New study shows key behavioral, physical impacts of increasing water temps on sculpin, headwaters

Susquehanna University graduate Danielle Tryon, center, recently completed a study on how sculpin react to thermal changes in streams. At left is a sculpin at Stony Run, near Lewisburg. Top right is the network of manmade stream channels Tryon used to study the sculpin at Susquehanna's Freshwater Research Institute and bottom right is a sculpin being measured in the lab.

​Riverkeeper note: The following story and podcast package was created/written by Middle Susquehanna Riverkeeper John Zaktansky. You can contact him directly here.

Much more active than originally anticipated, freshwater sculpin instinctively swim upstream when threatened by thermal changes in headwater environments even when cooler water options are not accessible according to a study by recent Susquehanna University graduate Danielle Tryon.

“We expected to see changes over time in their physical condition, but what we didn’t realize was that this species moves around as much as it does when stressed by water temperature changes,” said Tryon, who conducted the study over the course of a year using manmade stream channels at the university’s Freshwater Research Institute (FRI).
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“These channels are recirculating, and each is the same temperature throughout, but in channels with higher temperatures, the sculpin instinctively swam upstream to search for cooler water, which is fascinating,” said Matt Wilson, head of the FRI. “It would be easier to say they found cold water randomly and just sat there, but in these channels where temperatures were consistent across the moving water, they automatically swam upstream to look for relief. There wasn’t any randomness about it.”

Setting up the study
Tryon spent a year and a half repurposing 20-foot-long stream channels with the goal of using them to study sculpin and the species’ reaction to thermal changes in an effort to better understand how climate change could be impacting headwater fisheries.

“The past four years, these channels were basically sitting unfinished and I went in last spring and did all the engineering. I was under them with caulk guns and drills and saws getting them built to best replicate headwater stream environments for this study,” Tryon said.

“We incorporated UV light and made sure water was circulating at the same rate as you’d find in a natural stream setting. We added substrate specific to headwater streams and included macroinvertebrates and other elements to best replicate this environment because it is being impacted the most by climate change and can be so critical for our cold-water species.”

Tryon targeted sculpin because she saw them as a great indicator of thermal stress.

“They are in the same habitat as brook trout, which are a more recreationally vital species and usually get more funding,” she said. “Sculpin are a little smaller, so they can model things in the stream channel better. They are also benthic low-mobility fish, which means they don’t move very much.”

However, the sculpin – which Tryon collected from Stony Run near Lewisburg, were much more active than anticipated.
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“Within four hours of being put into the channels, they were all over,” said Wilson. “There is a lot that happens in our streams that we just assume, and observing these fish in this environment was a good example of how much more we have to learn.”

In fact, the original study wasn’t going to factor in fish behavior in relation to thermal changes – simply physical changes.

“We basically were just going to put them in, feed them and see what happened, and then take them out and see whether they gained or lost weight,” said Wilson. “But Danielle realized within the first couple of days that their movement was a key variable to consider.”

Within different channels, Tryon studied the sculpin in different water temperatures.

“The standard, which they were the happiest, was set to 10 degrees Celsius (50 degrees Fahrenheit),” she said. “Then we intentionally stressed them out in the other channels. Our moderate stress environment had water temperature at 16 degrees Celsius (60F) and in another we had them at one of the highest levels they could be, at 22 degrees Celsius (72F).”

Beyond the behavioral reaction to these different environments, the sculpin were impacted physically, as well.

“We were seeing declines in weight, with individuals moving out of higher-temp areas when they had the capability,” Tryon said. “However, among those not strong enough to get out of the stressed sections, we saw a noticeable decline in body condition.”

Listen to the full interview with Danielle Tryon about her research with sculpin and what we should learn from it in the most recent episode of the Middle Susquehanna Riverkeeper Podcast:

From left, Matt Wilson, Danielle Tryon and Daniel Ressler pose for a photo at a poster session for Tryon's sculpin research.

Waterway impacts
In both scenarios, regardless of whether a sculpin was impacted physically or behaviorally, there can be an immediate effect on the aquatic ecosystem, according to Tryon.

“Sculpin are just a specific part of a bigger food web, where trout are near the top of the aquatic food web. If sculpin react to thermal stress by moving out of a certain section of waterway, you are going to see an increase in macroinvertebrates and algae,” said Tryon. “It is like removing an important part of a puzzle, and then just telling the remaining species to figure it out on their own and hope for the best.”

Wilson agreed.

“Sculpin are middle predators – they eat macros and fish eggs while also functioning as food for trout. If you think about a stream with both sculpin and trout in it, you get this interaction where sculpin are at the bottom eating bugs and other things which allow the trout to feed more on the surface,” he said. “If sculpin aren’t there, it changes things for all the species remaining. This all requires more research to know more about what would happen specifically, but there is a definite change.”
 
What’s next
In fact, Tryon admits there are numerous potential next-step studies with sculpin that could help us better understand the aquatic ecosystem and how to better protect it.

“We could go in and add discharge at high flow rates that could be caused by different phenomenon or a low discharge to represent drought situations. As we change those discharge circumstances, we can pair it with thermal fluctuations and learn so much more,” she said. “We can also go in and add blocks in the channels to look at culvert or dam impacts to the species in relation to thermal changes, or put sediment in the water to look at turbidity and how mucking up the water influences species.”

Tryon’s efforts to make these stream channels at the Freshwater Research Institute viable for research opens many potential doors for future research, Wilson admitted.

“I have a couple of ideas around stream morphology and how particles move in a stream and to look at deposition and erosion. It would be cool to also experimentally measure how sediments build behind structures like beaver dams,” he said. “I am also interested in doing some bigger food web experiments. Like introducing various salamanders, species of fish and aquatic insects, but doing a much longer experiment.”

Tryon, who has moved to Alaska since her Susquehanna University graduation, where she works on research involving salmon weirs, admits that her time at Susquehanna and this study specifically has helped her realize a lifelong dream.

“Growing up, I always wanted to be a scientist. Being at Susquehanna and working in the labs and the Freshwater Research Institute, and then various opportunities with the (Middle Susquehanna) Riverkeeper association have provided so many great opportunities to be the scientist I always wanted to be,” she said. “I learned to be adaptable to be in the field doing studies, to see things in a different way and hopefully have been able to help in at least a small part with my work.”

Along those lines, everyone – scientist or not – has the ability to make a difference, Tryon added.

“Be curious and don’t be afraid to ask questions,” she said. “Find people in your community, whether it is through a nonprofit or a university or even a neighbor, and ask your questions, learn more about this world and your place in it and then get involved.”

Those interested in getting involved in various ways with the Middle Susquehanna Riverkeeper Association are encouraged to fill out the group's online Susquehanna Survey.