For our series, Reporting From the Mon, we’re talking to people with different perspectives on the Monongahela River. For this interview, we head east into the Laurel Highlands to a tributary of the Youghiogheny River, which feeds into the Mon, to find out how fish are faring in a warming world.
The Allegheny Front’s Kara Holsopple talked with David Argent, a biology professor and fisheries scientist at PennWest University’s California, Pa., campus. He and his colleagues recently published a study in the journal Environmental Management that compares the temperature changes of streams on Laurel Hill, a mountain in the Laurel Highlands of southwestern Pennsylvania, and the impact on native brook trout (Salvelinus fontinalis). They found that while trout in groundwater-fed streams did better than in surface water-fed streams, there was a widespread decline in populations of brook trout across the study area.
Kara Holsopple: What did you set out to learn in this study?
David Argent: This particular project started back in 2012. My colleague and I, Dr. William Kimmel, installed a series of temperature sensors on some selected streams in the Laurel Hill. And we had gone back in and sampled those streams using electrofishing gear to evaluate the current status of brook trout populations.
We were using a study that Dr. Kimmel had been involved with back in the late ’80s as a baseline. We were trying to compare the populations of brook trout today with what had happened in the past, and kind of fast-forwarding, then these temperature data loggers, we were keeping track of basically the summer, as well as the wintertime temperatures, and their relation to brook trout populations.
So we had about 10 years or so worth of data. We would go back every year and routinely sample these streams, looking for parallels between climate change and brook trout populations.
And the metric that you used was thermal sensitivity. What is that?
That is the relationship between air temperature and stream temperature. And what we were thinking was that streams that are relatively well-insulated, i.e. they have lots of overhead cover, and that are groundwater fed, would likely be able to not feel the effects of climate change as much as those that might be surface water fed, and or have a more open canopy. So we were expecting those streams to have less fluctuation in their stream temperatures on an annual basis.
And what did you find?
Well, exactly what we pretty much set out to. The streams that were groundwater-fed certainly seemed to be more stable, and they had better brook trout populations than did those that were surface water-fed and had more open canopies.
I will say that across the board, though in comparison to the study that was done in the ’80s, regardless of what type of stream we had, we saw a kind of widespread decline in populations of brook trout across the entire Laurel Hill, somewhere on the order of 60 to 70 percent.
And is that due to temperature change and climate or other factors?
We think that’s part of the reason. Every trout stream has its own unique set of circumstances. Some streams were influenced more by water withdrawal. Some were more influenced by terrestrial landscape disturbance – we had logging in the area. Other streams were influenced by local development, road construction and road improvement types of projects. So climate change certainly didn’t help. But it was one of, we think, two or three other probably mitigating factors.
David Argent
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PennWest University
Researchers use electrofishing to stun fish so that they can count them.
And how did you measure the impact of climate change? Is it just temperature?
We were specifically looking for a critical temperature for brook trout and their ability to complete their life cycle. So we scoured the literature and found 18 degrees Celsius, which is right around the mid-60s Fahrenheit as a benchmark, and anything above that we had identified as thermal stress.
We were looking for the number of days in which trout streams were exposed to this thermal stress or the number of days during which they had exceeded this 18-degree temperature threshold.
Based on your findings, what can be done to help protect brook trout from climate impacts?
Probably in these particular streams, the best course of action would be to protect the water source, try to protect those groundwater sources as best we can. Maintain an intact riparian buffer. I don’t really think fishing pressure is much of an issue because many of these streams are relatively remote. They do get some fishing pressure, but not to the extent, I don’t think, of the streams that perhaps the Fish and Boat Commission might stock with trout. Other than that, educate people and try to, if there are projects going on or logging, try to mitigate the potential impacts of those sorts of activities.
So, groundwater, can you just say a little bit about what would disturb groundwater?
People drilling wells. There are ski resorts that do water withdrawals to make snow, so really, any of those things could impact the water table.
And riparian boundaries?
The riparian zone is a transitional zone between an aquatic and a terrestrial area and in these what we call high gradient streams that are relatively steep there is a buffer width between about 30 to 100 feet wide in some cases that has been determined to be the most effective at not only insulating the stream but also guarding against the migration of sediment which be critical for brook trout reproduction. They are gravel spawners. When sediments get into the gravel, that can also disrupt their population dynamics.
And I hate to say it, but over the course of our study, we had seen Japanese knotweed begin to creep into some of the riparian areas. We hadn’t noted it at the beginning of our studies. But by the end, there were at least three or four streams that had knotweed already starting to grow. I could tell you from my own experience down on the Monongahela River and the tributaries that once that gets in, it does become a species-dominant. So, trying to eradicate that and get that under control quickly would also be something important, I think, to the maintenance of the riparian area.
What impact does it [Japanese knotwood] have?
It’s an annual plant. It doesn’t provide much cover in the summertime. You basically get monocrops of it. It’s not very good as a forage for macroinvertebrates. They’re the stream insects that the brook trout will consume. So it has kind of this cascading effect of ecological consequences if it gets in.
Is there anything that surprised you?
We were very concerned about the rather precipitous decline in populations. I mean, I wasn’t expecting a 60% decline [in brook trout]. A lot of these streams are hard to get to. That was quite surprising.
I was also surprised at the number of streams that received stocked fish, either through sportsmen’s clubs or the Fish and Boat Commission. We had captured a fair number of brown trout on some of these streams. Some streams that historically didn’t have fish in them, I think we were also genuinely surprised to see that they now had fish in them.
So where those fish came from, we’re not quite sure because we don’t really think they were stocked. They look like wild fish. So maybe they were hiding in tributaries or farther downstream. We’re not sure. So that was also kind of surprising.
David Argent is a biology professor and researcher at PennWest University.
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