An unusual mortality event has been declared by NOAAfor cetaceans in the northern Gulf of Mexico. However, the actual number of dead cetaceans may be 50 times higher than the number counted according to a new study published today.
The Deepwater Horizon oil spill of 2010 devastated the Gulf of Mexico ecologically and economically. However, a new study published in Conservation Letters reveals that the true impact of the disaster on wildlife may be gravely underestimated. The study argues that fatality figures based on the number of recovered animal carcasses will not give a true death toll, which may be 50 times higher than believed."The Deepwater oil spill was the largest in US 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 Dr Rob Williams from 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."
Cetacean mortality tabulated by NOAA based on observed strandings. "All stranded cetaceans (dolphins and whales) from Franklin County, FL to the Texas/ Louisiana border."
All stranded bottlenose dolphins from Franklin County, FL to the Texas/ Louisiana border.
Image Source: NOAA
A marine mammal advocate working for the NRDC calculates that thousands of dolphins have died.
...if more than 130 bodies have been recovered so far in the Gulf's bottlenose dolphin die-off, how many animals are actually dying? Just how big is that iceberg in the Gulf?Today, a group of well-respected marine biologists gave us a first look at the answer, and it’s not pretty. Their paper, which has just appeared in the journal Conservation Letters, pores over five years of stranding records for 14 Gulf species and, for each one, compares the number of reported bodies with what we know about their population size and survival rates. They conclude that, on average, only one in fifty whales and dolphins that die at sea are recovered on the Gulf’s shores.
Not surprisingly, the discovery rate varies by species, depending on such factors as habitat preference, physical size, and the sociality of the animals. Your odds of finding a dead sperm whale are slightly better than average (about one body for every thirty deaths), of finding an offshore striped or spinner dolphin are far worse (less than one in 200). The paper doesn’t assign a number to bottlenose dolphins, no doubt because of their complicated demographics in the northern Gulf. But presumably nearshore dolphins would have one of the best rates of discovery (the highest rate given in the paper is about one in sixteen), and offshore dolphins perhaps among the worst, with dolphins on the shelf lying somewhere in the middle.
Regardless of which numbers you pump in, the paper suggests that thousands of Gulf dolphins are dying.
Cold water has been proposed as a possible cause of death of dead baby dolphins at a rate of 5 times normal this February and March, but cold water cannot explain the high cetacean death rate that has been going on continuously since the BP blowout in the Gulf. The toxic effects of the oil and dispersants are the most probable cause.