April 2024 e-edition - 29

the innermost layers of the eye lens, representing
the time they were raised in the hatchery, " Fetzer
said. " Then they went through a transition period,
corresponding with when they were stocked, where
their sulfur values decreased until they matched
those of the naturally reproduced fish. Those naturally
reproduced fish maintained relatively low
sulfur values throughout their whole lives. "
These results demonstrated managers can collect
adult fish and use the innermost layers of the lens
to determine if the fish was raised in a hatchery
or not. This new method may be faster and more
cost-effective than traditional methods like fin clipping.
Following these results, Game and Fish began
collecting eye lenses from kokanee salmon in Rob
Roy Reservoir near Albany in the Laramie Region
to implement the same birthplace analysis. That
project is ongoing and will provide insights into the
success of naturally reproducing kokanee.
RESPONSE OF NATIVE FISH
TO AN INVASIVE SPECIES
Fisheries managers face the continuous challenge
and threat of aquatic invasive species. Some AIS
have well-documented impacts like zebra mussels
siphoning plankton out of the water and leaving less
food for native species. Zebra and quagga mussels
get a lot of attention for disrupting aquatic food
webs and human infrastructure, but there are many
other AIS whose impacts are less understood.
One found in several waters around Wyoming is
the brook stickleback. These little fish are native to
the central and northern United States and Canada,
but their distribution has expanded. They were first
documented in Wyoming in 1993. These fish are
only a few inches long but are known as aggressive
players in the food web, leading to concerns they
may outcompete native fish for food.
Jake Ruthven, at the time a graduate student at
UW and now a fisheries biologist for Game and
Fish in Lander, worked with Annika Walters and
Game and Fish personnel in the Laramie and Cody
regions to investigate whether brook stickleback
were disrupting the feeding habits of native fish
in Wyoming. Ruthven used carbon and nitrogen
stable isotopes to figure out where in the food web
brook stickleback appeared and whether native fish
were displaced by the invasive species.
" Even though brook stickleback were eating a lot
of the same food items as native species, the native
fish didn't seem to alter their own feeding behavior
because of it, " Ruthven said. " Generally speaking, if
brook stickleback were competing with native fish
for food, we would have expected to see a shift in
the diet of native fish to avoid that competition.
Not seeing that trend indicates that, as long as
Brook stickleback is an aquatic invasive species in Wyoming, but some recent research indicates these little fish
have not had a major impact on Wyoming's native fish species. (Photo by Jake Ruthven/WGFD)
there is plenty of food to go around, our native
Wyoming fish aren't being substantially affected
by the presence of brook stickleback. "
Ruthven's work was good news to fisheries managers.
Small fish tend to get less attention from
researchers and the public, but they play a critical
role in biodiversity and often serve as food web
links between primary producers and predators.
Protecting small, native fish is a priority for fisheries
managers at Game and Fish. Ruthven's work suggests
that while we do not want to see the species spread
any farther, brook stickleback may pose a lesser
threat than other aquatic invasive species in the state.
Stable isotope analysis has been around for
decades, but advancements in technology and in the
understanding of ecological patterns of isotope ratios
continue to improve our ability to answer fisheries
management questions using this technique. These
ongoing and recently completed projects showcase
a few of the many ways that stable isotope analysis
can contribute to better understanding fisheries,
leading to strong management decisions that will
improve Wyoming's fisheries into the future.
- Caroline Rosinski is the Game and Fish information and
education specialist in the Laramie Region. She received her
master's degree at the University of Wyoming where she
worked on various stable isotope analysis projects.
Wyoming Wildlife | 29

April 2024 e-edition

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