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.