Is Bigger Always Better?
There’s nothing like field work. Breathing in the fresh mountain air while hiking to a remote population of native trout. Watching the sunset over a stream after a long day’s work. And, getting back to the office sore and full of new research questions after seeing nature at play.
Unfortunately, not every research question I think of in the field, can actually be studied in the field. Nature if far too unpredictable and uncontrollable, and fish far too smart, for scientists to risk putting lots of equipment, time, and money into a field-based study. At least not without some careful pilot studies, often conducted in a laboratory. Before coming to Penn State, I used to dream of having a little indoor stream I could use to test some ideas I picked up along the way about fish behavior. Nothing too fancy- just a couple pools and riffles, and a nice population of brook trout. The possibilities would be endless.
Dreams came true within weeks of starting my Ph.D. and finding out that Than Hitt of the USGS Leetown Science Center in West Virginia had…you guessed it…an indoor stream. Complete with..you guessed it again…pools, riffles, and brook trout. We got to work quickly, setting our eyes on understanding how brook trout use thermal refugia- small areas of groundwater upwelling that, in the summer, have water temperatures that can be much lower than average stream temperature. When we started the research, we knew that studies had shown that trout that occupy areas of thermal refugia may be able to survive periods of thermal stress, which could mean that there might be some hope for trout populations facing future stream temperature rise.
But, observing how fish use a thermal refuge in the field had historically proven to be difficult and mostly led to a lot of confusion. For example, previous observations had shown that fish move really far to access a thermal refuge, but then frequently end up leaving the refuge shortly after. This made no sense. If the stream is too hot for the fish, and the thermal refuge is the perfect temperature for the fish, then shouldn’t the fish….you know…stay in the refuge? Welcome to science.
So, why? Why are fish leaving what seems like their own climate-controlled rooms for what surely seems like a death wish? We had two main thoughts. It could be because competition inside the refuge was so high, that fish that couldn’t hold their own got pushed out. Seems plausible, as brook trout are extremely territorial and aggressive. The second thought was maybe the refuge didn’t have other important resources. It might have thermal habitat, but maybe it doesn’t have food, cover, and good flow. So, fish might occupy the refuge for a while, but eventually they will have to leave to fulfill other requirements.
This is where the stream lab proved to be perfect. We could easily manipulate temperatures (thanks to the incredible team of USGS technicians and biologists at Leetown), monitor individual behavior, create some separation between thermal and forage habitats, and start teasing apart why fish were leaving their cushy thermal refugia. Frequent readers of this blog may have some déjà vu and realize that this isn’t the first time this study has been mentioned, as it’s been a topic that Ben Kline, the lab’s undergraduate research assistant, has been writing about for the last year. After we collected all the data in Leetown, Ben did some heavy lifting to analyze videos of fish aggression and millions of lines of data that documented fish resource use. And, I’m happy to say the data are finally in, and I’m confident to share some conclusions. Like….
Big fish really hate hot water. When stream temperatures were cool, big fish ruled the roost. Again, not surprising because brook trout are aggressive, and big fish are typically the most dominant. But, as stream temperatures increased, big fish stopped defending territories near a feeder in the warm part of the stream and spent most of their time in the thermal refuge. Surprisingly, once in the refuge, they basically stopped fighting. Huh. Now, it’s important to point out that fish don’t do anything “to be nice” to their neighbors. They are mostly selfish pricks. They didn’t stop fighting to let other fish into the refuge, but they probably stopped fighting because they didn’t have the energy to fight. The warm water was really sucking the life out of them.
So, the idea about competition influencing fish movement? Wrong. Fish were choosing to leave the refuge.
So, let’s consider the resource hypothesis. In our stream lab, the only area that fish could feed was outside of the thermal refuge. What we found was that, yes, fish did spend most of the time in the thermal refuge when stream temperatures were hot. But, all fish did occasionally make forays into hot water to feed. So, it would appear that our hypothesis about fish leaving the refuge in search of resources may hold some weight. It’s also interesting to note that smaller fish tended to leave the refuge more often, as well as stay outside of the refuge for longer, than bigger fish. So, this is another line of evidence to suggest that warm temperatures affected bigger fish more.
