Native
fish thrive in Big Sky
By Stephanie Lynn EBS CONTRIBUTOR
A study performed by the Greater
Yellowstone Coalition in collaboration with Montana Fish, Wildlife and Parks
and the Custer Gallatin National Forest confirmed westslope cutthroat trout in
the South Fork of the West Fork above Ousel Falls have a low percentage of
hybridization.
Silvery green with a slash of red
across their lower jaws, cutthroat trout are striking reminders of the West as
Lewis and Clark saw it. They also occupy a vital place in complex food webs.
Habitat loss, introduced species and
overfishing have precipitated the decline of these native fish resulting in
their designation as a species of concern by the state of Montana. Foreign
trout species, including brook and brown trout, outcompete juvenile cutthroat
for food and also prey on cutthroat trout, while rainbow trout engulf endemic
genes through interbreeding.
Hoping to protect threatened trout,
GYC and their agency partners surveyed three streams that flow into the
Gallatin River for westslope cutthroat trout in 2018. Promising preliminary
findings in the South Fork led to formal fish genetics analyses at seven
locations on this creek and its tributaries, funded in part by the National
Fish and Wildlife Foundation. After sampling, GYC planned to ensure native
trout persist in the South Fork, either by removing hybrid “cutbows” or by
using a technique known as “swamping” to infuse the population with
genetically-pure westslope stock.
“We expected to find a hybridized
westslope cutthroat population above Ousel Falls, but discovered a conservation
population with on average nearly 95 percent westslope cutthroat genes,” said Bob
Zimmer, GYC waters program coordinator.
The study estimated that the South
Fork shelters approximately 1,000 to 1,200 fish per mile with genes that are 93
to 95 percent westslope cutthroat and five percent Yellowstone cutthroat. In
addition, some fish had one to three percent rainbow genes. With these
unexpected results in hand, the partners doubled-down on other efforts to
protect the endemic population.
The headwaters of the South Fork are
located within the Yellowstone Club, where the YC manages guided trips through
stream rotation and closures in sensitive areas while educating their members
about fish handling and stream etiquette.
“The genetic testing last summer
provided similar results to the previous two samplings that have been done and
further proved that there is an incredible fisheries resource in the upper
South Fork watershed,” said Rich Chandler, environmental manager at the
Yellowstone Club. “We intend to maintain all the programs at YC that help
promote the westslope cutthroat trout’s important role in the ecosystem.”
Ousel Falls creates a natural
barrier that harbors one of six conservation populations of westslope cutthroat
trout in the Upper Gallatin watershed. Protecting these vulnerable fish through
habitat conservation and fisheries management sustains their vital ecological
niche and our natural heritage.
Stephanie
Lynn is the education and communications coordinator for the Gallatin River
Task Force.
