There are an estimated 350 bottlenose dolphins in the waters between the Normandy and Brittany coasts, making it the largest pod in Europe, according to France’s Groupe d’Etude des Cétacés du Cotentin.
During the past year marine experts in Jersey have been attempting to get a better understanding of the movements of the mammals around the Channel Islands.
Last spring the Société Jersiaise launched an app to enable Islanders to record sightings which are then reproduced in a live map.
And the group, along with Environment Department officials, dropped a hydrophone onto the sea bed off the east coast to record the chatter of dolphins as they swim past.
More than 300 sightings have been recorded on the app, with many off the east coast and around the Ecréhous reef. However, the high number of sightings in the zone is likely to be due to the area being popular with boat owners.
But the hydrophone, which picks up the clicking noise of dolphins within 1 km of the device and has so far recorded 158 ‘encounters’, has potentially given the experts an insight into the mammals’ rather repetitive daily activities.
Paul Chambers, marine and coastal manager at the Environment Department, said: ‘We put the hydrophone down in March and we want to get at least a whole year’s worth of data before we properly analyse the results.
‘However, we have noticed that the dolphins may have their own daily routine. We have noticed that the hydrophone is picking up a lot of encounters at about 8 am or 9 am and then another cluster between 3 pm and 4 pm, which suggests they may be in a routine going up and down the coast.
‘It may be that they are timing their movements with the tide.’
He added: ‘We also had a number of reports last year of a large lone dolphin coming very close to the shore. We had a couple of reports in Grouville Bay, another among the surfers in St Ouen’s Bay and then another at Rozel.
‘We can’t be sure that it is definitely the same dolphin but on each occasion it was described as a large lone dolphin. If it is then it may be an example of a dolphin repeating the same behaviour.’
Meanwhile, Gareth Jeffreys, from the Société, said that the majority of sightings logged on the app have been of bottlenose dolphins, but there have also been sightings of common dolphins and porpoises. A Risso’s dolphin, which are found worldwide in temperate and tropical waters, was also spotted off the Guernsey coast.
There has also been a rise in dolphin sightings in the Little Russel – the channel of water between Guernsey and Herm. A total of 25 sightings were recorded last year, compared to just two in 2012.
Jane Gilmour, Guernsey Botanical Records Officer manager, said increased commercial fishing restrictions in the area could have led to the increase.
*To find the app and associated website, search online for SJ dolphin watch.