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.
Dolphins continue to die but immediate reporting of dolphin deaths has been discontinued and tests to determine the cause of death have been delayed (Reported March 18).
Despite what she called an “unusual mortality event” killing dolphins in the Gulf of Mexico, the top federal scientist investigating the deaths, revealed Wednesday that the government has yet to send any tissue samples for laboratory testing to determine a cause. The National Oceanic and Atmospheric Administration’s Blair Mase blamed the delay on complications related to oil spill litigation. A letter sent by NOAA to groups authorized to collect tissue samples from dead dolphins described the work as “a criminal investigation,” according to Mase.
Nine more dolphin carcasses were recovered in Alabama and Mississippi between Saturday and Wednesday, bringing the total for the two states to 62 since Jan. 1, according to a list compiled Wednesday by the Institute for Marine Mammal Studies.
That list, which had been maintained online by the institute, has since been removed. The institute had been the only source for the specific locations and dates when dead dolphins were found.
And today NOAA reported that sea turtle deaths have suddenly spiked in the Gulf.
Federal scientists trying to figure out why dolphin deaths along the Gulf of Mexico are up this year now have a second challenge: a sharp jump in sea turtle deaths in some Gulf areas.
"In the past couple of weeks, we've seen an increase" in turtle deaths in the northern Gulf, Connie Barclay, a spokeswoman for the National Oceanic and Atmospheric Administration, told msnbc.com.
Since March 15, she noted, 39 deaths were confirmed in Mississippi, 4 in Alabama and 3 in Louisiana.
But the Federal government has clamped down on releasing information on the dolphin deaths while continuing to fail to conduct the measurements on the cause of death. Independent scientists are beginning to question the government's actions.
"It is surprising that it has been almost a full year since the spill, and they still haven't selected labs for this kind of work," said Ruth Carmichael, who studies marine mammals at the independent Dauphin Island Sea Lab in Alabama.
For more information and discussion see Lorinda Pike's Gulf Watchers Diary from last Sunday.Updated by FishOutofWater at Thu Mar 31, 2011 at 09:54 AM EDT
The Exxon Valdez spill in Alaska was observed to cause sterility in a pod of killer whales. Researchers were unable to determine how the oil caused the observed infertility. Infertility in Alaska caused by oil is consistent with the theory that the BP oil spill caused the deaths of the dolphin fetuses in the Gulf.
From the full article in Conservation Letters:
In the first year after the 1989 Exxon Valdez spill, the AT1 group of “transient” killer whales experienced a 41% loss; there has been no reproduction since the spill (Matkin et al. 2008). Although the cause of the apparent sterility is unknown, the lesson serves as an important reminder that immediate death is not the only factor that can lead to long-term loss of population viability.
Update
A number of people have asked about March 2010 which showed an increase cetacean mortality before the BP spill. Without a report from marine biologists on the causes of death, there's no clear answer to the question why.
NOAA provided one additional figure that sheds some light on the problem. Whatever happened in March, 2010, this March is worse and this February was much worse than 2010. If there was a problem with a virus or disease vector in March 2010, adding oil to the Gulf made the problem worse.