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

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

#### Situation in 1997
In 1997, 21% of black bass caught in Lake Biwa exhibited spinal abnormalities, raising concerns about their impact on the ecosystem. These abnormalities, characterized by bone deformation and curvature, were suspected to be caused by agricultural chemicals used in the watershed. Chemical runoff likely affected the skeletal development of fish, and reducing pesticide use or adopting alternatives was identified as a critical issue. Additionally, eutrophication-induced water quality deterioration was considered another contributing factor. At the time, comprehensive ecosystem management plans involving fishermen and research institutions were urgently needed to preserve the lake's ecosystem.

#### Progress in the 2000s
In the 2000s, efforts to address invasive fish species in Lake Biwa intensified, particularly in Shiga Prefecture. In 2003, the "Invasive Fish Removal Project" began, resulting in large-scale removal activities targeting black bass and bluegill. During this period, regulations prohibiting the transport of invasive fish and encouraging their removal during fishing tournaments were introduced. Efforts to reduce pesticide use were also enhanced, bolstering initiatives to improve the lake's environment.

#### Actions and Achievements in the 2010s
During the 2010s, measures to tackle invasive fish species progressed further. The biomass of invasive fish in Lake Biwa was reported to be approximately 1,400 tons in 2010, and by 2019, it had decreased to about 432 tons due to continued removal efforts. This led to partial recovery in the habitats of native species like ayu and topmouth gudgeon.

However, new invasive species, such as channel catfish, were observed, posing additional threats to native fish and crustaceans. Investigations into spinal abnormalities also reassessed the long-term impacts of pesticides and water pollution, underscoring the need for further research.

Collaborations between Shiga Prefecture, private companies, and local residents began using invasive fish control as a tourism resource. For instance, processed foods made from removed black bass and bluegill were developed and marketed, promoting both environmental conservation and regional economic revitalization.

#### Current State in the 2020s
The invasive fish problem remains a significant challenge for Lake Biwa in the 2020s. While no new large-scale surveys on spinal abnormalities in black bass have been conducted, pesticide reduction and the adoption of environmentally friendly agricultural technologies are ongoing. Long-term monitoring systems to assess the impact of chemicals on the lake's ecosystem are being established.

Although progress has been made in reducing the biomass of invasive fish, complete eradication remains elusive, and the introduction of new invasive species continues to be a concern. Additionally, climate change impacts, such as rising water temperatures and changes in lake environments, may be facilitating the proliferation of invasive fish.

#### Future Challenges
To protect Lake Biwa's ecosystem, further strengthening of invasive fish removal activities is essential, alongside revisiting pesticide usage and promoting the adoption of alternatives. Collaboration among local residents, companies, and government entities is crucial for advancing sustainable environmental conservation initiatives. These efforts are expected to lay the groundwork for passing on Lake Biwa's diverse ecosystem to future generations.

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From 1997 to the 2020s, Lake Biwa has faced ongoing challenges related to invasive fish species and water quality issues. However, collaborative efforts between the local community and government have steadily advanced environmental conservation activities.