Scientists Report Rise in Mass Die-Offs of Birds and Fish

Posted on January 22, 2015

Scientists from the University of California, Berkeley (UC Berkeley) say there has been a rise in mass die-off events in birds, fish and marine invertebrates. They say such invents are decreasing for reptiles and amphibians and remain unchanged for mammals. Overall, the study found that mass mortality events have been increasing by about one event per year over the past 70 years.

The scientists analyzed 727 mass die-offs of 2,500 different animal species from the past 70 years. The photograph above shows a mass die-off event of sunfish and largemouth bass. The event took place in Wintergreen Lake in Michigan in April 2014.

Study senior author Stephanie Carlson, an associate professor at the University of California, Berkeley's Department of Environmental Science, Policy and Management, say in a statement, "This is the first attempt to quantify patterns in the frequency, magnitude and cause of such mass kill events."

Mass die-off events often make the news with reports of large numbers of dead fish floating in the water or birds falling dead from the sky. The researchers acknowledge that some of their findings may be due to an increase in the media reporting these mass die-offs of creatures. However, they say they still found in increase in mass-die offs even after accounting for a reporting bias.

The researchers say these mass die-offs can kill off 90% of a local population of animals in a single shot. Disease is often the main culprit with 26% of the events linked to a disease outbreak. Environmental contamination accounted for 19% off the die-off events. Other causes of mass die-offs include biotoxicity trigged by things like algae blooms and weather extremes like heat waves. The study found that the most severe die-off events often have multiple causes happening at once.

Carlson also says, "The catastrophic nature of sudden, mass die-offs of animal populations inherently captures human attention. 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."

A research paper on the mass die-off study can be found here in the journal, Proceedings of the National Academy of Sciences.

ANIMALS
FISH
BIRDS