Great Lakes
The sinking of the steamship Straits of Mackinac to create a new artificial reef in Lake Michigan. 8 a.m. Docked at 117th and Torrance, to be towed up the Calumet River. (Charles Osgood/Chicago Tribune/TNS)

Fish eggs are suffocating in Lake Michigan reefs. What will it take to save these nurseries?

cross the Great Lakes, collections of underwater rocks have been incubators for native fish eggs.

In Lake Michigan, this reef habitat can vary from a field of cobblestones the size of baseballs to a hulking assemblage of boulders. Every fall, species like lake trout return to these spawning grounds to deposit eggs into crevices between the rocks, which protect the unhatched fry. For months, even after they’ve hatched, juveniles hide in these cracks to avoid being eaten by predators.

Over the past 30 years, scientists and fishery managers have tried to replicate that success, building numerous artificial reefs to boost fish populations. But experts question whether these reefs are a viable solution because of threats posed by invasive species and climate change.

Without a suitable nursery habitat, the fish population will keep shrinking, said Alex Gatch, a former fisheries technician with Cornell University and the U.S. Geological Survey who is researching approaches to restore spawning reefs for a master’s degree at Purdue University.

“It’s just one piece to the puzzle, but it’s an important one,” he said.

Many Great Lakes reefs, man-made and natural, have been smothered by invasive zebra and quagga mussels that have colonized the lake bottom, leaving eggs exposed and more vulnerable to predators. In other areas near the mouths of rivers and tributaries, scientists say, these reefs are being buried by sand and silt, the result of increased precipitation, soil erosion and runoff from climate change.

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