Le parc national du diawling (Mauritanie) : infrastructures hydrauliques pour la restauration d’une plaine d’inondation et la création d’un estuaire artificiel

L’hydrologie du bas-delta du fleuve Sénégal a été totalement modifiée par la mise en service du barrage de Diama et de ses digues annexes. Ceci a eu des impacts écologiques et sociaux considérables. L’article décrit les infrastructures hydrauliques construites et leur mode d’opération dans le cadre de la mise en œuvre du plan directeur d’aménagement d’une aire protégée dans le bas-delta mauritanien. Les résultats préliminaires de cet essai de restauration d’un écosystème sont présenté

Life history, growth and production of Neomysis integer in the Westerschelde estuary (S.W.

ABSTRACT: The Neomysis integer (Leach, 1814) (Crustacea, Mysidacea) population of the brackish part of the Westerschelde estuary was sampled on a fortnightly basis from November 1990 to December 1991. Denslty, biomass, population structure and brood size were recorded. The Bhattacharya method was applied to the length-frequency data for the detection and separation of cohorts. Growth is described both by a generalised von Bertalanffy function and by a von Bertalanffy function incorporating seasonal oscdlations in growth. Secondary production was estimated for each cohort using 4 approaches. The seasonal pattern in density and biomass showed 3 peaks: a relatively small, yet distinct, peak in early March (30 ind. m-2, 60 mg AFDW m-*) and 2 main peaks in late spring (160 ind. m-'. 225 mg AFDW m-2) and in summer (140 ind. m-2. 125 mg AFDW m-2). Throughout winter, N. integer density remained well below 30 ind. m-2 Three periods of increased reproductive activity and subsequent input of juveniles were found. Thls suggests that 3 cohorts were produced per year. The overwintering generat~on lived from autumn until the following spring. The spring generation was born in early spring and lived for about 3 mo, while the summer generation lived from summer until early winter. The 3 cohorts showed marked differences in their biology. The overwintering generation showed seasonal growth oscillations, larger brood size and a larger size at maturity. Individuals belonging to the other 2 cohorts generally grew faster, produced less young per female, and attained maturity at a smaller size. Within each cohort, both sexes exhibited different growth characteristics: females generally lived longer, grew faster and consequently became larger than males. The size-frequency, growth summation and removal summation methods yielded comparable production estimates. The annual production was 0 3 g AFDW yr-' with an annual P/B ratio of 6. The average cohort P/B was 3. The size-frequency method gave similar results only when applied to the 3 cohorts and to both sexes separately. The spring cohort accounted for almost half of the annual production. Despite the longer life span of the overwintering generation, it generated only a quarter of the annual production. An independent estimate of product~on using the mortality rate of the different cohorts resulted in values comparable to those obtained by the other methods for the overwintering cohort, while the production of the other 2 cohorts was overestimated

Fishery Characteristics and Management in the Floodplain Lakes of Tana River delta, Kenya

Tana River delta floodplain is maintained through a dynamic balance revolving around frequency, extent, and flooding duration. These seasonal and annual flooding variations strongly affect the floodplain communities' fisheries and livelihoods. In the delta, fishing is an important traditional source of livelihood, practiced alongside local agrarian livelihoods such as shifting cultivation and livestock keeping. Fishery utilization and management characteristics in the Tana River delta floodplain lakes are not well documented. This study investigated the characteristics and management of small-scale fisheries in the Tana River delta floodplain lakes. Information relating to past flooding events, fishery characteristics, prevailing regulatory regimes, and the impacts of seasonal flooding were collected using field observations. We collected the information at awareness workshops and key informant interviews between June and September 2018, which covers a significant flooding period of that year, and August 2021, a relatively dry period in the delta. We collected the information from communities living around floodplain lakes in Tarassa and Ngao in the southern part of the delta and Tamaso and Lango la Simba areas in the eastern part of the delta. Results indicate that fishery resources are more diverse during flooding (new species recruitment, presence of spawning, breeding, and foraging sites). The community does fishing all year round, and some part-time practice fishing to supplement shifting cultivation and dry season grazing that are greatly affected by periodic flooding. Floods were crucial in enriching floodplain lakes with diverse fish species. Women are involved in fish trading, acquiring fish primarily within their lineage. Fish is mainly sold in local markets due to poor preservation leading to low-value addition. This study recommends a comprehensive value chain analysis to improve it. Fishing communities around the villages are also most vulnerable to climate change because fishery resource governance needs strengthening, and most households are not involved in resource management. Besides, fishers have limited livelihood options due to lacking skills, technologies, and knowledge to undertake climate adaptation-related decisions. We recommend desilting floodplain lakes and improving connectivity with the main river channel. Additionally, an urgent need is to institute a co-management system to bring together different user groups around these floodplain lakes. Keywords: Fisheries, Flooding, Livelihoods, Floodplain lakes, Governance, Tana River delta DOI: 10.7176/JEES/13-2-02 Publication date:March 31st 202