Why do these results matter? Well, we typically assume that the presence of thermal refugia alone is good enough to increase population survival when stream temperatures rise. However, what our results may suggest is that the location of refugia relative to other resources in the stream may also be important. If a stream is too fragmented, then fish will need to spend too much time outside of the refuge in search of resources, and so the presence of refugia may do little to conserve fish populations. Alternatively, if resources are nearby, fish can likely make quick trips back and forth among habitat patches, equivalently “charging their batteries” in the refuge before going in search of food. But, also keep in mind, smaller fish may be the most successful at making these jaunts into warm water, so fish size may also be influenced by refuge habitats.
Another important finding is that small refugia may have large benefits to populations. Because of reduced competition in the refuge, and the constant movement of fish in and out, a lot of fish may be able to take advantage of the thermal properties of refugia. So, the population-level benefits of a single refuge habitat may be larger than we currently believe.
Now, to take it to the field…..
If You Build It, Can They Come?
For states fortunate enough to have cold water flowing through their hydrologic veins, native trout conservation tops the list of management goals for many state and federal fisheries biologists. Often times, we take a “if we build it, they will come (and stay)” approach to conservation. In other words, more habitat equals more fish. Every year, state and federal agencies, non-profit organizations, and local citizen groups spend millions of dollars on stream restoration and habitat additions. This includes everything from riparian plantings to decrease water temperature and sediment transport, instream structures to create pools and slow down stream flow, and even reconstruction of the stream channel.
Does it work? When done properly, yes. Stream restoration activities are great at increasing (sometimes for decades) local trout abundance and survival. But, habitat restoration does not discriminate between species. Good faith efforts to increase one trout species (like native brook trout on the east coast), will also increase populations of nonnative trout- in this case brown and rainbow trout.
If fish shared habitat peacefully, this wouldn’t be a problem. But, nothing in nature is ever that easy. Trout species share habitat like two toddlers in a toy box. Competitions for the best spawning and feeding spots are common, and champion fighters get a major advantage- their first pick of home territories; places that have the most food, the best hiding spots from predators, and not too much flow (otherwise the fish has to use too much energy to swim around). These spots are generally won by nonnative species, who’s faster growth rates and tolerance to warmer temperatures make them gold medal fighters. Worse yet, native species don’t just lose the fight, they are usually kicked entirely out of the playground.
Competition between brook and brown trout is not a new topic. We already know brown trout typically outcompete brook trout because brook trout grow slower and shift their habitat use when brown trout are present. However, figuring out exactly how the two species interact and divvy up space is more of a challenge. Streams are very complex environments with limited controllability. It’s hard to figure out how fish compete for small-scale habitat features (like the features we would typically add to a stream during restoration) when habitat quality changes so fast. We can develop very complex maps that accurately predict the best place in the stream for a fish, and then observe fish interact for those spots. But, one storm can completely change habitat availability and desirability. Likewise, one fish moving in to, or out of, a pool can shake up the competitive dynamics and turn winners into losers, and vice versa. It’s very difficult to make very small scale observations in natural systems.
Enter the experimental stream lab at the USGS Leetown Science Center in West Virginia. Than Hitt recently lead a study that looks at how brook and brown trout compete for different habitat requirements with rising stream temperature. The setup was fairly straightforward- four streams, each with three pools and two riffles. Stream temperature was gradually increased form 57°F to 73°F, all while the last pool was held at a constant 57°F to mimic cold water upwelling areas common in mountain streams. There was also a feeder that continually released food, but it was located at the top of the stream, far from the cold water upwelling. Two streams were stocked with 10 brook trout, and two streams were stocked with 5 brook and 5 brown trout.
The idea behind this design was to supply two areas of required habitat – food and cold water- and see how fish compete for each as temperature increased. When temperatures were cooler, food should be the most desirable resource, and competitions near the feeder should be fierce. But, as temperatures increased, competitions should shift away from food and towards spots in cold water. Brown trout added a layer of complexity, and the expectation was that brook trout should be the best fighters at cold temperatures and win access to food, but at warmer temperatures they would start losing competitions to brown trout.
The result? As expected, the desirability of the food patch declined with temperature. In the brook trout-only stream, fish slowly shifted from spending their time near the food, to spending the majority of their time in the cold water. Not a surprise. Fish can survive several days without food, but they can only survive a few hours in stressful temperatures.
