Les peuplements de poissons de la Camargue

Fish communities in the Camargue wetlands, both temporary and permanent marshes as weil as irrigation and drainage canals, were studied from 1977 to 1980. The main part of this work was carried out in wetlands isolated from direct contact with the sea by a dike, the Digue à la mer. Three major types of wetlands and their associated fish species are described in the Camargue : the freshwater (0-5 g/1 Cl-), the brackish (5-16 g/1 Cl-), and the very brackish (16-35 g/1 Cl-). A significant relationship (P < 0.01 ) was found between the species richness and the surface area. The slope of this regression (0.134) is lower than that found for other aquatic systems. Four associations of fish were determined and their meaning is discussed . The biomass of temporary freshwater marshes ranged between 13 to 76 kg/ha and was much lower than those found in the small freshwater canals : 112 to 2 544 kg/ha. Common carp, Cyprinus carpio L., is the dominant species in freshwater wetlands (70 to 85 % of total biomass). A space partitioning between the immature and the adult carp is described. ln one waterbody studied south of the Digue à la mer, linked temporarily with the sea, the fish community composition underwent frequent and rapid changes according to the variations of environmental factors. The salinity appeared to be the most important factor affecting diversity and eveness of the fish community in this etang. A canonical analysis was used to determine which of the environmental factors bad the greatest impact on the abundance of the different fish genus. Only 46.2 % of the fish species studied reproduce in the Camargue, while 35.9 % migrate to the sea for spawning. The importance of a link with the sea as weil as that of a sound water management plan for the Camargue as a whole are pointed ou

The diet of the mosquitofish Gambusia affinis (Baird and Girard) (Poecilliidae) in Mediterranean France

Le régime alimentaire de Gambusia affinis, espèce introduite en Camargue, est essentiellement constitué par des crustacés d'octobre à mai. Pendant la période de reproduction, de juin à septembre, les poissons mangent surtout des insectes aquatiques. Le régime alimentaire des mâles matures et celui des immatures se chevauche considérablement (61.9-95.6 %). Les femelles matures, présentes seulement de juin à septembre, mangent plus d'insectes terrestes à la surface de l'eau et d'insectes aquatiques que les autres classes de poissons. Par conséquent, leur régime alimentaire se distingue bien de celui des autres poissons. La même chose est observée si l'on considère la taille des proies ingérées. La grande taille des femelles matures leur permet d'exploiter une source de nourriture qui n'est pas disponible pour les autres classes de poissons. Lorsque la prédation par les poissons réduit l'abondance des proies les plus petites, il se crée une situation potentielle de compétition intraspécifique pour la nourriture. Les femelles matures, cependant, peuvent pleinement satisfaire leurs besoins alimentaires, intenses en période de reproduction, en exploitant des ressources différentes des autres classes de poissons, et elles peuvent ainsi maximiser leur succès de reproductio

Direct and indirect effects of environmental factors on dietary niches in size-structured populations of a wild salmonid

Dietary plasticity of populations can be associated to ontogenetic diet preferences and depends on the size-structure of populations. Dietary niche characterizes the functional role of organisms in a food web, as it reflects both resources' diversity used by a consumer and trophic interactions in the system. Dietary niches are controlled both by biotic and abiotic factors, but their interactions in natural systems remain poorly studied. Here, we investigated the variability of dietary niche in salmonid wild populations focusing both on inter-population and intra-population (through time) trophic changes, using marble trout (Salmo marmoratus) living in Slovenian headwater streams as a model system. Stable isotope analysis showed high variability of dietary niche and trophic diversity among six of the seven remnant marble trout populations. We observed substantial differences in dietary niche width among populations and within populations through time. Results of partial least square path modelling highlighted opposite effects of immature and mature trout on trophic niche structure. Direct effects of temperature and slope (stream and watershed) were opposite; temperature narrowed dietary niches while slope increased them. Environmental factors (e.g., temperature, stream and watershed slope) had indirect effects on trophic niches after accounting for fish density. Our results showed that size-distribution and sexual maturity are key determinants of the dietary niche width in a population. Increasing density of immature trout tended to widen the dietary niche while increasing density of mature trout tended to narrow it. Environmental factors had direct effects both on resources and consumers densities and indirect effects. Direct and indirect effects were often antagonistic

The Effect of Recurrent Floods on Genetic Composition of Marble Trout Populations

