12:00 PM - 12:15 PM
[MIS21-12] Quantitative Assessment of Marine Debris on Uninhabited Islands and Policy Implications: A Case Study of Tomogashima
Keywords:Marine plastic policy, Cleanup cost estimation, Community engagement, Marine debris on uninhabited islands
Abandoned marine plastic debris spreads microplastics and harms coastal ecosystems. Its persistence is influenced by multiple factors, including the low economic and political priority of certain beaches. This issue is particularly pronounced on uninhabited island shores, where designated management exists but is not effectively enforced, leading to continued neglect. Marine debris accumulation on uninhabited islands has been reported globally and is prevalent across many of Japan's uninhabited islands. This situation represents a social dilemma, where individually rational actions result in widespread environmental degradation. Addressing this challenge requires effective governance mechanisms to keep pollution within sustainable limits. However, data on marine debris accumulation and removal strategies on uninhabited islands remain scarce.
This study addresses this gap by employing multiple methods to quantify debris volume and estimate removal costs, providing essential data for policy discussions. It serves as a foundational study on uninhabited island debris in Japan, offering insights for future research and policymaking.
Focusing on Tomogashima, an island group in Seto Inland Sea National Park, this study compares two islands with different levels of human activity. Jinoshima, uninhabited since World War II, remains off-limits to the public and lacks mooring infrastructure. In contrast, Okinoshima is a tourist destination with a ferry route and intermittent volunteer-led cleanups. We quantified marine debris accumulation on Jinoshima and estimated its removal costs while assessing the impact of cleanup activities by comparing it with Okinoshima.
Field surveys were conducted at Sanbashi Beach (Jinoshima) and Minamitarumi Beach (Okinoshima), both on the islands' southern coasts and accessible for single-day studies. At Sanbashi Beach, total debris volume was estimated using UAV observation with AI-based image analysis, which detected debris >=15 cm, and manual measurement of smaller debris (>=2-3 cm) that UAVs could not capture. A 1m2 sample plot was used for manual collection, and small debris volume was extrapolated to the 1,650m2 beach area. The total debris volume was estimated at 25.03m3, with an estimated removal time of 83.3 hours and a total cleanup cost of 672,000 yen, including labor, transportation, and disposal.
The study also evaluated different estimation methods. Within the 1m2 plot, debris volume and count were estimated using smartphone-based AI image analysis and compared to manual measurement. The manual method recorded 0.044m3 and 110 items, while the smartphone method estimated 0.012m3 and 18 items, indicating that manual counting recorded 3.6 times more debris volume than the smartphone method. Estimated removal costs varied significantly: manual labor cost 1,705,000 yen, while the smartphone method estimated 425,000 yen, making manual estimation three times more expensive. These results demonstrate that estimation methods significantly influence projected cleanup costs.
Comparing Minamitarumi Beach (Okinoshima) with Sanbashi Beach (Jinoshima), the total estimated debris volume at Minamitarumi Beach was 63% lower, despite using the same manual measurement method. Additionally, cleanup costs at Sanbashi Beach were 5.7 times higher. This discrepancy may be attributed not only to natural and geographical differences, such as the slope and gravel composition of the beaches, which influence initial debris accumulation, but also to Jinoshima's poor accessibility and the absence of cleanup activities. These findings suggest that community-led efforts may reduce long-term debris accumulation and maintenance costs.
This study presents three key findings. First, cleanup costs on uninhabited islands are significantly higher, primarily due to accessibility constraints, highlighting the need for appropriate funding mechanisms. Second, measurement methods substantially impact debris volume estimates, affecting cost projections; therefore, methods should be selected based on policy objectives. Third, community-based cleanup initiatives may contribute to reducing long-term debris accumulation, suggesting stakeholder involvement could be an effective governance strategy. Future research should further explore cost-sharing mechanisms and institutional arrangements to enhance marine debris management on uninhabited islands.
This study addresses this gap by employing multiple methods to quantify debris volume and estimate removal costs, providing essential data for policy discussions. It serves as a foundational study on uninhabited island debris in Japan, offering insights for future research and policymaking.
Focusing on Tomogashima, an island group in Seto Inland Sea National Park, this study compares two islands with different levels of human activity. Jinoshima, uninhabited since World War II, remains off-limits to the public and lacks mooring infrastructure. In contrast, Okinoshima is a tourist destination with a ferry route and intermittent volunteer-led cleanups. We quantified marine debris accumulation on Jinoshima and estimated its removal costs while assessing the impact of cleanup activities by comparing it with Okinoshima.
Field surveys were conducted at Sanbashi Beach (Jinoshima) and Minamitarumi Beach (Okinoshima), both on the islands' southern coasts and accessible for single-day studies. At Sanbashi Beach, total debris volume was estimated using UAV observation with AI-based image analysis, which detected debris >=15 cm, and manual measurement of smaller debris (>=2-3 cm) that UAVs could not capture. A 1m2 sample plot was used for manual collection, and small debris volume was extrapolated to the 1,650m2 beach area. The total debris volume was estimated at 25.03m3, with an estimated removal time of 83.3 hours and a total cleanup cost of 672,000 yen, including labor, transportation, and disposal.
The study also evaluated different estimation methods. Within the 1m2 plot, debris volume and count were estimated using smartphone-based AI image analysis and compared to manual measurement. The manual method recorded 0.044m3 and 110 items, while the smartphone method estimated 0.012m3 and 18 items, indicating that manual counting recorded 3.6 times more debris volume than the smartphone method. Estimated removal costs varied significantly: manual labor cost 1,705,000 yen, while the smartphone method estimated 425,000 yen, making manual estimation three times more expensive. These results demonstrate that estimation methods significantly influence projected cleanup costs.
Comparing Minamitarumi Beach (Okinoshima) with Sanbashi Beach (Jinoshima), the total estimated debris volume at Minamitarumi Beach was 63% lower, despite using the same manual measurement method. Additionally, cleanup costs at Sanbashi Beach were 5.7 times higher. This discrepancy may be attributed not only to natural and geographical differences, such as the slope and gravel composition of the beaches, which influence initial debris accumulation, but also to Jinoshima's poor accessibility and the absence of cleanup activities. These findings suggest that community-led efforts may reduce long-term debris accumulation and maintenance costs.
This study presents three key findings. First, cleanup costs on uninhabited islands are significantly higher, primarily due to accessibility constraints, highlighting the need for appropriate funding mechanisms. Second, measurement methods substantially impact debris volume estimates, affecting cost projections; therefore, methods should be selected based on policy objectives. Third, community-based cleanup initiatives may contribute to reducing long-term debris accumulation, suggesting stakeholder involvement could be an effective governance strategy. Future research should further explore cost-sharing mechanisms and institutional arrangements to enhance marine debris management on uninhabited islands.