Finding sweet spots for brook trout in the Chesapeake Bay Watershed

Todd Petty has thought a lot about how he would restore historic brook trout habitat in the Chesapeake Bay Watershed if he were in charge. He’s put that thinking to good use as one of the creators of the new Chesapeake Bay Brook Trout Assessment and Decision Support Tool, funded by the North Atlantic LCC.

As a Professor of Aquatic Science at West Virginia University, Petty understands what’s at stake. Scientists estimate that brook trout have been extirpated from 60 percent of their historic habitat in the Chesapeake Bay watershed.

But he also recognizes the inherent challenge to taking action. 

“Much of the resistance to putting money to work on the ground is that in such a big world, it’s hard to know where to begin,” he said. “But if you can narrow down the universe to something manageable, you are empowered to act. That’s what we designed this tool for: To narrow things down.”

To prove it, Petty is also working on a proposal to demonstrate exactly how one could use the tool to direct work on the ground.  So what would Petty do if we were responsible for brook trout in the Chesapeake Bay? “I would look for priorities at the 12-digit HUC scale, or what I like to call ‘neighborhoods’.”

Petty elaborated: “Let’s say I’m interested in protecting brook trout in the Upper West Branch of the Susquehanna River. That’s a big area. You could use the tool to find to find specific stream reaches to restore, but that’s a small starting point,” he said.

“But if we can identify the priority neighborhoods to focus on, it becomes more like a neighborhood renewal project. Yes, you still need to fix individual houses, but the goal is to restore the overall function of the neighborhood.”

Petty and his team began the process of narrowing things down in the Chesapeake Bay by building a statistical model for brook trout upon a logical foundation: areas where brook trout are, and areas where brook trout are not. Then they plugged in the set of natural habitat variables (water temperature, precipitation, slope) and stressor variables (impervious surface, agriculture, mining) that are the key determinants for the presence or absence of brook trout.

Because these variables all interact in complex ways, it would be nearly impossible to differentiate between restoration sweet spots and restoration lost causes with the naked eye...unless there happened to be an acid mine draining into the stream in front of you.

More often than not, there isn’t, fortunately. But the downside is: “A lot times, we make decisions about where to expend effort arbitrarily, if a landowner wants work done for example,” said Petty. “It’s good to take advantage of those opportunities, but we should be able to prioritize more objectively, and even target areas that offer multiple benefits.”  

The model provides that objective perspective by interpreting what’s really going on behind the scenes, and the accompanying decision support tool gives practitioners the insight to target work on the ground by providing three lenses for analyzing potential actions:

1. Visualization Module:

In a nutshell: “You can view anything you want to view at whatever scale you want to view it.”

Yes, anything, from the percent of agricultural land in the Upper Gunpowder watershed, to areas where brook trout are most likely to be found in the Chesapeake Bay as a whole. Yes, whatever scale, from small sub-watersheds to major drainage basins like the Potomac River.

2. Ranking Module:

There’s more to deciding where to do habitat restoration work for brook trout than the presence or absence of brook trout. This module lets you mix, match, and yes, rank, all of the other factors that may influence your decision to invest money on the ground, such as locations of other restoration projects that are underway, proximity to populations centers, and vulnerability to climate change.

3. Scenario Analysis Modeling Module:

“We like to call it the futuring tool,” explained Petty. “Except ‘futuring’ is not really a word.” But it is an effective way to communicate what this module can do. By allowing you to change some meaningful aspect of the landscape, and see the potential ripple effects for brook trout populations, it provides a way to quantify the future payoff of conservation actions today. Important note: It works best if you change something realistic about the landscape, like converting agricultural land to forest land in the Morse Branch of the Potomac River, as opposed to adding a volcano to the Morse Branch of the Potomac River. That’d be neat though.

Once you’ve constructed the future scenario, you can rerun the model, and paint a picture of what the landscape would look like for brook trout if you were able to make that change. There’s more! You can run the model for current and future climate conditions, and compare both conservative predictions and worst case scenarios for that area.

“That allows you to identify areas that regardless of climate, could continue to offer benefits to brook trout,” Petty explained. “Areas that would be considered resilient.”

In a universe of big unknowns and urgent threats, that kind of fine-scale assurance is critical for species like brook trout that are up against the odds.

“When you are at the stream-to-stream scale in decision making, there is so much uncertainty, that’s why I’m a proponent of looking at the watershed scale and prioritizing more objectively,” said Petty. “So I know if I do work in a certain area, it’s going to provide benefits to brook trout somewhere. That’s a downstream strategy.”