Marc Léopold

The blue economy agenda has generated tensions over marine space use, often marginalising small-scale fisheries in development policies. Boat tracking technology has only recently begun to be applied in these fisheries, but it offers a promising approach to accurately map fishing distribution. In this study, we explored how environmental, technological, and social factors influenced fishers’ spatial behaviour and catches at sea in one of the Madagascar's most heavily exploited coral reef fisheries. We recorded boat movements at 30 s intervals and reef fish catches simultaneously during a 12-month participatory survey. The spatial distribution of annual fishing effort (h·ha ⁻¹ ) and fish catch rates (kg·ha ⁻¹ ) was characterised by fishing community and gear type (beach seine, mosquito net trawl, gillnet, handline, and speargun) at 250−m resolution. A total of 75 reef fish families were recorded in catches (1,466 t·yr ⁻¹ ) across approximately 218 km ² . Annual catch rates of the seven dominant families (comprising 62% of total catches) were highly variable and heterogeneous (mostly 1–391 kg·ha ⁻¹ ) across marine habitats. A total of 7,359 tracks by 521 boats were recorded. Fishing pressure was highly variable spatially (mostly 1−150 h·ha ⁻¹ ) among communities and gear types. The results revealed preferential target areas, informal marine tenure, limited travel distance to fishing grounds, and overexploitation patterns within the fishery, offering critical insights for fishery management and inclusive marine spatial planning. This study showed the usefulness and opportunities of deploying combined boat tracking and catch surveys in small-scale fisheries through participatory research.

Fishers’ spatial knowledge encompasses a diverse array of social, ecological, technical, experiential, and learning knowledge derived from local environmental and sociocultural contexts. In this study, we used a transdisciplinary framework to shed light on place names of fishing grounds in the context of small-scale fisheries through a case study in Madagascar. First, we jointly monitored fishing boat trajectories based on GPS tracking and recorded the vernacular names of fishing sites in a coral reef fishery from May 2018 to April 2019. This data was processed through spatial analysis to assess the dimensions of each named fishing site. A focus group discussion was conducted with fishers to determine the literal meanings of the toponyms (place names) in the local language. A total of 570 fishers (totaling 15,904 fishing trips) using five gear types were surveyed in eight communities. We identified 397 fishing sites over about 250 km², 304 of which (76.6%) were mapped. Overall, 371 toponyms (93.4%) were interpreted and categorized based on geographical features (n = 222), biodiversity (n = 86), and maritime uses (n = 63). The dimensions of the fishing sites varied significantly from 0.01 to 11.7 km², following spatially-explicit fishing distribution patterns and the level of precision of the delimitation method. Most fishing locations (63.3% of the total fishing grounds) were associated with multiple place names, particularly in heavily-targeted areas, indicating that individual fishers typically have their own names for their fishing sites. This study demonstrates that recording boat movements and vernacular toponyms simultaneously throughout an extensive monitoring survey in a coral reef fishery, effectively captured the rich and varied individual fishers’ conceptualizations of the coastal and nearshore marine environment. Our findings suggest that named fishing sites may be used as local spatial reference units with known precision and accuracy, which is relevant for addressing spatial data limitations in small-scale fisheries and incorporating fishers’ knowledge in collaborative fisheries science.

The use of mosquito nets, primarily for targeting small and/or juvenile fish, has rapidly increased in Western Indian Ocean shallow seagrass beds and coral reefs over the last 20 years. However, to date, invertebrate by-catch by locally-made fishing gear has not been reported. We studied the mosquito net trawl fishery in seagrass areas in the Bay of Toliara, Southwest Madagascar through the GPS tracking of fishers from August 2018 to February 2019. Catches were monitored through monthly landing surveys to characterize spatial temporal patterns in the abundance and diversity of macroinvertebrates in the seagrass beds. Fishing was carried out at low tide, mostly at night, by fishers pulling a hand-made trawl net of varying dimensions. Overall, 43 macroinvertebrate taxa were identified out of 217,080 individuals collected from 109 catch samples. Catches were generally composed of crustaceans (mainly Portunidae, Processidae, Penaeidae, and Alpheidae). The crab Thalamita mitsiensis largely dominated the abundance and biomass of the macroinvertebrate assemblage (from 6% to 100% and from 5 to 100% of the overall density and biomass, respectively). Macroinvertebrates composed 1.5% to 100% of the total catch per trip (i.e., 4–55 kg trip⁻¹). They were sold for human consumption or animal feed, which provided additional income to fishers (USD 1–24 trip⁻¹ and 1–72% of catch income per trip). This study revealed that macroinvertebrate resources provide valuable by-catch to small-scale fishers in Southwest Madagascar. This bycatch generates income that further encourages the use of mosquito net trawls and exacerbates their negative effects on coastal seagrass ecosystems and fisheries.

The prickly redfish Thelenota ananas (Jaeger, 1833) is a widely distributed tropical sea cucumber. Populations of this species have been increasingly harvested throughout its distribution area in the Indo-Pacific region, which led to significant overexploitation issues. In order to investigate the genetic structure, diversity and connectivity of its populations, 42 microsatellite loci were isolated from a T. ananas microsatellite-enriched DNA library. These loci were characterized on 24 individuals collected from the Seychelles. The number of alleles per locus ranged from 3 to 22. The observed heterozygosity ranged from 0.083 to 0.952, while the expected heterozygosity ranged from 0.162 to 0.974. No linkage disequilibrium was detected among all loci and 20 loci (48%) were at Hardy–Weinberg equilibrium. These 42 loci represent useful tools for assessing genetic diversity, structure and gene flow among T. ananas populations, providing relevant knowledge for the management and conservation of those major commercial resources.

Holothuria (Microthele) fuscogilva (Cherbonnier, 1980), Holothuria sp. type “Pentard” and Holothuria (Microthele) nobilis (Selenka, 1867) are three tropical sea cucumber taxa that are heavily fished worldwide for the beche-de-mer trade market. In order to investigate the population genetic structure, diversity and connectivity of these taxa, 16, 19 and 25 microsatellite loci were isolated from H. fuscogilva, Holothuria sp. type “Pentard” and H. nobilis DNA libraries, respectively. These loci were tested on 94, 60 and eight individuals of the respective species, collected from the Seychelles. The number of alleles per locus ranged from 2 to 30. The observed heterozygosity ranged from 0.245 to 0.890 for H. fuscogilva and from 0.200 to 0.950 for Holothuria sp. type “Pentard”, while the expected heterozygosity ranged from 0.231 to 0.952 and from 0.504 to 0.951, respectively. Several loci were at Hardy–Weinberg equilibrium and linkage disequilibrium was detected in only three pairs of loci. Cross-amplification was also tested and almost all loci (49 over 60) were polymorphic for at least two of the three studied taxa, showing high transferability among them. These loci represent useful tools for assessing genetic diversity and population structure of these three taxa in fishery areas, and therefore providing relevant knowledge for resource management.