bottlenose dolphins and pilot whales seem particularly attached to this area, and it's attractive too, with ospreys wheeling over the rough-hewn cliffs. The sea is often glassy smooth, especially in winter, making spotting easier. Recommended boats include Nashiro Uno, a comfortable catamaran with room for 90 passengers (00 34 922 861 918; maritimaacantilados.com ; €25 for a two-hour trip, €35 for three hours), and Flipper Uno (0034 922 862120; flipperuno.com ), a handsome, vintage-style sailing boat.

The crew of Flipper Uno made headlines in August 2008 when they witnessed a bottlenose dolphin giving birth near Masca Bay. Even for an operator that promises some kind of sighting on every trip, this was quite a coup, and the photos are considered unique.

To dose up on theory before or after your trip, make time to visit Secac's Museo de Cetáceos de Canarias (0034 928 849560; museodecetaceos.org ) in Puerto Calero, the swish marina complex on Lanzarote's south coast. It's the only natural history museum on Spanish territory dedicated entirely to whales and dolphins.

In a hall hung with life-size models, there are real bones and teeth to handle, whale songs to listen to and compelling facts about how cetaceans breathe, sleep and communicate. Just outside, a complete skeleton of a Bryde's whale is mounted like a sculpture. The centre is open from Tue-Sat 10am-6pm (admission €8) and is easy to reach by water taxi from Puerto del Carmen (return plus admission €17) or by road from any of Lanzarote's resorts.