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Animal deaths in BP spill possibly greatly underestimated: study

March 30, 2011
Courtesy of Wiley-Blackwell
and World Science staff

The im­pact on wild­life of last year’s BP Deep­wa­ter Ho­ri­zon oil spill in the Gulf of Mex­i­co may have been gravely un­der­es­ti­mated, a study sug­gests.

Writ­ing in the re­search jour­nal Con­serva­t­ion Let­ters, sci­en­tists ar­gue that fa­tal­ity fig­ures are mis­lead­ingly based on the num­ber of re­cov­ered an­i­mal car­casses, and that the true toll may be 50 times high­er than be­lieved.

The spill “was the larg­est in U.S. his­to­ry. How­ev­er, the recorded im­pact on wild­life was rel­a­tively low, lead­ing to sug­ges­tions that the en­vi­ron­men­tal dam­age of the dis­as­ter was ac­tu­ally mod­est,” said lead au­thor Rob Wil­liams of the Un­ivers­ity of Brit­ish Columbia. “This is be­cause re­ports have im­plied that the num­ber of car­casses re­cov­ered, 101, equals the num­ber of an­i­mals killed by the spill.”

The team fo­cused its re­search on 14 spe­cies of ce­ta­ceans, a group of sea mam­mals that in­cludes whales and dol­phins. The re­search­ers ar­gue that ma­rine con­di­tions and the fact that many deaths will have oc­curred far from shore mean re­cov­ered car­casses only ac­count for a small frac­tion of deaths.

Cal­cula­t­ions by the team sug­gest that only two per­cent of ce­ta­cean car­casses were ev­er his­tor­ic­ally re­cov­ered af­ter their deaths in this re­gion, so the death toll from the spill could have been un­der­es­ti­mated by 50 times. “Car­cass counts are hugely mis­lead­ing, if used to meas­ure the dis­as­ter’s death tol­l,” said co-au­thor Scott Kraus of the New Eng­land Aquar­i­um in Bos­ton.

The Deep­wa­ter dis­as­ter took place 40 miles off­shore in 1,500 me­ters (1,600 yards) of wa­ter, which is partly why es­ti­mates of oil flow rates dur­ing the spill were so hard to make. “The same fac­tors that made it dif­fi­cult to work on the spill al­so con­found at­tempts to eval­u­ate en­vi­ron­men­tal dam­ages caused by the spill,” said Wil­liams.

The in­ves­ti­ga­tors said the find­ings may al­so apply to off­shore an­i­mal deaths re­sult­ing from oth­er hu­man ac­ti­vi­ties. “The find­ing that strand­ings rep­re­sent a very low pro­por­tion of the true deaths is al­so crit­i­cal in con­sid­er­ing the mag­ni­tude of oth­er hu­man causes of mor­tal­ity like ship strikes, where the real im­pacts may si­m­i­larly be dra­mat­ic­ally un­der­es­ti­mated by the num­bers ob­served,” said study co-au­thor John Ca­lam­bokidis, a re­searcher with Olym­pia, Wash.-based Cas­ca­dia Re­search.


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The impact on wildlife of last year’s BP Deepwater Horizon oil spill in the Gulf of Mexico may have been gravely underestimated, a study suggests. Writing in the research journal Conservation Letters, scientists argue that fatality figures are misleadingly based on the number of recovered animal carcasses, and that the true toll may be 50 times higher than believed. The spill “was the largest in U.S. history. However, the recorded impact on wildlife was relatively low, leading to suggestions that the environmental damage of the disaster was actually modest,” said lead author Rob Williams of the University of British Columbia.”This is because reports have implied that the number of carcasses recovered, 101, equals the number of animals killed by the spill.” The team focused its research on 14 species of cetaceans, a group of sea mammals that includes whales and dolphins. The researchers argue that marine conditions and the fact that many deaths will have occurred far from shore mean recovered carcasses only account for a small fraction of deaths. Calculations by the team suggest that only 2% of cetacean carcasses were ever historically recovered after their deaths in this region, so the death toll from the spill could have been underestimated by 50 times. “Carcass counts are hugely misleading, if used to measure the disaster’s death toll,” said co-author Scott Kraus of the New England Aquarium in Boston. The Deepwater disaster took place 40 miles offshore in 1,500 meters (1,600 yards) of water, which is partly why estimates of oil flow rates during the spill were so hard to make. “The same factors that made it difficult to work on the spill also confound attempts to evaluate environmental damages caused by the spill,” said Williams. “Consequently, we need to embrace a similar level of humility when quantifying the death tolls.” The investigators noted that the findings may also apply to offshore animal deaths resulting from other human activities. “The finding that strandings represent a very low proportion of the true deaths is also critical in considering the magnitude of other human causes of mortality like ship strikes, where the real impacts may similarly be dramatically underestimated by the numbers observed,” said study co-author John Calambokidis, a researcher with Olympia, Wash.-based Cascadia Research.