Invasive fish species are upsetting the ecology of one of the world’s oldest lakes and one of the world’s largest river systems. The unique ecology of Lake Biwa, Japan, is threatened by bluegills and largemouth bass from North America, while the North American Great Lakes are now threatened by Asian carp that have been spreading up the tributaries of the Mississipi, including the Illinois River and the Chicago Sanitary and Ship Canal.
Lake Biwa hosts 491 species of plants and 595 species of animals. Recent studies of the lake bottom suggest that many more species remain to be discovered. About 50 species and subspecies are found nowhere else. These include such animals as the freshwater pearl mussel (Hyrlopsis schlegeri). Other species reach their southern limit in Lake Biwa, where they persist in the cooler temperatures of deep waters. An example of this are a small snail Cincinna biwaensis.
Other species have been intentionally or unintentionally introduced into the lake. In 1883, for instance, salmon were introduced and have supported a small fishery. Other species of fish, such as North American bluegills (Lepomis macrochilus) and largemouth bass (Micropterus salmoides) have come to dominate the fish community since the 1980s. These top-level predators have profoundly altered the ecosystem of the lake.
Among the species threatened are carp and crucian carp.
Naikos (attached lakes) of Lake Biwa served till mid sixties both as spawning grounds and as breeding areas for the endemic species such as round crucian carps. Environmental destruction over time and introduction of alien species drastically affected their biota. Nowadays, bluegills, one of the most rampant alien species in Japan, are dominant in all the naikos, while largemouth bass (commonly called “black bass” are dominant in more than two-thirds of all the naikos.
A series of field research in 2001 in Nodanuma naiko revealed that up to 95% of the collected larvae and juveniles were from invasive alien species. This has caused the occurrence of larval/juvenile carps and crucian carps, including some endemic species, to be limited to the earlier part of their original spawning period, namely from April through early and mid-June.
Asian carp have been found in the Illinois River, which connects the Mississippi River to Lake Michigan. Due to their large size and rapid rate of reproduction, these fish could pose a significant risk to the Great Lakes Ecosystem….
Two species of Asian carp — the bighead and silver — were imported by catfish farmers in the 1970’s to remove algae and suspended matter out of their ponds. During large floods in the early 1990s, many of the catfish farm ponds overflowed their banks, and the Asian carp were released into local waterways in the Mississippi River basin.
The carp have steadily made their way northward up the Mississippi, becoming the most abundant species in some areas of the River. They out-compete native fish, and have caused severe hardship to the people who fish there [except those fishermen who have begun to rely on the carp!].
The Chicago Sanitary and Ship Canal, where the barrier is being constructed, connects the Mississippi River to the Great Lakes via the Illinois River. Recent monitoring shows the carp to be in the Illinois River within 50 miles of Lake Michigan….
Asian Carp are a significant threat to the Great Lakes because they are large, extremely prolific, and consume vast amounts of food. They can weigh up to 100 pounds, and can grow to a length of more than four feet. They are well-suited to the climate of the Great Lakes region, which is similar to their native Asian habitats.
Researchers expect that Asian carp would disrupt the food chain that supports the native fish of the Great Lakes. Due to their large size, ravenous appetites, and rapid rate of reproduction, these fish could pose a significant risk to the Great Lakes Ecosystem. Eventually, they could become a dominant species in the Great Lakes.