Glenn R. VanBlaricom, University of Washington
$39,978

Testing a charismatic paradigm: Consequences of a growing sea otter population for nearshore benthic communities along the south shore of the Strait of Juan de Fuca

Sea otters are known to have ecologically and economically significant effects on coastal ecosystems of the North Pacific Rim as a result of their foraging activities and preferences. The sea otter population off Washington State was hunted to extinction early in the twentieth century, but was restored by translocation from Alaska in 1969 and 1970. The population now numbers about 550 animals and ranges from Cape Flattery to Kalaloch on the outer coast of Washington.

During winter months between 1995 and 2000, a large group of subadult male sea otters occupied nearshore habitat on the western portion of the south shore of the Strait of Juan de Fuca (SJDF). The group of otters returned to outer coast habitats each spring during the period. In each successive year during the period, the area of occupancy by the sea otters was farther to the east. By winter of 2000 sea otters were seen as far east as Pillar Point. Since 2001, winter occupation of western SJDF by sea otters has not occurred.

The purpose of this project was to resample abundances and size distributions of benthic invertebrates and algae at nineteen sites on the south shore of the central SJDF between Kydaka Point and Port Angeles. The sites were first established and surveyed in summer 1997, before any sea otters had been observed within the range of the sites. By the time of our resurvey, done in summer 2001, the westernmost eleven of the nineteen sites were within the range occupied by sea otters during winter months between the surveys. The 2001 resurvey data were compared with survey data gathered in 1997 to test hypotheses regarding direct effects of sea otters on prey populations and shellfish fisheries, and indirect effects of sea otter foraging on kelp forest communities in the region. We found that patterns of change in preferred sea otter prey populations in the eleven westernmost sites between 1997 and 2001 differed from patterns in the easternmost eight sites, and were generally consistent with known effects of sea otter predation based on studies in other locations.

In the case of sea urchins, effects of harvest by the urchin fishery complicate our ability to definitively attribute observed changes to sea otter foraging. Changes in kelp forest communities between 1997 and 2001 were generally not consistent with predictions of models linking sea otter foraging with increased abundance, diversity, and productivity in kelp forest ecosystems. We conclude that continued use of SJDF habitats will cause reduction in preferred prey populations and reduced yields in fisheries for crabs, clams, and possibly sea urchins.

We conclude that factors regulating kelp forest community structure in SJDF relate primarily to storm disturbance and substratum instability, and not to effects of sea otter predation on dominant grazers. The enigmatic pattern of use of SJDF habitat by sea otters since 2001 adds uncertainty to long-term predictions for interactions of sea otters and coastal ecosystems in SJDF. Long-term predictions are also complicated by the potential for eventual merging of the Washington sea otter population with the growing sea otter population on the outer coast of Vancouver Island, British Columbia, Canada.

Copy of complete final report in pdf format.

Chambers, M.D. Sea otter range expansion into the Strait of Juan de Fuca, WA: How does it impact benthic communities? Sixth Meeting of the Northwest Student Chapter, Society for Marine Mammalogy. Seattle, Washington, USA. Spoken presentation by Chambers. 27 April 2002.

VanBlaricom, G.R., M.D. Chambers, and S.K. Carter. Testing a charismatic paradigm: Consequences of a growing sea otter population for nearshore marine benthic communities along the south shore of the Strait of Juan de Fuca. First Biennial Marine Ecosystem Health Program Science Symposium. Orcas Island, Washington. Spoken presentation by VanBlaricom. 6 September 2002.

Chambers, M.D. Characterizing effects of sea otters on benthic communities in the Strait of Juan de Fuca. Annual Cooperator's Meeting, Washington Cooperative Fish and Wildlife Research Unit. Olympia, Washington, USA. Spoken presentation by Chambers. 2 October 2002.

VanBlaricom, G.R., S.K. Carter, M.D. Chambers, and S.C. Lubetkin. The dilemma of charismatic paradigms and conservation policy for marine mammals. Lessons from sea otters in the North Pacific Rim. Tenth South American Meeting of Marine Mammal Specialists. Valdivia, Chile. Spoken invited plenary presentation by VanBlaricom. 15 October 2002.