Locally sourced: Pelicans prefer native fish to sportfish at Utah's
strawberry reservoir

Date:
March 7, 2022
Source:
S.J. & Jessie E. Quinney College of Natural Resources, Utah State
University
Summary:
American white pelicans who pause their migration at Strawberry
Reservoir in Utah are filling their bellies with native species
like Utah sucker for the most part, leaving cutthroat trout to
the human anglers, according to new research.



FULL STORY ========================================================================== American white pelicans who pause their migration at Strawberry Reservoir
are filling their bellies with native species like Utah sucker for the
most part, leaving cutthroat trout to the human anglers, according to
new research from Phaedra Budy, Gary Thiede, Kevin Chapman and Frank Howe
from the Quinney College of Natural Resources at Utah State Univerisity.


========================================================================== Strawberry Reservoir is one of the most popular sport fisheries in Utah
and has considerable economic value for recreation purposes for the
state. It has also become a refuge for migratory birds who traverse the
deserts of the Great Basin along their path. Since man-made reservoirs
are relatively new to the ecological landscape, researchers have to
decipher how these introduced systems function on an ecological level, including understanding how birds interact with fish populations.

It's expensive to stock and maintain cutthroat trout populations, and
managers spend a lot of money and effort to keep stocked sportfish
hatchlings alive and thriving. But over the last two decades, the
abundance of cutthroat trout in the reservoir has varied -- from a high
of 464,000 adult fish in 2007 to lows of approximately 220,000 in 2012
and 2014. Beyond hatching and egg-to-fry survival, the primary culprits
for cutthroat demise is predation by other fish, death by pelican,
impacts from anglers (harvest and catch-and-release injury), disease
and age. The group's research sought to understand the impacts of the predator-prey relationships between fish-loving pelicans and cutthroat
trout by examining what the pelicans ate.

Pelicans tend to eat local, for the most part. Over a two-year period, researchers found that pelican diets at the reservoir consisted of 85%
Utah sucker, 6% Utah chub, 3% cutthroat trout, and 6% other prey. Utah
sucker and Utah chub are abundant native fish whose expanding populations
are a concern to managers, so the fact that birds use these fish as a
staple food is good news.

Diet samples collected from birds during the cutthroat spawning run
contained more Utah chub (24%) and cutthroat trout (10%), but Utah sucker
still comprised the majority of the birds' diet even then. The number
of adult cutthroat trout consumed by pelicans represented approximately
1% of the adult population of cutthroat trout in the reservoir, the
research found.

"Cutthroat trout are fast swimmers and can outswim native chubs and
suckers, and they stay too deep for pelicans when they are out in the
open water," said Budy, lead author on the research. "Pelicans eat what
they can easily catch, and chubs and suckers are relatively slow swimmers
and like shallow habitat where they are easy for pelicans to catch."
The researchers also observed (anecdotally) that cutthroat trout tended
to flee quickly when they sensed shadows of boats, while Utah chub and
sucker loitered, apparently less concerned about what was going on above
the waterline, she said.

Managers at the reservoir were also curious about the possibility of
pelicans inhibiting trout from spawning. Pelicans sometimes form feeding "fences" - - barriers at the edge of the reservoir blocking spawning tributaries, where they can easily catch fish in the shallows. The
researchers found that this didn't seem to be an issue at Strawberry
Reservoir most of the time. Trout made it into spawning streams whether pelicans were present or not, according to data from electronically
tagged fish. The researchers did find that on the days with the very
highest densities of pelicans, trout travel could be delayed, and they identified a threshold for managers to intervene in order to avoid
impacting trout populations long-term.

"Because pelicans are highly visible and congregate in large numbers at Strawberry Reservoir, anglers assume that they are eating tons of trout,"
Howe said. "But the study shows that pelicans are not interested in the
same fish species that are prized by human anglers. Knowing that the
impact from pelicans to cutthroat trout is minor and short-lived will let managers focus on more important factors impacting trout populations at
the reservoir." The pelicans actually seem to be doing managers a favor
by removing competing native fish in far greater numbers than they could
do themselves, and for free, Budy said. Meanwhile American white pelicans,
a protected species, are getting a good meal out of it.

========================================================================== Story Source: Materials provided by S.J._&_Jessie_E._Quinney_College_of_Natural_Resources,
Utah_State_University. Original written by Lael Gilbert. Note: Content
may be edited for style and length.


========================================================================== Journal Reference:
1. Phaedra Budy, Frank Howe, Kevin Chapman, Gary P. Thiede. Conflicts
among
protected native birds and valuable sport fishes: potential
pelican predation effects. Canadian Journal of Fisheries and
Aquatic Sciences, 2022; DOI: 10.1139/cjfas-2021-0228 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2022/03/220307190655.htm

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