A harsher climate for brook trout?

  • Wild Eastern brook trout like this may be in trouble, according to a recent study. PHOTO BY Eric Aldrich

  • Eric Aldrich—Photo by Eric Aldrich

  • Eric Aldrich—Photo by Eric Aldrich

Monday, March 28, 2016 7:47PM

In one of the Northeast’s most intensely studied streams, scientists have confirmed what has long been suspected: a warming climate is threatening our native Eastern brook trout.

That little stream is in Whately, Massachusetts – about an hour and a half drive southwest of Rindge – but the findings of this recent study could apply to streams across the northeast, including here in the Monadnock region.

It’s one sign of many that climate change is real. It’s here. It’s now. It’s being measured not only in the Arctic’s shrinking glaciers and New England’s rising seas, but also in our abbreviated maple sugaring seasons and brook trout populations. It’s also a sign that we need to put the brakes on greenhouse gases and move towards a clean energy economy.

The delicate, dazzlingwild brookie

If you’ve ever fished for wild Eastern brook trout, you’ll know how delicate and beautiful these amazing little fish are. These aren’t the bullish trout that are raised in hatcheries and thrown into streams and ponds in the spring by the bucket-full. These are the real thing. Our native trout – technically a char –  are often limited in our waters by habitat, genetics, water chemistry and other things to grow only a few inches long and survive a couple of years at best.  There are exceptions, of course, and some of our native non-stocked trout have grown to respectable – even legendary – sizes.

Maybe it’s the speckled beauty’s dazzling colors and remarkable resilience that make it a natural choice as New Hampshire’s official state fish. A native since the Ice Age’s retreat, the brook trout is a needy little thing, requiring clear, cold, well-oxygenated waters. Stream temperatures over 71 degrees is pushing it for brook trout and a few days over 75 degrees is pretty much fatal to Salvelinus fontinalis, the “dweller of springs.”

While brookies have managed to survive over the eons, resilience has its limits, as reported by authors of the recent study.

“Changes in Seasonal Climate Outpace Compensatory Density-Dependence in Eastern Brook Trout” is the title of the peer-reviewed study published in Global Change Biology. It’s a collaboration by Ben Letcher, a fisheries biologist with the U.S. Geological Survey and adjunct faculty in the Department of Environmental Conservation at the University of Massachusetts Amherst; Ron Bassar, an evolutionary ecologist at Oxford University; Keith Nislow, project leader with the U.S. Forest Service Northern Research Station; and Andrew Whiteley, geneticist, also at the Department of Environmental Conservation at UMass.

An EZ Pass for trout

For 15 years – with a small army of interns, grad students and post-docs – researchers studied an array of details along a one-mile stretch of West Brook in Whately and three of its tributaries. Over that time, they closely tracked air and stream temperature, water flow, rainfall and other data. Water temperature and depth were measured automatically every two hours throughout the study.

Tracking the trout

And then there were the brook trout. In West Brook and those three other tribs, researchers tracked more than 15,000 individual brook trout. Four times a year, they captured and tagged trout with little transponder tags, which work like an EZ Pass for fish. When the tagged trout pass readers placed in the stream, the readers keep track of exactly when and where individual fish would pass. They provide a mountain of data on life cycle events.

So, combined with the stream data over 15 years, researchers had a unique and complex look at a whole freshwater system and the wild Eastern brookie.

Among the take-home findings of their study is that conditions in spring, summer and fall are increasingly threatening brook trout populations.

In the spring, a growing number of big rain events spell trouble for trout, when their eggs are hatching and fry, or young trout, are emerging. In the summer, rising stream temperatures and lower stream flows mean higher mortality. The researchers found that stream flows dropped in all four of their streams in the summer and all three tributaries in the fall.

Even three years of extreme conditions of low flow, low oxygen, high temperatures and high spring mortality can wipe out a stream’s entire trout population. Gone. Compared with the geologic time frame of brook trout, three years is the blink of an eye.

Scientists studying West Brook and its tributaries in Whately are looking at the trout’s genetics to see if the brookie can adapt to harsher environments. Answers may be many years or decades off.

Findings from the Whately streams echo conclusions from other studies around North America. And with mounting science like this, we can expect that a warmer climate is affecting our own streams and forests here in the Monadnock region.

In the face of such warming trends, with their consequences to our forests and streams, our cities and coastal communities, we owe it to more than brook trout to nail down solutions. Soon.

Eric Aldrich writes from his home in Hancock. He can be reached at ericadine@gmail.com.