Great Lakes - Ecology

Ecology

The Great Lakes are an important source of fishing. Early European settlers were astounded by both the variety and quantity of fish; there were 150 different species in the Great Lakes. Throughout history, fish populations were the early indicator of the condition of the Lakes, and have remained one of the key indicators even in the current era of sophisticated analyses and measuring instruments. According to the bi-national (U.S. and Canadian) resource book, The Great Lakes: An Environmental Atlas and Resource Book: "The largest Great Lakes fish harvests were recorded in 1889 and 1899 at some 67,000 tonnes (66,000 long tons; 74,000 short tons) ."

By 1801, the New York Legislature found it necessary to pass regulations curtailing obstructions to the natural migrations of Atlantic salmon from Lake Erie into their spawning channels. In the early 19th century, Upper Canada's government found it necessary to introduce similar legislation prohibiting the use of weirs and nets at the mouths of Lake Ontario’s tributaries. Other protective legislation was passed, as well, but enforcement remained difficult and often quite spotty.

On both sides of the Canada–United States border, the proliferation of dams and impoundments multiplied, necessitating more regulatory efforts. Concerns by the middle of the 19th century included obstructions in the rivers which prevented salmon and sturgeon from reaching their spawning grounds. The Wisconsin Fisheries Commission noted a reduction of roughly 25% in general fish harvests by 1875. The states have removed dams from rivers where necessary.

Overfishing has been cited as a possible reason for a decrease in population of various whitefish, important because of their culinary desirability and, hence, economic consequence. Moreover, between 1879 and 1899, reported whitefish harvests declined from some 24.3 million pounds (11 million kg) to just over 9 million pounds (4 million kg). The population of giant freshwater mussels was eliminated as the mussels were harvested for use as buttons by early Great Lakes entrepreneurs.

Logging in the Great Lakes region may have removed tree cover near stream channels that provide spawning grounds which can affect shade and temperature-moderating conditions. Removal of tree cover destabilized soil, allowing soil to be carried in greater quantity into the stream beds and even brought about more frequent flooding. Running cut logs down the Lakes’ tributary rivers also stirred bottom sediments. In 1884, the New York Fish Commission determined that the dumping of sawmill waste (chips and sawdust) had impacted fish populations.

The influx of parasitic lamprey populations after the development of the Erie Canal and the much later Welland Canal led to two federal governments attempting to work together. By the mid-1950s, the lake trout populations of Lakes Michigan and Huron were reduced, with the lamprey deemed largely to blame. This led to the launch of the bi-national Great Lakes Fishery Commission.

The authoritative but now outdated 1972 book The Great Lakes: An Environmental Atlas and Resource Book noted: "Only pockets remain of the once large commercial fishery." Meanwhile, however, the great water quality improvements realized during the 1970s and 1980s, combined with successful salmonid stocking programs, have enabled the growth of a large recreational fishery.

Pollution can affect aquatic food chains, fish populations, and human health. Improved management of the Great Lakes ecology began in the 1960s and 1970s. In the 1960s, a very flammable brown, oily film, consisting of a combination of oil, chemicals, and trash floating atop the Cuyahoga River in Cleveland, Ohio, ignited and smoldered, creating international headlines.

The first U.S. Clean Water Act, signed by US President Richard Nixon in 1972, was a key piece of legislation, along with the bi-national Great Lakes Water Quality Agreement signed by Canada and the U.S. A variety of steps taken to process industrial and municipal pollution discharges into the system greatly improved water quality by the 1980s, and Lake Erie in particular is significantly cleaner. Discharge of toxic substances has been sharply reduced. Federal and state regulations control substances like PCBs. The first of 43 "Great Lakes Areas of Concern" to be formally "de-listed" due to successful cleanup was Ontario's Collingwood Harbour in 1994; Ontario's Severn Sound followed in 2003. Presque Isle Bay in Pennsylvania is formally listed as in recovery, as is Ontario's Spanish Harbour. Dozens of other Areas of Concern have received partial cleanups such as the Rouge River (Michigan) and Waukegan Harbor (Illinois).

Until 1970, mercury was not listed as a harmful chemical, according to the United States Federal Water Quality Administration. Within the past ten years mercury has become more apparent in water tests. Mercury compounds have been used in paper mills to prevent slime from forming during their production, and chemical companies have used mercury to separate chlorine from brine solutions. Studies conducted by the Environmental Protection Agency have shown that when the mercury comes in contact with many of the bacteria and compounds in the fresh water, it forms the very toxic, inorganic methyl mercury. This form of mercury is not detrimental to a majority of fish types, but is very detrimental to people and other wildlife animals who consume the fish. Mercury has been known for health related problems such as birth defects in humans and animals, and the near extinction of eagles in the Great Lakes region.