But, when brown trout were present, brook trout couldn’t get near the food. Not at cold temperatures, and not at warm temperatures. Brown trout excluded brook trout from habitat patches were food was most abundant and, overall, brown trout influenced brook trout habitat selection more than temperature.
What this study shows us is that just because habitat is available, doesn’t mean that your target species is able to use it. Instead, removing competing species may do more to increase habitat availability than physically increasing the amount of habitat in a stream. In fact, because nonnative species can exclude native species from desirable habitats, increasing habitat availability could increase nonnative species abundance without doing much to increase population size of native species.
In this study, brook trout were excluded from foraging locations and restricted to habitat that was still thermally suitable. What if they had been kicked out of cold water and into warm water? In this case, brown trout would be pushing brook trout into lethal habitats. This is likely to be the reality moving forward with stream temperature rise. There are a growing number of streams that get seasonally too warm for trout, yet they still maintain populations because trout move into areas of cold water refuge during temperature spikes. For fish that are thermally stressed, these refugia are their last lifeline, and fish are willing to spend their last bit of energy vying for even a few minutes in cold water. Inevitably, competition for such a limiting resource reduces populations sizes as not all fish can occupy the refuge and many are forced into lethal habitats. But, when two species start competing, it will likely result in extirpation of the less successful competitor. And, if history repeats itself, we already know that brook trout are likely to lose.
*Note: Content in this post is my own and may not reflect the opinion of the manuscript's authors or the agencies they represent. I encourage you to read the manuscript so you can contribute to the discussion.
Genetics Make Terrible Guests
Last week I presented some preliminary genetics results using the image to the right, and used it as evidence that brook trout moving into Loyalsock Creek likely spawn outside of their home stream in later years. To put it another way, the fact that we see a mixing of genes at most locations (except for Mill Run), means that these populations were at least historically connected (and the telemetry data suggest at least some of them probably still are now).
Genetics data are such terrible guests for a blog. They come in unannounced, make a mess of the place, and don’t know when to leave. In this case, the mess they created was a lot of questions about what we expected this data to look like. While I’m excited that people want to know more, the answer just isn’t that easy.
For starters, my expectations of this dataset were zero. As you may recall, I hate genetics. My feelings towards the field are starting to evolve into a past-tense form of repulsion, but every day remains a struggle.
Those with a basic understanding of population genetics may have looked at that figure with doom and gloom and wondered why in the world those populations are so isolated. Separated by only a stone’s throw, we would expect all of those populations to be genetically very similar. This is particularly true when we think of land dwellers, which are generally more mobile than aquatic species. In fact, for many terrestrial species and larger-bodied fishes, we’d probably have to separate populations by many miles before we start seeing genetic isolation similar to the above diagram.
But, those that study headwater fishes may have found the results to be of no surprise. Most headwater fishes have very limited dispersal, owning to the fact that downstream habitats become increasingly wider and hotter with faster flows, making them less suitable environments for species that have evolved to live in tiny streams. There are also more predators downstream, so small bodies that are perfect for small streams quickly get eaten by larger fish like bass, pike, etc.
All this to say, interpreting genetics data is a not entirely straight forward. We can get numbers that tell us things about genetic diversity, population isolation, and anything else you might be interested in knowing. But, that’s not the full story, and those numbers are actually meaningless, and potentially dangerous, if used out of context. Our expectations for what the results should be really depend on the species, study location, historic stream use, stocking, etc., etc. It’s a bit of a detective game. So, for those interested in specific numbers describing diversity, FST, AR, NE, rxy, you’re out of luck. They’ll appear in a publication eventually, but only sparingly in this blog.
What I will do is compare, in broad terms, how our data stack up against other studies of brook trout. For starters, our genetics data cover far more than just the sites in that figure. We sampled 28 streams across the Loyalsock Creek watershed, making our study one of the largest scale studies of brook trout population genetics.
Usually changing the scale of a dataset means that you can use your results to answer new questions, questions that may be more appropriate for how we manage species. For example, genetics data are usually collected at the scale of a single stream or maybe a few streams in a small area. However, we don’t generally manage fish at this small of a scale. We generally make management decisions for entire watersheds. So, given that we now have genetics data for an entire watershed, it makes sense that we can now shed new light into the population genetics and management of brook trout at a watershed-level.
