It's not news that oil spills and other man-made ecological disasters have horrific effects on wildlife. But, most often, scientists can't quantify just how horrific such disasters are, because they have no control group. Without studying an animal population before it's affected by an oil spill, there's no way to compare how the population has suffered from it. Of course, there are always exceptions -- which is why one group of Spanish researchers now has new insights into the damaging aftermath of oil spills for marine wildlife, according to Nature:
Back in 1994, marine biologist Álvaro Barros and his colleagues at Spain's University of Vigo started looking at the reproductive activity of 18 colonies of a diving bird known as the European shag (Phalacrocorax aristotelis). Then, on November 13, 2002, the hull of the Prestige oil tanker broke in half off the north-western coast of Spain, releasing 63,000 tonnes of oil. The oil heavily coated regions near seven of the colonies, and mostly missed the other 11, creating ‘oiled' and ‘unoiled' populations for the researchers to compare.
The team now reports in Biology Letters that reproductive success was 45% lower in oiled populations compared with unoiled colonies, whereas it had been much the same before the spill ... [the number of healthy offspring per nest] averaged 1.6 for both oiled and control colonies before the spill. Afterwards, while the control colonies maintained the 1.6 figure, the number for the birds in the oiled colonies dropped to 1.0.