Declining populations of brook trout in Shenandoah National Park (SNP)

Fly fishing for brook trout in Shenandoah National Park (SNP) is one of my favorite pastimes.  For me there is nothing more enjoyable than exploring waters of the SNP for native ‘brookies’.  The fact that these fish are stunningly patterned and generally frisky makes it even more enjoyable.  I was introduced to the waters of the SNP on an excursion several years ago with my local chapter of Trout Unlimited.  Now I regularly volunteer to lead excursions to some of our favorite waters in the SNP as part of the chapter’s “Fish with a Member” Program.

In the summer of 2023, I participated (along with more than 70 other volunteers) in an initiative undertaken by the National Park Service (NPS) to collect water samples from 130 different sites within the confines of the SNP.  The objective was to extract Environmental DNA (e-DNA) material to evidence the existence (or not) of brook trout in these streams.  The study was in response to years of monitoring that has suggested declining populations of brook trout within the SNP.  The results were recently made available to the volunteers, as well as the research that has been published in the NPS Park Science journal.

Hogcamp Branch leading to the Rose River in SNP

Neither study has produced encouraging news.  The latter monitoring program has encompassed nearly 30 years of results from electrofishing exercises by the NPS, with considerable involvement of biological technician, David Demarest.  Over three decades he has witnessed a gradual decline that has been confirmed by the official electrofishing exercises.  In the NPS journal article he specifically called out one of my favorite waters at Hogcamp Branch as having less than “100 trout in (the) monitoring site there”, and “in another stream, we’re down from hundreds of trout in the 1990s to single digits now.”

The authors of the paper, Evan Childress and Jeb Wofford, both of the NPS, have identified rising temperatures as the culprit.  Brook trout are cold water species and warm waters are not conducive to a healthy environment for them to thrive.  In their journal article, they indicated that over the past three decades, the brook trout population has declined by 50 percent in more than 70 percent of SNP streams.  That is fairly dramatic.  The more pronounced declines were in smaller, low elevation streams, which represent habitats that are less accommodating due to flow and temperature.

a higher elevation stream with reasonably good flow

The upside results indicate that high-elevation streams (which are cooler) and streams with greater flow trended toward more sustainable populations of brook trout.  Also, the reduction in acid rain as a pollutant has contributed to recovering populations in certain streams with a certain bedrock composition.

The results of the e-DNA sampling study mirrored the discouraging results of the SNP monitoring program.  Of the 130 sites from which samples were collected, only 79 of these produced e-DNA evidence of brook trout populations.  The map produced by the NPS does not show any correlative pattern relative to the waters containing evidence of brook trout relative to those that do not.  Instead, what appears is a very random occurrence of existing versus non-existent brook trout habitat.

white dots = existence of brook trout / red dots = absence of brook trout

If there is any upside to these results, it is that NPS staff now have intel on the more resilient waters and can take steps to protect them, such as “eradicating invasive aquatic species or managing forest pests”.  It may also mean creating strategies to regulate angling activity that could better secure habitat that is at risk.

As conservation-minded fly anglers we can lend support by being more responsible when visiting our favorite streams in the SNP, i.e. use barbless hooks, minimize the handling of the fish and refrain from fishing waters that are bordering on 65 degrees Fahrenheit (and above). We should also allow brookies to spawn in peace during October and November, but also avoid disturbing the eggs during December and January.