Wrong. But, don’t feel bad. I led you on.
The reason our dataset isn’t all that revolutionary, at least at the surface, is because brook trout populations are known to quickly isolate, even at fairly small spatial scales. Even side-by-side tributaries can be isolated from one another. So, if we see isolation at small scales, it’s not that surprising to see isolation at large scales. And, it’s no secret that that is what we’ve found in much of our dataset. Sites that are separated by 3+ miles are isolated from one another, and that’s pretty typical for brook trout.
That said, brook trout genetics are very diverse, particularly at sites separated by less than a mile. Sometimes they are genetically different, and other times they aren’t. To me, this is where things get interesting. If two sites are separated by the same distance and similar habitat, why do we sometimes see isolation and other times connectivity?
I don’t have an answer, but we’re hoping to explore this question with our dataset. And, we have some preliminary ideas. For example, we see that sites near a mainstem river system seem to have more connectivity than sites that are connected by a mid-reach run. What is it about mainstem rivers that makes them better for connecting fish populations? Or, to really wig your brain, what is it about fish living near a mainstem that makes them different (i.e., more mobile) than fish living higher in the headwaters?
That last question may seem a bit far-fetched, but brook trout are known for having a diverse range of life histories. Many of you may be familiar with “coasters,” brook trout living in Lake Superior that make long-distance migrations into the lake’s tributaries to spawn. There are also “salters” which spend a significant portion of their life in saltwater before returning to smaller freshwater tributaries to spawn.
Are fish moving between headwaters and mainstems (like we see in Loyalsock) a true life history variant? If so, how cool would that be? We’re a really long way from being able to say anything about behavioral variation in populations, but I will say that we aren’t the first study to document such dramatic differences in individual behavior. So, there’s support out there for the idea.
But, going back to the main question, how do our data compare to other brook trout population genetics studies? That’s an easy, albeit unsatisfactory, answer. Previous studies showed a lot of variation, and our study shows a lot of variation. So, Loyalsock Creek, as a whole, is not more or less isolated than we would expect given other studies. When we zoom in we see patterns were certain sites do seem oddly disconnected, and others more connected than we would have thought. And, seeing if we can explain that variation is going to be what makes our study so interesting.
How Do Fish Learn?
Today it might be snowing. And the days may still be getting shorter. But, before you know it spring will be here and the forest will come back to life. And, when it does, trout anglers will turn into entomologist and the phrase “what’s hatching” will be heard at tackle shops across the nation
“Match the hatch” is a common phrase among trout anglers used to describe the act of matching artificial lures to aquatic insects that are currently hatching from their juvenile into adult stages. When insects are hatching they are abundant, and so the probability of one floating downstream and being seen by a trout is fairly high.
But, trout are picky eaters. They develop a search image for one or two species of insects and become hyper-focused on eating only those species to the exclusion of all other food sources. Search images are helpful because it helps fish quickly tease apart an insect from little pieces of debris or rocks that could potentially look like food as it floats downstream. It’s kind of like putting together a jigsaw puzzle. There could be a pile of pieces in front of you that go together, but if you’ve developed a search image for edge pieces you’ll look past the other pieces for a long time.
Search images can be helpful because it quickly allows fish to categorize floating objects as ‘food’ or ‘not food’. But, they can also be problematic because hatches don’t last for very long. Sometimes by the time a fish has developed a good search image the hatch is nearly over. If that happens, the fish has a search image for an insect that is no longer common, and the fish will wait to see that specific species float by while allowing many other insects to pass by without being consumed.
More problematic is that search images can take a long time to form. It’s a long trial and error process where the fish has to keep trying to eat a lot of things that look similar to the hatching insect before it hones in on the exact characteristics that make the insect look different than a piece of stick or a leaf.
Search images where the first thing that got me interested in studying trout. At the start it seemed a little silly and a waste of time for a trout to need a search image. But, if you think about it, it makes a lot of sense. If a trout’s is willing to eat everything and has a search image that is too broad, then it will spend a lot of time chasing down little sticks or, worse yet, eat something potentially toxic. But, if their search image is too narrow, it will not eat enough to survive. It’s an interesting problem to have.
