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11. Aliens: Introduced Species
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100 Fish are constantly looking for new places to live. Alien species are deliberately or accidentally introduced into habitats far removed from their places of origin. These introductions can have disastrous consequences for native fish populations. Of all the nonnative fish found in Ohio, the European carp (also known as common carp), sea lamprey, and round goby have proven the most destructive. The European carp, a large member of the minnow family, was among the first species to be introduced. The releases began in 1879 and continued for another twenty years. Originally supplied to owners of ponds and small lakes, they soon escaped into surrounding streams. By 1890, they were found throughout the state. The turn of the twentieth century, however, saw carp as an important part of the commercial catch in Lake Erie, with smoked carp being a popular dish. As their numbers increased, they began to wreak havoc on aquatic environments, destroying aquatic vegetation through their rooting actions and causing irreparable damage to wetlands. Today, some lakes and reservoirs are almost devoid of vegetation, which greatly reduces numbers and abundance of other fish. Since the late 1980s, species like the bighead, silver, and grass carp have been imported and released in ponds to control algae and other types of unwanted vegetation. Not surprisingly, all have escaped from their enclosures . While the majority of the grass carp sold are sterile, bighead and silver carp are not and are spreading northward through the Mississippi Basin. These Asian carp pose a major threat to Great Lakes fisheries. They have already reached Chicago and are now poised to invade Lake Michigan, and it is possible they could also make their ruinous way north through Aliens Introduced Species C H A P T E R 1 1 Aliens 101 Ohio’s tributary streams. If they gain access to Lake Erie, the consequences for sport fishing and tourism could be catastrophic. Sea lampreys, as their name implies, are primarily anadromous, with adults living in marine environments then moving into freshwater to spawn. They occur on both sides of the Atlantic, primarily the eastern seaboard of the United States and the west coast of Europe. Niagara Falls was a major barrier preventing lampreys from moving into the Great Lakes until 1829, when the Welland Canal opened, allowing lampreys as well as ships access to the western Great Lakes. Colonization was slow, with the first sightings in Lake Erie occurring in 1921. Spawning individuals were observed in Swan Creek in Lucas County fifteen years later. Lake Erie populations remained small for a time, due in part to the poor habitat quality of tributaries required for spawning. Once firmly established, sea lampreys immediately started decimating trout and salmonid populations. Adult sea lampreys can reach twenty-five inches in length, and few fish are able to survive an attack by one of these parasites. To counteract lamprey infestations, the US Fish and Wildlife Service established a lamprey control group devoted entirely to reducing sea lamprey numbers in the Great Lake, primarily by using lampricides to kill ammocoetes in their spawning streams. In some streams, electrically charged barriers are used to block upstream movement. Cages are also employed to trap migrating adults. While the use of lampricides is highly destructive to lampreys, it also negatively affects some soft-bodied species, like mudpuppies and catfish. Round gobies are one of the latest in a long line of unwanted species introduced into the Great Lakes from ballast water carried by ocean-going freighters. Gobies are bottom-dwellers, with large heads and powerful jaws. Adults are typically brown or grayish, with black markings. Originally native to the Black and Caspian Seas, round gobies were first discovered in the St. Clair River near Detroit in 1990. They rapidly spread, colonizing all of the Great Lakes. By 2002, the Ontario Ministry of Natural Resources estimated the population inhabiting the western basin of Lake Erie at approximately 10 billion individuals (Johnson et al. 2005). This shocking explosion in numbers can be explained by the species’ high fecundity: females may spawn up to six times a year over a long breeding season, lasting from April to September. Multiple females may contribute to a single nest, which may contain up to five thousand eggs. Males aggressively defend the nest, eggs, and newly hatched young from all predators, resulting in successful hatching rates of 95 percent. The consequences for some of Ohio’s native fish have been catastrophic. They have out-competed the resident sculpins and darters, [3...