| Enregistrements |
Auteur  |
Travers, M.; Watermeyer, K.; Shannon, L.J.; Shin, Y.-J. |
| Titre |
Changes in food web structure under scenarios of overfishing in the southern Benguela : comparison of the Ecosim and OSMOSE modelling approaches |
Type |
Article scientifique |
| Année |
2010 |
Publication |
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Revue Abrégée |
Journal of Marine Systems |
| Volume |
79 |
Numéro |
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Pages |
101-111 |
| Mots-Clés |
and; Benguela; ecosystem; Fishing; Food; function; indicators; model; structure; Trophic; upwelling; web |
| Résumé |
Ecosystem models provide a platform allowing exploration into the possible responses of marine food webs to fishing pressure and various potential management decisions. In this study we investigate the particular effects of overfishing on the structure and function of the southern Benguela food web, using two models with different underlying assumptions: the spatialized, size-based individual-based model, OSMOSE, and the trophic mass-balance model, Ecopath with Ecosim (EwE). Starting from the same reference state of the southern Benguela upwelling ecosystem during the 1990s, we compare the response of the food web to scenarios of overfishing using these two modelling approaches. A scenario of increased fishing mortality is applied to two distinct functional groups: i) two species of Cape hake, representing important target predatory fish, and ii) the forage species anchovy, sardine and redeye. In these simulations, fishing mortality on the selected functional groups is doubled for 10 years, followed by 10 years at the initial fishing mortality. We compare the food web states before the increase of fishing mortality, after 10 years of overfishing and after a further 10 years during which fishing was returned to initial levels. In order to compare the simulated food web structures with the reference state, and between the two modelling approaches, we use a set of trophic indicators: the mean trophic level of the community and in catches, the trophic pyramid (biomass per discrete trophic level), and the predatory/forage fish biomass ratio. OSMOSE and EwE present globally similar results for the trophic functioning of the ecosystem under fishing pressure: the biomass of targeted species decreases whereas that of their potential competitors increases. The reaction of distant species is more diverse, depending on the feeding links between the compartments. The mean trophic level of the community does not vary enough to be used for assessing ecosystem impacts of fishing, and the mean trophic level in the catch displays a surprising increase due to the short period of overfishing. The trophic pyramids behave in an unexpected way compared to trophic control theory. because at least two food chains with different dynamics are intertwined within the food web. We emphasize the importance of biomass information at the species level for interpreting dynamics in aggregated indicators, and we highlight the importance of competitive groups when looking at ecosystem functioning under fishing disturbance. Finally, we discuss the results within the scope of differences between models, in terms of the way they are formulated, spatial dimensions, predation formulations and the representation of fish life cycles. |
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0924-7963 |
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LL @ pixluser @ |
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Torres-Irineo, E.; Dreyfus-Leon, M.; Gaertner, D.; Salas, S.; Marchal, P. |
| Titre |
Adaptive responses of tropical tuna purse-seiners under temporal regulations |
Type |
Article scientifique |
| Année |
2017 |
Publication |
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Revue Abrégée |
Ambio |
| Volume |
46 |
Numéro |
1 |
Pages |
88-97 |
| Mots-Clés |
atlantic; behavior; Closed season; eastern pacific-ocean; eastern tropical pacific; Fisher behaviour; Fisheries management; fishing strategies; fleet dynamics; mixed fisheries; model; Purse-seine fishing; state; trawlers; Tropical tuna |
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The failure to achieve fisheries management objectives has been broadly discussed in international meetings. Measuring the effects of fishery regulations is difficult due to the lack of detailed information. The yellowfin tuna fishery in the eastern Pacific Ocean offers an opportunity to evaluate the fishers' responses to temporal regulations. We used data from observers on-board Mexican purse-seine fleet, which is the main fleet fishing on dolphin-associated tuna schools. In 2002, the Inter-American Tropical Tuna Commission implemented a closed season to reduce fishing effort for this fishery. For the period 1992-2008, we analysed three fishery indicators using generalized estimating equations to evaluate the fishers' response to the closure. We found that purse-seiners decreased their time spent in port, increased their fishing sets, and maintained their proportion of successful fishing sets. Our results highlight the relevance of accounting for the fisher behaviour to understand fisheries dynamics when establishing management regulations. |
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0044-7447 |
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MARBEC @ alain.herve @ |
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2072 |
