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| Registros recuperados: 99 | |
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| Lorance, Pascal; Pawlowski, Lionel; Trenkel, Verena. |
| A database of tallybooks, from skippers' own logbooks, provided by the French industry involved in deep-water fishing to the west of the British Isles was used to standardise blue ling Landings per Unit of Effort (LPUEs). The data covered the years 1992-2008 with more extensive data for the period 2000-2007. For each haul, landings by species, tow duration, depth and location were reported. Compared to EU logbooks, this database is on a haul by haul basis instead of being aggregated by fishing sub-trips combining hauls from the same day, ICES rectangle and gear. Moreover, it includes depth, which is a major factor for catch rates in deepwater fisheries. LPUEs were estimated from Generalised Additive Models (GAMs) with depth, vessel, statistical rectangle... |
| Tipo: Text |
Palavras-chave: Molva dypterygia; Abundance indices; Fishing strategy; Tweedie distribution. |
| Ano: 2009 |
URL: http://archimer.ifremer.fr/doc/00102/21330/18953.pdf |
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| Rochet, Marie-joelle; Collie, Jeremy S.; Trenkel, Verena. |
| Competition and predation can play different roles in mediating the influence of external pressures, such as fishing or environmental variations, on marine communities. Pressure effects propagate through food webs along predation links. These predator-prey interactions may result in trophic cascades, but they can be buffered by competitive interactions. We investigated these mechanisms by taking a functional-group approach. Are functional groups affected by external pressures in a predictable way? Within functional groups, do all species respond in the same way, or does competitive release allow for compensation among species? We constructed a simple community model, with functional groups connected by predation links. Loop analysis was used to make... |
| Tipo: Text |
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| Ano: 2013 |
URL: http://archimer.ifremer.fr/doc/00154/26492/25465.pdf |
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| Trenkel, Verena; Berthele, Olivier; Lorance, Pascal; Bertrand, Jacques; Brind'Amour, Anik; Cochard, Marie-laure; Coppin, Franck; Leaute, Jean-pierre; Mahe, Jean-claude; Morin, Jocelyne; Rochet, Marie-joelle; Salaun, Michele; Souplet, Arnauld; Verin, Yves. |
| Depuis une vingtaine d'années, l'Ifremer organise des campagnes de pêche scientifique en mer du Nord, Manche, Atlantique et Méditerranée concernant les ressources pélagiques, démersales et benthiques. L'objectif prioritaire est de produire des indices d'abondance des principales espèces commerciales. Elles recueillent également des données sur les espèces capturées non commerciales. Les campagnes sont réalisées selon des plans d'échantillonnage standardisés. L'engin de pêche et son gréement, la position des stations, le tri des captures, les prélèvements biologiques suivent des protocoles fixés. Chaque zone étudiée est découpée en fonction de la profondeur, de la latitude ou d'autres critères. L'échantillonnage prévoit un nombre de traits de chalut... |
| Tipo: Text |
Palavras-chave: Populations; Halieutique; Bulletin; Méditerranée; Golfe de Gascogne; Manche; Mer du Nord; France; Pêche; Campagnes à la mer; Atlas; Survey; Mediterranean Sea; Bay of Biscay; English Channel; North Sea; France; Populations; Fishery science; Bulletin; Atlas. |
| Ano: 2009 |
URL: http://archimer.ifremer.fr/doc/2009/rapport-6976.pdf |
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| Daures, Fabienne; Rochet, Marie-joelle; Van Iseghem, Sylvie; Trenkel, Verena. |
| Thirty French fleets fishing primarily in the Bay of Biscay were defined based on techno-economic input criteria: i) 18 fishing gear or gear combinations ii) the location of fishing grounds visited during a year (<12 nautical miles from coast, beyond 12 nm or both) and iii) total vessel length (<20 m for trawlers and other gears <24 m). The fleets were then characterised in terms of horse power, economic dependence on a list of nine dominant commercial species (sole, Nephrops, sea bass, hake, monkfish, anchovy, cuttlefish, sardine and squid) and their contribution to the landings of these species from the Bay of Biscay. Most fleets derived the majority of their income from one or two among the nine species. Species dependencies changed little... |
| Tipo: Text |
Palavras-chave: Fishing methods; Fishing vessels; Fleet dynamics; Mixed fisheries; Catch distribution; Economy; Atlantic Ocean. |
| Ano: 2009 |
URL: http://archimer.ifremer.fr/doc/00000/11172/7530.pdf |
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| Blanchard, Julia L.; Coll, Marta; Trenkel, Verena; Vergnon, Remi; Yemane, Dawit; Jouffre, Didier; Link, Jason S.; Shin, Yunne-jai. |
| 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... |
| Tipo: Text |
Palavras-chave: Community; Ecological indicators; Ecosystem-based fisheries management; Ecosystem effects of fishing; Natural resource management. |
| Ano: 2010 |
URL: http://archimer.ifremer.fr/doc/00002/11373/8166.pdf |
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| Trenkel, Verena; Vaz, Sandrine; Albouy, Camille; Brind'Amour, Anik; Duhamel, Erwan; Laffargue, Pascal; Romagnan, Jean-baptiste; Simon, Julien; Lorance, Pascal. |
