Invasive Species are Altering the Fisheries of Lake Michigan

January 2016 – The forecasts for anglers targeting Lake Michigan trout and salmon is dismal. The changing condition of the fishery was reflected last year in the lowest catch of trout and salmon in decades despite a 4% increase in angler effort. DNR 2015 creel survey showed anglers caught 269,978 trout and salmon, a drop of 11% from 2014 and lowest since at least 1990.

Lake Michigan has changed dramatically in recent decades, primarily due to the introduction of invasive aquatic species. Non-native mussels, principally the quagga mussel, figure prominently in the declines. Brad Eggold, Lake Michigan DNR fisheries supervisor, reported “the Lake Michigan fishery continues to change with variability in the forage base due to quagga mussels as well as low numbers of available forage in the lake”. The 2015 USGS bottom trawl conducted at index sites around Lake Michigan, reported the alewife biomass was 70% lower than 2014, which makes it the lowest on record.

The lack of forage base is showing up in the condition of the fish. Nick Legler DNR fisheries biologist stated that “three-year-old female chinook salmon that returned last fall to Strawberry Creek near Sturgeon Bay weighed an average of 13.1 pounds, a drop from recent years.

In response to the declining forage base DNR will reduce trout and salmon stocking rates this year to re- balance the number of predator fish with the forage base. One bright spot is found in the walleye fishery on Green Bay, where the native fish has fared very well. Anglers caught more walleyes last year on Green Bay, which were all naturally reproduced.

The alewife is an invasive saltwater species invader that entered the great lakes through the St. Lawrence Seaway. The alewife population boomed causing massive die offs along Lake Michigan beaches in the 70’s creating a smelly nuisance to coastal cities. Salmon and Steelhead trout were non-native species stocked to control the alewife population, and that resulted in a thriving sports fishery which is now supported through stocking programs. Although not initially expected, the salmonids have become nativized and are beginning to reproduce naturally. The native lake trout population was virtually eliminated by the invasive sea lamprey.

Zebra Mussels (Dreissena polymorpha), once considered the scourge of the Lake, have been almost completely displaced in Lake Michigan by the perhaps even more invasion of Quagga Mussels (Dreissena rostriformis bugensis). Coming next? Gobies, whitefish, freshwater drum, lake sturgeon, as well as several species of ducks all eat mussels. David Boyarski; Northern Lake Michigan Fisheries Supervisor, states “it is a good hypothesis that the mussels will simply change the pathways of energy flow in a more of a benthic based system.  However, our fish community in Lake Michigan is not a mussel eating based system and even if it were as simple as changing the energy flow there may be substantial impacts to the species composition and abundance in Lake Michigan (e.g., reduction of pelagic species such as alewife, some trout and salmon)… So the take home is that we are experiencing big changes and exactly how this will all shake out is not clear”  

Updated: January 18, 2017 — 10:31 pm

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