I was recently publicly challenged in regard to my opposition in this column to stocking nonnative lake trout over rare wild native Arctic charr in Green Lake. The person behind the challenge, a well-known outdoor writer, defended their position by homing in on hybridization, or what they believe is a lack thereof, as the reason the stocking was not a concern.
To be fair, I used hybridization between introduced lake trout and native Arctic charr — the cause of the loss of Arctic charr of New Hampshire and Vermont — as one of the reasons the lake trout stocking on Green Lake in Hancock County should be suspended. The defender of the stocking countered that there was no evidence of lake trout reproducing in Green Lake, and therefore hybridization was unlikely an issue.
In the scientific world, absence of proof is not proof of absence. Therefore, just because we have not detected natural reproduction of lake trout doesn’t mean it is not happening. Ditto for hybridization.
At more than 3,100 acres, with a maximum depth of over 180 feet and an average depth of nearly 45 feet, detection would not be easy.
Stocking nonnative lake trout over rare wild native Arctic charr of low abundance in Green Lake is wrong. In doing so, we are placing a higher value on a purely manufactured nonnative recreational fishery than an exceedingly rare wild native fish population.
To do this at a time when we are trying to convince anglers to stop moving fish around sends the wrong message — do as we say, not as we do.
Just because the Arctic charr of Green Lake are still there doesn’t mean they are not stressed. In fact, per the Maine Department of Inland Fisheries and Wildlife, Arctic charr abundance in Green Lake is “very low.”
Was this always the case? And while lake trout have been stocked in Green Lake for more than a half a century, again, that doesn’t mean that it is not harming the wild native Arctic charr.
After nearly two decades of not finding any Arctic charr in Green Lake, in 2019 DIF&W found six small fish during a trapping exercise. On the surface, the data showed what appeared to be some level of physical separation between nonnative lake trout and native Arctic charr. This was also used to defend the stocking as being a non-issue, the idea being that the two species were staying out of each other’s way.
There were three examples of what appeared to be physical separation of lake trout and arctic charr. Between 168 feet and 181 feet, four Arctic charr were trapped but no lake trout. From 93 feet to 114 feet, five lake trout were trapped but no Arctic charr. Between 88 feet and 109 feet, 11 lake trout were trapped but no Arctic charr.
A closer look at the data shows a few interesting things that negate the claim that the two species have found separate habitat niches, at least in regard to the native Arctic charr. Between 146 feet and 160 feet, one lake trout and one Arctic charr were trapped. From 170 feet to 180 feet, the result was the same.
This means that stocked nonnative lake trout and wild native Arctic charr are in fact overlapping, at least between 146 feet and 180 feet, the only place charr were found.
Interestingly, between 88 feet and 109 feet, and from 93 feet to 114 feet, 11 and five lake trout were trapped, respectively. Conversely, no Arctic charr were encountered at these depths. This means that only lake trout were encountered between 88 feet and 114 feet. But again, this is not proof of absence.
Based on the data, stocked nonnative lake trout were confirmed between 88 feet and 180 feet, a band of water of more than 90 feet in depth. The only wild native Arctic charr encountered came from within this same band of water, 168 feet to 181 feet, meaning that there is no true separation of species, at least with regard to the rare wild native Arctic charr and lake trout.
This information matters because while hybridization between stocked nonnative lake trout and wild native Arctic charr may not be occurring, there is certainly competition for food and space. There is the possibility of predation of the smaller (5.5 inches to 7.5 inches) Arctic charr by the notably larger (up to 28 inches) lake trout. And is it also possible that the larger and more aggressive lake trout have displaced Arctic charr from certain depths?
Along with landlocked salmon and smelt, lake trout are one of the species that, unless they coevolved, present a serious threat to Arctic charr. It’s not as simple as whether the two species are hybridizing or not. When we stock nonnative fish over wild native fish, we create competition for food and space and, in cases like this, possible predation.