Long-term impacts of the
            <i>Exxon Valdez</i>
            oil spill on sea otters, assessed through age-dependent mortality patterns

Monson, Daniel H.; Doak, Daniel F.; Ballachey, Brenda E.; Johnson, Andrew; Bodkin, James L.

doi:10.1073/pnas.120163397

Cited by 87 publications

(96 citation statements)

References 37 publications

(40 reference statements)

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“…For example, sea otter (Enhydra lutris) numbers in heavily oiled regions of Prince William Sound were well below estimates of prespill numbers [1]. Also, sea otter survival in oiled areas was depressed through at least 1998 [39]. Similar evidence of postspill demographic problems was described for harlequin ducks [2].…”

Section: Discussionsupporting

confidence: 52%

Cytochrome P4501A biomarker indication of oil exposure in harlequin ducks up to 20 years after the Exxon Valdez oil spill

Esler

Trust

Ballachey

et al. 2010

Enviro Toxic and Chemistry

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Abstract-Hydrocarbon-inducible cytochrome P4501A (CYP1A) expression was measured, as ethoxyresorufin-O-deethylase (EROD) activity, in livers of wintering harlequin ducks (Histrionicus histrionicus) captured in areas of Prince William Sound, Alaska, USA, oiled by the 1989 Exxon Valdez spill and in birds from nearby unoiled areas, during 2005 to 2009 (up to 20 years following the spill). The present work repeated studies conducted in 1998 that demonstrated that in harlequin ducks using areas that received Exxon Valdez oil, EROD activity was elevated nearly a decade after the spill. The present findings strongly supported the conclusion that average levels of hepatic EROD activity were higher in ducks from oiled areas than those from unoiled areas during 2005 to 2009. This result was consistent across four sampling periods; furthermore, results generated from two independent laboratories using paired liver samples from one of the sampling periods were similar. The EROD activity did not vary in relation to age, sex, or body mass of individuals, nor did it vary strongly by season in birds collected early and late in the winter of 2006 to 2007, indicating that these factors did not confound inferences about observed differences between oiled and unoiled areas. We interpret these results to indicate that harlequin ducks continued to be exposed to residual Exxon Valdez oil up to 20 years after the original spill. This adds to a growing body of literature suggesting that oil spills have the potential to affect wildlife for much longer time frames than previously assumed. Environ. Toxicol.

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Section: Discussionsupporting

confidence: 52%

Cytochrome P4501A biomarker indication of oil exposure in harlequin ducks up to 20 years after the Exxon Valdez oil spill

Esler

Trust

Ballachey

et al. 2010

Enviro Toxic and Chemistry

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“…Also, birth rates of sea otters did not differ between oiled and unoiled portions of PWS (Johnson & Garshelis 1995, Bodkin et al 2000. Survival rates of older sea otters decreased with time after the spill (Monson et al 2000a), but given the better condition of sea otters in northern Knight Island, it is unlikely that the lower survival of older animals was caused by a lack of food.…”

Section: Discussionmentioning

confidence: 97%

“…The growth of food-limited populations is often constrained because of lower juvenile survival (Choquenot 1991). In the several years after the oil spill, survival rates of juvenile sea otters were lower than pre-spill rates (Monson et al 2000a) and lower weanling survival was noted in oil impacted vs unimpacted areas (Ballachey et al 1994). However, in more recent years (including the years 1996 to 1998 in which our study was conducted) survival rates for juveniles returned to pre-spill levels (Monson et al 2000a).…”

Section: Discussionmentioning

confidence: 99%

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Food limitation and the recovery of sea otters following the 'Exxon Valdez' oil spill

Dean¹,

Bodkin²,

Fukuyama³

et al. 2002

Mar. Ecol. Prog. Ser.

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We examined the potential role of food limitation in constraining the recovery of sea otters Enhydra lutris in Prince William Sound, Alaska, following the 'Exxon Valdez' oil spill. The spill resulted in the removal of a large number of sea otters in 1989, and as of 1998, the portion of the population in the heavily oiled northern Knight Island region had not fully recovered. Between 1996 and 1998, prey consumption rate was higher and the condition of sea otters was better at northern Knight Island than in an unoiled area of the sound (Montague Island). Estimates of prey energy available per unit mass of sea otter were about 4 times higher at Knight than Montague Island, albeit not significantly different between the 2 areas. Over this same period, the number of sea otters remained constant at northern Knight Island but increased at Montague Island. These data suggest that food was at least as abundant at Knight than at Montague Island, and that recovery of sea otters via intrinsic population growth was limited by factors other than food. However, the availability of food, the prey consumption rate, and the condition of sea otters were all much lower at both Knight and Montague Islands than in areas newly occupied by sea otters where the population growth rate was near the theoretical maximum. It is possible that the relatively short supply of food (compared to areas where sea otter population growth rate was high) may have inhibited immigration or interacted with other factors (e.g. oil-induced mortality or predation) to restrict sea otter population growth. Nonetheless, these data suggest that impacts of anthropogenic disturbances on large, often food-limited vertebrate predators can persist in spite of the availability of food resources that are sufficient for intrinsic population growth.

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“…These studies allow detection of the immediate impact of such events, but they do not assess the delayed impacts, which may be even more important for community health. Usually, major disturbances are studied because of their immediate impacts, but it is increasingly believed that the long-term effects of these events can also pose a significant risk to affected populations and ecosystems (Monson et al 2000).…”

Section: Introductionmentioning

confidence: 99%

Immediate and delayed effects of a mass mortality event on gorgonian population dynamics and benthic community structure in the NW Mediterranean Sea

Linares

Coma²,

Díaz³

et al. 2005

Mar. Ecol. Prog. Ser.

158

155

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In the boreal summer of 1999, many invertebrates of hard-bottom communities in the NW Mediterranean Sea suffered mass mortality. Our study assessed the population of the temperate octocoral Paramuricea clavata before the event and monitored the population over the following 4 yr. Spatial patterns showed decreasing mortality with increasing depth between 0 and 50 m, as well as high local variability. The temporal pattern was characterized by a sharp decrease in biomass (58%) shortly after the event caused by the combined effect of colony death (9% of the population) and an increase in the extent of colony injury (from 9% before the event to 52% shortly after it). After 4 yr of monitoring, our results indicated a large delayed effect of the event. Population density decreased continuously after November 1999, and by the completion of the study in November 2003 the accumulated density decrease was 48% of the initial population. This decrease was mainly due to the death of colonies subjected to extensive injury, and because recruitment did not offset mortality. After November 1999, biomass continued to decrease at a slow rate, becoming almost constant after November 2001. Overall, the delayed effect of the event accounted for a 70% loss in P. clavata biomass. The fact that a stabilization of the density and biomass of this species was observed during the last year of our study suggests that the delayed impact of the 1999 mass mortality event may be nearing its end. Nevertheless, given the low dynamics of P. clavata and its role as a habitat former, the delayed effect of the mass mortality event indicates the relevant role that disturbance can play on the population dynamics of this species and as a community structuring force on the coralligenous community.

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Long-term impacts of the Exxon Valdez oil spill on sea otters, assessed through age-dependent mortality patterns

Cited by 87 publications

References 37 publications

Cytochrome P4501A biomarker indication of oil exposure in harlequin ducks up to 20 years after the Exxon Valdez oil spill

Cytochrome P4501A biomarker indication of oil exposure in harlequin ducks up to 20 years after the Exxon Valdez oil spill

Food limitation and the recovery of sea otters following the 'Exxon Valdez' oil spill

Immediate and delayed effects of a mass mortality event on gorgonian population dynamics and benthic community structure in the NW Mediterranean Sea

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