Our undergraduate research assistant, Ben Kline, continues to make impressive progress on analyzing fish behavior videos from the laboratory study we did in Leetown, West Virginia last year. This week, I’m turning the blog back over to him to share a brief introduction on why this study was done. If you missed his first post, be sure to check it out here. Looking forward to getting some results soon!
It is no secret that all living organisms require a few basic resources to survive. Often when we think of these necessities we list things like food, water, oxygen, shelter, etc. While it is obvious to us that we need to meet these basic requirements to survive, we often neglect that our aquatic counterparts have needs that vary slightly from our own. My most recent project in the lab is investigating just how important one of these lesser-known resources is.
There are many factors that impact the availability of essential resources in any given habitat. At a basic level, aspects of the environment, such as climate and geography, limit resources to a fairly narrow range of possible conditions. Just consider the resources available in a mountain stream and those in a coastal estuary. These systems may be fairly close to one another, but the resources are very different because of the physical location of the waterway.
Then there are human practices, such as land and water use, that can further restrict resource availability and/or make habitats more hospitable to particular species. For example, dams have been known to cause considerable changes to species composition, all because of how they alter resource availability, especially flow and water temperature.
Taken together, the distribution and abundance of resources have a major impact on the type and number of organisms that can inhabit a certain space. As promised in my previous post, this week’s post will detail a resource that is less understood by us, but critical to the survival of numerous trout species and other coldwater fish: thermal refuge.
Thermal refuge, in its simplest form, describes the availability of a cold water in a body of water that warms. I don’t know about you, but I have taken an unintentional dip or two while fishing in late spring and early summer and I would be hesitant to say that there is any shortage of cold water available for the fish. So what’s the deal?
To understand the significance of temperature in trout habitat, we should take a closer look at how water temperature shifts with the seasons. In larger bodies of water, such as lakes and large reservoirs, the issue of cold water access during summer is less pressing because of the depth of the water. In these large bodies of water, thermal stratification creates zones with varying water temperatures. At the surface, water is exposed to high summer air temperatures and heats up. And, while wind can cause it to mix and circulate, warm water stays at the surface because cold water is more dense and sinks to the bottom. Thus, the surface water warms while the deeper layers, which are largely not exposed to air, remain cool, even in the hottest parts of summer. This deep layer provides of a site of refuge for coldwater species to retreat to when the rest of the lake becomes too warm.
While this is great news for our lake dwellers, fish that are native to creeks and streams often find it significantly harder to find cold water during the hot summer months. As I mentioned in my last post, the shallow nature of most creeks and streams means that there is no easy way for these waters to remain cold in the summer. Being close to a cold water source, such as a spring or upwelling, can help to keep the water cool. So can the presence of a dense tree canopy or sufficient riparian vegetation. Ultimately; however, the main body of water can warm to the point that the habitat may be unfit to support trout populations for an extended period of time.
Contrary to popular belief, the most serious danger in inhabiting warmer waters is not entirely due to the fact that the fish cannot tolerate warmer temperatures. All organisms have an internal set point known as a thermal maxima, which is the highest temperature an individual can tolerate before it perishes. While brook trout prefer cold water, they have actually been observed to have a thermal maxima of around 25C, which is quite warm in terms of water temperature in temperate regions of the US. In fact, it is not uncommon for trout to favor warming waters that are abundant in food supplies over cool, less productive water for a short period of time.
The real danger with warm water is a little more subtle and lies in the change to the dissolved oxygen content in the water as it heats up . Trout are very sensitive to drops in oxygen, and, compared to other species of fish, do not fare well when the oxygen concentration is too low. As water heats up, the solubility of oxygen (i.e., the maximum amount of oxygen that can dissolve in water) starts declining. As you can see in the graph below, at around 20°C the solubility of oxygen is less than 55% of what it is at 5°C. In short, this means that warmer water has less oxygen. And, with less oxygen in warmer water, trout start becoming metabolically and physiologically stressed and mortality increases.
But, the plot thickens even more. As mentioned above, in thermally diverse systems, there can be a trade-off between cold, oxygen-rich water and warmer waters where there is more food. Too much of either can be a bad thing, and trout have to constantly make on-going decisions about which habitat type they want to occupy at any given moment.
Often times, though, the decision may not be entirely theirs to make as cold water refuge is a very limiting resource. One of the most common sources of cold water refuge are spring-fed tributaries. These tributaries are much smaller than the main channels and provide less habitat and fewer resources to support larger populations. These zones are therefore a major source of competition among fish. There is significant evidence that shows trout populations actively uses these refuge zones during hot times of the year, but there has really been limited observation of just how individual fish use and compete for these limiting resources. Enter the study I am assisting with, where we seek to understand the subtleties behind how individuals seek out and defend cold water resources.
