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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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| Chassot, E; Rouyer, Tristan; Trenkel, Verena; Gascuel, D. |
| The trophic level mean and variance, and the degree of omnivory for five Celtic Sea fish predators were estimated using a database of stomach content records characterized by a high level of taxonomic resolution. The predators occupied a high position in the food web, i.e. 4.75 for Atlantic cod Gadus morhua, 444 for haddock Melanogrammus aeglefinus, 4.88 for European hake Merluccius merluccius, 5.00 for megrim Lepidorhombus whiffiagonis and 5.27 for whiting Merlangius merlangus. The level of taxonomic resolution of the prey did not greatly affect mean T-L predator values; an effect on variance was evident, low resolution masking intra-population variability in T-L. Generalized additive models (GAM) were used to explain the variability of predator T-L... |
| Tipo: Text |
Palavras-chave: Trophic level; Predation; Omnivory; Indicator; GAM; Food web. |
| Ano: 2008 |
URL: http://archimer.ifremer.fr/doc/2008/publication-4699.pdf |
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| Daures, Fabienne; Trenkel, Verena; Guyader, Olivier. |
| Ten years after the start of the European Data Collection Framework the availability of cost indicators for assessing the economic status of fisheries or bio-economic modelling is still deficient. Moreover, economic time series are difficult to maintain due to fishermen weariness and sample coverage is often insufficient. To overcome these problems, the paper builds predictive models per operational cost category (fuel, landing, other variable, fixed, salary and total) for the French Bay of Biscay fleet. The cost models had good fit and stressed the key role of gear and vessel size (length mostly) for explaining fishing costs. They suggested that only a small list of variables was needed to predict costs (days-at-sea, total revenue, vessel age, length and... |
| Tipo: Text |
Palavras-chave: Socio-economic; Empirical cost model; Fisheries performance; Gear type; GAM; Ecosystem Approach to Fisheries. |
| Ano: 2013 |
URL: http://archimer.ifremer.fr/doc/00149/26039/24410.pdf |
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| Koubbi, Philippe; Loots, Christophe; Cotonnec, Gwenaelle; Harlay, Xavier; Grioche, Alain; Vaz, Sandrine; Martin, Canterbury Christ Church University; Walkey, Mike; Carpentier, Andre. |
| The spring distribution of larval fish stages of flatfishes in the Dover Strait (eastern English Channel) was studied in 1995 and 1999. Fish larvae were identified and sorted according to developmental stages in order to study their ontogenic distribution. The French coastal waters are characterised by an unstable tide-dependent front, which influences larval dispersion. In spring, the French coastal waters have a high phytoplanktonic production. They have higher temperatures, lower salinities and differences in current intensity compared with the central English Channel waters. Generalised Additive Models (GAM) combined with Geographic Information Systems (GIS) were used to model the potential habitats of life stages considering data from three major... |
| Tipo: Text |
Palavras-chave: English Channel; Fish larvae; Geostatistics; GIS; GAM. |
| Ano: 2006 |
URL: http://archimer.ifremer.fr/doc/2006/publication-2090.pdf |
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| Dickey-collas, Mark; Payne, Mark R.; Trenkel, Verena M.; Nash, Richard D. M.. |
| The use of modelling approaches in marine science, and in particular fisheries science, is explored. We highlight that the choice of model used for an analysis should account for the question being posed or the context of the management problem. We examine a model-classification scheme based on Richard Levins' 1966 work suggesting that models can only achieve two of three desirable model attributes: realism, precision, and generality. Model creation, therefore, requires trading-off of one of these attributes in favour of the other two: however, this is often in conflict with the desires of end-users (i.e. mangers or policy developers). The combination of attributes leads to models that are considered to have empirical, mechanistic, or analytical... |
| Tipo: Text |
Palavras-chave: Climate; Fisheries; GAM; Management; Prediction; Projection; Recruitment; Time-series analysis. |
| Ano: 2014 |
URL: http://archimer.ifremer.fr/doc/00222/33371/32179.pdf |
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| Mahevas, Stephanie; Vermard, Youen; Hutton, Trevor; Iriondo, Ane; Jadaud, Angelique; Maravelias, Christos D.; Punzon, Antonio; Sacchi, Jacques; Tidd, Alex; Tsitsika, Efthymia; Marchal, Paul; Goascoz, Nicolas; Mortreux, Serge; Roos, David. |
| The impact of the fishing effort exerted by a vessel on a population depends on catchability, which depends on population accessibility and fishing power. The work investigated whether the variation in fishing power could be the result of the technical characteristics of a vessel and/or its gear or whether it is a reflection of inter-vessel differences not accounted for by the technical attributes. These inter-vessel differences could be indicative of a skipper/crew experience effect. To improve understanding of the relationships, landings per unit effort (lpue) from logbooks and technical information on vessels and gears (collected during interviews) were used to identify variables that explained variations in fishing power. The analysis was undertaken by... |
| Tipo: Text |
Palavras-chave: Catchability; Fishing power; GAM; GLM; Skipper skill; Technical characteristics. |
| Ano: 2011 |
URL: http://archimer.ifremer.fr/doc/00049/16043/15172.pdf |
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