Southwest Madagascar Research Articles

Improved accessibility and changing dynamics of small-scale fisheries and aquaculture activities in southwest Madagascar

Improved accessibility and changing dynamics of small-scale fisheries and aquaculture activities in southwest Madagascar

Coral recruitment in the Toliara region of southwest Madagascar: Spatio‐temporal variability and implications for reef conservation

AbstractInvestigating coral recruitment is critical to better understand replenishment and resilience capacities of coral reef ecosystems and to improve their conservation. Here, we examined the spatio‐temporal patterns of coral recruitment and the influence of confamilial adult coral cover in the region of Toliara, southwest Madagascar. Terracotta tiles were immersed from October to late January over a 3‐year period (2018–2021) at 10 stations located on major reef habitats. Overall recruitment rates were relatively high compared to those of other reefs in the Southwestern Indian Ocean, ranging from 219.20 recruits.m−2 in 2018–2019 to 156.30 recruits.m−2 in 2020–2021. Recruit assemblages were dominated by Acroporidae (45.5%) and Pocilloporidae (45.0%), whereas Poritidae (1.9%) and “other” recruits (3.6%) were rarely recorded. Recruitment patterns varied among stations and habitats, with higher rates in patch reef (187.06 recruits.m−2) and outer slope stations (156.99 recruits.m−2) compared to inner slope stations (108.04 recruits.m−2). With the exception of “other” recruits, recruitment rates decreased between 2018 and 2019 and 2019 and 2020, followed by an increase in 2020–2021 that reached or even exceeded initial values at some stations. The abundance of Pocilloporidae recruits was positively correlated with the cover of confamilial adult corals, highlighting potential stock–recruitment or recruitment–limitation relationships, or an aggregative settlement of young stages near the established adult colonies, whereas no such relationships were recorded for other coral family categories. This study identified sites on the outer slope and patch reefs to consider prioritizing for protection as recruitment hotspots, as well as degraded inner slope sites that could benefit from restoration, with the important caveat that any measures should be accompanied by alternative income‐generating activities through local involvement that suits the Malagasy context, such as locally marine managed areas.

Assessing stock of reef octopus Octopus cyanea in southwest Madagascar using age-based population modelling

The reef octopus Octopus cyanea fishery is the most economically important fishery in southwest Madagascar. The substantial increase of octopus exploitation in the region has raised concerns over the sustainability of this fishery. While a growing number of measures have been implemented to sustainably manage the octopus stock, there is a lack of information on the status of this octopus stock. In this study, we analyse the status of octopus stock in southwest Madagascar by investigating the interannual and seasonal variability in recruitment and fishing mortality using virtual population analysis (VPA) performed on monthly basis from 2020 to 2022. Yield per recruit is also predicted using a Thomson and Bell model. Our results indicate that octopus fishery national closures (December 15 to January 31 each year) result overall in increase of catches and stock biomass, evidencing the positive impacts of the implemented fisheries regulations in the region. Recruitment exhibits high interannual and seasonal variability with a peak observed between October and December. The simulation model suggests that yield per recruit remains almost unchanged from one year to the next and not exceeding the maximum yield per recruit. Overall, this study shows the importance of understanding the status of octopus stock for sustainable octopus fisheries in southwest Madagascar.

Participatory video as a tool for co-management in coastal communities: a case study from Madagascar

Here we examine participatory video (supporting a group to make a film around a specific issue) as a tool to facilitate input of local knowledge and empower communities in stewardship over their local marine resources. We draw from the “Voices of the Vezo” project, where researchers collaborated with a co-management partner organization and local youth to create participatory videos in traditional Vezo fishing communities in southwest Madagascar. The project focused on documenting and sharing local knowledge on shifting social-ecological conditions. Four communities participated in the project with 90 people interviewed and seven short films (7–15 min) created. The films were shared in the communities at public cinema nights and made widely available online. This paper describes the Voices of the Vezo project's process and outputs, examines participatory video's potential as a tool for community co-management, and outlines practical challenges and recommendations for implementing a participatory video project. We found videography to be a powerful tool for synthesizing local knowledge of shifting social and ecological conditions, especially where written records are scarce. We also identified specific examples where gathering and sharing community perceptions of marine ecosystem decline could foster discussion and action toward locally driven management interventions. Youth participants in the Voices of the Vezo project reported gaining knowledge and motivation to address marine management issues, indicating the potential for participatory video processes to cultivate local leadership. Finally, for participatory video practitioners, we found important practical considerations to help minimize biases when supporting communities with a participatory video process.

