September 29, 2011
When discussing all the exotic invaders parading through the Great Lakes, we may soon be forced to scratch zebra mussels from the conversation. Good news? Not quite. According to biologists, larger quagga mussels — also exotic invaders — have entirely extirpated zebes from Lake Michigan by outcompeting them. And quaggas can persist deeper, meaning they cover more total area and make up a larger percentage of the total bio-mass. As quaggas filter plankton out of the water (large adults can filter one liter of water per day), less is available for baitfish. Scientists at the US Geological Survey have reported recent declines in most major baitfish species in the Great Lakes, probably due to the influence of zebra mussels. If so, such reductions could come even faster in coming years, influencing the size, health, and overall population of prized predators like salmon, walleyes, smallmouth bass, and brown trout. Steelhead may be among the least affected, as they stay in the upper part of the water column. Steelhead have been known to transition to massive bug slicks that occur on the surface of the big lakes wherever warm and cool or cold water masses meet, especially when baitfish numbers are low. But overall size could diminish as a result.