La participation des communautés locales à la marchandisation de la Nature

Depuis quelques années, les éléphants d’Afrique sont à nouveau menacés d’extinction par un braconnage intense et prolongé. L’article s’appuie sur le récit d’un braconnier du Rufiji (Tanzanie) pour examiner les déterminants de la participation villageoise au braconnage des éléphants et les articuler aux résultats de l’examen critique des politiques ultralibérales de conservation de la nature.Intense and protracted poaching over the past few years is again driving the African Elephant towards extinction. Based on the account of a poacher in Rufiji (Tanzania) we examine the factors that drive villagers to partake in elephant poaching and articulate these findings with a critical assessment of ultraliberal nature conservation policies

Appropriation des ressources « naturelles » et criminalisation des communautés paysannes

La plaine inondable du Rufiji (Tanzanie) est occupée par des populations dont les activités économiques principales sont l’agriculture vivrière et la pêche commerciale. Les revenus de la pêche légale assurent avec peine la sécurité alimentaire des foyers mais ne permettent pas de faire face à des dépenses « exceptionnelles ». Ainsi, pour financer les études secondaires de leurs enfants, les villageois n’ont guère d’autre choix que de quitter les zones de pêches légales et de pénétrer, au risque de leur vie, la Réserve de Chasse du Selous (50 000 km²) où se trouvent de nombreux lacs poissonneux. La Réserve, située à proximité immédiate des villages, s’est constituée progressivement au cours du XXe siècle par une série de décisions autoritaires et coercitives. Les communautés locales ne bénéficient d’aucune manière des revenus substantiels issus de son exploitation tandis qu’elles en supportent l’essentiel des coûts induits. Les nouvelles politiques de conservation « participatives » (community based conservation) mises en place depuis une dizaine d’années restent à l’état de déclarations d’intention.In Tanzania, the Rufiji floodplain is populated by people earning their living from agriculture and fishing. Revenues from legal fishing hardly secure food security of households, and don't really allow for other investments or expenses. In order for instance to earn enough money to pay for secondary school fees, many villagers actually need to leave the legal fishing zones and to penetrate in the Selous Reserve, where several lakes abounding in fish are situated. The Reserve has been progressively constituted throughout the twentieth century, but local villagers do not beneficiate from the revenues it generates. New "participatory" approaches and conservation policies are only declarations of interest without concrete effects

Changing hydro-ecological dynamics of rivers and deltas of the Western Indian Ocean : anthropogenic and environmental drivers, local adaptation and policy response

This paper details common characteristics of the rivers flowing into the Western Indian Ocean as well as their specificities, the changes affecting their hydro-ecological rhythms, and their consequences downstream, especially in the deltas. In the river systems of the Western Indian Ocean, the flood pulse is the engine of productivity through the direct relationship between flood extent and ecosystem production. Large scale land conversions and the construction of dams create salt water intrusion and catchment degradation. On a multi-decadal time scale, the current approach is not sustainable. Coastal wetland systems are rapidly losing their value: between 1997 and 2011 swamps and floodplains lost 64% of their surface area, while tidal marshes and mangroves lost 22% globally

Rapid Acoustic Survey for Biodiversity Appraisal

Biodiversity assessment remains one of the most difficult challenges encountered by ecologists and conservation biologists. This task is becoming even more urgent with the current increase of habitat loss. Many methods–from rapid biodiversity assessments (RBA) to all-taxa biodiversity inventories (ATBI)–have been developed for decades to estimate local species richness. However, these methods are costly and invasive. Several animals–birds, mammals, amphibians, fishes and arthropods–produce sounds when moving, communicating or sensing their environment. Here we propose a new concept and method to describe biodiversity. We suggest to forego species or morphospecies identification used by ATBI and RBA respectively but rather to tackle the problem at another evolutionary unit, the community level. We also propose that a part of diversity can be estimated and compared through a rapid acoustic analysis of the sound produced by animal communities. We produced α and β diversity indexes that we first tested with 540 simulated acoustic communities. The α index, which measures acoustic entropy, shows a logarithmic correlation with the number of species within the acoustic community. The β index, which estimates both temporal and spectral dissimilarities, is linearly linked to the number of unshared species between acoustic communities. We then applied both indexes to two closely spaced Tanzanian dry lowland coastal forests. Indexes reveal for this small sample a lower acoustic diversity for the most disturbed forest and acoustic dissimilarities between the two forests suggest that degradation could have significantly decreased and modified community composition. Our results demonstrate for the first time that an indicator of biological diversity can be reliably obtained in a non-invasive way and with a limited sampling effort. This new approach may facilitate the appraisal of animal diversity at large spatial and temporal scales