Since the 1970s, Lake Superior temperatures have risen an average of five degrees Fahrenheit and ice cover has reduced by fifty percent. This makes the lake less hospitable to the fat siscowet or lake trout that favors its cold depths and more susceptible to invasive predators like the lamprey.

Walleye can now live in more areas of the lake than ever before. The Keweenaw Bay Indian Community, who run commercial fishing operations on Superior, have been raising walleye at their hatcheries since 2005, according to an article that ran last week in Scientific American.

A canny adaptation, but it’s clear from the same article that continuing change will require something even greater — a whole new orientation.

“With the changes in temperatures,” the article says at its most thoughtful moment, “the intimate knowledge of the lake that tribes and other anglers have cultivated over the years no longer jibes with reality.” Evelyn Ravindrian, a KBIC natural resource specialist, puts it this way: “people used to know, ‘Well, whitefish will be here this time of day, this time of year.’ Now they have to look around.” This is the bit that stuck with me.

The lake that fishermen came to know intimately is vanishing. It is undeniably a loss, and I found myself wishing the article had more to say about it: the end of a long intimacy, a bereavement, a disorienting absence — the kind of thing one feels after divorce, death or displacement. The end of the known world. I suppose an article written along those lines wouldn’t have had much chance of making it into the pages of Scientific American; but it would have gotten much closer to the heart of the matter.

As the new environmental reality takes hold, a social and cultural reality slips away: all the things “people used to know” about the lake, the seasonal and circadian knowledge that they cultivated and shared and that bound them together, as a people, or simply as Lake Superior fishermen.

They probably took most of those things for granted: that’s the nature of cultural habits, local knowledge, familiar ties — all the things that make up our sense of place. We know where we are without even trying. Now people will have to “look around,” as Evelyn Ravindrian says. They’re in a new and unfamiliar place, even though they have lived around Lake Superior and fished its waters for as long as anyone can remember.