A changing global climate can threaten the diversity of species and ecosystems. We explore the consequences of catastrophic disturbances in determining the evolutionary and demographic histories of secluded marble trout populations in Slovenian streams subjected to weather extremes, in particular recurrent flash floods and debris flows causing massive mortalities. Using microsatellite data, a pattern of extreme genetic differentiation was found among populations (global FST of 0.716), which exceeds the highest values reported in freshwater fish. All locations showed low levels of genetic diversity as evidenced by low heterozygosities and a mean of only 2 alleles per locus, with few or no rare alleles. Many loci showed a discontinuous allele distribution, with missing alleles across the allele size range, suggestive of a population contraction. Accordingly, bottleneck episodes were inferred for all samples with a reduction in population size of 3–4 orders of magnitude. The reduced level of genetic diversity observed in all populations implies a strong impact of genetic drift, and suggests that along with limited gene flow, genetic differentiation might have been exacerbated by recurrent mortalities likely caused by flash flood and debris flows. Due to its low evolutionary potential the species might fail to cope with an intensification and altered frequency of flash flood events predicted to occur with climate change

Determining individual variation in growth and its implication for life-history and population processes using the Empirical Bayes method

The differences in demographic and life-history processes between organisms living in the same population have important consequences for ecological and evolutionary dynamics. Modern statistical and computational methods allow the investigation of individual and shared (among homogeneous groups) determinants of the observed variation in growth. We use an Empirical Bayes approach to estimate individual and shared variation in somatic growth using a von Bertalanffy growth model with random effects. To illustrate the power and generality of the method, we consider two populations of marble trout Salmo marmoratus living in Slovenian streams, where individually tagged fish have been sampled for more than 15 years. We use year-of-birth cohort, population density during the first year of life, and individual random effects as potential predictors of the von Bertalanffy growth function’s parameters k (rate of growth) and L∞ (asymptotic size). Our results showed that size ranks were largely maintained throughout marble trout lifetime in both populations. According to the Akaike Information Criterion (AIC), the best models showed different growth patterns for year-of-birth cohorts as well as the existence of substantial individual variation in growth trajectories after accounting for the cohort effect. For both populations, models including density during the first year of life showed that growth tended to decrease with increasing population density early in life. Model validation showed that predictions of individual growth trajectories using the random-effects model were more accurate than predictions based on mean size-at-age of fish

Extreme variability in European eel growth revealed by an extended mark and recapture experiment in southern France and implications for management

WOS:000777836500009International audienceThe European eel (Anguilla anguilla) is endangered due to its peculiar life-history cycle, fishing pressure and difficulty in global population management. To improve our understanding of the population dynamics and refine conservation policies, an extended mark and recapture experiment and glass eel stocking were conducted in the River Rhone Delta (France) over 8 years. Around 1100 yellow eels were PIT-tagged and released in 2007, 2.5 kg of glass eels were released each year from 2008 to 2012, and the population was monitored using fishing between 2007 and 2015. After capture or recapture, the body parameters, sex and maturity were assessed. Age was estimated from otolith growth rings. At the end of the experiment, silver eels were between 352 and 875 mm long (age 17 to 185 months) and yellow eels between 170 and 868 mm long (age 12 to 123 months). Age estimates were validated using mark and recapture and showed 16% age underestimates and 5% inaccurate ages. The growth rates were extremely variable with lengths ranged by 2-fold at a given age. These results highlight the difficulty of eel population management, at least in the Mediterranean area

Morphological variation in hybrids between Salmo marmoratus, and alien Salmo species in the Volarja stream, Soca River basin, Slovenia

International audienceThere were significant correlations between colour pattern, LDH-5*, genotype and certain meristic characters in 59 hybrid trout Salmo, sp. from the Volarja stream, Soca River basin, Slovenia. It is concluded that panmixia between native Salmo marmoratus, and introduced S. trutta, of Atlantic, Danubian and Mediterranean origin had not been reached in this zone, despite the long period of introgression. The result is in agreement with other studies dealing with introgression in Salmo, and for management purposes certain morphological characters, especially colour pattern, can be a valuable tool in restoring the marble trout population in the Soca River

Status and development of the population of the globally threatened Dalmatian Pelican, Pelecanus crispus, in Turkey

