By Caitlin Birdsall
The days are becoming cold and wet along the coast of British Columbia as 2008 turns to winter. Mariners are staying off the water and as a result, the rate of cetacean and sea turtle reports begins to slow at the BC Cetacean Sightings Network. At this time of year sightings of many of the larger species become scarce close to the coast. Humpback whales and grey whales begin to wane, as the majority of their populations head south to tropical breeding grounds. Resident killer whales are seen less frequently as the salmon they target move offshore. With the larger animals away, it is often the sightings of smaller species, overlooked at other times of the year, which are reported. This November the Sightings Network received nearly 40 reports of one such cetacean, the little black and white speedster known as the Dall’s porpoise.
These small cetaceans are true BC residents; sightings arrive year round, and from all areas of the coastline. Reports of Dall’s porpoise make up 12% of the entire Sightings Network database, the third most spotted animal after the killer whale and humpback whale. Not bad for a species that is only slightly over 2 meters long! It is perhaps their unusually active behaviour that cause this small cetacean to be so obvious to observers. Dalls’ porpoise are known as an active bow-rider, many reports received by the Sightings Network are of these animals catching a ride along the front of a moving vessel. They are also incredibly fast, estimated to reach 55km/hour in quick bursts. These sprints result in a distinctive ‘rooster-tail’ splash that is hard to miss.
While often easy to spot on the water, the Dall’s porpoise remains a largely under-studied animal. Currently they are listed as ‘Not at Risk’ by the Committee on the Status of Endangered Wildlife In Canda (COSEWIC), though an accurate estimate of their population size is unavailable. Throughout the 1980s and ’90s thousands of Dall’s porpoises were caught as bycatch in driftnet fisheries. While the majority of drift net fishing has now been banned, these small animals may still occasionally end up in the nets of other fisheries. More concerning of late is the appearance of the fungus Cryptococcus gattii in this species. Between 2000 and 2006, 11 Dall’s porpoise found dead-stranded along the coast of Vancouver Island and adjoining archipelago tested positive for C. gattii in the post-mortem. This fungus can cause serious complications in the pulmonary and central nervous systems. It is still unclear why this fungus has emerged as a significant pathogen and how wide-spread it is among marine mammals.
While sightings of Dall’s porpoise (dead and alive) are teaching researchers about their threats, they are also uncovering an unusual occurrence of hybridization. In 1998, researchers published the first confirmation of hybridization between a Dall’s porpoise and harbour porpoise in a fetus found in southern BC. Since then, several researchers have been investigating this unique situation. In the cases of hybridization studied the maternal parent has always been the Dall’s porpoise, and the paternal parent the harbour porpoise. The animals are frequently spotted with Dall’s porpoise, but have never been seen with harbour porpoises. They also behave more similarly to a Dall’s porpoise, one sighting received this fall by the BCCSN reported two hybrids “bowriding, along with the black and white ones”. While these animals may act like Dall’s porpoise, their colouration is quite different. Instead of striking blacks and white, hybrids often are pale to medium grey. Pam Willis et al. looked at these hybrids in 1997 and 1998 in the Haro Strait region and found approximately 20 different hybrid individuals living in that area and that time. While Haro Strait may be a hotbed for this hybridization, the BC Cetacean Sightings Network is hoping to look at reports of hybrids throughout BC to learn more about their distribution.
While the larger species may be scarce for the season, you can still help with wild cetacean research on the Dall’s porpoise, hybrids, and other year-round coastal residents throughout the winter by reporting all your sightings to the BC Cetacean Sightings Network here.
John Ford
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