Fish Die-offs Linked to Hotter Summers

Fish Kills Expected to Quadruple in Wisconsin Lakes by 2100

This research takes a substantial step forward in connecting the dots between the occurrence of rare ecological catastrophes and climate warming.
– Samuel Fey

Fish die-offs in Wisconsin lakes are expected to double by mid-century and quadruple by 2100 due to warmer summer temperatures, according to a study published today in the journal Nature Climate Change.

To better understand how fish die-offs are changing, researchers from Reed College and the University of California, Davis, analyzed a database of freshwater fish die-offs in Wisconsin combined with lake temperature data and simulations. They found that more than 100 of 500 fish die-offs recorded between 2004 and 2014 in the state were strongly linked with heat waves and warmer average surface water temperatures.

“This research takes a substantial step forward in connecting the dots between the occurrence of rare ecological catastrophes and climate warming,” said lead author Samuel Fey, a mass mortality specialist and assistant professor at Reed College in Portland, Oregon. “Historically, the causes of animal die-offs have been difficult to study because these events tend to be rare and unpredictable.”

Summertime die-off events occurred in lakes that were warmer than lakes without die-offs, and during years of particularly high water temperatures.

The study indicates an uncertain future for fish like this rock bass found in a Wisconsin lake. (Andrew Rypel/UC Davis)

‘What climate change will look like’

The scientists used climate projections to forecast fish die-offs driven by warming summer temperatures over the coming decades. Their results indicate a sobering future for common species such as bluegill, walleye, largemouth bass and northern pike that inhabit these lakes. In the modeling, significant numbers of fish die-offs occurred with an increase of just 2 degrees Celsius, which the globe is on track to surpass by 2100.

The historic and predicted future distribution of summer fish-kill events in Wisconsin lakes. (a) reported summer kills from 2004-2013, (b) projections for die-offs by 2059, and (c) projections for 2100. (Nature Climate Change)

“This study is unveiling another reality of what climate change will look like for north-temperate lakes across the world,” said co-author Andrew Rypel, an associate professor at UC Davis and the Peter B. Moyle and California Trout Chair in Coldwater Fish Ecology. “Analyses provide an up-close view of how fish populations will die, and how species will die due to climate change. It’s particularly problematic for freshwater fishes in landlocked lakes, as they don’t have the ability to adapt to changing climates by migrating. Effects have to be dealt with by managers right where they are.”

Adaptation opportunities

The study shows most future fish kills are expected to occur in the southern portion of the state, which is the warmest and most populated part of Wisconsin. Urban, agricultural and industrial activities combine to impact lakes in the area.

Rypel says this presents a problem for fish but also opportunities for their management, adaptation and resilience. Cities, communities and resource managers could take measures to improve lake conditions through heightened efforts to manage phosphorous loads and restore forests around riparian areas to act as a sponge for contaminants that could otherwise enter the lake

Media contact(s)

Sam Fey, Reed College, feys@reed.edu, 503-777-7248

Andrew Rypel, UC Davis Department of Wildlife, Fish and Conservation Biology, rypel@ucdavis.edu, 530-752-9567

Kat Kerlin, UC Davis News and Media Relations, kekerlin@ucdavis.edu, 530-752-7704

Kevin Myers, Reed College Strategic Communications and Media Relations, myersk@reed.edu, 503-517-7815

Stay climate connected.

Sign up for our monthly newsletter highlighting our latest climate change research stories, blog posts, and features.


You have Successfully Subscribed!

UC Davis Logo