More interesting was that, at the time, no one had studied specifically how trout develop search images. Yes, at some level it’s a trial and error process. But, trout live in pools with other trout. And, they have eyes capable of watching what those other trout do. So, my advisor had a hunch. Perhaps they learn search images socially. That is, they watch other fish test out food of various shapes and sizes and that helps cut down the time it takes for a fish to develop a search image.
That was the theory we tested in 2008 in what still remains my favorite study I’ve ever done (a link to the publication that resulted can be found below). We started by going out and electrofishing trout from a small stream in Virginia. But, we had a bit of a unique problem. To track search image development, we needed to not only monitor fish behavior, but be able to trace the behavior of each individual over time. In short, we needed some sort of external that had unique identification for each fish and could be seen from about 50ft away from the stream bank.
The solution was ribbon tags- small pieces of plastic glued to a needed. After the fish is anesthetized, you thread the needle under the top layer of skin, out through the other side, and then tear the needle off the plastic tag. The plastic remains under the fish’s skin (and don’t worry, these tags fall out a few months after they are put in). So, now we had about a hundred fish in the stream swimming around with a little extra bling.
We then installed feeders in two pools that had a lot of fish. The idea was to train some fish to develop a search image and then move these trained fish to new pools to see if they helped new, untrained fish develop search images. The feeders were a series of PVC pipes, a small, battery-operated toy motor, and a photocell. Every 5 minutes the feeder would turn on, spin a little brush in the PVC tube, and out would come some mealworms.
The mealworms were their own story. They came in a can and were intended to be fed to reptiles. And, relative to hatching insects, these mealworms were king size candy bar- high in fat, calories, and exactly what a starving fish wants. But, there was a problem. The worms were fairly moist, and so when they hit the water they would sink. The majority of trout diet is made up of floating insects, and so we needed these mealworms to float. So, out came the frying pan and camp stove, and we fried the mealworms to a crispy golden brown (in what may or may not have been the same skillet we cooked dinner in).
So, with fish tagged and feeders in place we sat and watched. And every time the feeder went off we noted the behavior of every fish in the pool. And, for a long time, their behavior was to do nothing. Feeder goes off, worms float downstream (often right over top the trout), no one eats them. Repeat. For days. And, we did these observations from about 7am-7pm.
But, after a few days things started to change. It started with one brave fish finally eating the worm, but then spitting it up. There was clearly some hesitation. Then a few days later, the fish took the worm swallowed. After that the fish knew it had saddled up to a buffet and it would sit at the feeder anxiously awaiting the next round. In total, it took about 14 days for fish to develop search images. Remember that number.
Below is a video of what this whole process looks like. Look carefully for the tagged fish (his color code is blue-blue-blue) sitting on the far right of the screen. He is sitting in the current waiting for the feeder (the large blue bag) to release a worm, which happens around the 50-second mark. Continue watching after the tagged fish feeds and you'll see him try to fight with another untagged fish.
After these fish were trained, we electrofished out of their home pools and moved them to new pools throughout the study area and installed feeders in these new pools. Here is where we crossed and fingers and hoped. How long would it take a naïve fish to develop a search image for mealworms if they could watch another fish that already had a search image?
Maybe less. We didn’t immediately start observations, but by the time we did untrained fish were already consuming mealworms. To put it another way.
Without social learning it takes 14 days to develop a search image. With social learning it takes less than a day.
Why does that matter? Trout basically starve during summer. They need to be able to quickly switch their search images in order to consume the most calories possible, and social learning is a mechanism they have evolved to use to speed the process up as fast as possible.
Does this study help in trout conservation? Probably not. But, it does showcase how complex the species is socially and intellectually. When asked to give public seminars I often present on this study for several reasons. First, because it’s so unique and different from typical fish research. And, second, because it’s entertaining and, without fail, the audience really connects with the story. So, maybe this research does help in trout conservation. Not with directly improving population health, but in helping from empathetic connections with what is not the most charismatic of animals.
And, now trout anglers can blame social learning when they don’t get a bite.
To read more about this study, click here.
Timing is Everything
The last couple weeks we’ve started our mornings by standing around the truck in sub -freezing temperatures, pleading with the sun to shine a little brighter. This week, it was back to shorts, t-shirts, and hot breezes. Cruel joke, Mother Nature. Not only is it going to make winter feel a little more bitter, but the trout are now confused about whether it’s time to spawn.
