Carla Crossman is a current MSc student at UBC studying the elusive harbour porpoise.  She is using DNA to determine if geographically separate groups of harbour porpoise are mating together, or if they have become genetically isolated.  Harbour porpoise are particularly sensitive to acoustic disturbance and other types of habitat disruption and scientists fear that their tendency to avoid certain habitats may cause a drop in genetic diversity if mating does not occur across groups.  In this article, Carla shares some of her research findings, including fascinating insight into Dall’s porpoise x harbour porpoise hybrids!

What’s Happening with Harbour Porpoise?

By Carla Crossman, MSc Candidate, UBC Department of Zoology

While harbour porpoises may not win any awards for being the most exciting species to observe in the wild, they are still one of the most abundant cetaceans on our coastline. Unfortunately, harbour porpoises in BC have been overlooked by many researchers and as a result, we know very little about them.  Thanks to many people who report sightings to the BC Cetacean Sightings Network, we have a good idea about where they are found and concentrated, however we still don’t know if mixing of individuals goes on between these concentrated groups.  This question is what started my UBC Masters research.

With most cetaceans, we can use photo identification of unique scars or coloration patterns to identify and track individuals, and this is how we track and identify most of the killer whales and humpback whales in BC.  With larger whales, such as gray whales, we can attach satellite tags that can give us GPS positions for individuals (see news post from earlier this year: West Meets East Pacific).  Whereas harbour porpoises are lacking characteristic markings and are quite evasive with boats, these typical techniques cannot be appropriately applied.

I am implementing a very different and non-invasive method to answer this question.  Using skin samples from harbour porpoises that strand along the coast, I collect DNA to look at similarities in the genetic code of individuals.  If individuals are closely related to each other, they will have a very similar genetic code, while individuals that are distantly related will have divergent genetic codes. Once we know how related everyone is, we can compare this data to the stranding locations and a map and see if individuals that are found close to each other are more closely related than individuals found far apart.

Some of the results to date were very surprising (and exciting)!  We already knew there are harbour porpoise x Dall’s porpoise hybrids in southern BC, but it appears there are probably many more than we originally believed. A few known harbour porpoise samples had Dall’s porpoise DNA, and at least one Dall’s porpoise had harbour porpoise DNA!  Unlike some of the hybrids seen in the wild that can be rather distinct, these hybrids looked just like one of the parental species. Without the genetic data, we would have no way of knowing these were hybrids. Until now we thought all hybrids had harbour porpoise fathers and Dall’s porpoise mothers, but there is now evidence for crosses in both directions!

My research is filling in many knowledge gaps about one of our most common, yet poorly understood cetaceans, and there are many ways you can help and further this research! By reporting all sightings of harbour porpoises to the B.C. Cetacean Sightings Network and reporting any stranded or distressed cetaceans to the Marine Mammal Strandings Network, I will be able to use this additional data to expand my research and continue to help resolve these questions. Report your sighting in ‘real time’ by calling 1.866.I.SAW.ONE or reporting them online here.  Sightings of stranded or distressed animals can be reported directly to the BC Marine Mammal Stranding Network at 1-800-465-4336.

Carla Crossman

Daisy the harbour porpoise at the Vancouver Aquarium. Daisy was rescued as a 5 week old calf in 2008 and rehabilitated at the Marine Mammal Rescue Center.

Susan McKay: SG Images

Dall's x harbour porpoise hybrid (right) and an adult Dall's porpoise (left)