According to new research by Phaedra Badie, Gary Theede, Kevin Chapman, and Frank Howe of the Queenney College of Natural Resources at the University of Utah.
Strawberry Reservoir is one of the most popular sport fishing destinations in Utah and has significant recreational economic value to the state. It has also become a refuge for migratory birds crossing the deserts of the Great Basin on their way. Since artificial reservoirs are relatively new to the ecological landscape, researchers need to understand how these implemented systems work at an ecological level, including understanding how birds interact with fish populations.
Maintaining and maintaining the cutthroat population is costly, and managers spend a lot of money and effort to keep the stocked sportfish pups alive and thriving. But over the past two decades, the number of cutthroats in the reservoir has fluctuated, from 464,000 adults in 2007 to 220,000 in 2012 and 2014. Cutthroat extinctions include predation by other fish, death by pelican, angler strikes (harvesting and trapping and release injuries), disease, and age. The group’s study sought to understand the impact of the predator-prey relationship between fish-loving pelicans and cutthroat trout by examining what pelicans ate.
Pelicans tend to eat locally, for the most part. Over a two-year period, the researchers found that the pelicans’ diet at the reservoir consisted of 85% sucker poop, 6% chub poop, 3% cutthroat trout, and 6% other prey. The Utah suckler and the Utah chub are numerous native fish whose growing populations are causing concern to managers. Therefore, the fact that birds use this fish as a staple food is good news. Diet samples taken from birds during spawning at the spawning ground contained more Yuta chub (24%) and cutthroats (10%), but Yuta sucker still made up the majority of the birds’ diet at that time. According to the study, the number of adult cutthroats eaten by pelicans was about 1% of the adult cutthroat population in the reservoir.
“Cutthroat trout are fast swimmers and can swim faster than native chubs and suckers, and they remain too deep for pelicans in open water,” said Badi, lead author of the study. “Pelicans eat what they can easily catch, and chubs and suckers are relatively slow swimmers and like shallow water where pelicans can easily catch them. »
The researchers also noticed (accidentally) that cutthroat trout tended to run away quickly when they sensed the shadow from the boats, while chub and goof loitered around, apparently less concerned about what was happening above the waterline, she said. she.
Reservoir officials were also interested in the possibility that pelicans were preventing trout from breeding. Pelicans sometimes form fodder “fences” – barriers at the edge of the reservoir, blocking spawning tributaries, where they can easily fish in shallow water. The researchers found that most of the time on the Strawberry Reservoir, this was not a problem. According to the data of electronic marking of fish, trout arrived in spawning streams regardless of the presence of pelicans. The researchers found that on days when pelican densities were at their highest, trout travel could be delayed, and they determined the threshold at which managers should intervene to avoid long-term impacts on trout populations.
“Because pelicans are highly visible and congregate in large numbers at the Strawberry Reservoir, anglers assume they are eating tons of trout,” Howe said. “But the study shows that pelicans are not interested in the same types of fish that are valued by human anglers. Knowing that the effects of pelicans on cutthroat trout are minor and short-lived, managers will focus on the larger factors affecting the trout population in the reservoir. »
According to Badi, the pelicans are actually doing managers a favor by catching competing local fish in far greater numbers than they could do on their own, and for free. Meanwhile, American white pelicans, a protected species, are getting good food.