Mapping coastal marine debris using aerial imagery and spatial analysis

Area of Science:

• Environmental Science
• Marine Biology
• Remote Sensing

Background:

• Marine debris poses a significant threat to coastal ecosystems and marine life.
• Previous assessments of marine macro-debris in the main Hawaiian Islands (MHI) have been limited in scope and systematic quantification.
• Remote shorelines are often under-surveyed, leading to gaps in understanding debris distribution.

Purpose of the Study:

• To systematically quantify, categorize, and map marine macro-debris across the MHI.
• To establish a baseline dataset for marine macro-debris distribution, composition, and density.
• To identify priority areas for marine debris management and cleanup.

Main Methods:

• Aerial surveys utilizing high-resolution photography were conducted across all main Hawaiian Islands.
• Photographic data was processed into orthorectified imagery for detailed analysis.
• Geographic Information System (GIS) was employed to quantify, locate, and categorize macro-debris items (>0.05m²).

Main Results:

• A total of 20,658 marine macro-debris items were identified and mapped.
• Northeastern (windward) shorelines exhibited the highest densities of marine debris.
• Plastic debris, including nets, lines, buoys, floats, and foam, constituted 83% of the total items counted. Six vessels from the 2011 Tōhoku tsunami were also located.

Conclusions:

• This study provides the first comprehensive baseline of marine macro-debris across the MHI.
• Findings highlight the prevalence of plastics and identify key areas requiring targeted intervention.
• The data empowers resource managers and communities to prioritize cleanup efforts, particularly on remote and previously undocumented coastlines.