Lyme Bay White-beaked Dolphins head west

MARINElife is the leading organisation studying White-beaked Dolphins in UK waters, with projects in south-west and north-east English waters, and monthly monitoring of the wider UK population from commercial ferry surveys. Through this work a population, estimated to be in the region of 100-200 animals (best estimate ~130), has been described for the western English Channel, from 62 individually recognisable and re-sighted photographed animals. MARINElife small boast surveys indicate that the core area of distribution for these dolphins is in the deeper of waters of western Lyme Bay, though public sightings submitted to MARINElife show a wider distribution. The population is well mixed, with individuals moving freely between different pods of different sizes, suggesting one large single population of adults, juveniles, and calves.

The White-beaked Dolphin is a cold-associated species, mainly occurring in cold temperate and subarctic waters of the North Atlantic Ocean, and there are long-term concerns that south-west waters may become too warm for them as sea temperatures rise due to climate change. Sightings in Lyme Bay have been very thin on the ground in 2017, where water temperatures have been relatively high and (according to fishermen) there has been a shortage of Cod and other white fish, which the dolphins feed on.

There have been no White-beaked Dolphins sightings in Lyme Bay since March 2017 (though there have been few MARINElife dedicated surveys). The lack of sightings has prompted fears that the dolphins may have left the Channel and headed north in search of more suitable conditions. To this end, we have been pleased to hear of a recent spate of White-beaked Dolphin sightings, made exclusively by one of our partner organisations, AK Wildlife Cruises, who run daily dolphin watching trips out of Falmouth.

Thanks to Captain Keith Leeves of AK Wildlife Cruises, who has collated images and positions of animals from their trips, we are able to confirm there have been nine White-beaked Dolphin sightings made on seven dates between the 7th July and 3rd September 2017. This is not just one single pod of the same animals, there have been seven different pod sizes recorded, ranging from one to fifteen animals, though a pod of two has been seen three times.

Location of White-beaked Dolphin sightings in 2017 (red circles) in relation to core distribution in previous years determined from previous Marinelife surveys (yellow shaded area)

Though White-beaked Dolphins have been seen off Falmouth and Plymouth Bay in recent years, on dedicated MARINElife surveys, and by members of the public, the number of sightings on AK Wildlife trips in 2017 is unprecedented, suggesting a recent influx. The dolphins have been recorded over a wide area in deep (>50m) waters off east Cornwall, both south and east of Falmouth, in part reflecting the areas of search on AK Wildlife cruises. The sightings are in excess of 55 nautical miles (~100km) to the west of the Lyme Bay core area for White-beaked Dolphins determined through previous MARINElife surveys (occurring 2006-2016).

Through inspection of photo-identification pictures of dorsal fins and body marks, we are able to confirm that at least some (and most likely all) of the dolphins recorded offshore from Falmouth AK trips in 2017 are part of the same population residing in Lyme Bay in previous years. In particular, two well-marked animals recorded off Falmouth have been seen on multiple occasions in the past. Firstly, 'WB52' was seen with two other animals on the 7th July off the Manacles Reef, seven nautical miles south of Falmouth. This animal has been seen on five previous occasions between March 2011 and September 2014, including in central/western Bay, off Berry Head, and south west of Portland Bill. The latter sightings being some 95 nautical miles to the east of the Manacles sighting, demonstrating how wide-ranging individual animals can be. On each occasion, 'WBD 52' has been seen in a pod of different group sizes (of 4, 5,7, 12 and ~20 animals). In total 'WBD 52' has been seen with 17 recognisable individuals and as many as 27 other individual animals (with indistinct body marks).

WB Dolphin 52 Fin 01 Tom Brereton WB Dolphin 52 Fin 02 Tom Brereton

'WBD 52' seen off the Manacles, south of Falmouth 7th July 2014 (left picture, per Keith Leeves) and in the middle of Lyme Bay August 2012 (right picture, by Tom Brereton)

Secondly 'WBD 23' was seen with a group of 10 White-beaked Dolphins on the 30th August 2017, approximately nine nautical miles east of Falmouth. 'WBD 23' has been seen on seven previous occasions between 8th August 2009 and 19th June, mostly in central/western Lyme Bay, but also 12 nautical miles south west of Portland Bill on one occasion, and off Dodman Head (near the recent sighting) in August 2012. This animal has been seen with 25 recognisable individuals (40% of the total) in six different group sizes ranging from 1-~20 animals.

WB Dolphin 23 Fin 01 Tom Brereton WB Dolphin 23 Fin 02 Tom Brereton

'WBD 23' seen east of Falmouth 25th August 2017 (left picture, per Keith Leeves) and in the middle of Lyme Bay 23rd April 2011 (right picture, by Chris Townsend)

There are reports that white fish are once again returning in numbers to Lyme Bay, and with the coming of the autumn, sea temperatures will slowly cool down. It will be interesting to see if White-beaked Dolphins once more return to Lyme Bay in view of these changing conditions.

Professor Tom Brereton, MARINElife Research Director