That’s the narrative about invasive species that you’re most likely to hear. Whether it’s kudzu engulfing Southern forests, emerald ash borers wiping out the tree canopy in whole cities, or the beaver-like nutria devouring Louisiana like a swamp buffet, the prototypical invasive species story doesn’t leave a lot of room for the color gray.

But smelt are more complicated — which is to say they have more redeeming characteristics. Take, for instance, their relationship with lake trout. Smelt numbers exploded as wild lake trout declined in the 1950s and ’60s. Around the time Don Schreiner’s parents were refusing to take him to late-night fishing parties, commercial fisheries on Lake Superior were bringing in millions of pounds of smelt a year. For the trout that remained, those smelt became a crucial food source, as other, native food supplies were lost. In 1986, smelt accounted for 80 percent of a Lake Superior trout’s diet. Decades later, smelt are still a major food source for trout, even as the smelt themselves may be partly responsible for the shrinking numbers of the trout’s native food source — herring. Smelt also form the basis of the diet of the Lake Superior salmon, another species that came to the lake from somewhere else. The salmon are a mostly self-sustaining population now, but even though they’re not native to the lake, no state government is making an effort being made to eradicate them, Schreiner said, because, well, many people enjoy fishing for salmon.2