A comprehensive analysis of mass die-offs for the past seven decades revealed that the number of birds, fish and marine invertebrates being killed is steadily increasing by one percent each year.
Researchers at UC Berkeley, the University of San Diego and Yale University reviewed 727 mass die-off events of nearly 2,500 species recorded from 1940 to present day. Initial analysis showed that the incidents of mass die-offs have dropped for reptiles and amphibians and has remained unchanged for mammals, but gradually rose for birds, fish and other species.
Twenty-six percent of the mass die-offs among animals are caused by disease; environmental contamination accounts for 19 percent; while 25 percent was linked to climate change. The most severe die-offs were those consisting of multiple causes.
The study is the first to look at the trend of mass die-offs among animals.
"This is the first attempt to quantify patterns in the frequency, magnitude and cause of such mass kill events," Stephanie Carlson, the study's senior author and associate professor at the University of California, Berkeley's Department of Environmental Science, Policy and Management, said in a press release.
The researchers factored in the possibility that the numbers might be inaccurate due to reporting issues, but they maintained that even after eliminating that bias, their calculations remained the same. They recommend though that some changes need to be made in the documentation process of mass die-offs to improve future data analysis.
"While this might not seem like much, one additional mass mortality event per year over 70 years translates into a considerable increase in the number of these events being reported each year," said study co-lead author Adam Siepielski, an assistant professor of biology at the University of San Diego. "Going from one event to 70 each year is a substantial increase, especially given the increased magnitudes of mass mortality events for some of these organisms."
The study was published in the Jan. 12 issue of the Proceedings of the National Academy of Sciences.
