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GLIN==>> Alewife Die-Off Dumps on Wisconsin Beaches
For Release: IMMEDIATELY
July 2, 1999
For More Information:
Philip Moy, University of Wisconsin Sea Grant Fisheries Specialist,
Stephen Wittman, Assistant Director for Communications, (608)
An Old Alewife's Tale
WHAT CAUSED THIS YEAR'S BIG ALEWIFE DIE-OFF IN LAKE MICHIGAN?
MANITOWOC, Wis. (7/2/99) -- A couple of sharp drops in water temperature
that caught abundant numbers of elderly and weak young alewives in shallow
water is the likely cause of last month's larger-than-usual die-off of the
fish along Wisconsin's Lake Michigan shore, according to University of
Wisconsin Sea Grant Fisheries Specialist Philip B. Moy.
Thousands of dead alewives continued to wash up on Lake Michigan beaches
this week following one of the larger alewife die-offs in recent years,
posing a pungent threat to the plans of Fourth of July beach-goers.
"The spawning run of 1995 produced a large number of young alewives that
were quite robust," Moy said. "But these fish are now four years old and
getting towards the end of their life. The spawn of 1998 also produced a
large number of alewives, but these fish were weaker."
These two large age-groups -- one near the end of its lifespan, the other
young and weak -- had both moved into shallow nearshore waters to spawn, Moy
said, when on at least two occasions in June, there was a sharp drop in
water temperature. The effect of this temperature change would have been
most devastating around June 19-20, he said, when the lake's water was warm
enough (55°F) to induce spawning by the fish.
One other factor played an important part, according to Moy. "For the two
days before the temperature drop, the wind direction was predominantly
south-southwest. Then, for about two days after that, the wind was from an
easterly direction," he said. "Fish that became weak or died during the
rapid temperature change would have been blown in close to shore or washed
up in windrows on Wisconsin's beaches."
Alewife die-offs occur almost every spring and early summer, when the small
silvery fish come into nearshore waters to spawn. These waters are much more
subject to temperature fluctuations, Moy said, and a sudden severe change in
water temperature can be fatal to the fish.
While several factors figure into the annual alewife die-off in Lake
Michigan, the most fundamental one is a flaw in the fish's design resulting
from its oceanic origins.
"The alewife is native to the Atlantic Coast and not well adapted to life in
fresh water," Moy said. "Freshwater fish must constantly 'pump' water out
of their bodies, so they need larger kidneys than their saltwater
counterparts. Alewives don't have this adaptation, which means that they are
already fragile. Any disturbance in their Great Lakes environment can be too
much for them."
He said the good news is that the number of fish washing up on the beaches
should begin to diminish as water temperatures rise, spawning ends, and the
fish move out to deeper water.
For a more in-depth explanation of the die-off, visit Sea Grant's website at
# # # #
Created in 1966, Sea Grant is a national network of 29 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.
# # # #
-- Posted by Stephen Wittman
Assistant Director for Communications
University of Wisconsin Sea Grant Institute
voice (608) 263-5371 * fax (608) 262-0591