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Session B1: Fish-Friendly Management of First Dams in the Tidal Area of the Gironde Estuary (France, SW)
Abstract
The particular case of the first dams met by the European eel migrating in the tidal area of the Gironde estuary is examined here. For these obstacles, typological elements are proposed, based on the nature of the hydraulic dams, but also on that of its downstream and upstream areas. Various technical tries are already performed to minimize impact of these dams, in tidal areas. These obstacles exist to prevent and limit entrance of salt or brackish water in the swamp and to prevent floods. Glass eel and tidal and marine young species colonize theses areas carried by the stream. The actually management of these dams doesn’t permit to the different species to go upstream because the dams are closed only 5 minutes after the flow inversion. The good management of these dams would allow the colonization of 37% of the space in the tributary or the swamp. Since 2009, MIGADO Association, in collaboration with local users, tries to manage the dams with different systems adapted to the user needs and to the natural characteristics of the swamp. The tests consist in installing : · holds to prevent the closure of the tidal dams, · stiffeners (« raidisseurs ») to slow down the closure of the tidal dams, · optimized management of the present gate on the tidal dams, · telescopic gate allowing to keep a upstream water level defined.
The evaluation shows promising results, answering to users’ needs upstream (none floods), a management adapted to the needs, and increase of fish population in the swamp and tributary (multiplied density by 20). There is no impact of suspension material entry in the middle. All system can be adapted to each swamp and to user needs. This system, little expensive and autonomous, allows to glass eel to colonize swamp and tributaries in the tidal area
Le marais doux endigué de Bourgneuf-Machecoul (Pays de Loire) Premier éléments de connaissance du peuplement piscicole. Relation ichtyofaune-habitat et problèmes majeurs de gestion (Maroc)
Le peuplement ichtyologique d'un marais littoral endigué, géré en eau douce, a été étudié sur une zone de 2 700 ha, située au nord du marais Breton-Vendéen (Loire-Atlantique, France). Le réseau hydraulique, qui représente près de 16 % de cette surface, se compose, d'environ 91 m de linéaire de fossés par ha (en tout 234 km) et de bassins présents uniquement dans la partie d'origine salicole du marais. Les hauteurs d'eau, l'envasement et le recouvrement par la végétation aquatique dépendent de la gestion humaine et sont très variables (moyennes respectives : 42 cm; 43 cm; 70 %). Cela se traduit par un morcellement spatial de l'habitat pour les poissons. La stratégie d'échantillonnage adoptée, qui tient compte de cette hétérogénéité, a permis de décrire un peuplement comportant 21 espèces. Dominé par les poissons-chats et par les anguilles, ce dernier est caractéristique de la zone à brèmes des cours d'eau. Les abondances sont relativement élevées (en moyenne 315 kg/ha et 11 460 poissons/ha), mais elles sont très hétérogènes. L'évolution qualitative et quantitative de la répartition spatio-temporelle est décrite à l'aide d'une analyse factorielle des correspondances portant sur 74 échantillons prélevés par pêche électrique entre 1987 et 1989. Bien que l'approche de ce milieu soit complexe et les références bibliographiques relativement rares, l'analyse des premières données permet d'ores et déjà d'identifier quelques problèmes de gestion ayant des répercussions directes sur le peuplement piscicole de cette zone.The dammed up marshes of the French Atlantic coast cover about 200 000 ha between River Vilaine and the « Bassin d'Arcachon ». Eighty eight % are managed with freshwater. They constitute original environments initially created for agriculture or for salt production, and they are now threatened by land abandonment within the next decade. Concurrently to aquaculture (in created or existing ponds), exploitation of the fish stocks in the ditchweb is likely to encourage a diversification of agricultural activities. Unfortunately, bibliographic analysis reveals the relative scarceness of research about sampling methods and qualitative or quantitative characteristics of these fish communities. This is quite surprising considering the importance of the ditchwed of this kind of environment outlined by several authors. In the Netherlands, BELTMANN (1984) assessed that there is a total of 400 000 km of ditches. In France, the littoral dyked marshes of the Atlantic coast couid comprise 20 000 km of ditches and about 24 000 ha of open water. The present work provides for the first data on the fish community of Bourgneuf marsh.The northern part of the marsh of Bourgneuf, 2 700 ha provided whith f reshwater, contains nearly every kind of landscapes found throughout the whole Breton-Vendéen marsh. The pattern of the ditch network strongly changes from a zone to another (fig.1) : presence of former salt pans in the western part, regular geometric shapes in the recently created polders next to the River Falleron, irregular ditchweb pattern in the eastern part. The average density of the ditch network is 91 m of ditches per ha, totalizing 234 km in the study area. The total surface of open water, composed of ditches and basins (former salt pans), covers 411 ha (over 15 % of the study site). Diversity of ditch types occurs at fine scales (<1 000 m2), they vary according to their widths (0,3 to 7 m), depths (average, 42 cm; SD, 20,4), thickness of silt layer (average, 43 cm; SD, 42) and their hydrophyte vegetation cover (average, 70 %; SD, 60 %). As a consequence of this heterogeneity, available habitats are scattered over the marsh (mosaïc distribution). A nested sampling (FRONTIER, 1983) was carried out to take into account this high heterogeneity : 5 sampling areas were selected randomly. In each one, 3 to 5 ditches were chosen according to their characteristics (see above). Sampling stations were delimited by 2 stop nets (5 mm mesh) settled 30 m apart, in order to avoid fish migration. Field work was conducted using « Heron » electric fishing material (see LAMARQUE et al., 1978). In each ditch-section, we carried out as many successive catches as necessary to apply the maximum likelihood weighted estimation method of CARLE and