Lessons for ensuring continued community participation in a mangrove blue carbon conservation and restoration project in Madagascar

Successful conservation projects that restrict or change access to common pool resources require meaningful community participation not only through consultation but also by empowering communities to take a leading role from the early stages of its design. In this study, community participation was assessed in the Tahiry Honko community-led mangrove blue carbon project in southwest Madagascar using the Spectrum of Public Participation tool developed by the International Association for Public Participation. Trends of community participation at village meetings were assessed using the meeting records from 2014 to 2019. Performance in the project activities was assessed based on the indicators of success. It was learned that: (i) careful scheduling of meetings is crucial to avoid community fatigue; (ii) anonymous democratic votes are an effective, inclusive approach to address domination in a group activity and obtain informed consent; (iii) creating a comfortable space for women is vital to promote their participation in decision-making; (iv) voluntary approach with meal compensation is effective to engage all community groups in mangrove replanting; (v) competitive process is crucial to recruit motivated volunteers for mangrove forest patrols; and (vi) dissemination of patrol results is helpful in developing an adaptive strategy in the absence of effective enforcement of rules.

Social networks as risk-mitigation strategies in south-west Madagascar

Palaeoenvironmental data indicate that the climate of south-western Madagascar has changed repeatedly over the past millennium. Combined with socio-political challenges such as warfare and slave raiding, communities continually had to mitigate against risk. Here, the authors apply social network analysis to pottery assemblages from sites on the Velondriake coast to identify intercommunity connectivity and changes over time. The results indicate both continuity of densely connected networks and change in their spatial extent and structure. These network shifts coincided with periods of socio-political and environmental perturbation attested in palaeoclimate data and oral histories. Communities responded to socio-political and environmental risk by reconfiguring social connections and migrating to areas of greater resource availability or political security.

New datings and elevations of a fossil reef in Lembetabe, southwest Madagascar: eustatic and tectonic implications

The study of geological sea-level proxies formed during previous interglacials is a common approach to assess how global sea level will evolve under warmer climate conditions. Over the last decades, technical advancements in both survey and geochronology have allowed improving our knowledge of past sea-level highstands. This is of prime importance to refine our understanding of processes contributing to sea-level changes, and ultimately to improve both local and global sea-level projections. Last Interglacial sea-level proxies in the Western Indian Ocean (and more specifically the island nation of Madagascar), have been less investigated than in other intertropical oceans over the last decades. As a result, paleo sea-level data in this region are less abundant and less precise than elsewhere. Here, we report the results of two field campaigns aimed at studying the site of Lembetabe, southwest Madagascar, where a fossil reef was first described by the researcher René Battistini more than 50 years ago. We estimate paleo relative sea level history in space and time from 15 new U-series ages from a fossil reef platform mapped with differential GNSS and drone photogrammetry. Our data suggest that, between 129 ka and 115 ka, paleo relative sea level at this location was about 3.4 ± 1.4 m above modern. Once corrected for glacial isostatic adjustment, we find that paleo global mean sea level did not exceed 3 m above modern. Only slight crustal subsidence would reconcile the peak Last Interglacial sea level measured at Lembetabe with the 5–10 m range reported in the literature.

