Exxon Valdez Oil Walloping Mom and Pup Sea Otters

 Sea otter nursing pup.: Mike Baird via Wikimedia Commons.

Sea otter nursing pup: Mike Baird via Wikimedia Commons.

A new paper in MEPS reports on the strong lingering effects of oil on sea otters in western Prince William Sound from the Exxon Valdez disaster that killed hundreds of thousands of birds and thousands of marine mammals 23 years ago.

The researchers report that exposure to oil has hardly ended—and the likelihood of exposure is highest for mothers with pups than any other members of the otter population.

Although initial assessments found the Exxon Valdez oil decayed quickly and therefore was of little consequence long-term to wildlife, these assessments have not held up in the long term. From the paper:

[C]ontrary to claims of rapid recovery and limited long-term effects, ample evidence accumulated in the decades since the spill has demonstrated that not all injured species and ecosystems recovered quickly, with protracted recovery particularly evident in nearshore food webs… Sea otter population recovery rates in heavily oiled western [Prince William Sound] were about half those expected, and in areas where oiling and sea otter mortality were greatest, there was no evidence of recovery through 2000.

Click for larger image: James L. Bodkin, et al. MEPS. DOI:10.3354/meps09523James L. Bodkin, et al. MEPS. DOI:10.3354/meps09523

To get a better sense of why this might be, the researchers recorded the foraging behavior of 19 sea otters in waters where lingering oil and delayed ecosystem recovery have been well documented. They found that while otters can forage up to 302 feet (92 meters) deep, much foraging takes place in the more heavily-oiled waters of the intertidal zone. Here’s how that breaks down:

  • Between 5 and 38% of all foraging was in the intertidal zone.
  • On average female sea otters made 16,050 intertidal dives per year.
  • 18% of the females’ dives were at depths above the 262-foot-deep (0.80-meter-deep) tidal elevation.
  • Males made 4,100 intertidal dives per year.
  • 26% of male intertidal foraging took place at depths above the 262-foot-deep (80-meter-deep) tidal elevation.  

Joe Robertson via Wikimedia CommonsJoe Robertson via Wikimedia Commons

Overall, estimated annual oil encounter rates ranged from up to 24 times a year, with a conservative average of 10 times a year for females and 4 times for males.

Worrisomely, exposure rates increased in spring when intertidal foraging rates doubled and when females were nursing small pups. The problem apparently arises most from the otters’ habitat of digging in intertidal and subtidal sediment for clams:

Exposure levels [to oil] cannot be quantified, and the biological and ecological consequences of the exposure that results from the identified [clam-eating] path are difficult to assess and largely remain unknown. However, we now know that variation in individual and seasonal dive patterns means that some sea otters are much more likely to be exposed to oil than others. We also know that most exposure comes at a time of year when most adult females are giving birth, and that pups have few mechanisms to avoid or mitigate exposure to oil. 

The open-access paper:

  • Bodkin JL, Ballachey BE, Coletti HA, Esslinger GG and others (2012) Long-term effects of the ‘Exxon Valdez’ oil spill: sea otter foraging in the intertidal as a pathway of exposure to lingering oil. MEPS. DOI:10.3354/meps09523



Headshot of Editor in Chief of Mother Jones, Clara Jeffery

It sure feels that way to me, and here at Mother Jones, we’ve been thinking a lot about what journalism needs to do differently, and how we can have the biggest impact.

We kept coming back to one word: corruption. Democracy and the rule of law being undermined by those with wealth and power for their own gain. So we're launching an ambitious Mother Jones Corruption Project to do deep, time-intensive reporting on systemic corruption, and asking the MoJo community to help crowdfund it.

We aim to hire, build a team, and give them the time and space needed to understand how we got here and how we might get out. We want to dig into the forces and decisions that have allowed massive conflicts of interest, influence peddling, and win-at-all-costs politics to flourish.

It's unlike anything we've done, and we have seed funding to get started, but we're looking to raise $500,000 from readers by July when we'll be making key budgeting decisions—and the more resources we have by then, the deeper we can dig. If our plan sounds good to you, please help kickstart it with a tax-deductible donation today.

Thanks for reading—whether or not you can pitch in today, or ever, I'm glad you're with us.

Signed by Clara Jeffery

Clara Jeffery, Editor-in-Chief

payment methods

We Recommend