On the State of Invasive Species and Fish in Japan / Noriko Takamura [Contribution Text for Yudai Kamisato / Okazaki Art Theatre]
As a result of environmental changes since the emergence of life on earth such as climate shifts, changes in the crust, or land drift, and of the history of evolution of living creatures in response to these, living creatures are distributed around the planet with regionally specific attributes. The things that live in each place, whether it is a wood or forest, grassland, or a lake or marsh, maintain a relationship with other living creatures built up over a long time that may comprise both parasitical and symbiotic relationships or that of predator and prey, in this way adapting to each respective environment in how they live.
Today, however, when our society has become one in which human beings are frequently moving around the planet, we can now find many living things around us introduced by humans and which subsequently established themselves, but were never originally present in the area. These types of living creatures are known as invasive species. Examples may include species intentionally introduced by humans, such as raccoons as pets, American bullfrogs as a food source, or mongooses to exterminate snakes, and also species like insects or plants that arrived without people realizing by attaching themselves to luggage and so on.
Within invasive species, there are those that, by competing with and preying on native species, make native species extinct and destroy original ecosystems, cause damage to the agriculture, forestry, and fishing industries and harm humans. In order to prevent this severe influence and to control the invasive species that have already entered, the Invasive Species Law was enacted in Japan in 2005. This law designated particularly impactful living creatures as “special invasive species,” banning their import, transportation, sale, and release as well as, in principle, their breeding, and established penalties for violations.
Among fish, there are 26 species designated as special invasive species, almost all of which are freshwater fish with a strong tendency to feed on other fish (that is, they are piscivorous fish) or on crustaceans or insects. Examples of species that have already established themselves and spread nationwide include the largemouth bass, smallmouth bass, bluegill, and channel catfish, and, in the Kanto region, Acheilognathus macropterus and, in West Japan, the mosquitofish. According to a recent study, the yellowhead catfish has become established in the Lake Kasumigaura area. That such species of piscivorous fish invading and establishing themselves is causing serious damage to fishing in inland waters in Japan is scientifically evident from analysis of long-term inland waters fishing statistics.
On the other hand, 59 species—accounting for 63.4% of Japan’s pure freshwater fish species—were listed as endangered wildlife in the Ministry of the Environment’s 4th Red List in 2013, and their survival continues to be threatened. Though this is connected to such factors as artificial water management or changes in habits due to land development, competition from and being preyed on by invasive fish species is also a major reason for this extinction crisis. In Japan, there were originally few types of piscivorous freshwater fish and most of these have not adapted or evolved strategies that can counteract other piscivorous fish.
We cannot replace a species once it has become extinct. If we are to solve the environmental problems faced by contemporary society, we must always be thinking about sustainability in terms of how we act, not least using our planet’s natural resources responsibly so that they can be passed on to the next generation.
Noriko Takamura, PhD, is a scientist. She gained a master’s degree from Nara Women’s University in 1979. She is a fellow of the Center for Environmental Biology and Ecosystem Studies, based at the Lake Biwa Branch Office.She specializes in the study of freshwater ecosystems.