Combining Traditional Ecological Knowledge and Scientific Observations to Support Mangrove Restoration in Madagascar

Local communities play a key role in ecosystem restoration due to their invaluable traditional ecological knowledge. While community-led mangrove restoration has been practiced in Madagascar for decades, the factors influencing the success of the restoration remains understudied. Despite the extensive local knowledge, the complexity of factors influencing restoration success requires outside technical expertise. This study aimed to investigate the drivers of mangrove restoration success in southwest Madagascar. The survival rate of mangroves planted from 2015 to 2022, including Rhizophora mucronata, Bruguiera gymnorrhiza, and Ceriops tagal was assessed using the sampling methods for tree planting inventory with circular plots. R version 4.2.2 was used for descriptive statistics analysis. The correlation between the survival rate and plantation density, species composition, and number of participants was assessed using a Principal Component Analysis. As a result, the mean survival rate of the 440,990 planted mangroves, with a density of 4628 ± 317 trees/ha−1 was 82.5 ± 1.8%. Our study showed that plantation density and species composition are not correlated with survival rate. However, the survival rate is inversely correlated with the number of participants. The findings of this paper showed that both traditional ecological knowledge and scientific observations are vital to informing mangrove reforestation.

Recent demographic survey of the Radiated Tortoise (Astrochelys radiata) in southwest Madagascar

Abstract.—Effective management strategies for at-risk chelonian populations require sound knowledge of populationdemographics. Previous research on the Critically Endangered Radiated Tortoise, Astrochelys radiata (Shaw 1802),revealed a trend of increasing male bias in the sex ratio and a concomitant decrease in the proportion of juveniles inLavavolo, southern Madagascar. This location is one of the few remaining sites with a high concentration of this speciesand was last studied ten years ago. The aim of our study was to provide an updated snapshot of Radiated Tortoisedemographics at Lavavolo, which, when combined with previous studies, will provide insight into changes over 20years (1999–2019). Additionally, we provide the first assessment on the impact of soil types (calcareous, ferruginous,and sandy) on the distribution of individuals across the site. We used mark-recapture data to determine the sex ratio,age structure, and distribution of size classes. Overall, the study site contained mostly adults (76.87%) with only afew juveniles (23.13%). Though the proportion of juveniles is low, it has increased over the last ten years. However,the sex ratio has become increasingly skewed towards males, 1.8:1. We did not find any significant difference in sexratios between soil types, but there were significant differences in the distribution of size classes, with the smallest sizeclass 0–8 cm most prevalent in sandy soil and the juvenile size class 17–24 cm most frequent in ferruginous soil. Mostjuvenile size classes were less common than expected on the calcareous soil. In general, populations located on calcareoussoil appear to be more vulnerable, potentially due to the long-term existence of poaching activities in this habitat.

Seagrass macroinvertebrate bycatches support mosquito net trawl fishery in Madagascar

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.

Evidence of lithic blade technology in southwest Madagascar

This rapid communication describes a lithic blade that was recently recovered during excavations in the Velondriake Marine Protected Area in southwest Madagascar. This represents the only recorded archaeological lithic blade recovered from southwest Madagascar. The blade was recovered in situ at a depth of 1.66 m, a deposit dating to between 750 and 1200 BP at site G134, adjacent to the modern village of Antsaragnasoa. While similar in material choice (translucent-brown chert) and morphology (parallel-sided blade) to other lithics recovered at the northern sites of Ambohiposa and Lakaton’i Anja, it is significantly larger than other recorded lithics on Madagascar. More research is required but this finding suggests that lithic technology may have been more widespread on the island, particularly among coastal communities, than previously thought.

Spatial Analysis of the Occurrence and Spread of Wildfires in Southwest Madagascar

