A simulation model is developed to analyse the variability of production functions in an exploited virtual ecosystem. We assume that a complex food web can be represented by a set of trophic components interacting through predation. Each component has a set of recruitment, growth, and survival models, a catch level and trophic preference function. Prey are consumed according to their abundance and predators' trophic preference functions are estimated in a pristine system. A parameter for the food consumption per unit biomass describes foraging for each trophic component. The FishBase database is used to parameterise some of the major processes in a generic model. A commercial fishery targets mostly high trophic levels through a set selectivity function. Some key ecosystem features are assessed in simulations: the intensity of top-down and of bottom-up controls, and the degree of trophic opportunism. Top-down control is the regulation of lower food-web components by one or several upper-levels predators. Bottom-up control is the regulation of trophic components by their prey. Results show that biological production functions are highly dependent on predation parameters and vary differently according to trophic level. Fishing activity modifies the biomass distribution between components and strongly affects higher trophic levels more sensitive to exploitation. Trophic dynamics within the system are altered through the rates of predation mortality. In systems where predation mortality is high, top-down control dominates and fishing affects all food web components. These “fishing-controlled” systems display compensatory mechanisms through a released predation control. We also show that systems where productivity is dependent on prey abundance are more “environment-controlled” and seem more sensitive to overexploitation, particularly the higher trophic levels. Trophic opportunism tends to dampen the propagation of top-down or bottom-up controls through the food web and thus stabilizes the ecosystem. Trophic relationships are therefore essential ecosystems characteristics that determine production and response to exploitation. Their routine analysis is a key part of the ecosystem approach.

The present paper aims at identifying and assessing indicators of the effects of Marine Protected Areas (MPAs) in coral reef regions, based on a bibliography review in ecology, economics and social sciences. First the various effects studied within each of these domains and the variables used to measure them were censused. Potential ecological indicators were assessed through their link with the question used (here termed “relevance”) and their “effectiveness” which encompasses the issues of precision, accuracy and statistical power. Relevance and effectiveness were respectively measured by the frequency of use of each indicator and the proportion of significant results in the reviewed articles. For social and economic effects, the approach was not possible due to the low number of references; we thus discussed the issue of finding appropriate indicators for those fields. Results indicate: 1- the unbalance in literature between disciplines; 2- the need for protocols and methodologies which include controls in order to assess MPA effects; 3- an important proportion of ecological indicators with low effectiveness; 4- the large number of ecological effects still not studied or not demonstrated at present.

The effect of providing algal food to female Crassostrea gigas broodstock sampled at a favourable time of year was investigated using pre-defined indices of oocyte quality and subsequent larval and post-larval performances. Broodstock were collected in the Aber Benoît estuary (Brittany, France) at the end of April 2002 and were divided into two groups, a starved control (S, 1 µm – filtered seawater) and a fed group (F, ad libidum algal mixture of Isochrysisgalbana clone T-Iso and Chaetoceros calcitrans), maintained under these conditions for six weeks prior to fertilizations. For each conditioning type, two batches of larvae and post-larvae were reared from two identified females. Quality criteria were defined in terms of predictors (oocyte lipid contents, mature oocyte diameters, ovarian maturity and presence/absence of atresia) and validators (larval growth, algal consumption and time to settlement, and post-larval growth). Each female was considered as a treatment, and parametric and non-parametric ANOVAs were performed, where appropriate, on predictors and validators between each treatment. In both conditions, a surplus of oocytes was produced, in relation to expected market conditions. No effect of the conditioning treatment was detected either on oocyte quality predictors or on subsequent validators. It is likely that winter reserve accumulation is more important than trophic conditioning for successful gametogenesis in the productive Aber Benoît environment. Given the considerable cost of abundant feeding during the conditioning of broodstock collected at the end of winter and destined for gamete stripping (the prevalent practice in France), we suggest that feeding be minimal or suppressed altogether when the condition index is favourable.

Field studies describe echinoplutei not only as grazers but also as prey of naturally occurring fish and shellfish larvae. This finding suggests their potential as live feed in aquaculture. This paper reports on consistent spawnings of the captive sea urchin Paracentrotus lividus (Lamarck 1816) (Echinodermata: Echinoidea) throughout the year using diets of plant origin (yellow maize and/or dried seaweed) with fixed environmental conditions equivalent to field conditions during late spring (14 h of daily illumination and 18 °C of temperature). Broodstock maturation without unwanted spontaneous spawnings was achieved in two ways: extending the natural season of reproduction and inducing out-of-season wild specimens to mature. Controlled spawnings of captive sea urchins were induced every month of the year by KCl 0.5 M injections. The diet maize/seaweed combination gave the best results (79% of the tested urchins) in terms of consistent large spawnings throughout the year, followed by the pure maize diet (50%) and the pure seaweed diet (36%). When out-of-season wild sea urchins were induced to maturation, the majority (72%) of tested individuals required at least 60 days to spawn under KCl injection when fed the combination diet. The results demonstrate the feasibility of producing larval P. lividus in that high numbers of fertilized eggs (up to 5 million per female) can be obtained year round. The main limitation of exploiting P. lividus as planktonic feed seems to be the mortality of broodstock after injection with 1 ml KCl 0.5 M, which prevents reutilization. The 1-month post-injection survival rate was 30 ± 8% (mean ± SE). All surviving sea urchins spawned again after re-injection 1 month later, with a 1-month survival rate of 29%.

