Fisheries ecology of rice farming landscapes : self-recruiting species in farmer managed aquatic systems

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Marchés publics de l’Élysée : quand le droit de la commande publique s’invite (timidement) au Palais

International audienc

Fisheries production in Southeast Asian Farmer Managed Aquatic Systems (FMAS): II. Diversity of aquatic resources and management impacts on catch rates

Southeast Asian rice farmers often manage aquatic habitats and resources on their land to increase harvest of aquatic animals (Amilhat, E., Lorenzen, K., Morales, E.J., Yakupitiyage, A., Little, D.C., 2009. Fisheries production in Southeast Asian farmer-managed aquatic systems (FMAS). I. Characterisation of systems. Aquaculture 296, 219-226). We characterize the diversity of aquatic resources harvested from such Farmer Managed Aquatic Systems (FMAS) and evaluate the effectiveness of management practices within contrasting FMAS in Cambodia, Thailand and Vietnam. Farmers harvested diverse self-recruiting species (SRS) from FMAS in all study areas: 24 locally recognized species in Cambodia, 66 in Thailand and 17 in Vietnam. Fish accounted for the largest share of SRS by weight in all areas but frogs, snails, crustaceans and insects were also important. Amphibious species, well adapted to rice farming landscapes, dominated catches of both fish and non-fish SRS. Stocked cultured species (CS) comprised only fish, were less diverse and differed between countries according to aquaculture practices. SRS catch rates in FMAS were significantly higher than wild animal catch rates in open aquatic systems in Cambodia and Thailand, indicating an underlying difference in abundance. This positive effect is likely attributable to lower harvesting effort in FMAS (where access was restricted to owners), agricultural inputs, and management measures aimed specifically at increasing aquatic animal production. Various management measures were recorded, but only the construction of brush parks and fertilisation was associated with positive effects on catch rates in the SRS-dominated FMAS of Cambodia and Thailand. Ponds in Vietnamese FMAS were managed intensively as carp polyculture systems, and catch rates within them responded positively to a wide range of management inputs. FMAS support a high abundance of aquatic animals including diverse SRS and benefit nutrition and income of farming households, agro-ecosystem services, and biodiversity conservation

The European eel (Anguilla anguilla) in France: An Example of Close Cooperation Among Researchers and Fishers to Study and Manage an Endangered Species

International audienc

Fisheries production in Southeast Asian farmer managed aquatic systems (FMAS): I. Characterisation of systems

Southeast Asian rice farmers often manage aquatic habitats and resources on their land to increase production of aquatic animals. We introduce the concept of 'farmer-managed aquatic systems' (FMAS) to capture the diversity of these resource systems at the interface of aquaculture and capture fisheries and characterize FMAS in contrasting agro-ecosystems of Cambodia, Thailand and Vietnam. Cambodian and Thai FMAS yielded primarily self-recruiting species (SRS) and were managed to allow or attract them, while Vietnamese FMAS were managed more intensively to produce mostly hatchery-reared species. More than 90% of rice fanning households in the study areas of Cambodia and Thailand harvested aquatic animals from their land, and about 70% created aquatic habitats such as ponds in addition to rice fields in order to increase aquatic resource production. Cambodian households created and utilized a wide variety of man-made aquatic habitats, while Thai households created predominantly trap ponds. In contrast, less than half of Vietnamese farming households harvested SRS and very few undertook FMAS management specifically for them. Vietnamese FMAS were intensively stocked and managed as aquaculture systems. with SRS accounting for less than 30% of production. Nonetheless, SRS production per area of FMAS was comparable in the three countries. Contrasting FMAS characteristics in different study areas reflect underlying differences in agro-ecosystems, aquaculture technologies, farmer livelihoods and markets

First evidence of European eels exiting the Mediterranean Sea during their spawning migration

International audienceThe migration route and the spawning site of the European eel Anguilla anguilla are still uncertain. It has been suggested that the Mediterranean eel stock does not contribute to spawning because there is no evidence of eels leaving the Mediterranean Sea. To test this hypothesis, we equipped eight female silver eels from the south of France with pop-up satellite tags during escapement from coastal waters. Once in deeper water, the eels quickly established diel vertical migration (DVM) between the upper and lower mesopelagic zone. Five tagged eels were taken by predators within the Mediterranean, but two eels reached the Atlantic Ocean after six months and at distances greater than 2000 km from release. These eels ceased their DVM while they negotiated the Gibraltar Strait, and remained in deep water until they reached the Atlantic Ocean, when they recommenced DVM. Our results are the first to show that eels from Mediterranean can cross the Strait of Gibraltar and continue their migration into the Atlantic Ocean. This finding suggests that Mediterranean countries, as for other EU states, have an important role to play in contributing to conservation efforts for the recovery of the European eel stock. Although European eels are found in fresh and brackish waters throughout Europe and North Africa, they escape to sea to spawn towards the end of their lives. European eels, like American eels, are presumed to spawn in the Sargasso Sea, where eel larvae of both species are found in the greatest abundance 1–3. The evidence for a single spawning area is strong and modern genetic studies indicate a panmictic species 4,5. European eels therefore need to undertake a spawning migration of at least 5000 km from the western margin of the continental habitat in Europe; this distance is much greater for eels escaping from more easterly locations, including those in the Baltic and Mediterranean Seas. However, despite the advent of marine remote sensing, genetic and otolith analyses, electronic tagging, and investigative computer modelling in the century since Schmidt

