Increased harbor porpoise mortality in the Pacific Northwest, USA: understanding when higher levels may be normal

A 2015 paper in the journal Diseases of Aquatic Organisms examines potential causes of increased harbor porpoise strandings in Washington and Oregon.  

Harbor porpoise. Photo courtesy of the National Park Service.
Harbor porpoise. Photo courtesy of the National Park Service.


In 2006, a marked increase in harbor porpoise (Phocoena phocoena) strandings were reported in the Pacific Northwest of the USA, resulting in the declaration of an unusual mortality event (UME) for Washington and Oregon to facilitate investigation into potential causes. The UME was in place during all of 2006 and 2007, and a total of 114 porpoises stranded during this period. Responders examined 95 porpoises; of these, detailed necropsies were conducted on 75 animals. Here we review the findings related to this event and how these compared to the years immediately before and after the UME. Relatively equal numbers among sexes and age classes were represented, and mortalities were attributed to a variety of specific causes, most of which were categorized as trauma or infectious disease. Continued monitoring of strandings during 4 yr following the UME showed no decrease in occurrence. The lack of a single major cause of mortality or evidence of a significant change or event, combined with high levels of strandings over several post- UME years, demonstrated that this was not an actual mortality event but was likely the result of a combination of factors, including: (1) a growing population of harbor porpoises; (2) expansion of harbor porpoises into previously sparsely populated areas in Washington’s inland waters; and (3) a more well established stranding network that resulted in better reporting and response. This finding would not have been possible without the integrated response and investigation undertaken by the stranding network.


Huggins et al. (2015). Increased harbor porpoise mortality in the  Pacific Northwest, USA: understanding when higher levels may be normal. Diseases of Aquatic Organisms. Vol. 115: 93–102, 2015. doi: 10.3354/dao02887

About the Author: 
Jessica L. Huggins1,*, Stephen A. Raverty2 , Stephanie A. Norman3 , John Calambokidis1 , Joseph K. Gaydos4 , Deborah A. Duffield5 , Dyanna M. Lambourn6 , James M. Rice7 , Brad Hanson8 , Kristin Wilkinson9 , Steven J. Jeffries6 , Brent Norberg9 , Lynne Barre9; 1 Collective, 218 ½ W 4th Ave, Olympia, WA 98501, USA 2 British Columbia Ministry of Agriculture, Animal Health Centre, 1767 Angus Campbell Road, Abbotsford, British Columbia V3G 2M3, Canada 3 Central Puget Sound Marine Mammal Stranding Network, Orca Network, 2403 North Bluff Road, Greenbank, WA 98253, USA, and Marine-Med: Marine Research, Epidemiology, and Veterinary Medicine, 24225 15th Place SE, Bothell, WA 98021,USA 4 University of California Davis, UC Davis Wildlife Health Center−Orcas Island Office, 942 Deer Harbor Road, Eastsound, WA 98245, USA 5 Portland State University, 1825 SW Broadway, Portland, OR 97207, USA 6 Washington Department of Fish and Wildlife, Marine Mammal Investigations, 7801 Phillips Rd SW Lakewood, WA 98498, USA 7 Oregon State University, Marine Mammal Institute, Hatfield Marine Science Center, Newport, OR 97365, USA 8 NOAA Fisheries, Northwest Fisheries Science Center, 2725 Montlake Boulevard East, Seattle, WA 98112, USA 9 NOAA Fisheries, Office of Protected Resources, 7600 Sand Point Way NE, Seattle, WA 98115, USA