Climate change, invasive species drive native trout declines

Date:
January 4, 2022
Source:
The University of Montana
Summary:
Researchers have found that climate change drives native trout
declines by reducing stream habitat and facilitating the expansion
of invasive trout species.



FULL STORY ==========================================================================
In a new study published in Science Advances, University of Montana
researchers found that climate change drives native trout declines
by reducing stream habitat and facilitating the expansion of invasive
trout species.


========================================================================== "This study had three main questions: How have the distributions of
native and invasive trout shifted in Montana over the last 30 years,
how will they change in the future, and what factors are causing those changes?" said Donovan Bell, the study's lead author and a doctoral
candidate in UM's Wildlife Biology Program.

To answer those questions, scientists from UM, the U.S. Geological Survey
and Montana Fish, Wildlife & Parks quantified the impacts of climate
change on the distributions of five trout species (native westslope
cutthroat trout and bull trout and invasive brook trout, brown trout and rainbow trout) in the northern Rocky Mountains. They used an expansive long-term dataset collected and maintained by Montana FWP, analyzing
close to 22,000 data points from electrofishing surveys in Montana's
streams and rivers over the past 30 years.

The researchers found native bull trout and westslope cutthroat trout
occupancy -- defined as the amount of stream where a species is present
-- declined by 18% and 6%, respectively, between 1993 and 2018 and are predicted to decrease by an additional 39% and 16% by 2080. Although
invasive brook trout also were expected to decline, invasive brown and
rainbow trout have expanded their range due to rising water temperatures
and appear poised to prosper during future climate change.

The culprit for declines of both native trout species is likely climate
change, researchers found, but the specific mechanisms of the declines
varied by species.

Bull trout, a threatened species under the Endangered Species Act, require
cold streams with adequate flow. But warmer water temperatures and lower
summer water levels -- both driven by climate change -- have degraded
stream habitat and likely caused declines of bull trout. Meanwhile,
westslope cutthroat trout were strongly limited by the presence of
invasive trout species, including brook trout that can outcompete native
trout, and rainbow trout that readily hybridize with westslope cutthroat
trout. The threat from invasive rainbow trout is particularly concerning
as their range is expanding due to climatic warming.



==========================================================================
"Our two native trout species in Montana will decline in the future unless appropriate conservation action is taken," Bell said. "Our results suggest
that tailoring conservation strategies to specific species and specific climate- change threats is important for native fish conservation."
For example, the conservation of bull trout in streams and rivers may be
better aimed at protecting, reconnecting and restoring critical cold-water habitat. On the other hand, suppression of invasive trout species likely
is more effective for the conservation of westslope cutthroat trout.

"Globally, climate-induced changes to aquatic habitats are predicted
to threaten at least one-third of freshwater fishes, and some invasive
species could take advantage of such changes," said Clint Muhlfeld, a
USGS scientist and study co-author. "These scenarios seem to be playing
out in our backyard with native and invasive trout." The study also
highlights the importance of using and maintaining long-term datasets
covering large regions to shed light on the complex ways climate and
invasive species work in concert to affect native species.

"It's exciting to have the opportunity to use data meticulously collected
over decades in Montana to convincingly answer complex questions like
these," said David Schmetterling, fisheries research coordinator for
Montana FWP.

Andrew Whiteley, a study co-author and UM associate professor, said
Montana already has lost populations of cold-adapted native fish species,
and this likely will continue as climate change progresses over this
century.

"This is particularly troubling in a state where cold-water fisheries now contribute nearly $650 million a year to our economy," said Whiteley,
who studies fisheries and conservation genetics. "But all is not
lost for these economically, ecologically and culturally important
species as long as appropriate conservation action is taken." UM study co-authors include Bell, Paul Lukacs and Whiteley from the University's
W.A. Franke College of Forestry and Conservation and Diane Whited from
UM's Flathead Lake Biological Station. USGS co-authors include Muhlfeld, Timothy Cline and Robert Al-Chokhachy. Montana FWP authors include Ryan
Kovach and Schmetterling.

========================================================================== Story Source: Materials provided by The_University_of_Montana. Note:
Content may be edited for style and length.


========================================================================== Journal Reference:
1. Donovan A. Bell, Ryan P. Kovach, Clint C. Muhlfeld, Robert
Al-Chokhachy,
Timothy J. Cline, Diane C. Whited, David A. Schmetterling, Paul M.

Lukacs, Andrew R. Whiteley. Climate change and expanding invasive
species drive widespread declines of native trout in the northern
Rocky Mountains, USA. Science Advances, 2021; 7 (52) DOI: 10.1126/
sciadv.abj5471 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2022/01/220104095602.htm
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