### History and Current Status of the Black Bass Problem in Lake Biwa - From 1997 to the 2020s

### History and Current Status of the Black Bass Problem in Lake Biwa - From 1997 to the 2020s #### The Situation in 1997 In 1997, spinal abnormalities were confirmed in 21% of black bass caught in Lake Biwa, raising concerns about the impact on the ecosystem. These abnormalities were characterized by bone deformities and curvature, and the use of pesticides in the watershed was identified as a likely cause. In particular, it was considered highly probable that chemical runoff had affected the skeletal development of fish, making the reduction of pesticide use and the adoption of alternatives key challenges. At the same time, deteriorating water quality due to lake eutrophication was also considered a contributing factor. By this point, there was a growing need for a comprehensive management plan aimed at preserving the lake’s ecosystem, developed by fishermen and research institutions. #### Developments in the 2000s In the 2000s, measures to address invasive fish species gained momentum, centered on Shiga Prefecture. In 2003, the “Invasive Fish Eradication Project” was launched, leading to large-scale eradication efforts targeting largemouth bass and bluegill. During this period, Shiga Prefecture introduced regulations prohibiting the removal of non-native fish and promoting their eradication during fishing tournaments. Furthermore, efforts to reduce pesticide use were advanced, and initiatives to improve the lake’s environment were strengthened. #### Initiatives and Results in the 2010s In the 2010s, measures against non-native fish progressed further. During this period, the population of invasive fish in Lake Biwa was reported to be approximately 1,400 tons in 2010; through continued eradication efforts, this figure decreased to about 432 tons by fiscal year 2019. As a result, there were signs of partial recovery in the habitats of native species such as ayu and koayu. On the other hand, the invasion of new invasive fish species other than largemouth bass and bluegill—such as channel catfish—was confirmed, and the impact these species have on native fish and crustaceans emerged as a new challenge. Additionally, in surveys of spinal abnormalities, the long-term effects of pesticides and water pollution were reevaluated, and the need for further investigation was highlighted. During this period, Shiga Prefecture, private companies, and local residents collaborated to launch initiatives that utilized the removal of invasive fish as a tourism resource. For example, processed foods made from removed largemouth bass and bluegill were developed and sold, advancing efforts to balance regional economic revitalization with environmental conservation. #### Current Situation in the 2020s Even in the 2020s, the issue of invasive fish in Lake Biwa remains a serious challenge. While no new large-scale surveys on spinal abnormalities in largemouth bass have been conducted, efforts to reduce pesticide use and introduce environmentally friendly agricultural technologies are underway. A long-term monitoring system is being established to track the impact of pesticides and chemicals on the lake’s ecosystem. While efforts to eradicate invasive fish have achieved some success, complete eradication has not been achieved, and the introduction of new invasive species remains a challenge. Furthermore, it has been pointed out that rising water temperatures and changes in the lake environment due to climate change may be promoting the reproduction of invasive fish. #### Future Challenges To protect Lake Biwa’s ecosystem, it is necessary to further strengthen efforts to eradicate invasive fish, review pesticide usage, and promote the adoption of alternatives. Furthermore, local residents, businesses, and government agencies must collaborate to advance sustainable environmental conservation activities. It is hoped that these initiatives will lay the foundation for passing on Lake Biwa’s diverse ecosystem to future generations. --- From 1997 through the 2020s, Lake Biwa has continued to face challenges such as invasive fish and water pollution, but environmental conservation efforts are steadily progressing through cooperation between local communities and government.