My post last week described some of mating rituals brook trout go through before and during spawning. But, I forgot to mention a key part- water temperature! There’s no one set temperature that triggers spawning, but we know that as temperatures drop below 50°F the probability of spawning gets much higher.
Two weeks ago water temperatures in my Loyalsock Creek study streams were between 43-47 °F. We were seeing more fish in riffles, regular and moderate rains were keeping stream flows steady, and fewer fish were swimming away when we approached. Spawning seemed close.
Then, three days of 70°F+ air temperatures and, more importantly, overnight lows above 50°F, and the streams are now back to around 53°F. Reset the clock.
This temperature swing may not seem like much. In fact, it happened frequently during the summer when air temperatures soared into the 90s and forced stream temperatures close to brook trout lethal limits. However, while streams are still fairly cool, in the fall trout are less prepared for quick changes in stream temperature. In the summer, trout are already in deep pools where water is a little cooler. Plus, fish are conserving energy and limiting oxygen demands by moving less. Put another way, trout in the summer are like sunbathers on the beach. They might be hot, but they are lazily lounging and not exerting much energy. In the fall, they become marathon runners and need more oxygen, more energy, and do best when temperatures are lower.
This creates the potential for a perfect storm during the fall. Trout need a lot of energy and oxygen to move and spawn. But, they are not consuming a lot of calories because fewer bugs are hatching and emerging and trout are focused on spawning. Warmer water also carries less dissolved oxygen, and trout are seeking shallower riffles and runs which are prone to heating faster than deeper pools. In short, this means that sudden increases in fall water temperature have the potential to be very stressful despite being well below lethal limits.
And, that’s only the adults. Trout eggs require oxygen-rich, cool water. If trout spawn before a sudden temperature increase, eggs can quickly suffocate from a decline in oxygen or loss of adequate stream flow. If this happens enough, it could cause complete collapse of an entire year class and could quickly cause an entire population to become extirpated from a watershed.
This highlights the importance of another aspect of climate change that is often overlooked. Yes, there is projected to be an increase in stream temperature in the future. But, equally important is the increased variability and unpredictability in weather conditions. Centuries ago weather patterns were much more stable, making temperature a reliable cue that trout could use when deciding the best time to start spawning. Now that weather patterns are more unpredictable, environmental cues are giving false information about the suitability of habitat conditions. Trout can’t predict the future (and the unreliability of 10-day weather forecasts says humans aren’t great at it, either). It took many generations of evolution for trout to use stream temperature as a spawning indicator. So, it’s unlikely that they will quickly learn that they need to wait a few more weeks before water temperatures are safe and stable.
And, water temperature isn’t the only wild card in climate change. There is a fairly narrow range of stream flows that will deliver enough oxygen to eggs while not washing them downstream. And, unfortunately, precipitation is also going to become harder to predict in the future. Just this week Loyalsock Creek suffered devastating flooding that washed away several bridges and many homes. Any trout eggs that were already in the streams likely perished in the high flows. In this, increases in stream temperatures a few days earlier may have saved eggs, assuming the adults survived.
Timing is everything, and climate change is busting the clocks for many trout populations.
Get Out of the Streams
Yesterday I may have tagged the very last brook trout of my PhD. Nearly 200 fish later, it’s hard to believe I closed that chapter of my research. The tracking will continue for at least another month, and we’ll sample again at least one more time for tissue samples, but I have officially tied my last suture. One step closer.
You may recall that in the summer we did several retagging events so that we had most of our tags running at all times. Yesterday was the only retagging for Fall for two reasons. First, between higher stream flows, tagging larger fish, and an improved suturing technique, we are finding fewer dropped tags. Second, we are very close to spawning season.
We’ve seen signs of spawning for a few weeks. The fish we tagged in September were starting to show their iconic orange-bellied spawning colors, and yesterday they were in full force. We have also seen fish moving a lot, particularly out of deeper pools and into smaller riffles and runs. These areas of faster moving water carry more oxygen than slow water in pools, making them ideal habitats for females to build their nurseries, called redds. When a female is ready to spawn, she moves into a riffle ½-2 feet deep, turns on her side, and uses her tail to clear silt and sand from around the gravel. If you’re near a trout stream in the next few weeks, keep an eye out for an area of lightly colored gravel with depressions and mounds- you’re likely looking at the trout’s labor and delivery room.