At a basic level, our project involves observing brook trout behavior under a variety of thermal conditions. A population of brook trout, each tagged with a uniquely colored external tag, is placed into mock stream that we have created in the lab. The stream has three pools that we can manipulate to be different temperatures. Our goal is to compare individual interactions as stream temperature changes. So, I sit and watch, for endless hours, videos of fish being fish. I document how every individual interacts with every other individual in the stream and how much time fish spend in cold water vs. near food that is often in warm water. Why? Because we want to know how stable behavior is across temperatures. For example, we want to know how fish rank the importance of food vs. thermal refuge at various temperatures. We also want to see how fish interact among one another at different temperatures. We generally expect larger fish to rule the streams and dominate all other fish at cooler temperatures. But, when stream temperature heats up, larger fish become more stressed than smaller fish and may no longer be able to successfully compete for limiting resources. In short, big may not be better in warmer temperatures if you're a trout.
While it may be a bit soon to comment on the data we have gathered so far, this project definitely holds promise to shed some new light on how individual behavior may shape the complex populations of brook trout that we know and love. We also hope to demonstrate just how important these limiting resources are for sustaining trout populations in thermally complex environments.
It’s been awhile since I’ve posted a true research update. That’s because there’s not a lot going on. I mean, yes, I am working. And, I’m making good progress. But, not every day, or even week or month, leads to interesting results. But, I’m inching forward and I’ll reach the finish line eventually. Until then, I’m sparing you the details of how much pipetting and data entry I do on the average day. Trust me, it’s for your benefit.
This week I was able to get out of the lab and into the field to do my monthly tissue collections. While it’s great to get into the field, this work is always a little anti-climactic. The objective of this study is to determine how fish respond to temperature stress at a cellular level. So, we go out and collect tissue samples, hoping to capture increases and decreases in gene expression, the measure of stress, as stream temperature rises and falls. Seems like I would have a carefully designed, clear sampling plan, right?
Ha. My sampling dates are always a moving target. I try to predict stream temperature by looking at the five-day forecast. But, I’ve found that even obsessively checking all forecasting websites rarely gives a great prediction of air temperature or perception. Even if it did, air temperature doesn’t always predict stream temperature. But, it’s all I got. I then look at my calendar, try to scrounge up technicians and, voilà, I land on a date where it may or may not be the temperature I hoped for, but at least I have some help.
Once I’m in the stream, I have no idea what the temperature actually is. I have loggers recording stream temperature every 30 minutes. But, I don’t download the data until the end of the day so that I know what temperature was while sampling. Doesn’t really matter, though. After a two-hour drive I would sample regardless of the stream temperature.
So, we collect 20 or so fish. Sometimes it’s an easy 4-5 hours, other times it’s a 10-hour fight battling high flows and small fish sizes. When I return back to campus, the samples go in a deep freeze and sit. Sometimes for a few days, sometimes for a few months. Once they are delivered to our collaborator in West Virginia who actually measures gene expression, the samples sit again. Most samples from 2016 have been process at this point, so I have some idea of what the data show. But, it’s still a guess, and I just cross my fingers we’re doing it right.
So, I can’t tell you much about the data we are collecting. But, I can tell you, at least anecdotally, a little about how the populations are looking. Last summer was rough for trout. It was hot, it was dry, and our telemetry data showed that trout were getting picked out of the streams by birds and other animals left and right. There were then high rains in fall that washed away eggs, followed by a pretty mild winter. All in all, there was lot of concern in Pennsylvania about how the populations, particularly the young-of-years, were going to look this spring/summer.
Turns out, they are doing just fine. At least in the handful of streams we are sampling right now. Unfortunately, the one-year-old fish are still a little too small for us to sample just yet, but they are huge. And, come November, these fish will be recruited into our study. More impressive, the young-of-year and little floating footballs. I’m not sure I’ve ever sampled a trout stream with fish that were consistently so large. (You also notice I’m not telling you where we’re sampling. It’s a public stream, but I’d like to keep all the fish to myself, thank you).
Does that mean all the fish in Pennsylvania are doing well after the rough conditions over the last year? Absolutely not. The streams we sample are forested, have minimal fishing pressure, and at least one seems to have an exceptional forage base. In the weeks to come, a more extensive survey of Loyalsock streams will be undertaken by Susquehanna University. Until then, we won’t have a great picture on how Loyalsock populations faired over the last year.