The island of Madagascar, located in the southern hemisphere between the equator and the Tropic of Capricorn in the Indian Ocean, 450 km from the African continent, is particularly affected by wildfires. The vegetation of the phytogeographic Western Domain of the island consists largely of savannas, wooded grassland, and secondary grassland, maintained by the repeated action of fire operating each year on a seasonal cycle. Rural populations employ fire to manage land use. Depending on the burning practice and the environment in which the fires happen, the impacts vary. This paper supplement the studies that have so far located and quantified wildfires by taking into account their different behaviors, particularly their spread. We analyzed the modalities of the relationship between the two fire products, active fire and burned area, derived from Moderate Resolution Imaging Spectroradiometer (MODIS) data to establish a typology based on fire spread patterns. We identified three general patterns of fire behaviors, as well as their locations in the studied area. Spatial analysis of this patterns enabled us to understand spatial logics better. Type 1 fires are the least frequently observed and have many active fires, but little or no burned area. Type 2 fires are the most common and have areas that burn like a mosaic. Type 3 fires are observed slightly less frequently than the previous type and have few active fires and large burned areas. An inter-annual analysis reveals the spatial stability or variability of these fire types.

Cyclone Impacts on Coral Reef Communities in Southwest Madagascar

Tropical cyclones can cause severe destruction of coral reefs with ecological consequences for reef fish communities. Ocean warming is predicted to shorten the return interval for strong tropical cyclones. Understanding the consequences of cyclone impacts on coral reefs is critical to inform local-scale management to support reef resilience and the livelihood security of small-scale fishing communities. Here, we present the first analysis of a tropical cyclone disturbance on coral reefs in Madagascar. We investigate the impact of Cyclone Haruna (category 3 Saffir-Simpson scale) in February 2013 on coral communities, both adults and recruits, and explore the relationship between the severity of cyclone impact with cyclone parameters (wind speed, duration of storm impact and distance from cyclone track) and environmental variables (reef type and reef depth). We use survey data collected as part of a long-term citizen science monitoring programme at 21 coral reef sites between 2012 and 2015 in the Velondriake Locally Managed Marine Area along Madagascar’s southwest coast. Coral cover declined at 19 sites, however damage was spatially heterogeneous ranging from a decrease in coral cover of 1.4% to 45.8%. We found the severity of cyclone damage related to: distance from the cyclone track, duration of cyclone impact and reef depth. The taxonomic and morphological composition of coral communities was significantly different after the cyclone. Notably, there was a decrease in the dominance of branching morphologies, and an increase in the relative abundance of encrusting and massive morphologies. Two years after Cyclone Haruna, mean coral cover had increased and the density of coral recruits increased to above pre-cyclone levels indicating the potential recovery of coral populations. However, recovery to pre-disturbance community composition will likely be hindered by the increasing occurrence of acute and chronic disturbance events.

Application of DNA Barcoding for Monitoring Madagascar Fish Biodiversity in Coastal Areas

Madagascar is a marine biodiversity hotspot. A recent checklist recorded 1689 marine or transitional water fish species, 2.5% being endemic. To date, studies in this country were mostly focused on adult fishes using morphological-based identification. The early life stages of fishes remain largely understudied. The present work aimed to improve knowledge of fish biodiversity in Madagascar by focusing on post-larval reef fishes and settled juveniles in seagrass meadows of southwest Madagascar by using either species identification keys or DNA barcoding. Up to 119,500 individuals were collected, and 1096 individuals were successfully barcoded. We identified 387 species—85 through their morphology (with 58 unsuccessfully sequenced) and 302 by using CO1 barcoding corresponding to 302 barcode index numbers (BINs). This study added 27 new BINs for the BOLD database, 120 new for Madagascar, but only 159 were assigned a precise species name. By referring to the updated checklist of Madagascar fishes, 10 new species were detected for Madagascar. This number will probably increase when all the barcoded specimens become assigned to precise species names. These preliminary findings stress our poor knowledge of marine fish biodiversity in Madagascar and demonstrate the relevance of DNA barcoding in improving this knowledge.