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Shin, Y.-J.; Shannon, L.J.; Bundy, A.; Coll, M.; Aydin, K.; Bez, N.; Blanchard, J.L.; Borges, M.D.; Diallo, I.; Diaz, E.; Heymans, J.J.; Hill, L.; Johannesen, E.; Jouffre, D.; Kifani, S.; Labrosse, P.; Link, J.S.; Mackinson, S.; Masski, H.; Mollmann, C.; Neira, S.; Ojaveer, H.; Abdallahi, K.O.M.; Perry, I.; Thiao, D.; Yemane, D.; Cury, P. |
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Using indicators for evaluating, comparing, and communicating the ecological status of exploited marine ecosystems. 2. Setting the scene |
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Article scientifique |
| Année |
2010 |
Publication |
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Revue Abrégée |
Ices Journal of Marine Science |
| Volume |
67 |
Numéro |
4 |
Pages |
692-716 |
| Mots-Clés |
comparative approach; ecological indicators; ecosystem effects of fishing; exploited marine ecosystems; IndiSeas |
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Background is provided to the selection of ecological indicators by the IndiSeas Working Group, and the methodology adopted for analysis and comparison of indicators across exploited marine ecosystems is documented. The selected indicators are presented, how they are calculated is explained, and the philosophy behind the comparative approach is given. The combination of selected indicators is intended to reflect different dynamics, tracking processes that display differential responses to fishing, and is meant to provide a complementary means of assessing marine ecosystem trends and states. IndiSeas relied on inputs and insights provided by the local experts from participating ecosystems, helping to understand state and trend indicators and to disentangle the effect of other potential ecosystem drivers, such as climate variability. This project showed that the use of simple and available indicators under an ecosystem approach can achieve a real, wide-reaching evaluation of marine ecosystem status caused by fishing. This is important because the socio-economics of areas where fishing activities develop differs significantly around the globe, and in many countries, insufficient data are available for complex and exhaustive analyses. |
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1054-3139 |
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LL @ pixluser @ |
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107 |
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| Auteur |
Shin, Y.-J.; Shannon, L.J. |
| Titre |
Using indicators for evaluating, comparing, and communicating the ecological status of exploited marine ecosystems. 1. The IndiSeas project |
Type |
Article scientifique |
| Année |
2010 |
Publication |
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Revue Abrégée |
Ices Journal of Marine Science |
| Volume |
67 |
Numéro |
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Pages |
686-691 |
| Mots-Clés |
approach; comparative; ecosystem; Fishing; impacts; indicator; IndiSeas; marine; status |
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One of the challenges faced by the scientific community grappling with the ecosystem approach to fisheries is to propose a generic set of synthetic ecological indicators, which would accurately reflect the effects of fisheries on marine ecosystems, and could support sound communication and management practices. The IndiSeas Working Group was established in 2005 under the auspices of the Eur-Oceans Network of Excellence to develop methods to provide indicators-based assessments of the status of exploited marine ecosystems in a comparative framework. Here, we present the two main outputs of the first phase of the project: a suite of papers documenting a combination of indicator-based methods and results comparing the ecological status of the world's exploited marine ecosystems, and a website aiming to communicate these results beyond scientific audiences. |
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1054-3139 |
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LL @ pixluser @ |
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106 |
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Shannon, L.J.; Coll, M.; Yemane, D.; Jouffre, D.; Neira, S.; Bertrand, A.; Diaz, E.; Shin, Y.J. |
| Titre |
Comparing data-based indicators across upwelling and comparable systems for communicating ecosystem states and trends |
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Article scientifique |
| Année |
2010 |
Publication |
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Revue Abrégée |
ICES J. Mar. Sci. |
| Volume |
67 |
Numéro |
4 |
Pages |
807-832 |
| Mots-Clés |
adriatic sea; central chile; comparative approach; demersal resources; fishing impacts; food-web; global fisheries; humboldt current system; indicator; nw mediterranean sea; pelagic fish; regime shifts; southern benguela; upwelling |
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Shannon, L. J., Coll, M., Yemane, D., Jouffre, D., Neira, S., Bertrand, A., Diaz, E., and Shin, Y-J. 2010. Comparing data-based indicators across upwelling and comparable systems for communicating ecosystem states and trends. – ICES Journal of Marine Science, 67: 807-832. |
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1054-3139 |
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MARBEC @ isabelle.vidal-ayouba @ |
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482 |
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