WOS: 000298512300001The Dalmatian Pelican, Pelecanus crispus (Bruch, 1832), used to be a widespread breeding species in Turkey in the past. Until the 1990s, approximately 473-763 pairs were breeding at 20-25 sites. Of these, 53-59% have been lost due to drainage of wetlands, 17-19% due to direct persecution, 16-22% due to both drainage and persecution, and 6-8% due to water level increase. Currently there are only five active breeding colonies: Gediz Delta, Manyas Lake, Buyuk Menderes Delta, Aktas Lake and Isikli Lake. The colony at Isikli Lake was discovered in 2010 and comprises 6 pairs. Since 2000, the total breeding population of Dalmatian Pelicans increased moderately from 220-250 to 277-341 pairs. Likewise, the wintering population has also increased from 352 up to 2,344 individuals, which seems to be linked with the increase in the breeding population in the region. Nevertheless, the population size still renders the species susceptible to the risks affecting small populations

Données préliminaires sur la communauté d’amphibiens de la Réserve Naturelle de Roque-Haute dans le sud de la France

Seven species of amphibians have been recorded at the Roque-Haute Nature Reserve, two newt species : Triturus marmoratus and T. helveticus and five frog species : Hyla meridionalis, Pelodytes punctatus, Pelobates cultripes, Bufo calamita, Rana perezi. Many of these species have a geographic distribution restricted to southern France and the Iberian Peninsula, and are considered as vulnerable. Only 25% of the pools of the Roque-Haute Nature Reserve are used for amphibian reproduction. The larval period lasts from autumn to the end of the following summer. Two species have a reproduction in autumn as well as in spring : Pelodytes punctatus and Pelobates cultripes. More studies are needed on the demography and the genetics of these amphibian populations in order to assess their viability and to ensure their conservation.Sept espèces d’amphibiens ont été dénombrées dans la Réserve Naturelle de Roque-Haute, deux urodèles : Triturus marmoratus et T. helvéticas et cinq anoures : Hyla meridionalis, Pelodytes punctatus, Pelobates cultripes, Bufo calamita, Rana perezi. Beaucoup de ces espèces ont une distribution géographique restreinte au sud de la France et à la Péninsule ibérique et la plupart sont considérées comme vulnérables. Seulement 25% des mares de Roque-Haute sont utilisées par les amphibiens pour leur reproduction. La période larvaire dure de l’automne à l’été suivant. Deux espèces ont à la fois une reproduction automnale et printanière, ce sont Pelodytes punctatus et Pelobates cultripes. De nouvelles études sur le fonctionnement démographique et la génétique de ces populations d’amphibiens sont nécessaires afin d’évaluer leur viabilité et d’assurer leur protection.Jakob Christiane, Veith Michael, Seitz Alfred, Crivelli Alain J. Données préliminaires sur la communauté d’amphibiens de la Réserve Naturelle de Roque-Haute dans le sud de la France. In: Ecologia mediterranea, tome 24 n°2, 1998. pp. 235-240

Translocation of stream-dwelling salmonids in headwaters: insights from a 15-year reintroduction experience

Translocation programs are a common strategy to increase the number of viable populations of threatened freshwater fishes. Yet, only in a minority of cases the success or failure of translocations has been assessed through a quantitative analysis of demographic traits, compensatory responses, lifehistories and population dynamics of the threatened species. A paradigmatic case a translocation program combining both management- and research-oriented activities is represented by the Marble Trout Conservation Program, which started in 1993 in the upper reaches of the Soca, Idirjca and Baca river basins (Slovenia) for the conservation of stream-dwelling marble trout Salmo marmoratus. In order to enhance the viability of the species, two new populations were created in 1996 by stocking 500 marble trout aged 1? in previously fishless streams (Gorska and Zakojska) within the core habitat of the species. The new populations have been systematically monitored for 15 years by individually tagging and sampling marble trout. Our analyses show that deterministic extinction of marble trout populations are unlikely and that highmagnitude environmental stochasticity (i.e., severe floods) is the only main cause of local population extinction, despite the high resilience to flood-induced massive mortalities exhibited by marble trout through compensatory mechanisms (e.g., relaxation of density-dependent body growth and survival at low densities). Fishless headwaters, probably characterized by a history of recurrent severe floods, should not be considered as candidate sites for the creation of new populations. Fewer individuals than originally reintroduced (i.e., 500 fish aged 1? in each stream) might be sufficient to establish viable populations, since compensatory mechanisms are likely to regulate population size around stream carrying capacity in a few years. Besides enhancing the species viability, translocation programs can provide an excellent framework for the estimation of ecological traits (e.g., life-histories, demography, population dynamics etc.), identify potential vulnerabilities and thus guide well-formed management actions for the threatened species