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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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Ban, N. C., Maxwell, S. M., Dunn, D. C., Hobday, A. J., Bax, N. J., Ardron, J., et al. (2014). Better integration of sectoral planning and management approaches for the interlinked ecology of the open oceans. Marine Policy, .
Résumé: Open oceans are one of the least protected, least studied and most inadequately managed ecosystems on Earth. Three themes were investigated that differentiate the open ocean (areas beyond national jurisdiction and deep area within exclusive economic zones) from other realms and must be considered when developing planning and management options: ecosystem interactions, especially between benthic and pelagic systems; potential effects of human activities in open oceans on ecological linkages; and policy context and options. A number of key ecological factors differentiate open oceans from coastal systems for planners and managers: (1) many species are widely distributed and, especially for those at higher trophic levels, wide ranging; (2) the sizes and boundaries of biogeographical domains (patterns of co-occurrence of species, habitats and ecosystem processes) vary significantly by depth; (3) habitat types exhibit a wide range of stabilities, from ephemeral (e.g., surface frontal systems) to hyper-stable (e.g., deep sea); and (4) vertical and horizontal linkages are prevalent. Together, these ecological attributes point to interconnectedness between open ocean habitats across large spatial scales. Indeed, human activities – especially fishing, shipping, and potentially deep-sea mining and oil and gas extraction – have effects far beyond the parts of the ocean in which they operate. While managing open oceans in an integrated fashion will be challenging, the ecological characteristics of the system demand it. A promising avenue forward is to integrate aspects of marine spatial planning (MSP), systematic conservation planning (SCP), and adaptive management. These three approaches to planning and management need to be integrated to meet the unique needs of open ocean systems, with MSP providing the means to meet a diversity of stakeholder needs, SCP providing the structured process to determine and prioritise those needs and appropriate responses, and adaptive management providing rigorous monitoring and evaluation to determine whether actions or their modifications meet both ecological and defined stakeholder needs. The flexibility of MSP will be enhanced by the systematic approach of SCP, while the rigorous monitoring of adaptive management will enable continued improvement as new information becomes available and further experience is gained.
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Bănaru, D., Diaz, F., Verley, P., Campbell, R., Navarro, J., Yohia, C., et al. (2019). Implementation of an end-to-end model of the Gulf of Lions ecosystem (NW Mediterranean Sea). I. Parameterization, calibration and evaluation. Ecological Modelling, 401, 1–19.
Résumé: An end-to-end model named OSMOSE-GoL has been built for the Gulf of Lions, the main French Mediterranean fishing area. This spatialized dynamic model links the coupled hydrodynamic and biogeochemical model Eco3M-S/SYMPHONIE (LTL – low trophic level model) to OSMOSE (HTL – high trophic level model). It includes 15 compartments of living organisms, five from the LTL model (i.e. nanophytoplankton, microphytoplankton, nanozooplankton, microzooplankton and mesozooplankton) and ten from the HTL model (northern krill, southern shortfin squid, European pilchard, European anchovy, European sprat, Atlantic horse mackerel, Atlantic mackerel, blue whiting, European hake and Atlantic bluefin tuna). With the exception of northern krill and European sprat, all HTL species are commercially exploited and undergo fisheries mortality pressure. The modeled species represent more than 70% of annual catches in this area. This paper presents the parameterization, calibration and evaluation of this model with satellite data for phytoplankton and with biomass, landings, diet and trophic level data for HTL groups. For most species, the diets in output of OSMOSE-GoL are similar to field and literature data in terms of dominant prey groups and species. However, some differences were observed. Various reasons may explain the mismatch between the modeled diet and field data. Benthic prey sometimes observed in the stomach content of the HTL predators were not modeled in OSMOSE-GoL. Field studies were carried out at specific periods and locations, while our data concern the period 2001–2004 and the entire modeled domain. Inter- and intra-annual variations in spatial distribution and density of prey may also explain these differences. The model estimates trophic level values similar to those cited in the literature for all the HTL compartments. These values are also close to the trophic levels estimated by a previous Ecopath model for the same area and period. Even though some improvements are still possible, this model may already be of use to explore fishery or Marine Protected Areas scenarios for socio-ecosystem management issues.
Mots-Clés: Ecosystem modeling; Osmose; Fisheries; Food web; Eco3M
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BANARU, D., MELLON, C., ROOS, D., BIGOT, J. - L., SOUPLET, A., JADAUD, A., et al. (2013). Trophic structure in the Gulf of Lions marine ecosystem (north-western Mediterranean Sea) and fishing impacts. Journal Of Marine Systems, 111, 45–68.
Résumé: The Gulf of Lions ecosystemwas described using the Ecopath mass-balancemodel to characterise its structure and functioning and to examine the effects of themultispecific fisheries operating in this area. The model is composed of 40 compartments, including 1 group of seabirds, 2 groups of etaceans, 18 groups of fish, 12 groups of invertebrates, 5 groups of primary producers, detritus and discards. Input datawere based on several recurrent scientific surveys, two alternative datasets for fishing data, stock assessment outputs, stomach content analyses and published information. Results showed that the functional groups were organised into five trophic levels with the highest one represented by dolphins, anglerfish, Atlantic bluefin tuna, European hake and European conger. European pilchard and European anchovy dominated in terms of fish biomass and catch. Other fish with high biomass such as Atlantic mackerel and blue whiting were highly important in the food web. Seabirds, dolphins and cuttlefish–squids represented keystone species. Important coupled pelagic–demersal–benthic interactions were described. The 7 different fisheries analysed were operating at mean trophic levels situated between 2.6 for small artisanal boats, and 4.1 for purse seines (>24 m) targeting large pelagic fish, indicating an intensively exploited ecosystem. Large trawlers (24–40 m) had the highest impact on most of the groups considered; while purse seines (12–24 m) targeting small pelagic fish had the lowest impact. Preliminary results highlighted the importance of data sources for further ecosystem and fisheries analyses and management scenarios.
Mots-Clés: Gulf of Lions; Ecopath with Ecosim; Food web; Fishing impacts
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Batsleer, J., Marchal, P., Vaz, S., Vermard, V., Rijnsdorp, A. D., & Poos, J. J. (2018). Exploring habitat credits to manage the benthic impact in a mixed fishery. Mar. Ecol.-Prog. Ser., 586, 167–179.
Résumé: The performance of a combined catch quota and habitat credit system was explored to manage the sustainable exploitation of a mix of demersal fish species and reduce the benthic impacts of bottom trawl fisheries using a dynamic state variable model approach. The model was parameterised for the Eastern English Channel demersal mixed fishery using otter trawls or dredges. Target species differed in their association with habitat types. Restricting catch quota for plaice and cod had a limited effect on benthic impact, except when reduced to very low values, forcing the vessels to stay in port. Quota management had a minimal influence on fishing behaviour and hence resulted in a minimal reduction of benthic impact. Habitat credits may reduce the benthic impacts of the trawl fisheries at a minimal loss of landings and revenue, as vessels are still able to reallocate their effort to less vulnerable fishing grounds, while allowing the fishery to catch their catch quota and maintain their revenue. Only if they are reduced to extremely low levels can habitat credits potentially constrain fishing activities to levels that prevent the fisheries from using up the catch quota for the target species.
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