Native or not?

“I think it’s important for people to rethink how we see lakes and the things that live in ’em,” says Dr. Curt Stager, professor of biology at Paul Smith’s College, nestled in the heart of New York’s Adirondack Mountains. Stager says we’re used to thinking of lakes as playgrounds and resources, places where we go to catch fish or cool down on a hot summer day, but we should also recognize that lakes, and the organisms that live in them, might have something to teach us. “They’re marvels of evolution,” Stager says. “They’ve got amazing stories.”

One lake in particular has a story to tell, a story that has been collecting in the sediment at the bottom of the lake for more than 2,000 years. It’s a story that the humans living on the shores of the lake haven’t been able to hear, until now.

Yellow perch have long been considered non-native to the Adirondacks – the range map for the species shows a big blank spot in the northeastern corner of New York State, where the Adirondacks are located. Because of its non-native status, the New York State Department of Environmental Conservation has eradicated yellow perch (and other non-native fish) from several ponds to make way for brook trout, a highly prized native species which has declined in recent decades.

But what if yellow perch aren’t non-native to the lakes and ponds of the Adirondacks?

“I was skeptical that perch were not native to the Adirondacks,” Stager says. “It just doesn’t make sense that they’re in mountainous areas all over eastern North America . . . and then there’s just one little spot here where they’re not supposed to be.”

So Stager and a team of researchers from Paul Smith’s College decided to investigate the claim that yellow perch were introduced to the region, rather than a native species. They recently published the results of their study in the journal PLoS ONE.

As aquatic plants and animals living in a lake go about their lives, shedding cells and scales and waste products, that material falls through the water and builds up on the bottom as sediment – the top layer of sediment contains the most recently shed cells and scales, and deeper layers hold progressively older records of what used to live in the lake.

On a bright and cold winter day, Stager and his team drilled through the snow and ice covering Lower St. Regis Lake, on the edge of Paul Smith’s College’s campus, and used a long, skinny tube to extract a core of sediment, just under four and a half feet tall, from the bottom of the lake. The deepest part of the sediment core they lifted out of the lake was between 2,131 and 2,315 years old – well before the relatively recent era of non-native fish introductions in the Adirondacks.

The researchers took samples from the middle of the core, where the edges of the tube couldn’t have smudged and mixed the sediment, and analyzed them for yellow perch DNA.

Study co-author Dr. Lee Ann Sporn extracting samples from a sediment core in the lab. 

(Image by Dr. Curt Stager)

They found evidence of yellow perch throughout the entire sediment core – meaning that yellow perch have likely been living in Lower St. Regis Lake for over 2,000 years. (They also analyzed samples from cores taken from lakes without any yellow perch, to make sure that they hadn’t contaminated their tools with perch DNA, and those samples all came back negative.)

Based on the evidence contained within its sediment, Lower St. Regis Lake is telling us that yellow perch are native to the Adirondacks after all.

Still, something has been changing in the lakes of the Adirondacks – as brook trout declined, yellow perch became more numerous than they were in the past. In the 1800s and early 1900s, there were so few perch in the Adirondacks that naturalists usually didn’t find them at all during net surveys – which is why they were thought to be non-native in the first place – but as Stager says, “a net survey is not a reliable way to tell if something’s not there. If you catch it, you know you have it, but if you don’t catch it, it doesn’t mean it’s not there.”

So why have yellow perch done so well in recent decades? Stager says there are lots of possible explanations – climate change and warming lake temperatures, overfishing of brook trout, human activity fueling ecosystem production, and probably others, too, all of which created conditions that were detrimental to brook trout but advantageous to perch.

Stager and his team only looked for yellow perch DNA in the core from Lower St. Regis Lake, but they have big plans for the future. Brook trout are cherished partly because there are unique strains of the fish that exist only in the Adirondacks; now that they know that yellow perch have been there for thousands of years, the researchers wonder if they could have evolved unique strains, too. Stager believes he can use the DNA stored in sediment cores to reconstruct the history of entire lake communities.

And he hopes that people will start paying closer attention to the stories that lakes can tell us. “I hope this kind of thing really helps us see there’s a much richer heritage we’ve got here than just something to snag on a hook.”

The researchers drilled through snow and ice to extract a sediment core from Lower St. Regis Lake in the Adirondack Mountains of New York State.

(Image by Dr. Curt Stager)