Why are so many dead invasive fish washing up on Lake Michigan beaches?
Dead alewives have been washing up on Lake Michigan beaches in larger numbers than usual.
Walking along the beach at Sleeping Bear Dunes, National Park Service wildlife biologist Vince Cavalieri said it’s not good.
“They are coming up in piles in some places. It’s a relatively heavy year, at least, compared to the last decade or so.”
The invasive fish from the Atlantic is believed to have entered the Great Lakes through the Welland canal which allows ships to bypass Niagara Falls.
“Alewife, ever since they’ve been in the Great Lakes, have had die-offs. But their condition is down compared to what it used to be because quagga mussels (are) taking out the zooplankton that they need,” said Jay Wesley, the Lake Michigan Basin Coordinator in the Fisheries Division of the Michigan Department of Natural Resources.
Besides its food supply being diminished, Wesley said one theory is the invasive fish from the Atlantic can’t tolerate the more rapid temperature changes in the Great Lakes. The Atlantic has more gradual shifts in temperature.
Additionally, a tough winter and the lack of food together can weaken the fish, leading to more of them dying.
In the 1960s, alewife die-offs were so bad that heavy equipment had to be brought in to scoop up the piles of dead fish and bury them. The Michigan DNR started introducing salmon to reduce the number of alewives. Chinook salmon feed almost exclusively on alewives. The alewife population has been down for years to the point the DNR decreased stocking Chinook salmon. They didn’t want the alewife to completely disappear because other sport fish now rely on the fish since it’s displaced native prey fish.
The larger than typical die-off could mean the alewife population has increased. With little food and more fish, more of them could be stressed. Fisheries managers might have to adjust how they stock salmon to better control the alewife population.