STRUB (1978). Nine to 19 stations were sampled at 5 periods, between 1987 and 1989. A total of 74 samples were collected.The fish community was composed of 21 species (table 1) and corresponded to the bream zone of Verneaux's classification (1977). The densities and biomass were quite high (on average 315 kg/ha and 11 460 fishes/ha) but very variable (0 to 2 120 kg/ ha and 0 to 39 300 fishes/ha). The catfish, Ictalurus nebulosus (170 kg/ha), the eel, Anguilla anguilla (47 kg/ha) and the tench, Tinca tinca (28 kg/ha), represented on average 77,5 % of the standing crop, but their spatial distribution was very irregular. These estimates are assumed to be reliable considering that the data used for the calculations were provided by a sampling design which permits to respect the basic assumptions of the removal method. (f) The population size could only change because of the fishings (no migration because of the stop nets; no recruitment/death because of the short duration of the fishing sequences). (ii) The standard sampling design permitted to reduce the variations of the catch probabilities between the successive removals. Several studies have shown that this removal method under-estimates by about 20 % the true size of the fish populations (e. g. BOHLIN and SUNDSTROM, 1977; MAHON, 1980). But they were based on Zippin's method, and the estimator of CARLE and STRUB (1978), that we used, was shown to be more robust (COWX, 1983; GERDEAUX, 1987). Nevertheless, we assume that the values presented in this paper provide for an approached information on the sizes of the studied fish populations.To assess the fish-habitat relationship, a correspondence analysis (fig. 2) was performed on the 74 samples X 17 species matrix (excluding the sticklebacks, Gaslerosteus aculeatus and Pungitius pungitius, which population size estimations failed because of their low catchabilities). Four groups of samples were ordinated according to their specific richness and the species they contained. Several habitat parameters were projected on F1-F2 factorial map (fig. 3). Hydrophyte cover, thickness of silt layer, water depth (fig. 3 and 4), which are directly controlled by human maintenance, appeared to be the major structuring habitat parameters for the fish community. In the deepest and less silted stations, the communities were rich (on average 11 species; group 4, fig. 2). Predators such as pike-perch, Stizostedion lucioperca, and perch, Perca fluviatilis, occurred, and cold water species were found, such as minnow, Phoxinus phoxinus, or chub, Leuciscus cephalus. When the silt layer was thicker and the water level was intermediate, the specific richness decreased (average, 6,2 species) and the community was either dominated by the cattish (group 2, fig. 2) or by the rudd, Scardinius erythrophtalmus (group 3, fig. 2), according to the importance of the aquatic vegetation cover. Habitats with thickest silt layers, shallowest waters and maximum aquatic vegetation cover contained the poorest communities (average 3,9 species) dominated by eel (group 1, fig. 2). There is also evidence that the diversity of the community has progressively decreased since 1987 (fig. 5). The most stenothermous species disappeared, and the importance of the catfish increased : it doubled between May 1987 and September 1989 (fig. 6). Although the eel is the species most adapted to this environment, we emphasize the diminution of its biomass (fig. 7). These phenomena could be partly due to the climate (cold winter in 1987, important swelling in January 1988 and 2 droughts in summers 1988 and 1989). But they are mainly caused by the water management policy which is intended to favour agriculture by keeping stable water levels (evacuation of swellings) and by preventing the freshwater part from the marine influence (collective sluice gates). This does mot permit an optimal breeding of the species that have to spawn on flooded meadows, neither a proper colonisation of the marsh by elvers
Genetic and morphological differentiation of the crab <i>Dissodactylus primitivus</i>, ectoparasite of two sympatric echinoids
Recueil de réferences bibliographiques françaises concernant l'Anguille (Anguilla anguilla L.) sur la période 1987-1994
Episodes of falling among elderly people: a systematic review and meta-analysis of social and demographic pre-disposing characteristics
CONTEXT: The multifactorial nature of falls among elderly people is well-known. Identifying the social-demographic characteristics of elderly people who fall would enable us to define the typical profile of the elderly who are at risk of falling. OBJECTIVE: We aimed to isolate studies in which the social-demographic risk factors for falls among the elderly have been evaluated and to carry out a meta-analysis by combining the results of all of these selected studies. METHOD: We did a systematic literature review using the key words "accidental fall / numerical data" and "risk factors." Inclusion criteria entailed the selection of articles with the following characteristics: population of subjects aged 60 years or over, falls that took place in everyday life, and social-demographic risk factors for falls. RESULTS: 3,747 indexed articles published between 1981 and 2007 were identified, and 177 studies with available data were included, of which 129 had data on social-demographic risk factors for falls. Difficulties in activities of daily living (ADL) or in instrumental activities of daily living (IADL) double the risk of falling: The OR and 95% Cl were 2.26 (2.09, 2.45) for disturbance ADL and 2.10 (1.68, 2.64) for IADL. The OR and 95% Cl for Caucasians were 1.68 (0.98 - 2.88) and 0.64 (0.51 - 0.80) for Hispanics. In the subgroup of patients older than eighty, being married protected people from falling with an OR and 95% Cl =0.68 (0.53 - 0.87). CONCLUSION: Defining factors that create a risk of falling and protect elderly people from falls using social-demographic characteristics lets us focus on an "at risk" population for which a specific program could be developed
Étude de l'anguille en marais d'eau douce. Première analyse des probabilités de capture observées lors des inventaires par pêche électrique
Association between an index of consumption of hand-rub solution and the incidence of acquired meticillin-resistant Staphylococcus aureus in an intensive care unit
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