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.
Pennsylvania plans to stock over 4.5 million adult trout this year, of which about half will be rainbow trout. Yet, despite such high stocking densities, we don’t see many stocked rainbow trout establishing breeding populations. How could this be?
For starters, stocked fish mortality can be upwards of 99%. And, dead fish don’t reproduce (science at its finest!).
But, I won’t focus on that today. For a more interesting roadblock, we have to think a little harder about stream ecology and the conditions rainbow trout evolved under. Opposite to brook trout, rainbow trout spawn in early spring from about January-May. In rainbow trout’s native range along the Pacific coast, snowmelt and heavy rains cause consistently high flows during early spring. Predictably high spring stream flows are critical for rainbow trout, as high flows scour the streambed, removing silt, gravel, and debris. Effectively, high flows are the street cleaners that come in after Mardi Gras and prepare the streambed for rainbow trout to spawn. After spawning, predictable summer low flows protect rainbow trout eggs from washing down stream until they can hatch a few months later.
In short, rainbow trout like predictability. Predictably high flows in winter, and predictably low flows in spring and summer.
Now, let’s think about Pennsylvania. Yes, early spring flows are generally higher than summer flows. But, they are far from predictable. One year there might be deep snowpack, the next year there might be no snow at all. Plus, summer flows can be equal to, if not exceed, winter flows. The combination all but assures near 100% mortality for rainbow trout eggs laid in the northeastern United States. Of course, there are exceptions to this statement, and the northeast does have naturally reproducing rainbow trout populations. However, it usually takes some assistance, with most occurring downstream of impoundments (which make flows more predictable) or selectively bred to reproduce in fall.
But, the story doesn’t end there. In the southeastern United States, at the southern edge of the brook trout’s native range, climate change is resulting in more frequent winter rain events and summer drought-like conditions. In short, the more predictable stream flows that rainbow trout need for reproduction. Down south, rainbow trout are not only reproducing, but are starting to outnumber brook, and even brown trout. This is, in part, due to rainbow trout’s higher thermal tolerance, but also because high winter flows decrease brook and brown trout egg survival. It’s not uncommon for entire year classes of brown and brook trout to fail because of high winter flows killing eggs.
Thinking ahead, with changing climates, could rainbow trout eventually becomes more successful at establishing in the northeast United States? Possibly. And, when if/when they do, we’ll see further declines to not only brook, but also brown, trout populations.
Low detection probabilities.
After our failed attempts to collect fish during the March deep freeze, I assumed we could hang up out waders until early May. Our dataset that looks at how brook trout express stress proteins in response to rising stream temperatures was looking great, but it also was missing data for fish collected around 50°F. So, I thought, I just need to hit the waters around early May when I knew temperatures would be in that range.
But, at the last minute I was able to plot our data from May 2016, back when we started this project and stream temperatures were around 50°F. Surprisingly, that is when stress protein production was highest. Now the question becomes- was that truly the peak in stress protein production, or do fish start producing the proteins even sooner in the year? The only way to know is to collect data at cooler temperatures.
No problem, I thought. We’ll move sampling up a few weeks. Plenty of time. But, a quick look at the weather and I realized that Pennsylvania was going from snowing to summer-like conditions practically overnight. Because stream temperatures respond quickly to changes in air temperature, I knew they would be rising quickly. So, it was all systems a go- sampling needed to happen immediately.
Thankfully, Danielle, a technician in our lab working on flathead catfish, was itching to get outside and was ready for the journey. We hit the road at 6am Monday, and pulled 12-15 hours on the creek for most of the week. With recent heavy rains and snowmelt, stream flows were roaring. Pools were too deep to wade through, runs were rapids, and very few fish were in the shallow edges that are surely only temporary additions to the high flow channels. At one point we were only catching about one fish an hour. With Danielle running equipment up and down the banks and me electrofishing through the rapids, those were easily some of the most exhausting field days I’ve ever had.
But, we got the data…18-20 fish per site. Not exactly what we wanted, but it will be enough. Now, we wait in anticipation to get the gene expression data back. Knowing when fish start expressing these stress proteins is turning out to be a more interesting question than I originally thought. From the data we already have, we know that expression is basically zero during peak summer temperatures. This seems a little suspicious, as we would expect stress protein expression to increase with increasing temperatures (more stress=more stress proteins). But, in reality, it seems that fish express stress proteins in highest abundance at the first sign of increased temperatures.
So what? Well, if stream temperatures rise too soon in spring, fish start expressing stress proteins earlier. But, there is a finite amount of proteins that can be expressed and, by summer peak temperatures, fish have essentially run out of stress proteins. To put it another way, the fish we study are wired to produce stress proteins that were probably more adequate for past climates where stream temperatures rose later in the year and didn’t get as hot. Today, with higher maximum temperatures and longer duration of warm temperatures, trout may not have enough stress proteins to adequately protect their cells.
As with everything, the story is much more complicated than that. Stress proteins stick around long after expression, so expression is not a complete indicator of presence. And, we are studying only one of many stress proteins. But, we do know there seems to be a finite amount of stress proteins that a fish can express before the machinery gets turned off; a conclusion that is a bit troubling when considering the impacts of climate change on brook trout.
With this round of sampling, we also bid farewell to my three telemetry sites. I’ve spent the better half of the last year walking around those sites, and to have left there for the very last time was a bit surreal. I’ll be back Loyalsock, but I’m definitely transitioning out of the field and into data analysis. The beginning of the end? Maybe.
