Growth and metabolism of juvenile European sea bass of a Western Mediterranean population were assessed at six constant temperatures (13, 16, 19, 22, 25 or 29 °C) in an 84-day trial. Duplicated groups of 84 fish (initial weight 80±1 g) were held under O2-concentrations close to saturation (8-7 mg l−1) and were fed to satiation. Mass gain increased as temperature increased from 13 to 25 °C. At 25 and 29 °C, growth was similar up to day 72, but a 6% decrease was observed by day 84 at 29 °C. Days 0-84 specific growth rates (SGR) were 0.45%, 1.29% and 1.21% day−1 at 13, 25 and 29 °C, respectively. The estimated temperature (T) for maximum SGR was 26 °C (SGR=1.715−0.322T+0.022T2−4.233e−4T3). Feed intake (FI) increased with temperature being 1.45-1.46% day−1 at 25-29 °C and the estimated temperature for maximum FI was 27.5 °C (FI=1.453−0.214T+0.016T2−2.916e−4T3). Feed efficiency (FE) averaged 1.01-1.04 at 19-25 °C, was lower at 16 and 13 °C (0.9) and maximum FE was estimated to occur at 24 °C (FE=1.318−0.103T+7.174T2−1.395T3). The main difference in fish body composition related to temperature was a higher crude fat concentration at 13-16 °C at the end of the experiment (day 84). Protein retention was 38% (g g−1) at 25 °C (NS differences in 22-28 °C range). Ammonia excretion (TAN, mg N kg−1 day−1) was positively correlated to temperature as it was dependent on feeding rate (FR, g kg−1 day−1) (TAN=−496.5 FR+24.4 FR2+2685). O2-consumption (MO2R, mg kg−1 h−1) was influenced by temperature (MO2R=10.83T+4.48) and by FR (MO2R=−206.8FR+10.6FR2+1142).

Rochet, M-J., Prigent, M., Bertrand, J. A., Carpentier, A., Coppin, F., Delpech, J-P., Fontenelle, G., Foucher, E., Mahé, K., Rostiaux, E., and Trenkel, V. M. 2008. Ecosystem trends: evidence for agreement between fishers' perceptions and scientific information. – ICES Journal of Marine Science, 65: 1057–1068. The results of a survey on fishers' perceptions of recent changes in the eastern English Channel ecosystem carried out in 2006 were compared with fishery and bottom-trawl survey data. A hypothesis-testing framework was used, testing the null hypothesis that fishers' statements were true, which permitted evaluation of both agreement and disagreement. Overall good agreement between fishers' statements and scientific data was found, and both sources suggested that the fish community in the Channel is undergoing large changes, among which are decreases in some commercially important species; in addition, a number of human pressures impact the ecosystem. Fishers had an accurate perception of changes and their time-frames, but not necessarily of their causes. They had a greater power than survey data to detect recent changes, showing that fishers' perceptions have great potential as early warning signals.

Mahe, K., Amara, R., Bryckaert, T., Kacher, M., and Brylinski, J. M. 2007. Ontogenetic and spatial variation in the diet of hake (Merluccius merluccius) in the Bay of Biscay and the Celtic Sea. – ICES Journal of Marine Science, 64: 1210–1219. Analysis of the diet of trawl-caught hake (Merluccius merluccius) from three locations in the Bay of Biscay and the Celtic Sea in autumn 2001 showed that small hake fed almost exclusively on crustaceans (mainly euphausiids), but that there was a significant shift towards a fully piscivorous diet in hake >23 cm. A change in fish prey was also size-dependent, because smaller hake (<30 cm) preyed on small pelagic fish (3–12 cm), such as horse mackerel, anchovy, and pilchard, and larger hake on larger demersal prey (12–23 cm), such as blue whiting. There was a significant positive relationship between hake and fish prey length. In terms of fish prey selectivity, hake exhibited particular preference for small pelagic prey (anchovy, pilchard, and argentine) and for other hake. The diet did not generally reflect fish prey availability. Although horse mackerel and blue whiting were the two most abundant fish prey species in the environment, they were not positively selected by hake. Cannibalism accounted for a non-negligible part of the diet and was observed mainly in large hake (>30 cm). For all sizes analysed, conspecifics constituted 19.2%W of the diet and the frequency of occurrence of hake in the stomachs was 10.53%. Most hake prey were 0-group juveniles (<20 cm). Hake cannibalism appeared to be influenced mainly by the abundance of juveniles and the overlap between distribution patterns of juveniles and adults.