Ten years after my very first field season as an undergraduate, the field season that solidified my love for trout ecology, I have all the data I need for my Ph.D. dissertation. While I’m still working on a side project that occasionally allows me to get my feet wet, the time has finally come to hang up my waders and turn hard-earned data into results.
This is the first summer in that time span that I’ve been home more than away. And, I don’t know how I feel about that. Sure, it’s great buying perishable groceries, taking hot showers, and having a roof over my head. And, I definitely don’t miss the unexplained bruises and deep soreness felt after carrying equipment that was a little too heavy for a little too long. But, I do miss the comradery of being in the field.
For the last ten summers, I’ve put my friends and family aside and welcomed a whole new family into my life. My field family. People who often started as complete strangers, but who quickly learned my favorite foods, my quirky sleep habits, and every one of my pet peeves (including how to push them, when they wanted). Some joined the field family for only a few weeks as temporary technicians. Others were with me for several years and have since become more like members of my real family. From all I learned something, even if just bad habits and the drinking preferences of a retired army vet.
There’s something special about a field family. Field partners see a completely different side of you that many of your closest friends and relatives may never know. I have a hard time describing why there is such a shift in demeanor, but the moment I begin packing the truck things change. It’s a mix of relaxation as you let go of any hopes of cell phone service and internet, but also a black cloud of anxiety as you’re trying to collect as much good data as possible despite constant equipment malfunctions and roadblocks. It doesn’t take long for pleasantries to fall to the wayside, particularly after you haven’t showered in days or seen another person outside of the crew. Everyone is always at some baseline level of exhaustion and frustration, but no one dare complain. Instead, you find laughter. You rib on each other, tell stories, and design elaborate practical jokes. At the end of the day, you squeeze out the last bit of sunshine doing various camp chores, preparing for the next day, and maybe even enjoying a few pages of a book. But, come nightfall, it’s just the crew and a campfire. And, let me tell you, campfire chat gets deep.
You spend a lot of time, celebrate a lot of holidays, and share a lot of experiences with your field crew. As a result, you’ll form a lot of memories with those people that only they will understand. A Corey Smith song playing while you’re driving around the backwoods of Virginia on a foggy evening. A YouTube video of movie outtakes from This Is 40. “Feesh, feesh.” Basement felonies. Fajitas. I can tell you the story behind every one of those, but it’s just not the same.
Nostalgia aside, field partners are also people who you blindly trust to keep you safe. Entering into a field family is an unspoken pact that you will have the other person’s back at all times. And, you take it seriously. Great data can’t be collected when fearing for your safety. Unfortunately, one of the toughest lessons every biologist must learn is where the fine line is between “probably safe” and “that was really, really stupid.” While young scientists dance back and forth around the line often, I don’t think you ever truly learn to not cross it. So, the best you can do is trust that someone won’t put you into the stupid category too often, and will be able to safely get you out when they do. If you can find that level of trust, you’re guaranteed a great friendship. And, nothing will bring you closer than having to test it. Close calls are harrowing experiences, but make for great stories for many years to come.
Even when you’re not pushing the limits, accidents happen and the only way to recover is to come together. I tore my ACL walking next to a stream, and then refused surgery for over a year until my field seasons were complete. I could do that because I am insanely stubborn, but also because I knew my field partner would pick up my slack. He became the defacto person to hike the furthest, carry the most weight, and even support me when my knee starting popping out under the force from high velocity stream flows. Why? Because he’s a great person, but also because we shared a common goal. We needed the data. There’s something special about being part of a large crew that is willing to do whatever it takes to accomplish the goals and see each other succeed.
So, yea, I’m excited that I can see a small light flickering at the end of the tunnel. But, you’ll have to excuse me if I’m feeling just a little sad to be entering into this next stage of my degree. The work may be mentally and physically exhausting, but many of my fondest memories and greatest achievements where made while in the stream with my field family.
Our team is growing! At the end of the semester, Ben Kline, an undergraduate at Penn State, contacted the lab looking for volunteer opportunities. We're always happy to introduce prospective fish biologists to our field, but with limited field time I wouldn't blame any volunteer for losing interest in the work we're doing right now. Not only has Ben not lost interest, but he's taken it upon himself to collect some really great data looking at how individual fish compete for access to thermal refuge. Ben has volunteered to provide some guest posts over the summer, which will chronicle his experience in the lab and a little about what interests him in fisheries science. So, welcome Ben with his looks at Penns Creek, and learn more about him here.
Down along a stream called Penns Creek, there’s a place for me
For as long as I can remember, Penns Creek has always been a part of my life. To be fair, I might be somewhat biased considering that my family farm has sat nestled on the bank of the Penns for over a hundred years. I often think back to my childhood sitting alongside the streambed, gazing into the murky water and just enjoying the quiet. If you have had the pleasure of spending some time on Penns Creek, then there is no denying that this location is certainly a lesser known gem of central Pennsylvania.
