Injury and Recovery of Sea Otters and Harlequin Ducks ... Population Recovery from the Exxon Valdez...

Injury and Recovery of Sea Otters and Harlequin Ducks following the Exxon Valdez

Oil Spill: a Quarter-Century PerspectiveDan Esler

Research Wildlife Biologist

Alaska Science CenterU.S. Geological Survey

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- 42 million liters spilled

- 40% landed on beaches

Background – The Spill

- Some still remains

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Oil in the Environment

Ingestion from

Preening

Ingestion of Contaminated

Prey

External Oiling

Background - Varying Mechanisms of Spill Effects on Wildlife

- Direct - Indirect

- Acute - Chronic

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Background - Varying Vulnerabilities to Oil Spill Effects

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

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- 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 nochronic effects were observed (Bowman et al. 1997)

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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)

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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

1970s 2010s

Exxo

n Va

ldez

spi

ll

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Varying Vulnerabilities to Oil Spill Effects – Lingering Oil

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Sea Otter and Harlequin Duck Recovery Constrained by Lingering Oil

- Oil persisted in subsurface sediments

- Lightly weathered and toxic

- Lower intertidal zone affected

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Population Recovery Research

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Why Harlequin Ducks?

- concerns about population recovery in the immediatepost-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

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1995 to 1998

Harlequin Duck Demography

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2000 to 2003


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PWS - All

Years after spill0 5 10 15 20 25 30 35

Num

ber o

f fem

ales

0

4500

5000

5500

6000

6500

PWS - Unoiled area


Num

ber o

f fem

ales

0

4000

4500

5000

PWS - Oiled area


0500

1000

1500

2000


2013

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- 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)

Harlequin Duck Biochemical Indicators of Exposure

Cytochrome P450 1A

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18


0

25

50

75

100

125ER

OD

Activ

ity (p

mol

/min

/mg) = oiled areas

= unoiled areas

November2006

March/April2007

March2009

March2011

March2013

March2014

Average (± SE) EROD Activity of Harlequin Ducks

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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 populationrecovery was between 20 and 25 years

Results for harlequin ducks indicate:

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Why Sea Otters?

- concerns about population recovery in the immediatepost-spill years

- attributes that suggest vulnerability to spill effects:- nearshore habitats - benthic invertebrate diet- thermoregulatory/metabolic challenges

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Sea Otter Demography

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Sea Otter Abundance – Western Prince William Sound

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Sea Otter Abundance – Heavily Oiled (N. Knight Island)

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Years76-89 (pre-spill) 89 (spill) 90-08 10-13

Rel

ativ

e Fr

eq.

0.0

0.1

0.2

0.3

0.4

0.5

0-1 yrs 2-8 yrs >8 yrs

(215)

Sea Otter Ages-at-Death –Western Prince William SoundSea Otter Ages-at-Death –Western Prince William Sound


Rel

ativ

e Fr

eq.

0.0

0.1

0.2

0.3

0.4

0.5


(215) (419) (530)

Sea Otter Ages-at-Death –Western Prince William Sound


Rel

ativ

e Fr

eq.

0.0

0.1

0.2

0.3

0.4

0.5


(215) (419) (530) (166)


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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 populationrecovery was between 20 and 25 years

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- 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

Overall Implications

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What’s Next?

Exxon Valdez

Oil Spill Trustee Council

http://www.gulfwatchalaska.org/

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ACKNOWLEDGEMENTS

Photo Credits: Randy Davis, Tim Bowman, Mandy Lindeberg, Dan Esler, Ken Wright, Exxon Valdez Oil Spill Trustee Council, John Pearce

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 peopleover the years – thanks to all.

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Injury and Recovery of Sea Otters and Harlequin Ducks ... Population Recovery from the Exxon Valdez...

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