A few months ago I explored the story behind the names for two fish-themed beers- one from Bell’s Brewery (Two Hearted Ale) and another from Hardywood Park Craft Brewery (The Great Return). This morning I saw the new t-shirt design for another fish-centric brewery, Coelacanth Brewery and thought “hey, maybe I should bring back the mini-series for this week’s blog.”
And then I realized that today is National Beer Day.
Okay world, I’m listening.
The slogan for Coelacanth Brewery is “ugly fish, beautiful beer,” and boy did they hit the nail on the head with that one. Because this is a fish blog, I’ll focus on the first half of that slogan (but I assure you, the second half is also no lie).
Located in Norfolk, Virginia, Coelacanth Brewery (which you can see the phonetic spelling of on their t-shirt design, along with the proper Virginian pronunciation of Norfolk) is named after one of the most ancient fish species still alive. Long thought extinct, the first living coelacanth was discovered in 1938 off the coast of Africa. The African coelacanth enjoyed it’s status as the only living species for nearly 60 years until it was joined by another species of coelacanth found off the coast of Indonesia (ironically this species was first discovered at a market, but it was caught alive a year later).
Coelacanths are the fisheries equivalent to a living dinosaur, and critical pieces of evolutionary history. Though later genomic studies debunked this myth, it was once thought that coelacanths were the ancestors to modern-day tetrapods (four-limbed vertebrates including amphibians, reptiles and, that’s right, even humans). It was later determined that lungfish, a close relative to coelacanths, were the first to walk out of water. But, looking at a coelacanth’s fins it is easy to see why scientists were mistaken. Those weird looking, oddly placed appendages are not the ray fins that we typically find on fish. Rather, coelacanth fins are fleshy and lobed, much like we might associate with a salamander or frog. Moreover, they move their fins in an alternating pattern similar to how a dog moves their legs when trotting. This unique fin structure is what classifies coelacanths into the class Sarcopterygii, of which most species belonging to that class are now extinct.
But, the weirdness of the coelacanth doesn’t end with its fins. While most fish lay eggs, coelacanths actually give birth to live young, known as ‘pups.’ These pups are able to immediately start fending from themselves and feed with the help of an electrosensory organ on their nose. This organ allows coelacanths to detect changes in electrical signals around them, which can be used to detect prey and even navigate around their environment. Coelacanths also enjoy the benefits of a hinged jaw which, much like a snake, can be opened far wider than their heads so they can consume a very large meal at once.
Living up to 60 years old and growing up to 6 feet long, an adult coelacanth is one of the longest lived species of fish. However, scientists don’t know that much about coelacanths because they live in the deep sea and are most active at night, two conditions that make studies difficult to near impossible. But, with the limited information in hand, our best guess is that coelacanth populations are endangered, with some estimating as few as 1,000 individuals remaining across the two species.
Our inability to study coelacanths means that we really lack great information on what threatens their populations and what we might be able to do to increase population sizes. But, we can rule out with some certainty that populations are declining from targeted predation (both human and animal), because coelacanths are about as appetizing as they look. Much of their flesh is oily and waxy, including their braincase which is nearly 99% filled with fat and only a small fraction of actual brain tissue. They even lack vertebra and instead of a bony backbone, they have an oil-filled tube known as a notochord (which is another throwback to primitive body plans that was once common in many now extinct species). While possible predators of coelacanths know to avoid these swimming wax candles, one possible source of preventable mortality is as by-catch in deep sea fishing trawls.
So, part tetrapod, part snake…mostly fat and full of ugly. I can’t say coelacanths will ever top my list beautiful fish species, but you have to appreciate their history…and the fact that there’s now a brewery that bears their name.
Science communication is quickly becoming a necessary item on every scientist’s resume. It’s no longer good enough to convince other like-minded Ph.Ds that your research is worthwhile. You somehow have to get the general public to buy-in to the fact that the work you do is necessary and worth funding. And, no amount of graphs, statistics, and confusing jargon is going to accomplish that.
For those in natural resources, scientific communication is particularly necessary for accomplishing our research goals. Not only are most projects funded by tax dollars, but the long-term success of our work is only possible when a community wants to see the ecosystem restored and/or conserved. Simply put, I can restore the stream, but only the community can keep it healthy.
Ironically, despite our jobs being so intertwined with the public, many of us in natural resources struggle to communicate our research outside of academia. I’m willing to bet that many of us, myself included, got into natural resource careers because we thought we would spend more time holding fish than shaking hands. So, now presented with the task of communication, we take entire workshops on using social media (Facebook, Twitter, etc.), writing to a lay audience, and hosting outreach events. Yet, it still feels like we’re pulling teeth sometimes.
Thankfully, I enjoy telling stories. And, ultimately, I think that’s what scientific communication is about- telling the story of how the world works, including pieces of the plot that I think are still missing (i.e., my research), and convincing you that you also want me to solve that mystery. But, sometimes people don’t want to read the story. Sometimes they just want to flip through the pictures. Enter science art.
I started drawing some years ago while bored in a fish lab. It evolved into a little painting and, most recently, the scratchboard piece featured in this blog. The piece itself doesn’t tell much of a story. But, we don’t share long blocks of texts, graphs, or presentations over social media. We share images. And, if someone happens to see the image and clicks on my website, then it helps communicate my science and tell my story.
The other story it tells it that our fearless leader is getting older! I don’t usually hang on to my artwork, and decided to give this piece to Ty for his birthday last week. Now I can haunt him forever!