7 results on '"Trenkel, Verena M."'
Search Results
2. Do changes in environmental and fishing pressures impact marine communities? An empirical assessment.
- Author
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Rochet, Marie-Joëlle, Trenkel, Verena M., Carpentier, Andr, Coppin, Franck, de Sola, Luis Gil, Léaut, Jean-Pierre, Mah, Jean-Claude, Maiorano, Porzia, Mannini, Alessandro, Murenu, Matteo, Piet, GerJan, Politou, Chrissi-Yianna, Reale, Bruno, Spedicato, Maria-Teresa, Tserpes, George, and Bertrand, Jacques A.
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MARINE ecosystem health , *ENVIRONMENTAL management , *APPLIED ecology , *BIOTIC communities , *FISHING & the environment , *FISH populations , *GROUNDFISHES - Abstract
1. The development of ecosystem approaches to environmental management implies the need to account for multiple pressures on ecosystems. Trends in multiple metrics that respond differently to changes in major environmental pressures need to be combined to evaluate the impacts of fishing and environmental changes on fish communities. 2. An exploited fish community is viewed as a three-level food chain in which the two upper levels, or functional groups, are targeted by fishing fleets, while the lowest level is subject to environmental variation. Qualitative modelling is used to predict changes at the two upper levels, that is, top-down vs. bottom-up perturbations. Abundance and length metrics are calculated from survey data for 14 Mediterranean and East-Atlantic groundfish shelf communities at both population and functional group levels. The joint likelihood of time trends in metrics is used to evaluate the evidence for different causes of changes. 3. A wide diversity of impacts is found to have equal evidence at the population level within each community. Consistency between the impacts identified and changes in pressures known from independent information is found at the functional group and community level. The results suggest that there is some compensation between species within functional groups. 4. Synthesis and applications. The method can be used to conduct an integrated assessment of community dynamics subject to multiple pressures. Joint trends in metrics provide evidence of which known pressures are having an impact on the community, and thus, which management actions should be taken to mitigate these changes. [ABSTRACT FROM AUTHOR]
- Published
- 2010
- Full Text
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3. Trend analysis of indicators: a comparison of recent changes in the status of marine ecosystems around the world.
- Author
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Blanchard, Julia L., Coll, Marta, Trenkel, Verena M., Vergnon, Rémi, Yemane, Dawit, Jouffre, Didier, Link, Jason S., and Shin, Yunne-Jai
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BIOINDICATORS ,MARINE ecology ,BIOTIC communities ,FISHERY management ,FISHING ,RESOURCE exploitation - Abstract
Blanchard, J. L., Coll, M., Trenkel, V. M., Vergnon, R., Yemane, D., Jouffre, D., Link, J. S., and Shin, Y-J. 2010. Trend analysis of indicators: a comparison of recent changes in the status of marine ecosystems around the world. – ICES Journal of Marine Science, 67: 732–744.Time-series of ecological and exploitation indicators collected from 19 ecosystems were analysed to investigate whether there have been temporal trends in the status of fish communities. Using linear and non-linear statistical methods, trends are reported for six indicators (mean length of fish in the community, mean lifespan, proportion of predatory fish, total biomass of surveyed species, mean trophic level of landings, and inverse fishing pressure), and the redundancy of these indicators across ecosystems is evaluated. The expected direction of change for an ecosystem that is increasingly impacted by fishing is a decline in all indicators. A mixture of negative and positive directions of change is recorded, both within and among all ecosystems considered. No consistent patterns in the redundancy of the ecological indicators across ecosystems emerged from the analyses, confirming that each indicator provided complementary information on ecosystem status. The different trends in indicators may reflect differing historical exploitation patterns, management, and environmental regimes in these systems. Commitment to monitoring programmes and development of system-specific baseline, target, and threshold reference levels are required. Improved understanding of the responsiveness and performance of ecological indicators to management actions are needed to address adequately whether ecosystems are recovering from, or being further impacted by, fishing, and whether management targets are being met. The relative effects of multiple environmental and ecological processes as well as multiple human-induced stressors that characterize exploited ecosystems also need to be quantified. [ABSTRACT FROM PUBLISHER]
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- 2010
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- View/download PDF
4. Qualitative modelling and indicators of exploited ecosystems.
- Author
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Dambacher, Jeffrey M., Gaughan, Daniel J., Rochet, Marie-Joëlle, Rossignol, Philippe A., and Trenkel, Verena M.
