Professor investigates the Jackson River’s declining trout population

Alleghany County, Virginia – The Jackson River’s tailwaters have long been regarded as one of the top trout fishing locations in the Eastern United States. Anglers on the Jackson River, however, have reported seeing and catching fewer trout in the river’s waters during the past several years.

A biology professor from Washington and Lee is now trying to figure out why.

Robert Humston is Washington and Lee’s John Kyle Spencer Director for Environmental Studies. The Virginia Departments of Wildlife Resources and Environmental Quality have awarded him a $29,000 grant to oversee a group of student researchers who would evaluate the trout population in the river, determine the causes of the population loss, and suggest ways to improve circumstances.

According to Humston, the DWR has asked him to assist in evaluating the Jackson River’s trout population twice, the first time being in 2019. He claimed that while there was no indication of a population decline at the time, things have altered in recent years.

Three years or so later, a number of fishermen, myself included, began to see that the quantity of trout we were capturing had significantly decreased. In fact, the DWR biologists acknowledged that they were catching a lot fewer fish than they had previously. Thus, we began discussing last year looking more closely at what is happening in the river,” Humston added. “What you think of when you see a decline in abundance is that the numbers go down because of a poor breeding record or something like that, where they suddenly had trouble reproducing for a few years.”

Humston’s team, which consisted of three students from Washington and Lee and one from VMI, started the project by investigating the river’s trout spawning conditions during the summer.
Among other things, this endeavor involved investigating the characteristics of the optimal trout spawning habitat.

In essence, trout will construct a nest, and they will lay their eggs there. They depart the nest rather than staying to protect it like other fish do. The conditions must be ideal for there to be sufficient water flow down so that the growing embryos can receive oxygen, but also for the fry to be able to swim out of the gravel when they emerge and hatch. The eggs are essentially situated beneath a thin layer of gravel, according to Humston.

The team spent the summer mapping the whole river to find possible spawning locations, tracking trout growth conditions, sampling the quantity of larval insects trout consume, and determining whether the river’s spawning gravels were stable during high flows. They took this action in order to assess the river’s spawning conditions holistically.

The research Humston is doing now was made possible by that summer’s work.

“At the moment, the DWR scientists and I go out two or three times a week to check for signs of trout spawning. The Brown trout are currently beginning to spawn, so we go out and search areas that may be used for spawning and look for signs that they have been constructing nests and other structures,” Humston said.

According to Humston, it is now hard to pinpoint the precise cause of the population reduction.
“An ecology like this is always a very complex system. Therefore, when you detect a significant or dramatic change, there are a lot of factors at play that make it difficult to identify a single culprit and declare, “That was the problem.” That would make fixing things much simpler, so I’m hoping that’s what we find. We’re probably going to discover that a few factors have contributed to the fall of the trout population in certain age groups,” he stated.

According to Humston, recent droughts that have reduced water flows, warmer temperatures that inhibit trout growth, and greater fishing pressure are all potential causes of the population drop. But according to him, there isn’t reliable information on the number of fisherman who utilize the river every day.

After the Brown trout spawn is over, Humston stated, “My next steps are to go back into the data and try to find evidence that perhaps there was an event somewhere along the line where things changed drastically all at once, and then try to look at conditions around that time to see if there’s anything we can point to that was to blame.”

In the spring, when Rainbow trout are spawning, the trout-spawning surveys will be conducted again, and the regions where the trout were spawning will be sampled.

The attention will next turn to the survival of baby trout, which DWR biologists are already investigating, if study indicates that there haven’t been any problems with spawning, according to Humston.

From there, he added, “we can begin to get an idea of what their habitat needs are in this particular river, and see if there are ways that we can either try to find what is stressing them out and see if we can fix that, or make conditions better for spawning and survival.”

The good news, according to Humston, is that if the issues are recognized, trout populations may recover quite rapidly.