Perceptions of access and benefits from community-based aquaculture through Photovoice: A case study within a locally managed marine area in Madagascar

Small-scale fishers face a range of local and global environmental pressures including declining fish stocks and climate change. In coastal southwest Madagascar, community-based aquaculture (CBA) projects have been established within a locally managed marine area (LMMA) to provide alternative income streams for small-scale fishing communities and support community efforts in reducing local fishing pressures. This study focused on understanding community perceptions of both access to, and benefits from, two CBA projects within the Velondriake LMMA involving seaweed and sea cucumber aquaculture. Participants included seaweed farmers, sea cucumber farmers, and non-farmers, and research considered the impacts of the projects at the individual and community level. Participatory field research was conducted in Tampolove, Madagascar during 2018 using an adapted Photovoice method with participant-based photos and in-depth interviews. The integration of CBA projects into the LMMA resulted in a new governance model, with the aquaculture sites requiring ‘private access’ within a historically ‘open-access’ setting. Results showed that community members accepted this access change for the community's coastal area, with aquaculture benefits including more predictable income generation and benefit-sharing across the community, appearing to outweigh the loss of access to part of their traditional fishing grounds. However, further research is required to better understand how women and other marginalised community members are affected. Due to the benefits cited by community members, the CBA-LMMA model may have applicability to other coastal community settings in the Western Indian Ocean (WIO) where there is both a need and opportunity for positive alignment of community-based alternative livelihoods and marine conservation.

Goat Breeding: A Possible Sustainable Way to Manage Xerophytic Thickets in Southwestern Madagascar

Spiny thickets or xerophytic thickets (XTs) are a type of shrubby vegetation found in the far south and southwest of Madagascar, the driest parts of the island. This type of vegetation, which is rich in endemic animal and plant species, is endangered. Extensive local goat breeding (Capra hircus, for meat and milk production) based on XT browsing is an important source of household income. The aim of this paper is to analyse the possibility of using improved goat breeding as an alternative to wood charcoal (WC) production and slash-and-burn agriculture (SBA), which are unsustainable activities. The literature on (i) the impacts of SBA, WC production, and goat browsing on the XT ecosystem and (ii) the income provided by these three activities is reviewed to determine the sustainability level of improved goat husbandry. SBA and WC production reduced XT biomass and XT cover area, while goat browsing alone, at a stocking rate of one head per hectare, did not affect XT leaf biomass production and shrub regeneration. Furthermore, batch breeding and flushing techniques provided the highest annual income, mainly from the sale of surplus animal products. This improved goat husbandry may be a sustainable alternative to WC production. However, increasing the current stocking rate is necessary to surpass the combined income of WC production and SBA. An estimation of the XT carrying capacity would offer a basis to assess whether this ecosystem would support a higher stocking rate.

Human-Lemur Coexistence in a Multiple-Use Landscape

Human impacts on the natural world are increasing and are generally considered a threat to wildlife conservation and the persistence of species. However, not all human activities are antithetical to conservation and not all taxa are impacted in the same ways. Understanding how wildlife respond to human activities at the population and individual level will help inform management of landscapes where humans and wildlife can coexist. We examined the effects of anthropogenic activities on a critically endangered primate, Verreaux’s sifakas (Propithecus verreauxi), at a multiple-use reserve in southwest Madagascar. Specifically, we sought to determine which activities the sifakas perceived as disturbances, using the framework of the risk disturbance hypothesis (RDH). The RDH holds that animals will respond to perceived disturbances as they do to predation threats. We therefore predicted that sifakas would be more vigilant, spend more time in high forest strata, reduce their daily feeding time, and occur at lower densities in response to high levels of perceived disturbance. Using data on sifaka behavior and spatial distribution, and the frequencies of anthropogenic activities, we found that sifakas increased vigilance and their height above the ground in response to certain human-related activities, notably those of domestic dogs. Contrary to our predictions, however, we did not find a negative effect of anthropogenic activities on daily activity budgets or population density. The relationship between the occurrence of sifakas and the intensity of tree cutting was actually positive. Our results indicate that sifakas perceive certain anthropogenic activities as threats and respond with immediate behavioral shifts, but that these activities do not have a discernible negative impact on the reserve’s population at this time. These results suggest that lemur conservation can be successful even in areas that are subject to moderate human use.

