Harbor porpoise (Phocoena phocoena) are considered to be a sentinel species throughout much of their range due to their sensitivity to a number of anthropogenic threats, including pollution, interaction with fisheries, boat traffic and sound. They also depend on healthy stocks of forage fish and squid to maintain their population. Harbor porpoise were the most common cetacean in the Salish Sea in the 1940s, and were seen year round in the Puget Sound. Abundance was greatly reduced by the 1960s, with harbor porpoise being virtually extirpated from the Puget Sound. Surveys in the 1990s and early 2000s revealed an increase in harbor porpoise abundance in the Juan de Fuca Strait and Washington Sound. Due to lack of evidence of a resident harbor porpoise population, no complete line transect surveys were conducted within Puget Sound before 2013. Reports of harbor porpoise sightings within the Puget Sound began to increase in the 2000s, yet the lack of survey data made it impossible to document the timing and extent of their recovery. Washington Department of Fish and Wildlife (WDFW) has conducted winter aerial seabird surveys from 1995-2014, covering the Washington portion of the Salish Sea, recording all sightings of both seabirds and marine mammals. Analyses of these data reveal Salish Sea harbor porpoise within Washington increasing >10% annually, with a progressive expansion into Puget Sound. The survey also noted a concurrent decline in Dall’s porpoise (Phocenoidies dalli) during the same period. Reports from the 1940s suggest that Dall’s porpoise were not found in these waters, so perhaps they were partially filling a niche vacated by the harbor porpoise. As a sentinel species, the recovery of harbor porpoise may be seen as an indicator of change in some aspects of the health of the Salish Sea ecosystem, most notably the changes in gill-net fisheries.
Citation:
Anderson, D., J.R. Evenson, B. Murphie, T. Cyra, and J. Calambokidis, 2016. Recovery of a sentinel species in the Salish Sea: documenting Washington harbor porpoise abundance through 20 years of aerial seabird surveys. Presentation at Salish Sea Ecosystem Conference, Vancouver, BC. 13-15 April 2016.