Subscribe now

Log in

Your login is case sensitive

I have forgotten my password


Short Sharp Science: A New Scientist blog

Deaths of dolphins in Gulf of Mexico underestimated

Michael Marshall, environment reporter

As dead dolphins wash up along the shores of the Gulf of Mexico, it is tempting to attribute the deaths to the Deepwater Horizon oil spill. That remains to be seen, but a new study suggests that whatever the cause, as many as 50 times more whales and dolphins may have been killed than is being reported.

The most recent report on wildlife deaths from the US government's task force states that 100 marine mammals have been collected dead in the Gulf of Mexico. Yet according to a paper in Conservation Letters, as few as one in 50 carcasses are ever recovered, suggesting the US government's figure is an underestimation of total deaths.

Now, it shouldn't be surprising that not all the carcasses of dead marine mammals will eventually wash up on our shores.

Rob Williams, who was at the University of British Columbia in Vancouver, Canada when he did the research, has tried to estimate how many deaths have been missed. Recovered carcasses are "the tip of the iceberg," he says. "We need a way to estimate the size of the iceberg."

To prove his point, Williams and colleagues compared the number of carcasses found in the gulf each year with year-on-year estimates of marine mammal deaths produced by the US National Oceanic and Atmospheric Administration. On average, only 2 per cent were found.

That implies a 50-fold underestimate of the current death toll in the Gulf of Mexico, but it may not be that bad because the Gulf has been closely monitored since the disaster. Having said that, species that live in the open sea are more likely to die without trace.

It's well-known that recovered carcasses are only a fraction of total deaths, says Stan Senner, a director of the Ocean Conservancy in Austin, Texas. The statements on the government's website "bend over backward to imply the opposite", he says.

Senner says that the wildlife agencies involved know the uncertainties, but they are not the ones telling the public about the disaster:

There is no question that various folks in the news media have misinterpreted the carcass recovery data following the Deepwater Horizon event.

Senner and Williams both point to an article in Time from July last year, entitled The BP Spill: Has the Damage Been Exaggerated?, which says:

Yes, the spill killed birds - but so far, less than 1 per cent of the number killed by the Exxon Valdez spill in Alaska 21 years ago. Yes, we've heard horror stories about oiled dolphins - but so far, wildlife-response teams have collected only three visibly oiled carcasses of mammals.

Senner calls that a "gross misinterpretation or misuse of data". He says the consequences of understating the spill's effects will be felt for years to come:

Understating acute mortalities gives everyone - from emergency responders to decision-makers to the public - a false sense that things aren't as bad as they really are or could have been. This can come back around to subvert the public interest when it is time to collect fines or compensation or to negotiate a settlement. If there is a wide perception that nothing significant happened to the environment and everyone has "moved on", that kind of political climate reduces the chances for obtaining a fully compensatory settlement.

It's also worth bearing in mind that an environmental accident doesn't have to kill animals outright to do serious harm. Williams points to an example:

After Exxon Valdez, one population of killer whales was impacted dramatically and has never successfully reproduced since.

In recent months 87 dead bottlenose dolphins have washed up on the shores of the Gulf of Mexico, half of them infants or stillborn fetuses. The government is probing the deaths, but scientists involved in the investigation have been told to keep their results confidential. So we don't know what caused the deaths, but Williams points out that the stillborn calves would have been conceived around the time of the spill.

Journal reference: Conservation Letters, DOI: 10.1111/j.1755-263X.2011.00168.x

Facebook iconDigg iconDelicious iconStumbleUpon iconTwitter iconTechnorati iconReddit iconAddThis icon
Subscribe to New Scientist Magazine
Twitter Follow us
Twitter updates


Your login is case sensitive

I have forgotten my password


© Copyright Reed Business Information Ltd.