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BIOTIC communities ,FISHERIES ,FISHING ,MARINE ecology ,FISHES - Abstract
Implementing ecosystem-based fisheries management requires indicators and models that address the impacts of fishing across entire ecological communities. However, the complexity of many ecosystems presents a challenge to analysis, especially if reliant on quantification because of the onerous task of precisely measuring or estimating numerous parameters. We present qualitative modelling as a complementary approach to quantitative methods. Qualitative modelling clarifies how community structure alone affects dynamics, here of exploited populations. We build an array of models that describe different ecosystems with different harvesting practices, and analyse them to predict responses to various perturbations. This approach demonstrates the utility of qualitative modelling as a means to identify and interpret community-level indicators for systems that are at or near equilibrium, and for those that are frequently perturbed away from equilibrium. Examining the interaction of ecological and socio-economic variables associated with commercial fisheries provides an understanding of the main feedbacks that drive and regulate exploited ecosystems. The method is particularly useful for systems where the basic relationships between variables are understood but where precise or detailed data are lacking. [ABSTRACT FROM AUTHOR]
- Published
- 2009
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5. Choosing survey time series for populations as part of an ecosystem approach to fishery management.
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Trenkel, Verena M. and Cotter, John
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FISHERY management , *FISH populations , *BIOTIC communities , *NATURAL resources , *AQUATIC resources , *FISH surveys , *DATA analysis - Abstract
Ecosystem assessments of fisheries based only on survey data will often have to use surveys that were designed historically for special purposes, e.g. for assessing abundances of two or three target species, or for tuning VPAs. An important question then is whether the previously collected data can provide informative time series of abundance indices and other state indicators for a wider range of target and non-target species. Some potential shortcomings of existing data series are treated in this paper leading to four questions which can guide the user to determine the suitability of an existing time series: did the survey cover the stock of each species adequately? Did survey catchability vary significantly between length or age classes? Did survey catchabilities vary significantly in space or time? Was the sampling effort sufficient? Simple methods for investigating these questions are proposed and illustrated with examples. [ABSTRACT FROM AUTHOR]
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- 2009
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6. Towards an ecosystem approach to fisheries management (EAFM) when trawl surveys provide the main source of information.
- Author
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Cotter, John, Petitgas, Pierre, Abella, Alvaro, Apostolaki, Panayiota, Mesnil, Benoit, Politou, Chrissi-Yianna, Rivoirard, Jacques, Rochet, Marie-Joëlle, Spedicato, Maria Teresa, Trenkel, Verena M., and Woillez5, Mathieu
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FISHERY management ,FISH populations ,BIOTIC communities ,AQUATIC resources ,FISH surveys ,TRAWLING ,FISHERIES ,POPULATION biology - Abstract
Ideas and considerations are put forward for managing fisheries and marine populations using primarily trawl surveys to supply biological and spatial indicators of the state of stocks, and to permit catch per unit effort (CPUE)-based assessments. Trawl surveys seldom allow absolute estimates of fish population sizes but, if appropriately located, timed, and designed, can provide a broad range of information about catchable fish species and the ecosystem that supports them. This information may be more conducive to sustainable management of fisheries than the traditional focus on the abundances of selected stocks. The paper first briefly proposes how survey-based methods might supplement existing fishery-dependent stock assessments, as would be necessary during a transition phase to a more ecosystem-orientated system of management. Full survey-based management is then considered in relation to management objectives, the selection of indicators, survey design, reference periods, levels and directions, statistical aspects, CPUE-based assessments, and management responses to good and bad signals from the ecosystem. We argue that existing fishery-dependent stock assessments cannot be claimed to produce absolute estimates of stock abundance and fishing mortality because natural mortality (M) is seldom known accurately and, therefore, that they should not be presumed superior to the relative information from surveys, and an agreeable form of adaptive management. [ABSTRACT FROM AUTHOR]
- Published
- 2009
- Full Text
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7. Ecosystem trends: evidence for agreement between fishers' perceptions and scientific information.
- Author
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Rochet, Marie-Joëlle, Prigent, Magali, Bertrand, Jacques A., Carpentier, André, Coppin, Franck, Delpech, Jean-Paul, Fontenelle, Guy, Foucher, Eric, Mahé, Kelig, Rostiaux, Emilie, and Trenkel, Verena M.
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SURVEYS ,FISHERS ,BIOTIC communities ,FISHERY management ,MARINE science research - Abstract
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. [ABSTRACT FROM PUBLISHER]
- Published
- 2008
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