Mass mortality events (mass die-offs) are increasing in frequency of occurrence — with regard to fishes, birds, and many other marine animals — according to new research from UC Berkeley’s Department of Environmental Science, Policy and Management; the University of San Diego; and Yale University.

The findings are the result of a comprehensive analysis of 727 mass die-offs — of around 2,500 different animal species — that occurred over the past 70-years. According to the findings of this analysis — die-offs amongst bird, fish, and marine invertebrate species, have been increasing in frequency notably over these last 7-decades.

Worth noting here is that the increase hasn’t been of an enormous scale, according to this analysis, but such mass die-offs do have their effect on populations — and they are cumulative, for that matter.

Also worth noting is that mass die-offs amongst reptiles and amphibians seem to be decreasing in frequency. Though of course isn’t that simply because there aren’t many of them left any more? The last few decades have seen a number of previously abundant amphibian species disappear completely, after all.

To be clear on the terminology being used here — “mass die-offs” are defined by the researchers involved in this analysis as mass-mortality events where a large-percentage of a population dies in a fairly short time-frame. During such events more than 90% of a population (genetic diversity included) can cease living rather quickly.

Despite the fact that many oft-quoted scientists/researchers have in the past stated that such mass die-offs have always happend, and there’s no evidence that they are increasing in frequency, this is actually the first “quantitative analysis of the patterns of mass mortality events among animals”.

And what do you know, once the work was done, the evidence was there.

An effective illustration of the way that many phenomena are claimed to not exist by the scientific paradigm when in fact no quality research of any kind on the phenomena/subject has actually ever even been done. That’s what people throughout many walks of life would refer to as a blindspot. (On that subject, see: What Is The Scientific Method? Definition, Criticisms, & Steps)

Anyways, back to the new research…

“This is the first attempt to quantify patterns in the frequency, magnitude and cause of such mass kill events,” stated Stephanie Carlson, the senior author of the new study, and an associate professor at the UC Berkeley’s Department of Environmental Science, Policy and Management.

Here’s the details straight out of the fish’s mouth, so to speak:

The researchers reviewed incidents of mass kills documented in scientific literature. Although they came across some sporadic studies dating back to the 1800s, the analysis focused on the period from 1940 to the present. The researchers acknowledged that some of their findings may be due to an increase in the reporting of mass die-offs in recent decades. But they noted that even after accounting for some of this reporting bias, there was still an increase in mass die-offs for certain animals.

Overall, disease was the primary culprit, accounting for 26% of the mass die-offs. Direct effects tied to humans, such as environmental contamination, caused 19% of the mass kills. Biotoxicity triggered by events such as algae blooms accounted for a significant proportion of deaths, and processes directly influenced by climate — including weather extremes, thermal stress, oxygen stress or starvation — collectively contributed to about 25% of mass mortality events.

The most severe events were those with multiple causes, the study found.

The study found that the number of mass-mortality events has been increasing by about one-event per year over the 70-years the study covered.

“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,” explained 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 research was born of out Carlson’s observations of mass die-offs during the course of her studies of fish in California streams and estuaries.

“The catastrophic nature of sudden, mass die-offs of animal populations inherently captures human attention,” stated Carlson. “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 initial patterns are a bit surprising, in terms of the documented changes to frequencies of occurrences, magnitudes of each event and the causes of mass mortality,” noted study co-lead author Samuel Fey, a postdoctoral fellow in ecology and evolutionary biology at Yale. “Yet these data show that we have a lot of room to improve how we document and study these types of rare events.”

The new research is detailed in a paper recently published in the Proceedings of the National Academy of Sciences.

Image Credit: Public Domain; Screen Capture