As females are building redds, males are nearby fighting with one another for the right to spawn with that particular female. They ‘strut their stuff’ and chase, bite, and engage in lateral displays until the most dominant male wins the contest and others are chased away from the redd. At that point, a male and female pair have been established, and the female will lay eggs and males release milt into the substrate. The female then uses her tail to make some final adjustments and move substrate around to ensure that the eggs have just enough flow to survive, but not too much that they get washed downstream during high flows.
The video below by my friend Derek Wheaton of Enchanting Ectotherms Photography does an excellent job of capturing redd construction and male competition.
Each female releases up to 14,000 eggs, which will overwinter in redds. During this time there is high mortality due to lack of fertilization, floods, predation, or disturbance. But, come spring, the surviving eggs hatch into alevins. At this stage, the fish continue to live in the gravel and feed off of a yolk sac that is still attached to the fish. After the yolk sac is consumed, fish transition into the fry stage and are given a cruel welcome to the real world. Tiny fry consume a lot of energy, and so need to quickly find food, avoid predators, and not get washed downstream. Fry also start competing with one another for access to good habitats, so they need to quickly gain some social skills. Once fry grow a few inches in length, they become parr named for the black ‘fingerprints’ running down their side known as parr marks. It takes about a year for parr to lose those black markings and then, nearly two years after starting as an egg, the trout is now an adult. What a cycle!
During spawning season brook trout are hyper focused on building redds or defending territories. They very often stop paying attention to predators- humans included-and are easy to sneak up on without them swimming away. Many times you’ll see a breeding pair of large trout sitting in the middle of the stream, refusing to move, but ready to eat. The easy catchability and gorgeous bright spawning colors often makes fall a popular time to fish for brook trout. For many states trout season is now closed. But, for states like Pennsylvania where it is still legal to fish for brook trout,
STOP FISHING FOR BROOK TROUT.
At least for a few weeks. Hooking and handling are significant stresses on trout, and juvenile health is a direct reflection on how healthy the parents were during spawning. And, no matter how gentle you handle them, you very likely will cause trout to vacate their territories and seek sub-optimal spawning habitats. Plus, redds are hard to spot with even the most trained eyes, so there’s a good chance you will tromp through and either directly cause egg mortality or interrupt the stream flow the female worked so hard to achieve.
If you hit the streams this winter, remember that redds are active through spring, so keep an eye out and walk on the banks when possible.
Animals Eat The Darndest Things
Monday was a day I had been dreading for some time. With the fish tagged and recovered, Dan and I hit the streams trying to locate all the new brook trout we recruited into the study (calling them recruits makes it sound like they had a choice in this matter. They, of course, did not.).
In the summer, I had basically memorized the location of every fish and they rarely moved. So, tracking was as simple as walking to the fish, fine-tuning the location, and entering the data into the GPS. Now, with 60 more tags, higher stream flows, and movement for spawning season, I have to assume none of the fish are where they were last time. Plus, tags are spread across six frequencies, so it takes a lot more focus and time. But, we tentatively set the next sample date for mid-November, which will also signify the end of fall telemetry. Just keep tracking.
The job did get marginally easier, though. We found a few dropped tags which had signs of mammalian predation (teeth marks). We also finally did what I hoped we would never do- tracked a tag into a snake.
I had walked around the tag all morning because I was struggling to get a good signal. This should have been the first tip that it was out of the water. I’ve learned that consistently weak signals are usually the result of pointing the antenna in the wrong direction (i.e., only focusing my attention on the stream, and not the banks. Because fish don’t usually wind up land. Keyword: Usually). Right as we were leaving I finally got a signal strong enough to follow and we scampered up a steep slope trying to hone in on the signal. I was traipsing around a tiny area, wondering why I couldn’t get the signal higher. Dan was starting to wipe leaves away looking for the tag when, you guessed it, he pawed right over the snake. The snake definitely wasn’t happy to see us, but thankfully it was a cold morning or otherwise one of us would have surely gotten bitten.
