Potential for Sea Otter Exposure to Remnants of Buried Oil From the Exxon Valdez Oil Spill

Abstract

A study was conducted in 2005 and 2006 to examine the hypothesis that sea otters (Enhydra lutris) continue to be exposed to residues of subsurface oil (SSO) while foraging on shorelines in the northern Knight Island (NKI) area of Prince William Sound, Alaska more than 17 years after the Exxon Valdez oil spill. Forty-three shoreline segments, whose oiling history has been documented by prior surveys, were surveyed. These included all shoreline segments reported by a 2003 NOAA random site survey to contain SSO residues in NKI. Sites were surveyed for the presence and location of otter foraging pits. Only one of 29 SSO sites surveyed was identified as an otter foraging site. Most buried SSO residues are confined to tide elevations above +0.8 m above mean lower low water (MLLW), above the range of intertidal clam habitat. More than 99% of documented intertidal otter pits at all sites surveyed are in the lower intertidal zone (-0.2 to +0.8 m above MLLW), the zone of highest clam abundance. The spatial separation of the otter pits from the locations of SSO residues, both with regard to tidal elevation and lateral separation on the study sites, coupled with the lack of evidence of intertidal otter foraging at SSO sites indicates a low likelihood of exposure of foraging otters to SSO on the shores of the NKI area.

Long-term effects of the ‘Exxon Valdez’ oil spill: sea otter foraging in the intertidal as a pathway of exposure to lingering oil

“…The former is pro vided by and Monson et al (2000Monson et al ( , 2011 and here we present evidence for the latter. The presence of oil in intertidal sediments (Short et al 2006, Boehm et al 2007 (14) 1 (1) 277 (11) 355 (12) 1315 (38) 10 0.0 -0.5 m 3283 (54) 517 (7) 1113 (31) 2155 (51) 7068 (143) (29) 71 (5) 622 (28) 2887 (63) 4457 (129) 33 -0.5 --1.0 m 11 (1) 1 (1) 78 (3) 188 (6) 278 (11) 2 Table 5. Comparison of hydrocarbon chemistry data from 4 beach segments in formerly oiled sites (41 samples) and from 2 reference sites (20 samples) that were not directly oiled by the 'Exxon Valdez'.…”

“…Means are geometric; cut off for background was 17 ppb total PAH (TPAH), supported by the alkane data including CPI (carbon preference index), UCM (unresolved complex mixture), phytane, and source modeling (PetPyr) that identifies oil as the source when ≥4.0 through which foraging sea otters may be exposed to that oil. Some models suggest that exposure levels are so low as to provide negligible risk to sea otters (Boehm et al 2007, Harwell et al 2010. Alternatively, Bodkin et al (2002), Monson et al ( , 2011, and Short et al (2006) suggest that exposure to lingering oil may be contributing to the lack of recovery of sea otters, as has been documented for other nearshore consumers , Fukuyama et al 2000, Trust et al 2000.…”

“…In contrast, Boehm et al (2007) found only 1% of sea otter foraging pits at tidal elevations ≥ + 0.8 m along known oiled shorelines at northern Knight Island in 2006. They concluded that there was little spatial overlap between the distribution of oil as measured by Short et al (2004Short et al ( , 2006 and the distribution of sea otter foraging pits, and therefore sea otters had little risk of exposure to lingering oil through intertidal foraging.…”

“…This is significant because estimating oil exposure risk to for aging sea otters will be influenced by seasonal patterns, and estimates that do not account for seasonality can produce biased exposure risk (e.g. Boehm et al 2007Boehm et al , 2011.…”

“…Exposure of upper trophic level consumers to lingering oil through an invertebrate pathway has been widely recognized as a potential mechanism contributing to protracted eco system recovery (Dean et al 2000, Fukuyama et al 2000, Trust et al 2000. However, empirical data quantifying use of intertidal habitats by consumers in WPWS has been lacking, leading to controversy surrounding the extent of exposure to EVO (Boehm et al 2007 or the potential effects of long-term ex posure (Harwell & Gentile 2006, Harwell et al 2010.…”