| The negative impacts that scientific monitoring may have on marine ecosystems has been a neglected topic, mainly on the basis that its magnitude is minor compared to commercial fisheries, even though this raises ethical and, in certain cases, conservation issues. We argue that ethical principles should lead us to reconsider marine wildlife resource monitoring such as the fish and shellfish trawl surveys providing the science-based evidence needed for fisheries management and assessment of how environmental change impacts marine shelf communities worldwide. Recent scientific and technological progress has provided methods and tools which might now be harnessed to reduce the impact of marine monitoring. We review these alternative methods, consider... |
| Tipo: Text |
Palavras-chave: Monitoring ethics; Marine surveying; Impacts of bottom trawling; Genetic methods; Ecosystem-based management. |
| Ano: 2019 |
URL: https://archimer.ifremer.fr/doc/00470/58161/60665.pdf |
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| Trenkel, Verena. |
| In my work, which is summarised in this paper for obtaining accreditation to supervise research (the HDR), I addressed three areas: i) statistical methods of estimating the density of living resources, ii) mathematical models of population dynamics for estimating the abundance of marine populations and iii) methods for detecting temporal changes in the status of exploited populations. My work has focused on: i) Many studies of the observability of fish by trawling and by video and the development of stochastic models to better assess local fish densities. ii) Development of models without commercial catches, using Bayesian and frequentist approaches; the study of multi-specific relationships and the proposal for a threshold predator-prey model. iii)... |
| Tipo: Text |
Palavras-chave: Statistics; Abundance estimation; Stock assessment; Statistiques; Estimation d'abondance; Evaluation des stocks. |
| Ano: 2006 |
URL: http://archimer.ifremer.fr/doc/2006/rapport-1545.pdf |
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| Dickey-collas, Mark; Mcquatters-gollop, Abigail; Bresnan, Eileen; Kraberg, Alexandra C.; Manderson, John P.; Nash, Richard D. M.; Otto, Saskia A.; Sell, Anne F.; Tweddle, Jacqueline F.; Trenkel, Verena. |
| Marine environmental legislation is increasingly expressing a need to consider the quality of pelagic habitats. This paper uses the European Union marine strategy framework to explore the concept of good environmental status (GES) of pelagic habitat with the aim to build a wider understanding of the issue. Pelagic ecosystems have static, persistent and ephemeral features, with manageable human activities primarily impacting the persistent features. The paper explores defining the meaning of "good", setting boundaries to assess pelagic habitat and the challenges of considering habitat biodiversity in a moving medium. It concludes that for pelagic habitats to be in GES and able to provide goods and services to humans, three conditions should be met: (i) all... |
| Tipo: Text |
Palavras-chave: Marine strategy framework directive; MPA; Pelagic habitats; Plankton; Seascape. |
| Ano: 2017 |
URL: http://archimer.ifremer.fr/doc/00414/52596/53551.pdf |
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| Lorance, Pascal; Pawlowski, Lionel; Trenkel, Verena. |
| Haul-by-haul data derived from skippers' personal logbooks, from the French deep-water fishery to the west of the British Isles, were used to calculate standardized blue ling (Molva dypterygia) landings per unit effort (lpue) for the period 2000-2008. Lpue values were estimated using generalized additive models with depth, vessel, statistical rectangle, area, and year as explanatory variables. Because of their statistical distribution, landings were modelled by a Tweedie distribution, which allows datasets to contain many zeros. To investigate how to track stock trends reliably, lpue values were estimated in five areas for different subsets of the data. The subsets consisted of hauls during the spawning season (when blue ling aggregate), outside the... |
| Tipo: Text |
Palavras-chave: Abundance indices; Fishing strategy; GAM; Molva dypterygia; Tallybook. |
| Ano: 2010 |
URL: http://archimer.ifremer.fr/doc/00016/12713/9647.pdf |
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| Trenkel, Verena; Le Loch, Francois; Rochet, Marie-joelle. |
| In the summer of 2004, a video survey was carried out in the northern part of the central mud bank (Grande Vasiere) of the Bay of Biscay to study the small scale relationship between the dominant crustacean megafauna Nephrops norvegicus, Munida rugosa and Goneplax rhomboides and juvenile hake (Merluccius merluccius). Using a towed body, high-resolution videos were recorded in six sampling sites. Statistical modelling using generalised additive models (GAM) revealed variations in activity patterns for two species. More N. norvegicus were observed outside their burrows at dawn and somewhat at dusk (no observations during night) while G. rhomboides was less observed in the morning. In addition, reduced spatial overlap between G. rhomboides and N. norvegicus... |
| Tipo: Text |
Palavras-chave: Competition; Variations in activity patterns; Video; Benthos. |
| Ano: 2007 |
URL: http://archimer.ifremer.fr/doc/2007/publication-2614.pdf |
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| Trenkel, Verena. |