Lost tags are always a little frustrating. The analyses we hope to complete are very data hungry, meaning every fish counts. That said, dropped tags, particularly tags that end up in odd locations, always spark some curiosity. What happened to the fish, and how did the tag end up where we found it? Sometimes I’m curious because we find the tag really far away; much further than it should have traveled in two days. Other times we find tags next to a nest of fishing line (not so hard to figure out what happened to that fish, but I do wonder want the angler thought when they saw the antenna. Robofish?).
When I find a tag with clear signs of predation, it really reminds me that streams aren’t isolated habitats. Fish biologists spend a lot of time with their eyes in the water and it’s sometimes easy to forget that aquatic and terrestrial habitats are intimately connected. The bugs on the land feed the fish, and the fish feed the land animals (among other things). It’s a tight food web that, if interrupted, can really collapse entire ecosystems. This example was set by 4-foot snake that gobbled up a 7.5-inch trout. An impressive feast. And, the only question that remains for me is how the snake feels about having that transmitter pass through its digestive system.
We were hoping to track on Friday, but Pennsylvania is currently under a black cloud of rain. Hopefully it eases up by Monday and the fish will have done something interesting.
In case you missed it, be sure to check out our special on Pennsylvania Outdoor Life (videos can be found by clicking here). A special thanks to anyone who left comments or feedback, I’ll return all your messages soon! And, if you’re in the area, mark your calendars for October 12th at 7 pm when I’ll be giving a presentation to the Susquehanna Chapter of Trout Unlimited. Come hear more about my research and some early results that are rolling in.
When I’m doing monotonous field work I often purposefully get a song stuck in my head to help pass the time. This week Johnny Cash’s “Ring of Fire” was a perfect fit for the conditions in Loyalsock. Streams continue to heat up and dry out, and the weather forecast shows no end in sight. Fish movement has largely stalled and tags are now found almost exclusively in pools where there is some refuge from predation and somewhat lower water temperatures. Last week I wrote about how fortunate we were for such severe conditions, but I’ve since changed my tune and have had to completely overhaul the upcoming sampling schedule to avoiding stressing during tagging. But, if there’s one thing I know for sure, it’s that field work never continues as planned.
Now that we’ve hit a bit of a lull in the telemetry updates I can introduce another aspect of my project. From movement to genetics, we spend a lot of time collecting data on individual fish. Why? Well, we are interested in what causes individuals to behave differently and while it could be genetic differences it could also be due to differences in personality.
Yes, I just said that fish have personalities. And, much like humans, there is a bit of a ‘nature vs. nurture’ debate about what causes personality to develop. We know that both genes and environment are involved, but we’re curious as to whether certain genes tend to produce certain personalities. More importantly, we want to know if certain personalities tend to move more than others.
In humans, the five major personality traits, also known as the “Big Five” by psychologists, are openness, conscientiousness, extraversion, agreeableness, and neuroticism. While we can’t exactly measure a fish’s neuroticism, there are reliable test for fish that measure such things as aggression, exploratory tendency, and sociability. The most tested personality trait in fish is boldness, and it’s the trait we are attempting to relate to fish movement and genetics.
In addition to being comparable among many other studies, boldness is also relatively easy to measure. You simply place a fish in a tank, allow it a few minutes to calm down, and then record the amount of time the fish spends moving around and in the center. The idea is that when a fish is scared it will try to seek shelter by the sides of the tank. The less a fish is scared in this new environment the more it spends moving around and the bolder it is.
Last year I assessed boldness for nearly 400 fish across 16 sites in Loyalsock. This is one of the first field studies of personality, and by far the largest sample size (the next largest is probably well under 100 individuals). This year we will assess personality for tagged fish to look at how our personality assessments relate to genetic and telemetry data. Ultimately we’d like to find the driver for personality, and provide some information about how and why personality should be considered in conservation plans. For example, stocking only fish that are bold and move really far may not be advantageous when trying to re-establish a population or when surrounding habitat is not suitable for trout.
There’s also other reasons to consider personality in conservation (for example, some personalities are smarter than others), but you’ll have to stay hooked for that.
Behavior was filmed with an overhead camera and I'm in the process of quantifying boldness. I use special software to track the fish around the tank so I can determine how much time it spends moving around the tank (which is indicative of boldness) vs. on the sitting on the side (a sign of shyness).