The amount of raw sewage dumped into the waters was the primary focus of both the first Great Lakes Water Quality Agreement and federal laws passed in both countries during the 1970s. Implementation of secondary treatment of municipal sewage by major cities greatly reduced the routine discharge of untreated sewage during the 1970s and 1980s. The International Joint Commission in 2009 summarized the change: "Since the early 1970s, the level of treatment to reduce pollution from waste water discharges to the Great Lakes has improved considerably. This is a result of significant expenditures to date on both infrastructure and technology, and robust regulatory systems that have proven to be, on the whole, quite effective." The commission reported that all urban sewage treatment systems on the U.S. side of the lakes had implemented secondary treatment, as had all on the Canadian side except for five small systems.

However, those treatment system upgrades have not, contrary to federal laws in both countries, yet eliminated Combined sewer Overflow events. This describes when older sewerage systems, which combine storm water with sewage into single sewers heading to the treatment plant, are temporarily overwhelmed by heavy rainstorms. Local sewage treatment authorities then must release untreated effluent, a mix of rainwater and sewage, into local water bodies. While enormous public investments such as the Deep Tunnel projects in Chicago and Milwaukee have greatly reduced the frequency and volume of these events, they have not been eliminated. The number of such overflow events in Ontario, for example, is flat according to the International Joint Commission. Reports about this issue on the U.S. side highlight five large municipal systems (those of Detroit, Cleveland, Buffalo, Milwaukee and Gary) as being the largest current periodic sources of untreated discharges into the Great Lakes.

Phosphate detergents were historically a major source of nutrient to the Great Lakes algae blooms in particular in the warmer and shallower portions of the system such as Lake Erie, Saginaw Bay, Green Bay, and the southernmost portion of Lake Michigan. By the mid-1980s, most jurisdictions bordering the Great Lakes had controlled phosphate detergents, resulting in sharp reductions in the frequency and extent of the blooms.

Since the 19th century an estimated 160 new species have found their way into the Great Lakes ecosystem, with ship ballast being a suspected pathway, causing severe economic and ecological impacts. According to the Inland Seas Education Association, on average a new species enters the Great Lakes every eight months.

Introductions into the Great Lakes include the zebra mussel, which was first discovered in 1988, and quagga mussel in 1989. The mollusks are efficient filter feeders, competing with native mussels, and can reduce available food and spawning grounds for fish. In addition, the mussels may be a nuisance to industries by clogging pipes. The U.S. Fish and Wildlife Service estimates that the economic impact of the zebra mussel could be about $5 billion over the next decade.

The alewife first entered the system west of Lake Ontario via 19th-century canals. By the 1960s, the small silver fish had become a familiar nuisance to beach goers across Lakes Michigan, Huron, and Erie, as periodic mass dieoffs resulted in vast numbers of them washing up on shore; estimates by various governments have placed the percentage of Lake Michigan's biomass, which was made up of alewives in the early 1960s, as high as 90%. The various state and federal governments began stocking several species of salmonids in the late 1960s, including the native lake trout as well as non-native chinook and coho salmon; by the 1980s, alewife populations had dropped drastically. The ruffe, a small percid fish, became the most abundant fish species in Lake Superior's St. Louis River within five years of its detection in 1986. Its range, which has expanded to Lake Huron, poses a significant threat to the lower lake fishery. Five years after first being observed in the St. Clair River, the round goby can now be found in all of the Great Lakes. The goby is considered undesirable for several reasons: it preys upon bottom-feeding fish, overruns optimal habitat, spawns multiple times a season and can survive poor water quality conditions.

Several species of exotic water fleas have accidentally been introduced into the Great Lakes, such as the spiny waterflea, Bythotrephes longimanus, and the fishhook waterflea, Cercopagis pengoi, potentially having an effect on the zooplankton population. Several species of crayfish have also been introduced that may contend with native crayfish populations. More recently an electric fence has been set up across the Chicago Sanitary and Ship Canal in order to keep several species of invasive Asian carps out of the area. These fast-growing planktivorous fish have heavily colonized the Mississippi and Illinois river systems. The sea lamprey which has been particularly devastating to the native lake trout population, is another example of a marine invasive species in the Great Lakes. It has been suggested that invasive species, particularly zebra and quagga mussels, may be at least partially responsible for the collapse of the deepwater demersal fish community in Lake Huron, as well as drastic unprecedented changes in the zooplankton community of the lake.