Nebkhas: An essay in aeolian biogeomorphology

Nebkhas are a type of anchored dune that forms by sediment accumulation around grasses, shrubs or trees. This paper outlines their importance, their distribution at global and local scales, summarises what is known about their morphology, discusses those plants with which they are associated, draws attention to the materials of which they are composed, and then concludes with a discussion of their ages. Nebkhas are very widespread in dry and coastal environments. They have considerable importance because they can be ‘islands of fertility’ and have major hydrological and biological effects. They can, if eroded, be major sources of dust emission. Examples of coastal nebkhas are known from both temperate areas and from lower latitude drylands, as along the Caspian shoreline in Iran, Kuwait, northern Peru, Namibia, Western Sahara, the Makran, southwest Madagascar, and Mauritania. Dryland nebkhas have been described from numerous areas, with concentrations of studies in Kuwait, the southwest USA, northwest China, and Iran. Within an area with suitable climatic conditions, nebkhas do not occur everywhere. Certain conditions need to be met for their development and these are illustrated with examples from the Tarim and Qaidam basins of China, the Lut of Iran, northwest Argentina, and the Namib. For this, Google Earth was employed. The heights of these features range from a matter of centimeters to as much as 20 m. There is a considerable quantity of data on the plants that are associated with the development of nebkhas. They have to have certain qualities for this role: ability to withstand drought, tolerate salt, thrive on sand burial, have wide shallow rooting systems to obtain water from fog and occasional rain events, extract moisture from groundwater, withstand sand abrasion, and develop adventitious roots. Although nebkhas are normally thought of as a type of sand dune, and most nebkhas are indeed composed of sand-sized material, largely consisting of quartz, there are many nebkhas which contain appreciable amounts of silt and clay, as well as salts such as gypsum. Although some nebkhas are ephemeral features, various dating techniques have shown that they can be decades, centuries and even millennia old.

Tortoise panopticon: Linkages between taboos and conservation management in Madagascar

Species-specific taboos are relevant to nature conservation, yet the relation of conservation with such social mechanisms and connected traditional ecological knowledge (TEK) is underexposed in both conservation science and nature conservation practices. This paper researches taboos of the Mahafaly and Antandroy tribes in South and Southwest Madagascar in relation to the critically endangered radiated tortoise (Astrochelys radiata). We develop the idea that the collection of taboos denotes a ‘panoptic’ self-surveilling system, which we call a ‘tortoise panopticon’. Theoretically, using performativity as a lens, we analyse the dynamic relation between practice and meaning in species-specific taboo systems, in the context of conservation management. Empirically, we define tortoise conservation potential and threats in the current state of the site-specific tortoise panopticon and the internal and external factors that shape it. This is particularly important in light of identifying favourable site locations for potential tortoise release. Based on (semi-)structured interviews with 282 Mahafaly and Antandroy respondents from 12 communes across 9 sites, we identify influential factors and components of the tortoise panopticon to measure its strength in each region and determine the extent to which favourable social situations for radiated tortoise conservation exists. Developing a connection between panopticon theory and practice theory, this paper presents a novel model that aides the assessment of the dynamics of species-specific taboo systems.

Southern Hemisphere controls on ITCZ variability in southwest Madagascar over the past 117,000 years

Migration of the inter-tropical convergence zone, driven by changes in seasonal insolation and high northern latitude temperatures, is the primary control on tropical rainfall on geologic timescales. We test this paradigm using the timing of growth of stalagmites from southwest Madagascar to infer the timing of expansion of the ITCZ to the south at its southern limit. Over the past 117 ky, speleothems grew in the study area primarily when two conditions are met: summer insolation greater than the mean and relatively high Southern Hemisphere temperatures as indicted by maxima in Antarctic ice core oxygen isotope ratios. We observe little influence of Northern Hemisphere, millennial scale temperature variability on the pluvial periods. Further, we observe periods during which the ITCZ simultaneously expands or contracts in both hemispheres. Because Antarctic isotope maxima are periods of increased atmospheric CO2, our results have implications for how tropical rainfall in the Southern Hemisphere might respond to global warming.