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Filmalter, J. D., Cowley, P. D., Potier, M., Menard, F., Smale, M. J., Cherel, Y., et al. (2017). Feeding ecology of silky sharks Carcharhinus falciformis associated with floating objects in the western Indian Ocean. J. Fish Biol., 90(4), 1321–1337.
Résumé: The silky shark Carcharhinus falciformis is commonly associated with floating objects, including fish aggregating devices (FADs), in the Indian Ocean. While the motives for this associative behaviour are unclear, it does make them vulnerable to capture in the tuna purse seine fishery that makes extensive use of FADs. Here, the diet of 323 C. falciformis, caught at FADs in the Indian Ocean, was investigated to test the hypothesis that trophic benefits explain the associative behaviour. A high proportion of stomachs with fresh contents (57%) suggested that extensive feeding activity occurred while associated with FADs. Multiple dietary indices showed that typical non-associative prey types dominated, but were supplemented with fishes typically found at FADs. While the trophic benefits of FAD association may be substantial, our results suggest that associative behaviour is not driven solely by feeding. (C) 2016 The Fisheries Society of the British Isles
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Forget, F., Dagorn, L., Mérigot, B., Gaertner, J. C., Robinson, J., Cowley, P. D., et al. (2020). Beta diversity of pelagic assemblages at fish aggregating devices in the open ocean. African Journal of Marine Science, 42(2), 247–254.
Résumé: Owing to difficulties in accessing the vast open ocean, the beta (β) diversity of pelagic fish assemblages remains poorly studied. We investigated the relationship between assemblage similarity and geographical distance between anchored fish aggregating devices (FADs), sampled by standardised underwater visual censuses in three anchored FAD arrays in the Indian Ocean—at the Maldives, the Seychelles and Mauritius. The use of two complementary indices of β-diversity, based on presence/absence data (Jaccard similarity coefficient) and abundance data (Bray–Curtis index), revealed that geographical distance between sampling sites (from 4 to 257 km) appeared to have no effect on the similarity of fish assemblages associated with FADs within each array. The results of this preliminary study question the generalisation of the paradigm of an increase in β-diversity with geographic distance to the open-ocean fish community. Large-scale studies using a variety of datasets should be conducted to further investigate patterns of β-diversity in the open ocean.
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Gaertner, D. (2010). Estimates of historic changes in total mortality and selectivity for Eastern Atlantic skipjack (Katsuwonus pelamis) from length composition data. Aquatic Living Resources, 23, 3–11.
Résumé: Catch-at-size data of the eastern Atlantic skipjack were used to estimate changes in total mortality from 1969 to 2007. We used a transitional model of mean length that generalized the Beverton-Holt mortality estimator to allow change in mortality rate under nonequilibrium conditions. Then, from homogeneous periods of time, length-converted catch curves were used to access qualitative changes in selectivity patterns for two surface fisheries (the baitboat fishery operating from Dakar, Senegal, and the European and associated purse seine fisheries). To explore the impact of catch on the mortality rate, a Bayesian change-point analysis was conducted on the catch time series to detect concomitant variation between mortality rates and catch. Finally, potential causes of these changes are discussed in relation to the implementation of new fishing technology, such fish aggregating devices (FAD). The general pattern depicted by total mortality is in agreement with previous knowledge on this fishery: a state of complete or practically complete exploitation during the nineties followed by the decrease in nominal purse seine fishing effort in the last decade, combined with the effect of a seasonal moratorium on FAD fishing operations. There was no evidence of a change in selectivity between the two contrasted periods of time considered: 1969-1979 and 1986-1999; the second period being characterized by the introduction of new technology onboard vessels. In contrast, the covariation over time between total catch and mortality rate three years later highlights the effect of the fishing pressure on the stock of eastern Atlantic skipjack.
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Geay, F., Culi, E. S. I., Corporeau, C., Boudry, P., Dreano, Y., Corcos, L., et al. (2010). Regulation of FADS2 expression and activity in European sea bass (Dicentrarchus labrax, L.) fed a vegetable diet. Comparative Biochemistry and Physiology B-Biochemistry and Molecular Biology, 156(4), 237–243.
Résumé: Supplies of marine fish oils are limited, and continued growth in aquaculture production dictates that lipid substitutes in fish diets must be used without compromising fish health and product quality. In this study, the total substitution of a fish meal and fish oil by a blend of vegetable meals (corn, soybean, wheat and lupin) and linseed oil in the diet of European sea bass (Dicentrachus labrax) was investigated. Two groups of European sea bass were fed with fish diet (FD) or vegetable diet (VD) for 9 months. VD, totally deprived of eicosapentaenoate (EPA; 20:5n-3) and docosahexaenoate (DHA; 22:6n-3), revealed a nutritional deficiency and affected growth performance. Whilst VD induced a significant increase in fatty acid desaturase 2 (FADS2) and sterol binding regulatory element-binding protein 1 (SREBP-1) mRNA levels, the desaturation rate of [1-C-14]18:3n-3 into [1-C-14]18:4n-3, analysed in microsomal preparations using HPLC method, did not show an upregulation of FADS2 activities in liver and intestine of fish fed VD. Moreover Western-blot analysis did not revealed any significant difference of FADS2 protein amount between the two dietary groups. These data demonstrate that sea bass exhibits a desaturase (FADS2) activity whatever their diet, but a post-transcriptional regulation of fads2 RNA prevents an increase of enzyme in fish fed a HUFA-free diet. This led to a lower fish growth and poor muscle HUFA content.
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Guyader, O., Robert, B., & Lionel, R. (2017). Assessing the number of moored fishing aggregating devices through aerial surveys: A case study from Guadeloupe. Fish Res., 185, 73–82.
Résumé: Moored fish aggregating devices (MFADs) are increasingly being used in small-scale tropical fisheries to access pelagic fish species that are otherwise difficult to harvest in large numbers. Little attention has yet been paid to monitoring MFADs in coastal areas, however. This is most likely due to the small-scale nature of most fisheries that utilize them and the presumed lower impact of those fisheries on fish stocks and their ecosystems. In this paper, we examined the abundance and density of MFADs around Guadeloupe, using aerial line transect surveys. Estimated MFAD densities were found to be high compared with previously reported densities in this area, especially within the 22-45 km range offshore. We examine and discuss possible reasons for these high densities. The main drivers appear to be the target species dolphinfish (Coryphaena hippurus) and yellowfin tuna (Thunnus albacares) and related fishing behaviour. We present different approaches for reducing and monitoring MFADs densities, including the co-management of MFAD territorial use rights by fishing communities. (C) 2016 Elsevier B.V. All rights reserved.
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