Injury and Recovery of Sea Otters and Harlequin Ducks following the Exxon Valdez Oil Spill: a Quarter-Century Perspective

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1 Injury and Recovery of Sea Otters and Harlequin Ducks following the Exxon Valdez Oil Spill: a Quarter-Century Perspective Dan Esler Research Wildlife Biologist Alaska Science Center U.S. Geological Survey 1

2 1989 2

3 Background The Spill - 42 million liters spilled - 40% landed on beaches - Some still remains 3

4 Background - Varying Mechanisms of Spill Effects on Wildlife - Direct - Indirect - Acute - Chronic Ingestion from Preening External Oiling Oil in the Environment Ingestion of Contaminated Prey 4

5 Background - Varying Vulnerabilities to Oil Spill Effects 5

6 Examples of Varying Timelines and Mechanisms of Population Recovery from the Exxon Valdez Oil Spill 6

7 Examples of Varying Timelines and Mechanisms of Population Recovery from the Exxon Valdez Oil Spill - Bald Eagle acute mortality observed - Around 250 estimated to have died (about 10% of PWS population) - Reproduction impaired for at least one year By 1995, the Bald Eagle population had recovered and no chronic effects were observed (Bowman et al. 1997) 7

8 Examples of Varying Timelines and Mechanisms of Population Recovery from the Exxon Valdez Oil Spill Killer Whale numbers, in both resident and transient pods, dropped in association with the oil spill; acute mortality Pre-spill numbers had not been achieved by 2013; indirect effects (demographic lags) (Matkin et al. 2012) 8

9 Examples of Varying Timelines and Mechanisms of Population Recovery from the Exxon Valdez Oil Spill Exxon Valdez spill 1970s 2010s Marbled murrelets and pigeon guillemots have been declining since the 1970s, due to changes in ocean conditions There were almost certainly direct and indirect effects of the spill, but these are overwhelmed by larger processes 9

10 Varying Vulnerabilities to Oil Spill Effects Lingering Oil 10

11 Sea Otter and Harlequin Duck Recovery Constrained by Lingering Oil - Oil persisted in subsurface sediments - Lightly weathered and toxic - Lower intertidal zone affected 11

12 Population Recovery Research 12

13 Why Harlequin Ducks? - concerns about population recovery in the immediate post-spill years - attributes that suggest vulnerability to spill effects: - nearshore habitats - benthic invertebrate diet - high site fidelity - small body size - near northern range limit - life history 13

14 Harlequin Duck Demography 1995 to

15 Harlequin Duck Demography 2000 to

16 Harlequin Duck Demography 6500 Number of females Years after spill PWS - All Number of females PWS - Unoiled area Years after spill PWS - Oiled area Years after spill 16

17 Harlequin Duck Biochemical Indicators of Exposure Cytochrome P450 1A - one of a family of enzymes involved in metabolism and detoxification - Cytochrome P450 1A (CYP1A) is induced by exposure to polycyclic aromatic hydrocarbons (PAHs) and PCBs - CYP1A is a sensitive and specific indicator of oil exposure (as PCBs are not an issue in PWS) 17

18 Harlequin Duck Biochemical Indicators of Exposure 18

19 Harlequin Duck Biochemical Indicators of Exposure Average (± SE) EROD Activity of Harlequin Ducks EROD Activity (pmol/min/mg) November 2006 March/April 2007 March 2009 March 2011 = oiled areas = unoiled areas March 2013 March

20 Critical Conclusions: Results for harlequin ducks indicate: - Population-level effects of the Exxon Valdez oil spill and lack of population recovery persisted into late 2000s - Recent data are consistent with recovery criteria set by the EVOSTC, indicating timeline to population recovery was between 20 and 25 years 20

21 Why Sea Otters? - concerns about population recovery in the immediate post-spill years - attributes that suggest vulnerability to spill effects: - nearshore habitats - benthic invertebrate diet - thermoregulatory/metabolic challenges 21

22 Sea Otter Demography 22

23 Sea Otter Demography 23

24 Sea Otter Demography Sea Otter Abundance Western Prince William Sound 24

25 Sea Otter Demography Sea Otter Abundance Heavily Oiled (N. Knight Island) 25

26 Sea Otter Demography Sea Otter Ages-at-Death Western Prince William Sound 0-1 yrs 2-8 yrs >8 yrs 0.5 (215) (419) (530) (166) 0.4 Relative Freq (pre-spill) 89 (spill) Years 26

27 Critical Conclusions: - Population-level effects of the Exxon Valdez oil spill and lack of population recovery persisted into late 2000s - Recent data are consistent with recovery criteria set by the EVOSTC, indicating timeline to population recovery was between 20 and 25 years 27

28 Overall Implications - Wildlife species vary widely in vulnerability to oil spill effects - Spill effects on wildlife can be manifested through a wide array of mechanisms, not just direct, acute - For some species, chronic exposure to residual oil can have effects as large as direct, acute effects - The timeline over which recovery occurs varies by species; for some, it may be measured in decades 28

29 What s Next? Exxon Valdez Oil Spill Trustee Council 29

30 ACKNOWLEDGEMENTS Funding and Support: Exxon Valdez Oil Spill Trustee Council, USGS Alaska Science Center, USGS Western Ecological Research Center, Simon Fraser University, Pacific Wildlife Foundation, Gulf Watch Alaska, National Park Service, NOAA Field, lab, and administrative work conducted by a small army of people over the years thanks to all. Photo Credits: Randy Davis, Tim Bowman, Mandy Lindeberg, Dan Esler, Ken Wright, Exxon Valdez Oil Spill Trustee Council, John Pearce 30