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Alewife die-off hopefully last of summer

Kevin Naze
For USA TODAY NETWORK-Wisconsin, Wisconsin

A massive die-off of alewives of all sizes in the past week likely was due to a rapid drop in water temperatures.

Dead alewives are seen at McKinley Beach in 2014. Researchers found a record low biomass of alewife in Lake Michigan in 2016, according to a preliminary review of data by the U.S. Geological Survey.

Temperatures plunged about 20 degrees after wind and currents from storms upwelled very cold water. Surface temps the mid-40s were seen, and readings as low as the upper 30s were recorded 50 feet down.

Anglers hope that there are no more major die-offs for two reasons: One, catches tend to slow down for a week or more during such events because there are lot of weakened baitfish doing death spirals; and two, alewives appear to be making a comeback this season, and preserving as many as possible to fuel the fishery is a priority.

Alewives are the favored forage of salmon and trout, key players in a multi-million-dollar Lake Michigan sport fishery.

However, a combination of factors — including quagga mussels impacting the bottom of the food chain and more wild-hatched salmon — has led to a drop in alewife year classes and size over the past 15 years or so.

Fisheries biologists implemented a series of salmon stocking cuts in hopes of preventing a baitfish collapse such as occurred in Lake Huron more than a decade ago, and salmon size and condition has improved.