ML070160349

JAFNPP - SEIS Web Reference - Alewives Great Lakes Wisconsin Grant

ML070160349
Person / Time
Site:	FitzPatrick
Issue date:	01/16/2007
From:	State of WI, Dept of Natural Resources, Univ of Wisconsin
To:	Office of Nuclear Reactor Regulation
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Download: ML070160349 (4)

Text

Text Only The best use for dead alewives?

Compost them! Our brochure shows how. Send an email to Linda , include your postal mailing address, and ask for "The Compost Solution." Why are the alewives dying?

There are several factors involved in the recent alewife die

-o f and the apparently large numbe rs that are washing up on the beaches. These factors are origin and life history of the fish, population abundance, and weather.

Origin The alewife (Alosa pseudoharengus) is native to the Atlantic Coast; alewives entered the Great Lakes through the Welland Canal and made their way to Lake Michigan by 1949.

Alewives are not well adapted to the osmotic stress associate d with life in fresh water. Freshw ater fish must constantly 'pu m water out of their bodies; fish that are well adapted to a freshwater environment have la rger kidneys than their saltwa t counterparts. Because of this physiological stress, alewives a r rather sensitive to disturbances in their Great Lakes environ m Life History Alewives spend most of the year in the deeper waters of the o lake, but come into near shore waters in the summer when th e are ready to spawn. Alewives be gin to spawn when the water temperatures reach about 55-60 o F. In their native habitat alewives are anadromous , swimming upstream to spawn in t h spring. In the Great Lakes, the fish congregate near the outlet s rivers or streams or near harbors that occur at the outlet of a r i Generally, alewives begin repr oducing at about two years of a Alewives do not necessarily die after they spawn, but when t h fish move from the deeper water to near shore areas they are exposed to fluctuating temperat ures. A severe change in watetemperature, such as can occur with upwelling , can cause the to die. Pa ge 1of 4 1/16/2007 file://c:\tem p\2G6T1X8B.htm So, we see there are two underlyi ng factors that relate to ale w mortality in the spring: their fragile condition due to poor os m b alance and being exposed to environmental changes when t h enter near shore waters to spawn. This year, two other factor s involved: age and abundance.

Abundance The spawning run of 1995 produced a strong year class of alewives. In addition to being abundant, these fish were robu s larger than fish produced in other years. These fish are now f o years old, getting towards the e nd of their life. The spawn of 1 produced a strong year class as well, however, these fish, tho u numerous, were not as robust.

Though these were relatively strong year classes, the population is not considered to be 'ov e abundant' and the numbers of alewife in the lake are much lo w than they were in the 1960's.

Weather As these two strong year classes, and other smaller year class moved from the deeper waters to near shore areas this spring, they were exposed to temperat ure fluctuations. These fluctua t probably contributed to the die off and the large numbers of d fish that subsequently washed upon the beach. The graphs be l (see end of story) illustrate the daily high and low Lake Mich isurface water temperat ures from areas near Port Washington a Sturgeon Bay.

Notice that the water temperature generally increased throug hJune, but that on at least two occasions, there was a sharp dro p temperature with a 24-hour period, probably related to upwel levents. The effect of this temperature change on the alewives would likely have been most pr ofound in the latter part of the month, around the 19 th or 20 th. By this time, the water temperature had reached about 55 o F and the fish had probabl y begun to spawn. As indicated by the mid-lake buoy, wind direction in the two days pr eceding the temperature drop, wa s predominantly south, southwest.

For about two days after the upwelling event, the wind was fr om as easterly direction. Fis h that became weak or died duri ng the rapid temperature chang e would have been blown into wi ndrows close to shore or was h onto the beaches.

Thus, in addition to the normal, die-off of alewives, this year had large two relatively abundant year classes, one of older fi and one with small, weaker fi sh near shore during an upwelli n event. The upwelling of cold water occurring during the spa w season probably weakened or killed many of these fragile, saltwater-adapted fish. East winds following the upwelling e v contributed to the large numbers of fish accumulating on the shoreline. The number of fish washing up on the beaches sho u begin to diminish as water temp eratures rise, spawning ends, the fish move out to deeper water.

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--Philip Moy, UW Sea Grant Fisheries Spec Pa ge 3of 4 1/16/2007 file://c:\tem p\2G6T1X8B.htm Comments l Credits l About Us What's New l Research News l Fish IDs l Special Features l Kids' Page l Site Map copyright University of Wisconsin Sea Grant Institute Alewife drawing copyright Wisconsin Dept. Natural Resources Brook trout logo illustration copyright 1998 Gina Mikel Last updated 05 February 2002 by Seaman Pa ge 4of 4 1/16/2007 file://c:\tem p\2G6T1X8B.htm