Allozyme and Random Amplified Polymorphic DNA (RAPD) variation was surveyed in the freshwater crayfish Cherax destructor Clark, an ecologically and commercially important species that is widespread throughout the freshwater systems of central Australia. At the intra-population level, allozymes revealed a similar level of variation to that found in other freshwater crayfish; RAPDs showed less diversity than allozymes, which was unexpected. At the inter-population level, both techniques revealed significant population structure, both within and between drainages. RAPD results were consistent with phylogeographic patterns previously identified using mtDNA. Although allozyme data showed little geographic pattern in relation to genetic variation based on multidimensional-scaling (MDS) plots on matrices of genetic distance, results of AMOVA and Mantel tests indicated significant population structuring. Each of the mtDNA lineages proposed in a previous study also showed significant genetic structure at similar levels as revealed by RAPDs but different levels by allozymes. These results reject hypotheses previously put forward on genetic homogenisation within the species due to wide-scale translocation. The implications of the findings for conservation and aquaculture of C. destructor are also discussed.

The level of genetic differentiation between anadromous and non-andromous trout (Salmo trutta L.) coexisting in a Norman river (Oir river) was examined at 15 microsatellites markers. Despite a large amount of variation, no genetic differentiation was found between forms. Four domesticated stocks were also genotyped with the same loci. Highly significant differences were found with natural samples allowing to exclude a recent stocking effect on the Oir population. We conclude that the resident and anadromous trout form a single naturally reproducing unit in this river system. However, this conclusion could reflect particular ecological or demographic conditions in the Oir basin and needs to be validated in other hydrographical and ecological contexts.

Une analyse phylogéographique de quinze échantillons de Dicentrarchus labrax dont cinq sont originaires de Méditerranée occidentale, sept de Méditerranée orientale et trois échantillons d'élevage en provenance de trois piscicultures françaises a été effectuée à partir du polymorphisme de six locus microsatellites. Parmi les échantillons orientaux, trois ne se regroupent pas en fonction de leur origine géographique, mais plutôt avec le groupe occidental. Ces échantillons présentent également une diversité allélique légèrement réduite, indiquant qu'ils proviennent d'un nombre limité de géniteurs d'origine occidentale. Parmi les stocks d'élevage, un seul montre une réduction significative de la variabilité génétique, ce qui indique que ces cheptels sont ouverts et font largement appel à des géniteurs sauvages. L'utilisation d'alevins d'origine occidentale pour ensemencer les premières fermes d'élevage du bassin oriental remonte au plus tard au début des années 80. Ceci soulève la question des mécanismes biologiques expliquant le maintien de poissons d'origine occidentale dans un contexte oriental pendant au moins deux ou trois générations.

The nuclear DNA content in Dicentrarchus labrax, Sparus aurata, Liza ramada, and Anguilla anguilla, was measured by flow cytometric analysis. Male human leukocytes were used as internal reference cells. Nucleated fish erythrocytes were stained simultaneously to human leukocytes with a staining buffer containing propidium iodide (PI). Nuclear DNA contents of target species were estimated in relation to an assigned value of 7.0 pg DNA for male human leukocytes. The DNA content/nucleus (±CI) was 1.55 ± 0.02 pg for D. labrax, 1.90 ± 0.03 pg for S. aurata, 1.57 ± 0.02 pg for L. ramada, and 2.43 ± 0.04 pg for A. anguilla. Intraspecific DNA content variations ranged from 0-9% and averaged around 4% in all taxa. The results did not evidence significant differences in genome size between males and females in either D. labrax or L. ramada. / Anguilla anguilla

Five polymorphic microsatellite DNA loci were identified in Labeo dero (Hamilton Buchanan), through cross-species amplification. Thirty-one primers developed for three cyprinids were tested in the study. The genetic variation detected at each polymorphic microsatellite locus was analysed. Significant genotype heterogeneity indicated that the samples are not drawn from same genepool. The identified microsatellite loci exhibited promise for use in fine scale population structure analysis of L. dero.

Mediterranean demersal fisheries have experienced an ongoing decline in catches over the past 20 years as a result of excessive increases in effort caused both by growth in trawler engine power and by rapid technological advances in fish finding and fishing technology. This has led to an overexploitation of these resources. An increasing share of the catches consists of immature individuals. This study was undertaken to test a sorting grid with a bar spacing of 20 mm as a means of excluding juveniles in the commercial hake (Merluccius merluccius) fishery in the Catalan Sea, western Mediterranean. The grid was placed in the extension section of the gear 5 m in front of a cod-end. Divided cod-end design was used to collect the escapees and target species. The mean selection length (L50) of the ten hauls was 14.2 ± 0.7 cm SE, with a selection range of 7.3 cm ± 0.4 SE. The biomass of hake under L50 that escaped through the grid represented 50.1% ± 6.7 SE of the total hake biomass. These results are promising and indicate that a sorting grid can be used in excluding young hake. This was a first step toward implementation of sorting grids in commercial trawl gears as means of avoiding unwanted catches of small individuals in the hake fisheries in the Mediterranean Sea. Further trials are required to improve the sorting efficiency of the grid.