Common dolphins in Washington State waters: An increase in sightings and strandings

Common dolphins (Delphinus sp.), specifically long-beaked common dolphins, typically inhabit warmer temperate waters and are not usually present north of California; however, sightings of live common dolphins and dead stranded individuals have been increasing in Washington State waters since the early 2000s. Since 2006, eight common dolphin strandings have been recorded; seven on the outer coast and one inside Puget Sound. Sightings of live dolphins throughout inside waters and Southern Puget Sound have been recorded in 2003, 2011-12, and 2016 –17. Group size ranged from 2 (in 2003 and 2011-12) to 5-12 (in 2016-2017) and some of these groups stayed in the region for several months. Sightings of these live animals mostly began in summer and early fall sometimes extending into winter months, but the strandings generally occurred in winter months (October to March) some of these were determined to have various neurologic diseases. Live dolphins in 2011 showed significant diatom growth; however, in 2016-17 dolphins appeared to be in good body condition and displayed active surface behaviors including bow riding, leaping, and appeared to be feeding. Puget Sound is also experiencing a recovery of harbor porpoise (Phocoena phocoena) populations, which may share a similar diet. Shipboard surveys off the coast of California, Oregon, and Washington have recorded few common dolphins north of the California/Oregon border. A long-term pattern of seasonal and interannual shifts in the California populations have been noted, likely as a response to changing oceanographic conditions which is consistent with our observations of most of these stranding and sighting events occurring proximally to El Niño events. Long term warming trends may increase the occurrence of this species in the future.

Citation:

Shuster, L., J. Huggins, D. Anderson, A. Douglas, J. Calambokidis. 2017. Common dolphins in Washington State waters: An increase in sightings and strandings. Abstract (Proceedings) 22nd Biennial on the Biology of Marine Mammals, Halifax, Nova Scotia, October 22-27, 2017.