This study investigated and compared asymmetry in sagittal otolith shape and length between left and right inner ears in four roundfish and four flatfish species of commercial interest. For each species, the effects of ontogenetic changes (individual age and total body length), sexual dimorphism (individual sex) and the otolith's location on the right or left side of the head, on the shape and length of paired otoliths (between 143 and 702 pairs according to species) were evaluated. Ontogenetic changes in otolith shape and length were observed for all species. Sexual dimorphism, either in otolith shape and length or in their ontogenetic changes, was detected for half of the species, be they round or flat. Significant directional asymmetry in otolith shape and length was detected in one roundfish species each, but its inconsistency across species and its small average amplitude (6·17% for shape and 1·99% for length) suggested that it has barely any biological relevance. Significant directional asymmetry in otolith shape and length was found for all flatfish species except otolith length for one species. Its average amplitude varied between 2·06 and 17·50% for shape and between 0·00 and 11·83% for length and increased significantly throughout ontogeny for two species, one dextral and one sinistral. The longer (length) and rounder otolith (shape) appeared to be always on the blind side whatever the species. These results suggest differential biomineralization between the blind and ocular inner ears in flatfish species that could result from perturbations of the proximal-distal gradient of otolith precursors in the endolymph and the otolith position relative to the geometry of the saccular epithelium due to body morphology asymmetry and lateralized behaviour. The fact that asymmetry never exceeded 18% even at the individual level suggests an evolutionary canalization of otolith shape symmetry to avoid negative effects on fish hearing and balance. Technically, asymmetry should be accounted for in future studies based on otolith shape.

Otolith shape analysis is an efficient fish stock identification tool. However, most applications used left and right otoliths or only one of them arbitrarily chosen without testing for biases resulting from potential directional bilateral asymmetry (DA) in otolith shape, i.e. a unimodal population-level deviation form bilateral symmetry between right and left otolith shapes. In this study, 560 bogues (Boops boops) were sampled from 11 geographical locations from the Canary Islands to the Aegean Sea and elliptical Fourier descriptors were used to describe their otoliths’ shape. First, a significant otolith DA was observed at the global scale with an average amplitude of 2.77%. However, at the scale of sampling locations, DA was not always significant and varied in amplitude and direction. Second, population structure was investigated using the shape of either right otoliths or left otoliths or both together. Analyses based on right otoliths or both otoliths together, suggested three stock units: a North-Western Mediterranean Sea stock, an Eastern Mediterranean Sea stock, and a Central-Eastern Atlantic Ocean and South-Western Mediterranean Sea stock. In contrast, no coherent geographical pattern was found based on left otoliths. Our results highlight the importance of accounting for potential otolith DA in otolith shape-based stock identification.

Mercury (Hg) is one of the main chemicals currently altering Mediterranean ecosystems. Red mullet (Mullus barbatus and M. surmuletus) have been widely used as quantitative bio-indicators of chemical contamination. In this study, we reassess the ability of these species to be used as efficient bio-indicators of Hg contamination by monitoring during 18 months Hg concentrations in muscle tissue of mullet sampled from 5 French Mediterranean coastal areas. Mean concentrations ranged between 0.23 and 0.78 μg g(-1) dry mass for both species. Values were consistent with expected contamination patterns of all sites except Corsica. Results confirmed that red mullets are efficient bio-indicators of Hg contamination. Nevertheless, the observed variability in Hg concentrations calls for caution regarding the period and the sample size. Attention should be paid to environmental and biologic specificities of each studied site, as they can alter the bioaccumulation of Hg, and lead to inferences about environmental Hg concentrations.

International audienceStock identification is of primary importance for population structure assessment of economically important species. This study investigates stocks of striped red mullet using three automatic methods of stock identification based on otolith shape and growth marks. Otolith shape is known to be a promising approach for stock identification but interpreting patterns of variance is a difficult problem. In this study, images in reflected and transmitted light were acquired from 800 otoliths sampled in the Northwest European seas from South Bay of Biscay to North Sea. The growth marks are pointed out manually by an expert. The external shape of otoliths was automatically extracted by computer vision process and then three automatic classification methods were compared, two classical state-of-the-art methods based on Fourier descriptors and principal component analysis (PCA), and a recently proposed method based on shape Geodesics. From a methodological point of view, results show that the shape geodesic approach significantly outperforms other classical methods. From a biological point of view, this study shows that the population of striped red mullet in Northwest European seas can be divided in three geographical zones: the Bay of Biscay, a mixing zone composed of the Celtic Sea and the Western English Channel and a northern zone composed of the Eastern English Channel and the North Sea (67% of correct classification rate using both shape and growth pattern information). Moreover, it shows that for a given zone, two subsets of the same year have a lower variability in shape than two subsets from two consecutive years

While gradual allometric changes of shells are intrinsically driven by genotype, morphometrical shifts can also be modulated by local environmental conditions. Consequently the common use of a unique dimension (usually length) to assess bivalves’ growth may mask phenotypic differences in valve shape among populations. A morphometric exhaustive study was conducted on Manila clam,Ruditapes philippinarum, by acquiring data in the French Arcachon Bay (intrasite phenotypic variability) and by comparing with other sites in the literature (intersite phenotypic variability). 2070 shells were subsampled, weighted, and automatically measured using TNPC software. Some ratios’ values indicate a relatively round and globular shape shell in comparison with other sites confirming poor conditions for some individuals. Among adult clams, three main morphological groups were identified and discussed according to spatial considerations. Allometric relations for pairs of shell descriptors were determined by testing classical linear and piecewise regression models on log-transformed relation of Huxley. A significant shape change correlated to size was observed; it corresponds to the second year of life of the clam. Relationships between density, disease, and shell shape are demonstrated and discussed related to other potential factors affecting shell shape. Finally, consequences on population regulation are addressed.