The Lake Huron fishery has been depleted from over-fishing, destruction of spawning grounds, and the introduction of exotic species (lamprey eel, alewife, smelt) that compete with species native to the lake.
Chemical contamination is a problem in Lake Huron. There are low concentrations of heavy metals, and pesticides, and PCB's have been found. Higher levels (especially of lead) are found in the sediments and near industrialized centres.
In Lake Huron, it's the alien species that have taken a major toll. Of course, the most destructive of all alien species is us--humans. In particular, the humans that came from Europe and, later, from other parts of the world.
The small numbers of First Nations people who lived in the Great Lakes Basin prior to European settlement had no impact on the landscape. With European settlement came large-scale farming, industrialization, and the growth of massive cities. These have altered the complex environment beyond recognition.
One such alteration was the digging of the Welland Canal. Until the early 1800s, Niagara Falls presented an impassable barrier to navigation from Lake Ontario to Lake Erie and thence to the upper Great Lakes. So, a 43.5-kilometre bypass was built across the Niagara Peninsula.
The first canal opened in 1829 and has been widened and modified several times since.
If the Welland Canal made it possible for ships to ignore the perils of Niagara Falls, it did the same for other invaders. Some, such as the sea lamprey, swam into the upper lakes under their own power. Others have hitched a ride on, or in, ships coming up the St. Lawrence Seaway system from foreign ports.
The opening of the St. Lawrence Seaway in 1959 greatly increased the number of oceangoing vessels entering the Great Lakes. As a result, there was a dramatic rise in the entry of exotic species (that's what the experts call non-native life forms) via ships.
Among the most trouble some invaders are sea lamprey, alewife, smelt, and zebra mussels. But, these are by no means the only aliens causing trouble. There's the blueback herring, ruffe, tubenosed gobies and, the ever-popular spiny water flea. These are all recent arrivals that have come in ship ballast water.
Vessels load ballast water into their hulls to give them stability. Without ballast water an empty cargo ship would bob about on the open ocean like a cork, something that could put the ship and its crew in danger. So, a ship coming from the Mediterranean Sea to pick up wheat in Thunder Bay will load up with ballast water before it leaves. When it gets to the grain terminal, the ship will pump out its ballast water to compensate for the grain being loaded. So, several thousand tonnes of Mediterranean water and all the organisms that live in it end up going into Lake Superior.
Ships are now supposed to exchange ballast water in mid-ocean. The hope is that this will reduce the likelihood of other alien species from entering and disrupting the Great Lakes ecosystem. But, there's nobody out in the middle of the Atlantic to check on whether or not this is done.
A small number of exotic species get here by clinging to a ship's hull and then dropping off in lake water.
The alewife showed up in Lake Ontario in 1873, and reached Lake Michigan in 1943. They're little guys--up to about 15 centimetres long. What they lack in size they make up for in numbers. They travel in schools of millions and scoop up vast quantities of plank ton.
After sea lampreys destroyed the large predators (see sidebar on page 17) that had kept the alewife population in check their numbers exploded.
They out-competed native species, such as lake herring, whitefish, chub, and perch, for plankton. The local species have been starved into a population decline.
Smelt offer a similar story. This small, ocean fish was introduced to Michigan's inland waters as food for stocked salmon. Some of the smelt escaped into Lake Michigan. By 1930, the rapidly growing smelt population had expanded into Lake Superior, and then to all the other lakes. Smelt were said to be competing with and preying on the eggs of native species.
Human activity has also brought microscopic predators to the Great Lakes. Bacterial infections have caused massive die-offs among some species. These lead to hundreds of thousands of rotting fish turning up on beaches: just the thing to keep the tourists away.
Then, there's the not-so lovable little zebra mussel.
About as big as a finger nail, these natives of the Caspian Sea are causing trouble out of all proportion to their size. The first ones arrived in ballast water that was discharged into Lake St. Clair, near Detroit, where the mussel was discovered in 1998. Since that time, they have spread rapidly to all of the Great Lakes and waterways in many states, as well as Ontario and Quebec. They have now been joined by quagga mussels, another invasive species that likes deeper water.