Outside of the mainstream: managing aquatic resources in human-dominated wetlands of the lower Mekong

A large proportion of fisheries production from the Mekong basin is generated in wetland areas outside of the mainstream and major tributaries. Most of these wetlands are embedded in agricultural landscapes and used intensively for agricultural water supply, capture fisheries and sometimes aquaculture. We review case studies of aquatic resource management in such wetlands including fisheries conservation in irrigated rice farming systems, stocking of non-native species for fisheries enhancement, and aquatic habitat enhancement in farmer-managed and public water bodies. Management outcomes in such human-dominated systems are found to be strongly influenced by local bio-physical conditions and human actions. We recommend adopting a systems perspective to guide the sustainable development of these resources, considering a wide range of management options, and conducting rigorous experimental or observational studies to assess actual development outcomes

The arrival of the American blue crab, Callinectes sapidus Rathbun, 1896 (Decapoda: Brachyura: Portunidae), in the Gulf of Lions (Mediterranean Sea)

International audienc

Movements of Non-Migrant European Eels in an Urbanised Channel Linking a Mediterranean Lagoon to the Sea

Transitional ecosystems and, particularly, Mediterranean lagoons represent important habitats for the European eel (Anguilla anguilla) population. In these habitats many anthropogenic pressures can disturb eel movements and, in turn, negatively affect the population. Despite the importance of movements during the non-migrant growing stage in eels, this topic is understudied in Mediterranean lagoons. We thus aim to describe the diel and seasonal phenology and the effect of environmental drivers on non-migrant eel movements. Videos obtained from an Adaptive Resolution Imaging Sonar (ARIS) acoustic camera that continuously recorded from October 2018 to April 2020 were processed to evaluate the daily number of eels swimming toward the lagoon. More than 60% of the 7207 eels observed were females with a size >45 cm. Movements were year-round and predominantly during the night. A Boosted Regression Tree analysis demonstrated that, among the 10 environmental drivers studied, flow velocity, water temperature, discharge of the main tributary, wind velocity and atmospheric pressure, had the strongest influence on eel movement activity. Non-migrant eel movements should be better incorporated into lagoon management plans through actions such as limiting dredging activities from 18:00 to midnight, especially when the water flows toward the lagoon and when the water temperature is higher than 12 °C

Influence of introduced vs. native parasites on the body condition of migrant silver eels

Because parasitism is among the reasons invoked to explain the collapse of Anguilla anguilla, we evaluated the parasitic constraint on body condition (BC) of migrant silver eels as a proxy of fitness with inter-site comparisons. Metazoan parasites were studied in 149 silver eels from five sites (northern Europe). In total, 89% were infected by 13 species including Myxozoa, Monogenea, Cestoda, Nematoda, and Acanthocephala. Anguillicoloides crassus was most common (56%), then Acanthocephalus clavula (30%), and Pseudodactylogyrus sp. (17%). BC, calculated for 58 females, was negatively correlated by abundance of the introduced Pseudodactylogyrus sp. but not by other parasite taxa. Nevertheless, the introduced A. crassus was considered as a severe pathogen based on previous data, whereas the native A. clavula was supposed to have limited impact. Parasite component communities and BC were different between sites. Silver eels from Stockholm Archipelago (Sweden) were the least parasitized (40% vs. 90–95% for other sites) with no parasites on the gills. Burrishoole (Ireland) differed by the absence of A. crassus and high prevalence of A. clavula (84%) but without consequences on BC. Gudenaa (Denmark), Corrib (Ireland), and Frémur (France) were close due to high prevalence of A. crassus (89–93%). Gudenaa and Corrib were the most similar because Pseudodactylogyrus sp. was also highly prevalent (respectively 71% and 60%) whereas absent in Frémur. Our results suggest that the fitness loss induced by the introduced parasites could affect the spawning success of migrant silver eels from Gudenaa and Corrib, and to a lesser extent from Frémur, but probably not those from Stockholm Archipelago and Burrishoole