Packing on the pounds – or ounces – indicates that fish have what they need to survive and grow. “Fish production is a great way to estimate ecosystem productivity,” says U.S. Forest Service researcher Andy Dolloff.
Production refers to how quickly fish gain weight and grow in size. “Production is a function of how many fish there are, how big they are, and how fast they grow,” says Dolloff. “It’s very comprehensive, and it’s very labor intensive to measure.”
In 2012, the scientists scoured short sections of 25 streams, capturing 6,743 fish. They used the data to estimate fish production and species composition. Bonnie Myers, who at the time was a student at Virginia Tech University, led the study. The scientists published their results in the journal Ecology of Freshwater Fish.
There were 20 study streams in the southern Appalachians. Streams were selected from a database of all streams in the eastern U.S. that support brook trout – or had supported brook trout at one time. Brook trout are the only trout native to the study area, and require cold waters.
“We also included 5 northern sites in Massachusetts and Vermont,” says Dolloff. “We wanted to ensure that we had true cold water streams.”
The scientists installed temperature gauges in all the streams. The temperature results showed that only 8 of the 20 southernmost sites could still be considered cold-water streams. Ten sites were cool water, and the remaining 2 were warm.
On average, cold streams were only 3.5 degrees Fahrenheit colder than cool streams, suggesting that slight warming could have large effects. Fish that require cold water may already be at the edge of their temperature thresholds.
At sites where they were present, cold water species such as brook trout accounted for much of the total abundance, biomass, and yearly production.
In many of the study streams, fish production was very high. “Fish production in some eastern U.S. streams is among the highest recorded,” says Dolloff. Some of the study streams were more productive than foothill streams in New Zealand, tropical rainforest streams in Borneo, lowland trout streams in Minnesota, and neotropical streams in Brazil.
“The bad news for trout is that all this biomass is not in trout,” says Dolloff. Most of the fish that were thriving were species that can do well in a broad range of water temperatures.
Fish in 3 of the 20 southernmost streams were more typical of warm water streams. Most of the other streams were not very cold either, and were more typical of cool water streams.
“It’s not a great time to be a brook trout in the Southern Appalachians,” says Dolloff. “However, there is still some great brook trout habitat – mostly in small mountain streams that are groundwater fed.” Some of the best brook trout habitat is at high elevations in the Nantahala and Pisgah National Forests.
“Southern Appalachian streams are productive, but they’re not necessarily producing brook trout,” says Dolloff. “While other species have value, they’re generally less desirable to anglers.”
“The study provides a snapshot understanding of production across different temperatures,” says Dolloff. “This is useful information for anyone interested in Appalachian fish and their response to disturbance.”
For more information, email Andy Dolloff at firstname.lastname@example.org.