In the 1980’s, the exotic species we knew of in the Great Lakes were pretty big and their impacts very noticeable. Sea lampreys that reached 17 inches in length latched onto lake trout and other game fish and did not let go until the fish was dead or at least emaciated.
Alewife, another species that entered the Great Lakes area via the St. Lawrence Seaway, were also obvious to everyone who used the Great Lakes or its shoreline. The pale-colored fish had died by the millions in the 1960’s and 70’s and washed up on beaches in stacks several feet high.
Today, we still have plenty of sea lampreys, and exotic species are entering the Great Lakes arguably faster than when we were less enlightened. There are now 183 invasive species known to already be in the Great Lakes and a new species arrives on average every 7 months. Few of today’s newcomers swim in on their own through the St. Lawrence Seaway, rather, they ride on the hulls or in the ballast water tanks of ocean going ships. Among the more notorious are the zebra mussel and quagga mussel and two small fishes- the round goby and the ruffe (pronounces as two syllables: ruff-ee). But the list also includes things we can hardly see such as the spiny water flea, the fishhook flea, and other zooplankton forms. Fishermen spot them fouling their lines, but most Michigan citizens aren’t aware of them. Instead of scarring fishes or making messes on beaches, the new breed of Great Lakes exotics mess up the food chain and affect the clarity of the water.
Problems associated with ruffe and gobies are not as dramatically apparent as with sea lampreys or alewife, but they are also detrimental. Young ruffe eat the same food and compete for the same habitat as native yellow perch, walleye and a variety of other species. Because of this, ruffe can have a serious impact on perch and walleye fisheries without leaving external scars as a calling card. Gobies eat small fish and eggs and in low light conditions have a major competitive advantage over native fish such as darters and sculpins.
Zebra and quagga mussels, on the other hand, feed by filtering from the water large amounts of microscopic algae, which are an integral part of the Great Lakes’ food chain. They kill native clams and crayfish by attaching to their bodies, increase aquatic plant growth by increasing water clarity, and compete with larval fish and other aquatic organisms for food. Zebra and quagga mussels have so thoroughly cleared the Great Lakes water that plants such as Cladophera (an algae) can now grow in much deeper water.
Biologists acknowledge that for today’s exotic species the only effective strategy is prevention. Once ruffe, gobies, or the host of exotic zooplankton, mussels, crayfish and other life forms become established you can’t control them. So, the emphasis has shifted to educating the public as to how to keep them out of inland waters, and on legislative action to stop the introduction of new species by requiring the treatment of ballast water in ocean-going ships.
Prevention is also supposedly the strategy for dealing with the Asian carp, another disaster in the making. The alien invaders have been swimming north since the 1970’s when floods washed them from Arkansas fish farms and lagoons into the Mississippi River. For more than 35 years the Army Corps of Engineers, U.S. Fish and Wildlife Service, Environmental Protection Agency and numerous state fish and wildlife agencies have documented their progress towards the Great Lakes, spending millions on research and planning. But they have failed to place a long-term barrier to entry of Asian carp into Lake Michigan.
On land, control (or lack thereof) of invasive exotic species is perhaps our biggest and most important natural resources management issue. In the 1980’s, some conservationists were sounding alarms but the general public and land managers were just beginning to get it. There was a long period when federal and state biologists actually recommended planting exotics such as Autumn olive and mutiflora rose which have since fallen from grace. Our state’s failure to recognize the inherent threat posed by exotics also led, in part, to inadequate containment of the emerald ash borer. The insect has spread over much of the state, leaving millions of dead trees in its wake. Now, wild boars and other invasive, exotic species are recognized by many as the foremost threat to Michigan’s wildlife. The tragedy is that it took so long for some, especially in management, to get the memo.
The next article will appear on October 15, 2012.