A sighting of a dolphin sharing characteristics of a bottlenose dolphin and a Risso’s dolphin was photographed by Peter and Rach Hazlehurst close to the shore of the Butt of Lewis Lighthouse, Isle of Lewis, in the Outer Hebrides!
The animal was sighted on May 15th as part of a larger pod of 25 bottlenose dolphins including a single adult Risso’s and three calves one of which resembled a Risso’s calf photographed swimming in close association with an adult having markings typical of a bottlenose dolphin.
One Risso’s dolphin calf swimming with an adult dolphin atypical of Risso’s. Photo credit: Peter Hazlehurst
Nevertheless, the adult possessed a shorter beak and a more rounded and pronounced head shape than normal bottlenose dolphins, those features being more typical of Risso’s.
Two apparent bottlenose dolphins surfacing together; however, the dolphin in front shows atypical features including a shorter beak and more pronounced head shape, reminiscent of Risso’s. Copyright: Peter Hazlehurst
“There were dolphins swimming around and feeding, and we were there taking photos when we realized we had captured Risso’s dolphins swimming in association with bottlenose dolphins. We are still buzzing from this incredible encounter, what a great day we had!” recounts Peter.
Potential hybridisation between free ranging Risso’s dolphins and bottlenose dolphins was first reported by Whale and Dolphin Conservation (WDC) off north-east Lewis where seven sightings of atypical dolphins were photographed in the area between 2010 and 2013. Further sightings have also been made in more recent years. In all cases, the intermediate morphology was mainly apparent in the very short rostrum and unusually steep forehead similar to what was observed on May 15th. Their observations were part of a long-term Risso’s dolphin project off the Isle of Lewis conducted by WDC which built upon studies on Risso’s dolphins in the area undertaken by Sea Watch in the late 1990’s, part-funded by WDC. In July 2001, Sea Watch’s Director, Peter Evans, observed a solitary adult bottlenose dolphin closely associating with a pod of Risso’s dolphins in the north Minch, and these potential hybrids suggest that such close associations have continued since.
Both bottlenose dolphins and Risso’s dolphins are known to occur in the Outer Hebrides although Risso’s are more common than bottlenose dolphins in that area. These recent images provide evidence of the most recent mixed-species sighting, reporting both species interacting with one another in the area.
“It’s fantastic that Peter managed to get such great photographs and has shared them with us. These images help to show the importance of the area for a variety of species of dolphin, and sightings such as these will help us to understand more about the possible hybridisation of the two species. While it is unknown why Risso’s and bottlenose dolphins choose to mate together, one interesting feature is that we seem to have a group of bottlenose dolphins with just one adult Risso’s. This suggests that it is a two-way process and there are Risso’s dolphins which occasionally leave their own pods and join up with bottlenose dolphin pods as well as the other way around. Whilst this has been observed from time to time in the past, a clear understanding of reasons for it is not yet available”, said Chiara Giulia Bertulli, Sightings Officer for Sea Watch Foundation.
Anyone who would be interested in spending more time looking for whales, dolphins and porpoises around the UK should visit the Sightings Network webpage (www.seawatchfoundation.org.uk/regional-groups/) or submit their sightings online at www.seawatchfoundation.org.uk/sightingsform/.
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If you want to know more about the first recorded sighting of a possible hybrid between Risso’s and bottlenose dolphin: http://uk.whales.org/news/2014/10/wild-dolphin-crossbreeding-in-uk-revealed-by-wdc
To read the 2014 published article (Hodgins et al 2014) on hybridism between Risso’s and bottlenose dolphins: https://www.researchgate.net/publication/265301567_Potential_hybridism_between_free-ranging_Risso’s_dolphins_Grampus_griseus_and_bottlenose_dolphins_Tursiops_truncatus_off_north-east_Lewis_Hebrides_UK
FOR FURTHER INFORMATION ABOUT SEA WATCH FOUNDATION OR THIS PRESS RELEASE PLEASE CONTACT: Chiara Giulia Bertulli at chiara.giulia.bertulli@seawatchfoundation.org.uk.
