By Iain Smith
A number of sightings of Risso’s dolphins have been reported to the BC Cetacean Sightings Network in recent weeks. This is exciting news as sightings of Risso’s dolphins off the coast of BC are very rare; the BC Cetacean Sightings Network (BCCSN) has received only 57 Risso’s sightings since 1978! These notoriously elusive dolphins were spotted multiple times around Bag Harbour on the southern end of Moresby Island (the southern island in the Queen Charlotte Islands) in mid to late July.
Risso’s dolphins (Grampus griseus) are very distinctive looking animals. Calves are usually born dark grey with a white patch on their underbelly but their colour changes dramatically as they age. The adult body of a Risso’s dolphin is unmistakable– their skin lightens as they age and their bodies usually end up covered with white scars and scratches. Apart from the dorsal fin, which remains a dark grey, older Risso’s can appear to be almost entirely white. Adults can reach up to four metres in length and possess one of the tallest dorsal fins in proportion to their length of any cetacean. The head of the Risso’s dolphin is also very unique—a very prominent ‘melon’ makes for a decidedly square-shaped head.
Risso’s are believed to be very social dolphins that generally travel in groups of 10-50 animals. While they have been observed to bow ride and harass grey whales, they usually avoid areas of human activity. This, combined with the fact that Risso’s appear to prefer deep offshore oceanic shelf habitats has resulted in a dearth of knowledge regarding Risso’s dolphins.
Therefore it was exciting news when four separate sightings of Risso’s Dolphins in the same area were received by the BCCSN between 15th and 25th of July from kayakers, boaters and ecotourism operators. Most sightings estimated the dolphins to be in a group of 5, circling the shallow waters of Bag Harbour. This isn’t the first time the Risso’s have been spotted in this area. In 2005, Wild Whales reported that up to 40 Risso’s Dolphins were spotted in the same harbour.
The reason for their appearance in Bag Harbour is a bit of a mystery. What prompted the normally deep water dwellers into the shallows of Bag Harbour? The experts can only theorize. Was there a movement of the Risso’s favourite meal (squid) into Bag Harbour, prompting the dolphins to follow for an easy meal? Were the dolphins fleeing potential predators like transient killer whales? Or did the dolphins accidentally stray into the harbor, disoriented in the shallow water surrounding the area? The exact reason remains unknown.
What is known is that without dedicated observers passing along their sightings, these questions wouldn’t even get asked. For scientists to learn more about Risso’s dolphins they need to know where they’ve been spotted. To help, please report sightings of Risso’s dolphins or any other cetaceans or sea turtles to the BC Cetaceans Sightings Network or by calling 1 866 I SAW ONE.