Another Big Alewife Die-Off Likely This Year
By Stephen Wittman
MADISON, Wis. (6/16/00) — Coastal residents should watch out for a repeat of last year’s unusually large alewife die-off in Lake Michigan, according to University of Wisconsin Sea Grant Fisheries Specialist Philip Moy.
“Much depends on the weather over the next few weeks, but two factors make it likely we will have another large die-off this year,” Moy said. “We still have lots of alewives from the large 1995 year-class that are near the end of their normal 6- to 7-year life span, plus a large population of weak young alewives from the 1998 year-class that are now reaching spawning age.”
Originally
from the Atlantic Ocean, alewives
are poorly adapted to life in fresh water and more vulnerable to fluctuations in
water temperature than native freshwater fish, according to Moy. The stress of
winter can leave them in a weakened condition, he said, and spawning puts
additional stress on them. When the nearshore water temperature reaches 55-60
degrees Fahrenheit and the alewives move from deep water to mouths of streams
and rivers to spawn, they are then exposed to the added stress of relatively
rapid changes in water temperature. A
temperature change of as little as 10 degrees over a 24-hour period can be too
much for them, he said.
“If we get a gentle warming with no sudden temperature drops, we may still see a die-off but not the huge numbers we saw last year,” Moy said. “But if we get a nice warm-up to spawning temperatures and then a change in weather – such as prolonged strong westerly winds that cause an upwelling of cold water along the coast – we’ll probably see lots of dead fish on the beaches again.”
Windrows of dead alewives piled up on Wisconsin’s Lake Michigan shores in June 1999 after two fatally steep drops in near-shore water temperature caught the fish as they congregated in shallow waters to spawn and easterly winds washed millions of the dead fish onto Wisconsin beaches.
“I’m tracking daily nearshore water temperatures via the NOAA Great Lakes Environmental Research Laboratory’s Coastwatch Web site, which provides lake surface temperature data from NOAA weather satellites,” Moy said. “I’ll be graphing daily water temperatures off Milwaukee, Manitowoc, Sheboygan, Kewaunee and Algoma on my UW Sea Grant Fisheries Advisory Services Web site – I call it the ‘Alewife Death Watch 2000’ page.”
For More Information:
Philip Moy, UW Sea Grant Advisory Services Fisheries Specialist, (920) 683-4697Conceived in 1966, Sea Grant is a national network of 30 university-based programs of research, outreach and education dedicated to the protection and sustainable use of the United States' coastal, ocean and Great Lakes resources. The National Sea Grant Network is a partnership of participating coastal states, private industry and the National Sea Grant College Program , National Oceanic & Atmospheric Administration , U.S. Department of Commerce. The University of Wisconsin Sea Grant College Program is administered by the Sea Grant Institute on the UW-Madison campus in Madison, Wisconsin.
© University of
Wisconsin Sea Grant Institute 
all audio, images and video used with permission
last updated 22 June 2000
posted 6/16/00 by wittman
www.seagrant.wisc.edu/communications/news_releases/2000/die-off.html
