Group characteristics, site fidelity, and photo-identification of harbor porpoises, Phocoena phocoena, in Burrows Pass, Fidalgo Island, Washington
A 2017 paper in the journal Marine Mammal Science examines harbor porpoise group structure and site fidelity in the Salish Sea.

Harbor porpoises are the most common cetacean in the Salish Sea. A new study off Fidalgo Island demonstrated that photo-identification can be used to track harbor porpoises long-term and revealed how their group structure is influenced by factors such as season, behavior and calf presence. It was found that many harbor porpoises regularly return to the area, indicating some level of residency. This study demonstrates the importance of understanding harbor porpoise populations at the local level.
Citation
Elliser, C. R., MacIver, K. H., & Green, M. (2017). Group characteristics, site fidelity, and photo‐identification of harbor porpoises, Phocoena phocoena, in Burrows Pass, Fidalgo Island, Washington. Marine Mammal Science.