Lake trout require a lot of cold, oxygenated water to survive. Lakes in the Adirondacks of upstate New York are at the southern edge of their natural range. Although about 100 Adirondack lakes and ponds are still home to lake trout, even a small increase in temperature could sharply cut that number.

Martha Foley and Curt Stager discuss the long-term prospects of a signature Adirondack aquatic species.

Martha Foley: Let’s talk about lake trout, because there’s been a pretty intense study done of the lake trout populations in the Adirondacks, and unfortunately, how that relates to climate change.

Curt Stager: Yeah, it’s really interesting work. Mary Thill, a researcher with the Nature Conservancy has put out this amazing summary of what do we know about lake trout and what are the environmental challenges they’re facing, and it struck me, as someone who likes to go fishing, that I’ve really overlooked lake trout in favor other things, brook trout or bass.

MF: Yeah, I assume that they’re not as common, just because we don’t think about them. I mean, when I think about lake trout I think about Lake Ontario, you know, big lakes.

CS: Well one reason we don’t think about them is they tend to be down deep, as opposed to the ones up near the surface for someone lazy like me. You’ve really got to try to get lake trout.

MF: It’s because its cold down there.

CS: Yeah, so, in the summer, let’s say the surface of the lake is warming up, that’s where you get the stuff I go after. Down below is another layer, if it’s a deep enough lake, more than 30 feet or so, that’s cooler, and that’s a refuge for lake trout.

MF: So that water just stays down there? Because it’s colder, denser, more oxygenated, right? Because it’s colder?

CS: Yep, cold water holds more oxygen, so they’re down in there but if the lake is not deep enough to have that big reservoir of cold, oxygenated water then over the summer you can’t have them in there. So there are only certain kinds of lakes and certain conditions, so the real key is partly the temperature, but it’s mainly how much oxygen. It really only recharges that bottom water in the spring and the fall when the temperature is just right in the top and the bottom of the lake stir up and it brings oxygen in to recharge that.

MF: Oh, so there’s nothing producing oxygen down there, it has to be replenished. So there has to be that difference between warm and cold, there just has to be enough of it to make that happen.

CS: It’s like refilling the oxygen tank, basically, so the lake’s got to be that way. The concern then is if anything makes that run out quicker, then that can be a problem for lake trout and of course with the area warming now, the weather records are clear, we’re getting less ice as well. The fear is that some of the lakes that don’t have that gigantic, cold bottom reservoir could actually lose that refuge, and lose their lake trout.

MF: So I know this was a really extensive study, are already seeing that? Are we already losing habitat and some lakes are losing their lake trout?

CS: It’s hard to know exactly, we know that we’ve lost a lot of them for other reasons like over-fishing and pollution and invasives. So far, right now it looks like there are about 100 lakes out of the 3,000 lakes and ponds that have them, and the fear is, we do know the warming is happening, we’ve seen evidence of some of the lakes with brook trout that also like cold water, becoming too warm for the brook trout already.

MF: So, are we looking at the trout genetics? I mean we’ve talking about fish that even from pond to pond in the Adirondacks are a little bit different. I mean, you’ve got the XX perch here and the YY perch — they’re different. Are they finding that in lake trout?

CS: Now with genetics really becoming a big thing in fisheries biology, it’s not just interesting scientifically but it’s got practical applications. The Adirondack lake trout are darker colors, and are a little mottled and darkish compared to silvery ones you would find in the Great Lakes let’s say, and that’s probably adapted to the brown water in our lakes. Apparently some genetic strains can handle slightly warmer water too, so it’s well worth working out not just for the scientific purposes but for practical purposes as well to find out what are the different genetic strains out there? And which ones are most resilient to environmental change?

MF: Thanks very much.