| n this paper, I argue that we have at hand what is needed to provide scientific advice for ecosystem-based management of small pelagics and other species groups now. The ingredients for this advice are (i) large marine ecosystems as spatial management units; (ii) maintaining ecosystem productivity and exploiting at multispecies maximum yield as overarching management objectives; (iii) assessment of ecosystems by evaluating changes in primary productivity; (iv) an operational management procedure in which single-species catch proposals are adjusted to ecosystem productivity using a set of control rules. Inspection of historic landings for small pelagics and other small species in the Northeast Atlantic (ICES area) reveals that most likely fisheries... |
| Tipo: Text |
Palavras-chave: EBFM; Fisheries management; Fisheries yield; Primary production. |
| Ano: 2018 |
URL: https://archimer.ifremer.fr/doc/00416/52784/53851.pdf |
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| Rochet, Marie-joelle; Cadiou, Jean-francois; Trenkel, Verena. |
| During the VIITAL cruise in the Bay of Biscay in summer 2002, two devices for measuring the length of swimming fish were tested: 1) a mechanical crown that emitted a pair of parallel laser beams and that was mounted on the main camera and 2) an underwater auto-focus video camera. The precision and accuracy of these devices were compared and the various sources of measurement errors were estimated by repeatedly measuring fixed and mobile objects and live fish. It was found that fish mobility is the main source of error for these devices because they require that the objects to be measured are perpendicular to the field of vision. The best performance was obtained with the laser method where a video-replay of laser spots (projected on fish bodies) carrying... |
| Tipo: Text |
Palavras-chave: Auto focus method; Laser method; Error estimation; Measurement methods; Fish lenght. |
| Ano: 2006 |
URL: http://archimer.ifremer.fr/doc/2006/publication-978.pdf |
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| Trenkel, Verena; Beecham, Jonathan A.; Blanchard, Julia L.; Edwards, Charles T. T.; Lorance, Pascal. |
| The status of an exploited population is ideally determined by monitoring changes in abundance and distributional range and pattern over time. Area of occupancy is a measure of the current distribution. Unfortunately, for many populations, scientific abundance and distribution information is not readily available. To evaluate the reliability of commercial fishing data for deriving occupancy indicators that could serve as proxies for stock abundance, we investigated four questions: 1) Occupancy changes with stock biomass, but is this change strong enough to make occupancy a sensitive indicator of population biomass? 2) Fishing boats follow fish, but when does such activity alter the positive macroecological relationship between occupancy and abundance? 3)... |
| Tipo: Text |
Palavras-chave: Catch per unit effort; Spatial patterns; Macroecology; Fisheries management; Marine Strategy Framework Directive; MSFD. |
| Ano: 2013 |
URL: http://archimer.ifremer.fr/doc/00176/28759/27232.pdf |
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| Doray, Mathieu; Mahevas, Stephanie; Trenkel, Verena. |
| Few analyses have been performed to estimate the efficiency of trawls targeting demersal fish using the ratio of catches and acoustic densities. In summer 2006, acoustic and fishing data were collected simultaneously over 3 d by three fishing vessels equipped with identical pelagic trawls in the Bay of Biscay. Variography identified moderate spatial autocorrelation in the acoustic backscatter at a mean scale of 3 km, a scale slightly smaller than the mean haul length (3.5 km), indicating that fish horizontal availability did not influence trawl efficiency. Acoustic backscattering densities expressed as nautical area scattering coefficients (NASCs) recorded in the trawled layer were compared with equivalent NASC (ENASC) values calculated from the species... |
| Tipo: Text |
Palavras-chave: Availability; Bay of Biscay; Catchability; Generalized linear model; Geostatistics; Hake; Vulnerability. |
| Ano: 2010 |
URL: http://archimer.ifremer.fr/doc/00002/11372/7980.pdf |
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| Rochet, Marie-joelle; Trenkel, Verena; Bellail, Robert; Coppin, Franck; Le Pape, Olivier; Mahe, Jean-claude; Morin, Jocelyne; Poulard, Jean-charles; Schlaich, Ivan; Souplet, Arnauld; Verin, Yves; Bertrand, Jacques. |
| We present a method for combining individual indicator results into a comprehensive diagnostic of fishing impacts on fish populations and communities. A conceptual framework for interpreting combined trends in a set of simple indicators is proposed, relying beforehand on qualitative expectations anchored in ecological theory. The initial state of the community is first assessed using published information. Which combinations of trends are acceptable or undesirable is decided, depending on the initial status. The indicators are then calculated from a time-series and their time trends are estimated as the slopes of linear models. Finally, the test results are combined within the predefined framework, providing a diagnostic on the dynamics of fishing impacts... |
| Tipo: Text |
Palavras-chave: Scientific surveys; Multispecies fisheries; Indicators; Ecosystem approach to fisheries management. |
| Ano: 2005 |
URL: http://archimer.ifremer.fr/doc/2005/publication-773.pdf |
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| Registros recuperados: 99 | |
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