A new study of mass die-offs amongst animal species shows a marked increase in deaths of birds, fish and marine invertebrates. The findings come from an analysis of 727 mass die-offs of 2,500 animal species over the past 70 years. The study also shows decreasing deaths for reptiles and amphibians,and an unchanged rate for mammals. Die-offs can kill more than 90 percent of species’ population, and this study is the first attempt to quantify patterns in the frequency, magnitude and cause of such die-offs.
The research was led by participants at UC Berkeley, the University of San Diego and Yale, and involved analysis of mass kills documented in scientific literature, primarily focusing on 1940 to the present.
Key findings from the study include:
• Disease was the deadliest killer, accounting for 26 percent of die-offs.
• Climate, including weather extremes, thermal stress, oxygen stress and starvation included 25 percent of die-offs
• Human-related causes, including environmental contamination, caused 19 percent
• Die-offs with multiple causes were the most severe
• Die-offs have been increasing by one per year over the last 70 years. This is a quite considerable increase in mortality.
“The catastrophic nature of sudden, mass die-offs of animal populations inherently captures human attention,” said Stephanie Carlson, associate professor at the University of California, Berkeley’s Department of Environmental Science, Policy and Management. “In our studies, we have come across mass kills of federal fish species during the summer drought season as small streams dry up. The majority of studies we reviewed were of fish. When oxygen levels are depressed in the water column, the impact can affect a variety of species.”
The study also documented numerous ways to improve our approach to die-offs. That this was the first such study conducted is shocking—and shows how far we have to go in understanding, let alone counteracting, the damage we are doing to the biosphere.
Via Science Daily