Trout- Goldilocks or Big Bear?
There’s been a reoccurring theme in my posts- stream flow is really important. When streams rise too far, trout can wash downstream and die. When there isn’t enough flow, stream temperatures rise, oxygen availability declines, fish become trapped in isolated pools, and, you guessed it, they can die. But, trout aren’t the Goldilocks I may have led you to believe.
Headwater streams are some of the harshest environments an animal can live in. They are a complex mosaic of habitats- riffles, runs, pools, glides- all connected by the unpredictable flow of water. Flood stages and drought conditions can be separated by only a few hours. Stream temperature changes quickly with rain and air temperature. Aquatic macroinvertebrates, a trout’s major food source, follow their own schedule, and fish have to sit and wait for a causality to float downstream (and in doing so expose themselves to predators). The only thing predictable about headwater streams is that they are unpredictable.
Rivers and large streams are less erratic than headwater creeks, but these larger systems are often too warm for trout and don’t have the right food sources (though, some trout can use these habitats…a story for later). So, for most of the year, trout are basically stuck in these unpredictable headwaters. To survive, trout need to be tough. But, it also takes a team effort. In this case, the “team” I’m talking about is the ecosystem. And on this team, unpredictability isn’t just something that organisms have evolved to survive, but is a necessary player. And, one element of unpredictability needed for survival are what we humans have decided to call “natural disasters.”
Take floods, for example. Loyalsock Creek has had its fair share of flooding the last five years. In 2011 there was a 500-year flood (meaning stream flows are predicted to get that high only once every 500 years). And, just last week, parts of Loyalsock were hit hard with floods that washed away bridges and homes. These events are devastating for humans because we’ve decided to build structures alongside streams. But, trout depend on floods for long-term health for several reason:
Floods clean streams: Trout hate sediment. It scratches their gills, suffocates their eggs, and decreases overall water quality. It can also be a source for diseases and parasites. Even the healthiest streams receive sediment from erosion of riparian land, and the only way to clear it from the stream is with high-velocity stream flows. In a forested watershed, the average rain event will cause little change in stream flows. Streams flows may increase more in an unforested watershed (because there are fewer trees and plants to absorb rain water), but total stream sediment increases because of more riparian erosion. Really high flows and floods are needed to completely clean the system. These high flows cause fine sediment and small gravel to become suspended in the water column and wash downstream. As sediment is passing by, it scrubs algae off rocks and boulders and uncovers a fresh stream bed. What’s left is cleaner trout habitat with less fine particles.
Floods create habitat. If you fish, you know some of the best trout habitat includes submerged logs and large boulders. These features create deep pools and are good hiding spots for trout trying to avoid predators. But, they are extremely heavy. Luckily, water is very powerful. Heavy rains erode banks and cause riparian trees to fall into the stream. But, really heavy floods mobilize trees and boulders from much further away. A large pulse of water can cause a downed tree from the hillslope to enter the stream and become trout habitat. In fact, the lack of fallen trees in watersheds that have been historically logged is a common source of habitat loss in trout populations. Forests less than a century old may appear healthy, but most trees are likely to still be standing and so less wood is available to enter streams during floods.
Floods reconnect populations. On average, trout are good at hunkering down and staying put during high flow events. But, in flood conditions, many fish do get washed downstream. Some likely perish, but survivors find new habitats. This can cause new streams to become colonized or temporarily connect otherwise isolated populations. This is extremely important because connectivity is key to long-term population survival. Populations that are connected have higher genetic diversity, meaning there are more forms of a gene present in the population. This is critical, particularly in highly variable environments like streams, because different genes are better at surviving different forms of stress. Let’s think about a fake example that will bring this point closer to home. A population with low genetic diversity in humans may have, for example, a high proportion of people with blue eyes. If there is a lethal disease that effects only people with blue eyes, then that population would quickly die. However, a population with high genetic diversity may have an equal number of people with blue, green, and brown eyes. Now, if the blue-eyed killer hits, the population declines, but the damage is limited to a small subset of individuals and the population survives. Though this is a fictitious example, similar scenarios do happen in natural populations frequently.
A population with high genetic diversity (represented here as dot colors) is more capable of surviving a catastrophe or disturbance. Here, only the red and blue genes were capable of surviving, but the population did not die. Had the population had less diversity, perhaps only green and orange dots, the population would have died following the catastrophe.
So, in short, trout thrive on human catastrophes. At this point in my research, I would expect nothing less of my study organism.
In the week ahead- it’s (maybe) our last full week of tracking! Hard to believe after six months I can see the finish line. And, I think we are finally documenting the movement patterns we were hoping to see when we started this study. Vague? Yes, but I don’t want to get too excited just yet.
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.
I was recently told that my blog is reaching several young scientists ranging anywhere from middle school students all the way to undergraduate. Welcome aboard! This post is for you and meant to both warn you about the life of a fisheries ecologist but also get you excited by how cool my job is.
The inspiration for this post was a trending hashtag on Twitter last week. When I saw #WhenIWas12IThought I took a moment to think back to my middle school self. I was a B student, hated science, and thought for sure I would become a medical doctor. While I looked forward to lazy Sundays fishing with my grandfather, I thought fish were gross and certainly not something you would (or should) ever devote a career to studying.
And here I am today, devoting my entire life to studying fish.
What changed? Honestly, a series of random events. I wanted to take an Advanced Placement class senior year of high school and Environmental Science seemed like the easiest option. I didn’t realize it until later, but that was the first class I took that I actually enjoyed. As a freshman in college I was randomly placed into another environmental studies class that focused on streams. Having now spent nearly 20 years in school, I can faithfully say that class was the hardest I will ever take and made me question weekly if I was smart enough for college. At the same time, I loved everything about it including long days in the cold rain collecting data and even longer nights in the library trying to write research papers for a professor with exceedingly high expectations. I then needed a summer job, and that same professor was willing to pay me to research trout behavior. I call this my “Monopoly moment.” From there I passed go, collected $200 (not really that far from the truth...fish research pays very little), and have been running laps around the game board ever sense (and even managed to stay out of jail).
The moral of my story is that career paths don’t need to be straight and paved. That’s probably not new advice. And, there are a lot of articles giving more great pointers about how to get a job in the field after you graduate college- volunteer at various organizations, do undergraduate research, and network with professionals in the field, etc. While I could reiterate all of those points, they won’t help you decide whether fisheries science is actually a good fit for you. For that, I have a few points of advice:
Another way to develop communication skills is by presenting an oral or poster presentation at a conference. You can usually get conferences paid for by your advisor, so these are actually like free vacations. Here I am standing at my poster at the American Fisheries Society meeting in Portland Oregon.
So, bottom line, the old adage has a lot of truth- if you pick a job you love, you’ll never work a day in your life.
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.