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Blog

Good News for Brook Trout?

leah kirk

By Sarah Farmer

trout.jpg

It's not always the case that the "further research" scientists call for in their journal articles brings good news, but sometimes collecting more detailed data yields the unexpected. Results from collaborative research by the US Forest Service and the US Geological Survey may not only bring a sigh of relief to native trout lovers but also provide a precise planning tool for land managers in the Appalachian region faced with rising temperatures from climate change.

The Appalachian Mountains stretch from Maine to northern Georgia in an area crisscrossed by a web of headwaters, creeks, and rivers that teem with fish, crayfish, mussels, salamanders, and a host of aquatic insects. Anglers are drawn to the high-elevation streams of the mountains because of the native eastern brook trout that inhabit the cold, clean waters. Brook trout require cold water for survival, and cannot thrive in streams that warm beyond 70 degrees. Suitable eastern brook trout habitats are scattered along the spine of the Appalachian Mountains, with the southernmost populations of brook trout found in northern Georgia.

Dubbed brookies by locals, adult brook trout boast olive-green sides speckled with golden squiggles and red spots surrounded by blue-gray spheres. Brookies are beautiful, and they're the Southeast's only native trout-though they have company these days. Beginning in the late 1800s, people started stocking mountain streams with non-native rainbow and brown trout brought in from the western United States and Europe. Since then, non-native trout have flourished, often crowding out the native brook trout.

Federal agency managers, conservationists, anglers, and people, in general, have coalesced around the brook trout's plight in relation to the robust non-native trout, in some cases completely removing all trout from a stream and then starting over with brookies. But in 2006, Forest Service research on the possible effects of rising air temperatures on stream water temperatures sent new ripples of alarm through the community of land managers and trout advocates. The research found that over the next century projected rises in temperature might leave only very high mountain headwaters as refuges for coldwater-dependent native brook trout.

The dismal projection relied on widely accepted assumptions about the relation between air and water temperatures; if the air temperature rises by a degree, the water temperature will follow suit, rising by approximately 0.8 of a degree. Since most climate change models predict a 4-degree rise in air temperature over the next century, this would mean a 3.2-degree increase in stream temperatures. For trout and other coldwater creatures that are already at the southern-most extent of their range, this temperature increase could make their homes too hot for comfort-and maybe for survival.

This seemed like very bad news, but it got Forest Service researcher Andrew Dolloff thinking about factors other than temperature rise-slope aspect, forest canopy, and elevation-that aren't taken into account in the large-scale climate models used in the trout habitat studies. "The models used in the coldwater fish habitat studies assumed a pretty close correspondence between rising air and water temperatures," says Dolloff. "My colleagues and I decided to try to verify this and to provide some very specific information for future planning by measuring air and water temperatures in streams that fell within patches identified as brook trout habitat."

When studies, including one by researchers in Dolloff's team, suggested drastic reductions in the historical range of native eastern brook trout based on predictions of temperature rise from the major climate change models, scientists from the National Forest System and the Forest Service Southern and Northern Research Stations, launched a pilot study. Fifty study sites were randomly selected from habitats that presently or historically hosted brook trout populations. Mark Hudy, Forest Service Washington Office National Aquatic Biologist at James Madison University, identified the habitats or patches, which are located on both public and private lands. The researchers adorned each of the 50 study sites with two thermographs (digital thermometers) one in the water at the outlet of a brook trout stream and another dangling from a nearby tree.

Day in and day out, the thermographs record air and stream temperatures every 30 minutes. Originally the researchers intended to show how factors like slope and aspect might affect stream temperature but were in for a surprise when they got readings back from the pilot study in Virginia. "Even in the 50 sites we used for the pilot study it was soon apparent that water temperatures are not always coupled with air temperature, sometimes not at all," says Dolloff. "This suggests that it's really a local matter, and that brook trout might not be as vulnerable to climate change as first projected." During the pilot study, Dolloff began collaborating with Paul Angermeier, a scientist with U.S. Geological Survey (USGS) also based in Blacksburg, to start developing models that combine stream information from the Forest Service and the USGS, a task long in the making and now in process because of a joint climate change research project launched in 2010. For Dolloff it was an easy fit: he and Angermeier have a 25-year history of collaboration.

What started in Virginia has spread, both conceptually and geographically and grown into a full collaboration between the Forest Service and USGS. The study now includes 204 sites and extends from Georgia to Maryland, and the first full year of data has brought good news for trout; the relationship between water and air temperature is relatively insensitive, which means that a rise in air temperature does not lock in a corresponding rise in water temperature. "That said, we also found that the correspondence between water and air temperatures varies a lot from one site to the next," says Dolloff, "It really matters where you are." In sites with a larger drainage area, for example, the water temperature tends to be much more sensitive to air temperature."

To see if the relationships they found in cold water apply to warm water streams, the scientists started looking at air and water temperatures in the Piedmont and Coastal Plain. This part of the project will make use of the extensive data USGS has collected in this area, and will combine models from both agencies to look at how ecosystem services-basic needs provided by the environment might be affected as temperatures rise in the region.

For both this and the cold water part of the study, USGS scientists are also looking at fish as part of a larger universe of ecosystem services. Their approach to ecosystem services goes beyond social benefits like fishing, swimming and boating, and includes the provision of clean water and the processes that regulate stream temperatures. Although essential to human and fish quality of life these ecosystem services are difficult to quantify in dollar amounts. The USGS approach to ecosystem services is unique in that it aims to bridge ecosystem service and fishery domains to look at how services flow from nature to human society, the ecosystem's capacity to provide services, and the degree to which the services are used by people.

For the latest addition to the coldwater streams study, Andrew Rypel, Fisheries Professor at Virginia Tech, and graduate student Bonnie Myers, new members of Dolloff's team, will start summer 2012 collecting detailed information about the abundance, growth, and health of trout in study streams in 20 habitats representative of the study region that extends from Maryland to Georgia. Their work will focus on what's called fish production, which includes the number of fish in each stream and their age, length, and weight. Coupled with information such as the composition of the stream beds, the type and amount of cover, and water chemistry fish production will give the researchers a more accurate picture of the factors that influence the quality of stream habitats.

While difficult to obtain and time-consuming, fish production is the most comprehensive measurement of how fish are doing and whether they're thriving or just getting by. "Fish production will bring our models and projections to life, literally put flesh on the bones," says Dolloff.

Genetic analyses will be part of the fish production work too, giving researchers an idea of whether inbreeding is occurring and offering a general snapshot of how much genetic diversity is within and among the population, and how closely related 'trout families' across streams and watersheds are.

This information is particularly pertinent if the temperature in streams is changing. Healthy streams can host at least 30 to 40 native trout families, each of which spawns in the fall. The eggs incubate over the winter, emerging as fry in the spring. "This life cycle is susceptible to disruption from climate change, as warm winter temperatures may cause the trout to emerge too early, when there's nothing to eat, and many could starve," says Dolloff. "It looks like the winter effects of climate change's effects could impact coldwater species, but the resistance of stream temperatures to changes in air temperature we've found promises some protection."

Project scientists will use the data from the coldwater sites to identify, rank and map the resiliency of the mountain watersheds in the study area to climate change. "This will give managers an effective tool to help prioritize locations for native brook trout survival," says Dolloff. "The unexpected good news is that it looks as if there are many streams that can provide resilient habitat over the next century."