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Andrello, M., Guilhaumon, F., Albouy, C., Parravicini, V., Scholtens, J., Verley, P., et al. (2017). Global mismatch between fishing dependency and larval supply from marine reserves. Nat. Commun., 8, 16039.
Résumé: Marine reserves are viewed as flagship tools to protect exploited species and to contribute to the effective management of coastal fisheries. Yet, the extent to which marine reserves are globally interconnected and able to effectively seed areas, where fisheries are most critical for food and livelihood security is largely unknown. Using a hydrodynamic model of larval dispersal, we predict that most marine reserves are not interconnected by currents and that their potential benefits to fishing areas are presently limited, since countries with high dependency on coastal fisheries receive very little larval supply from marine reserves. This global mismatch could be reversed, however, by placing new marine reserves in areas sufficiently remote to minimize social and economic costs but sufficiently connected through sea currents to seed the most exploited fisheries and endangered ecosystems.
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Ba, K., Thiaw, M., Fall, M., Thiam, N., Meissa, B., Jouffre, D., et al. (2018). Long-term fishing impact on the Senegalese coastal demersal resources: diagnosing from stock assessment models. Aquat. Living Resour., 31, 8.
Résumé: For the first time in Senegal, assessments based on both stochastic and deterministic production models were used to draw a global diagnosis of the fishing impact on coastal demersal stocks. Based one national fisheries databases and scientific trawl surveys data: (i) trends in landings since 1971 were examined, (ii) abundance indices of 10 stocks were estimated using linear models fitted to surveys data and commercial catch per unit efforts, and (iii) stock assessments were carried out using pseudo-equilibrium Fox and Pella-Tomlinson models and a Biomass dynamic production model fitted in a Bayesian framework to abundance indices. Most stocks have seen their abundance sharply declining over time. All stocks combined, results of stock assessments suggest a 63% reduction compared to virgin state. Three fifth of demersal stocks are overexploited and excess in fishing effort was estimated until 75% for the worst case. We conclude by suggesting that the fishing of such species must be regulated and an ecosystem approach to fisheries management should be implemented in order to monitor the whole ecosystem.
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Bakker, J., Wangensteen, O. S., Chapman, D. D., Boussarie, G., Buddo, D., Guttridge, T. L., et al. (2017). Environmental DNA reveals tropical shark diversity in contrasting levels of anthropogenic impact. Sci Rep, 7, 16886.
Résumé: Sharks are charismatic predators that play a key role in most marine food webs. Their demonstrated vulnerability to exploitation has recently turned them into flagship species in ocean conservation. Yet, the assessment and monitoring of the distribution and abundance of such mobile species in marine environments remain challenging, often invasive and resource-intensive. Here we pilot a novel, rapid and non-invasive environmental DNA (eDNA) metabarcoding approach specifically targeted to infer shark presence, diversity and eDNA read abundance in tropical habitats. We identified at least 21 shark species, from both Caribbean and Pacific Coral Sea water samples, whose geographical patterns of diversity and read abundance coincide with geographical differences in levels of anthropogenic pressure and conservation effort. We demonstrate that eDNA metabarcoding can be effectively employed to study shark diversity. Further developments in this field have the potential to drastically enhance our ability to assess and monitor elusive oceanic predators, and lead to improved conservation strategies.
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Boulanger, E., Dalongeville, A., Andrello, M., Mouillot, D., & Manel, S. (2020). Spatial graphs highlight how multi-generational dispersal shapes landscape genetic patterns. Ecography, .
Résumé: Current approaches that compare spatial genetic structure of a given species and the dispersal of its mobile phase can detect a mismatch between both patterns mainly due to processes acting at different temporal scales. Genetic structure result from gene flow and other evolutionary and demographic processes over many generations, while dispersal predicted from the mobile phase often represents solely one generation on a single time-step. In this study, we present a spatial graph approach to landscape genetics that extends connectivity networks with a stepping-stone model to represent dispersal between suitable habitat patches over multiple generations. We illustrate the approach with the case of the striped red mullet Mullus surmuletus in the Mediterranean Sea. The genetic connectivity of M. surmuletus was not correlate with the estimated dispersal probability over one generation, but with the stepping-stone estimate of larval dispersal, revealing the temporal scale of connectivity across the Mediterranean Sea. Our results highlight the importance of considering multiple generations and different time scales when relating demographic and genetic connectivity. The spatial graph of genetic distances further untangles intra-population genetic structure revealing the Siculo-Tunisian Strait as an important corridor rather than a barrier for gene flow between the Western- and Eastern Mediterranean basins, and identifying Mediterranean islands as important stepping-stones for gene flow between continental populations. Our approach can be easily extended to other systems and environments.
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Crochelet, E., Barrier, N., Andrello, M., Marsac, F., Spadone, A., & Lett, C. (2020). Connectivity between seamounts and coastal ecosystems in the Southwestern Indian Ocean. Deep-Sea Res. Part II-Top. Stud. Oceanogr., 176, 104774.
Résumé: Understanding larval connectivity patterns is critical for marine spatial planning, particularly for designing marine protected areas and managing fisheries. Patterns of larval dispersal and connectivity can be inferred from numerical transport models at large spatial and temporal scales. We assess model-based connectivity patterns between seamounts of the Southwestern Indian Ocean (SWIO) and the coastal ecosystems of Mauritius, La Reunion, Madagascar, Mozambique and South Africa, with emphasis on three shallow seamounts (La Pemuse [LP], MAD-Ridge [MR] and Walters Shoal [WS]). Using drifter trajectory and a Lagrangian model of ichthyo-plankton dispersal, we show that larvae can undertake very long dispersion, with larval distances increasing with pelagic larval duration (PLD). There are three groups of greater connectivity: the region between the eastern coast of Madagascar, Mauritius and La Reunion islands; the seamounts of the South West Indian Ridge; and the pair formed by WS and a nearby un-named seamount. Connectivity between these three groups is evident only for the longest PLD examined (360 d). Connectivity from seamounts to coastal ecosystems is weak, with a maximum of 2% of larvae originating from seamounts reaching coastal ecosystems. Local retention at the three focal seamounts (LP, MR and WS) peaks at about 11% for the shortest PLD considered (15 d) at the most retentive seamount (WS) and decreases sharply with increasing PLD. Information on PLD and age of larvae collected at MR and LP are used to assess their putative origin. These larvae are likely self-recruits but it is also plausible that they immigrate from nearby coastal sites, i.e. the southern coast of Madagascar for MR and the islands of La Reunion and Mauritius for LP.
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