M3 AM Ecological Risk Assessment (Part 1)
Monday, 14 November 2005: 8:00 AM - 11:40 AM in Ballroom 3

(GEN-1117-801130) Ecological Significance of the Exxon Valdez Oil Spill.

Harwell, M¹, Gentile, J², ¹ Harwell Gentile & Associates, LC, Palm Coast, Florida, US² Harwell Gentile & Associates, LC, Cape Cod, Massachusetts, USA

ABSTRACT- The ecological risk assessment framework is used to assess the current ecological significance of risks to Prince William Sound (PWS), Alaska, from the Exxon Valdez oil spill (EVOS) after 15 years. Criteria to assess ecological significance include whether a change in a valued ecosystem component (VEC) is sufficient to affect the structure, function, and/or health of the system and whether such a change exceeds natural variability. EVOS occurred on 24 March 1989, releasing over 250,000 barrels of crude oil into PWS. Because PWS is highly dynamic, the residual oil was largely eliminated in the first few years, and now only widely dispersed, highly weathered or isolated small pockets of residual sources remain. Many other sources of PAHs exist from past or present human activities or natural seeps. Multiple-lines-of-evidence analyses indicate residual PAHs from EVOS no longer represent a significant ecological risk to PWS. To assess the ecological significance of any residual effects from EVOS, we examined the extensive literature on more than 20 VECs, including primary producers, filter feeders, fish and bird primary consumers, fish and bird top predators, a bird scavenger, mammalian primary consumers and top predators, biotic communities, ecosystem-level properties of trophodynamics and biogeochemical processes, and landscape-level properties of habitat mosaic and wilderness quality. None of these has any ecologically significant effects at present, with the possible exception of one pod of orcas and one subpopulation of sea otters; however, in both those cases, PWS-wide populations have fully recovered. Many other stressors continue to affect PWS adversely, including climate and oceanographic variability, increased tourism and shipping, invasive species, the 1964 earthquake, and over-exploitation of marine resources, with associated cascading effects on populations of PWS fish and predators, but the ecosystems of PWS have now recovered from EVOS.

Key words: ecological significance, ecological risk, Exxon Valdez oil spill