| Summary: | Harbour porpoises (Phocoena phocoena) are one of the most abundant small cetaceans in the world and, while they are extensively studied across most of their range, little is known about their biology in British Columbia, Canada. Recent management plans have identified a need to better understand the population structure of harbour porpoises in this region. I investigated the genetic population structure of harbour porpoises in British Columbia using mitochondrial DNA (mtDNA) and eight microsatellite loci. My findings are consistent with a single population of harbour porpoises inhabiting the coastline between Haida G’waii and the southern Juan de Fuca Strait. I also confirmed that hybridization between harbour porpoises and Dall’s porpoises (Phocoenoides dalli) has occurred over a larger geographic region than previously known and I present evidence that the resultant hybrids are reproductively viable and have the potential to successfully backcross with both parental species. Building on these findings, I examined patterns of hybridization across the order Cetacea. I found that species pairs that share a greater number of ecological, morphological, and behavioural traits have a higher propensity to hybridize than species pairs that do not. This trend is largely driven by behavioural and morphological traits such as vocalization frequency and body size. My study aids in understanding harbour porpoise population structure in British Columbia, and highlights the occurrence of widespread cetacean hybridization.
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