The mussels colonize docks, boat hulls, and buoys, but they seem to have a par ticular fondness for water intakes. They reproduce so fast (a single female produces one million eggs each year in its two to three-year life span) so when they settle on a water intake they can clog it up very fast.
Keeping water intakes unclogged for industry and cottages alike now costs millions of dollars a year. But, the huge numbers of mussels have disrupted entire ecosystems. They out compete other species for food and have wiped out the native freshwater pearly mussels (also called mother-of-pearl clams) in some locations. Some fish species have gone into decline and this affects the whole balance of interrelated life forms from plankton to waterfowl.
There is concern that the zebra mussel may change the nitrogen-to-phosphorous ratio in Great Lakes near shore waters. This would lead to an increase in blue" green algae and a reduction of the more desirable species of green algae, which are an important component of the food chain.
The newest invader is the round goby. It first appeared in the Great Lakes in the St. Clair River in 1990; probably carried there in ballast water. Once introduced into new waters, the population of this bottom-dwelling fish increases rapidly. The round goby displaces native fish, eats their young, takes over optimal habitat, spawns up to six times per season, and survives in poor quality water (of which there is plenty)--giving them a competitive advantage.
Efforts have been made to beat off the attacks of most alien species. So far, the invaders seem to be winning. Chemicals have been sprayed on the larvae of sea lamprey. This has certainly reduced the numbers but scientists are concerned the lamprey might be developing a resistance to the spray.
Pacific salmon were introduced to combat alewife and smelt problems. But, bringing in one alien species to eat another alien species is not a perfect solution; it can create a whole new set of problems.
INVASION OF THE BLOOD-SUCKING ALIENS
All of Nature's creatures have a purpose, but it's tough to overlook the sea lamprey's disgusting habits and accept it as a necessary part of the biosphere. It is an aggressive parasite. With a tooth-filled mouth, the lamprey fastens onto its prey's body. Then, it rasps out a hole in the skin of its victim with its rough tongue. An anti-clotting agent in the lamprey's saliva keeps the wound open for hours or weeks while it sucks out blood. The lamprey stays attached until it's had enough blood or, more likely, its victim dies.
Some experts say these eel-like critters have always been in Lake Ontario and the St. Lawrence River, Another school of thought says the sea lamprey entered Lake Ontario from the Hudson River via the Erie Canal. The canal, which was opened to barge traffic in 1819, connects the Hudson River and Lake Ontario drainages via Lake Oneida. It took them more than a century to figure out that the Welland Canal gave them access to Lake Erie and a whole new food source.
The first lampreys were found in Lake Erie in 1921, From there, they rapidly colonized all the upper Great Lakes, with especially large infestations developing in Lakes Michigan and Huron. The lamprey have cut a swathe through lake trout and several other large species of fish that had supported the sport and commercial fisheries.
While exotic fish species get a lot of attention, new plants are also causing problems. Purple loosestrife (pictured below) is now firmly established in the Great Lakes Basin. The weed first arrived in the early 1800s from Europe and has spread across the entire country. A mature plant will produce more than two million seeds a year and chokes out native plants in wetlands. Once it moves in, purple loosestrife kills about half the other plants, many of which provide habitats for native birds and animals,
Eurasian water milfoil is another plant that is creating problems in the Great Lakes, Massive beds of the plant can make boating and swimming impossible and can reduce fish and invertebrate populations. Introduced species of algae are disrupting local environments as well.
The Great Lakes' coastline accounts for four percent (10,000 kilometres) of the total length of Canada's coasts.
At least 160 non-native species have entered the Great Lakes since 1800.
Great Lakes Environmental Research Laboratory http://www.glerl.noaa.gov/
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|Title Annotation:||Lake Huron.|
|Publication:||Canada and the World Backgrounder|
|Date:||Jan 1, 2005|
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