Our Tribal hatchery stocks over 250,000 trout per year on the Qualla Boundary – but not all of them are captured by anglers. What happens
to the trout that die in the streams?
In May of 2017, EBCI’s Caleb Hickman decided to find out. The results of his study with colleague Shem Unger, a biologist at Wingate
University, were published this month in the scientific journal Fishes.
Scavengers in our streams
Caleb is the Supervisory Biologist in the Fisheries & Wildlife Management office here at Natural Resources. His idea for the project
arose from questions about the role of stocked fish in our streams’ food chains. “Fishermen aren’t taking them all. We know that,” he says. “Eventually, they’ll die.”
Studies on other ecosystems have found that remains of dead fish are a massive food resource for scavengers – in fact, a whole scientific
field of “scavenging ecology” focuses on these communities. Recent studies on streams in western North America and Russia have shown that dead fish – especially salmon, a close relative of trout – support diverse scavenger communities and provide a massive influx of nutrients to their ecosystems. But few scientists have looked at the fate of stocked fish in eastern streams.
Shem and Caleb wanted to know what happens to dead fish on the Qualla Boundary – are their carcasses getting scavenged? What kind of
animals eat them? Does EBCI fish stocking support increased scavenger populations? And – most importantly – how can we find out?
They answered that last question with an innovative setup:
using GoPro™ cameras to record underwater video of fish carcasses placed out in the Oconaluftee River. Each carcass was attached to a wire mesh tray and weighted down to the river bottom.
All in all, Caleb and Shem set out 10 brook trout and 10 rainbow trout carcasses, and monitored what happened to them for five days.
They recorded video intermittently over that time, in one-hour chunks, and obtained a total of 77 hours of footage.
The most frequent scavengers seen over that time were river chub, which visited during 75% of all videos, and crayfish, which visited
during 25% – both common residents of our streams.
The mystery of the disappearing trout
Often, though, when Shem or Caleb went back to check on the trout carcasses, they simply weren’t there anymore. Within a few hours, 20% of
the carcasses were gone. Within two days, half had disappeared. This was far too fast for small animals like crayfish and river chub to eat an entire trout – or even enough of it for the carcass to break up and drift away. What happened?
“It was a very big surprise,” says Caleb – but he thinks he knows the answer.
At three of their sites, he and Shem put up trail cameras in addition to recording underwater video, allowing them to see what mammals and
other terrestrial visitors frequented the sites. Among the most common visitors were river otters – fish-eating scavengers capable of diving to the river bottom and cleanly removing trout carcasses from their trays.
Otters at large
River otters are a relatively new presence on the Qualla Boundary. They were nearly wiped out of western North Carolina before being
reintroduced in the early 1990s, and their populations have been growing since. Now, Caleb is wondering if stocked trout is supporting a larger otter population than might otherwise live here – and what effects that has on the rest of the ecosystem. How many otters are there, and what else are they eating? Should we be concerned about their potential impact on at-risk aquatic species like the sicklefin redhorse and the eastern hellbender?
The next step is to find out. This spring, Caleb and other members of the Fisheries & Wildlife Management team are planning a study to
learn more about the diets of river otters on the Qualla Boundary. Stay tuned for what they discover!
More Information: Unger, S.; Hickman, C. Report on the Short-Term Scavenging of Decomposing Native and Non-Native Trout in Appalachian Streams. Fishes 2019, 4,17. DOI: https://dx.doi.org/10.3390/fishes4010017
Featured Image: A river otter eating a cutthroat trout at Yellowstone National Park. Photo by Nathan Varley/NPS via Wikimedia Commons.