Penns Creek is a tributary of the Susquehanna River, which ultimately empties into the Chesapeake Bay and has a long running history in the state of Pennsylvania. The original name “John Penn’s Creek” was named for William Penn’s younger brother, but was eventually adapted to simply “Penns Creek”.
Penns Creek is considered to be Pennsylvania’s most impressive limestone stream in terms of size and length at a formidable 67.1-mile run. A limestone stream is characterized as being sourced primarily from groundwater, meaning that underground aquifers or springs are the source of water for the stream. This means the origin of the water feeding the stream could be countless miles from where the stream actually begins. Limestone streams are known to be shallow and slow moving, and typically are more resistant to changes in temperature once a certain set point is reached. The stream bottom consists primarily of gravel, mud, and sand substrate. Portions of the stream are littered with large boulders that add significant structure and habitat to the waterway and provide host to a variety of aquatic species.
The recreational use of Penns Creek is something that is well known to locals. Spending a day floating down the creek with your best buds or a nice day trip in the canoe or kayak sounds like the perfect way to spend a sunny Saturday in June. Aside from a nice paddle down the creek, Penns Creek also hosts countless opportunities for wildlife watchers with a large population of birds of prey, particularly Kingfishers and Bald Eagles. If birds aren’t for you, this is still a great place to catch a glimpse of painted turtles, muskrats, or even a mink along the streambank.
While Penns Creek offers a great number of opportunities in recreation, perhaps the most noteworthy way to spend ones time on Penns Creek is fishing. Penns Creek is one of the most productive trout fisheries in all of Pennsylvania. However, the Penns is also host to a number of other desirable species such as smallmouth bass, various panfish, and even the occasional walleye. These legendary trout waters are known to host extremely high densities of trout in certain sections of the creek, of which some portions are even considered Class A Wild Trout streams. Anglers have even reported catches exceeding 20 inches in length in some of these locations.
There are a few contributing factors to this highly productive environment. The secluded nature of much of Penns Creek aids in the preservation of these natural populations, with some portions of the creek only accessible by foot, or in some cases, bicycle. These portions of the creek contain large rocks that make excellent trout habitat and help to form deep pools and riffles. The stands of old growth forest that hug the banks of Penns Creek provide an excellent source of refuge for hatching insects from heavy spring rains and predators, which allows for abundant food supply in these locations. The nature of a natural limestone stream is that which enables the water to support abundant natural life, which in this case, is a dense insect population. Droves of caddisfly, stonefly, and mayfly nymphs provide for these productive trout waters. Penns Creek is well known for its hatches, and perhaps the most famous of all is the green drake hatch, which is sought by anglers across the entire country.
Habitat structure and food availability are two factors that make trout abundance high in Penns Creek; however, there is one resource that is becoming increasingly difficult to come by: cold water. Trout require thermal refuge, especially in the summer months when stream temperatures are known to rise significantly. In Penns Creek, the natural springs and seeping of cold groundwater provides cold habitat in the uppermost reaches of Penns Creek all the way into late August, which provides the trout with this limiting resource on a year-round basis.
Despite the presence of consistent cold water in the upper reaches of the Penns Creek that make for excellent trout habitat, the middle and lower sections face significant thermal issues. As the water moves father from its source, the shallow and slow-moving nature of Penns Creek causes the water temperature to rise. As stated before, the nature of the stream makes Penns Creek highly resistant to temperature changes once a significant increase is reached. Since trout require cold water to thrive, many trout populations begin to seek cold water tributaries as refuge in these lower reaches of the Penns.
This fragmented habitat may be the answer to sustaining these trout populations in times of thermal distress from rising stream temperatures. The lower third of the Penns becomes so warm in the summer that it is practically devoid of trout before it empties into the Susquehanna, and is now home to limited panfish and smallmouth bass populations only.
With climate change on the rise and cold water to support natural trout populations on the decline, we are currently seeking answers that may help us to better understand these growing concerns. I am currently working on a study that seeks to understand how individuals respond to a number of thermal conditions. This experiment hopes to identify what characteristics a fish might display that would make that individual more able to seek out and utilize these cold water refuges than others in a population. To do this, we are looking at a variety of data including movement, individual behavior, and genetics. The bulk of the work I am completing right now focuses on analyzing individual behavior and the interaction that individuals have with other members of the population.
There is much more to share about this upcoming project, but I will save that for another post. A very exciting summer awaits, so stay tuned to find out about the gritty details of our new project in the weeks to come.