Fine-scale distribution of fishing effort and catches highlights opportunities for marine spatial planning in coral reef ecosystems

Effective Marine Spatial Planning (MSP) is essential for the sustainable management of coastal and marine resources, particularly in urbanized areas where multiple human activities overlap. Small-scale fisheries, aquaculture, tourism, and other marine uses share the same space, creating both opportunities and challenges. In that perspective, understanding the spatial distribution of fishing activities (fishing effort and associated catches) is fundamental for effective MSP as it helps identify such interaction patterns and vulnerable fisher communities, and develop targeted marine resource management strategies that can support both resource conservation and fishing livelihoods.

We present a novel approach combining intensive and participatory GPS tracking and catch monitoring to map fishing effort and catches in coral reef ecosystem, with an application in the Bay of Toliara, Madagascar's second-largest reef complex (about 1,000 fishers over 250 km²). Over one year, we tracked fishing trips across several villages, representing 63% of the local fishing fleet, while simultaneously collecting catch data. Mapping results (250 m x 250 m resolution) revealed concerning signs of overexploitation, with annual catches estimated at 4.8t/km² and showing a significant decline of about 50% over the last 30 years. Fishing effort was highly concentrated, with three villages accounting for over 60% of total effort, highlighting limited mobility of the artisanal fleet. While gillnets dominated fishing activities (41% of total fishing effort), we observed spatial segregation among fishing gears, with beach seine and mosquito trawl net use concentrated in shallow areas and handline and speargun used predominantly located in reef and lagoon zones.

Our findings indicate an "overexploitation trap," where fishers are constrained by traditional non-motorized vessels and limited capital and intensify pressure on nearby reef resources rather than accessing distant, less-exploited areas. This pressure on the seascape is exacerbated by the rise in fisher number, the diversification of fishing gear, the emergence of powerful non-selective practices, and the expansion of marine aquaculture and commercial port and tourism activities. The study provides essential baseline data for implementing spatial management measures within the study area, e.g. for protecting juvenile fish habitats in seagrass beds.

This research contributes to SDG 14 targets by providing a cost-effective, participatory, and accurate methodology for mapping small-scale fisheries. The approach generates high-resolution spatial quantitative knowledge relevant for evidence-based management decisions while raising awareness within fishing communities. Our findings also emphasize the urgent need for intervention through marine spatial planning and alternative livelihood development to prevent fishery collapse and ensure sustainable resource use for coastal communities. The study further demonstrates how detailed spatial analysis can inform interactions and competing interests within a coastal seascape, while guiding equitable access to marine resources from different perspectives and supporting conservation objectives.