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| Registros recuperados: 13 | |
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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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| Poulard, Jean-charles; Trenkel, Verena. |
| Survey indices play an important role in stock assessments as they provide information on stock trends. In certain cases large interannual variations have been observed which are unlikely to reflect true underlying stock changes but are rather outliers. When survey indices for several species appear to be outliers for the same year, the suspicion is raised that something happened during the survey of that year. This is called a year-effect in survey catches. To study the potential year-effect in survey catches for the French autumn groundfish survey taking place in the Bay of Biscay, several indicators for survey design and wind conditions were derived as explanatory variables and Principal Component Analysis was used to study the relationship between... |
| Tipo: Text |
Palavras-chave: Bay of Biscay; Survey conditions; Time trends; Catchability; Survey index. |
| Ano: 2007 |
URL: http://archimer.ifremer.fr/doc/2007/publication-2690.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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| Laurans, Martial; Fifas, Spyros; Demaneche, Sebastien; Brerette, Stéphane; Debec, Olivier. |
| Fishers from Le Croisic (France) measure all the lobsters (Homarus gammarus) they capture, indicating their sex and whether the females are ovigerous or non-ovigerous. Between 2003 and 2006 and mainly between April and September, 16 884 lobsters were measured in this manner. These self-sampled data were used to study catchability and functional maturity of lobsters. The sex ratio was 50%, and catchability did not change if a female was ovigerous or non-ovigerous. With the help of a logistic function, a relationship was established between body size and the proportion of ovigerous females. For the study area, 100% of the females were mature upon reaching a carapace length (CL) of 115 mm, and the proportion of ovigerous females reached 70% each year. The L50... |
| Tipo: Text |
Palavras-chave: Self sampling; Homarus gammarus; Functional maturity; Catchability. |
| Ano: 2009 |
URL: http://archimer.ifremer.fr/doc/2009/publication-7319.pdf |
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| Trenkel, Verena; Rochet, Marie-joelle; Mahevas, Stephanie. |
| Norway lobster, Nephrops norvegicus (L.) was found to show diel activity patterns with more individuals outside their burrows at dawn and dusk in the Bay of Biscay in August 2004 and catchabilities were higher at these times. Using data from an onboard observer programme of Nephrops trawlers in 2002-2005, we investigated whether the expected variability in catchability was visible in commercial catches. Catch numbers per haul varied spatially and between months but no signal for diel variations was found. Fishing strategies developed by the Nephrops trawlers had several components. On a seasonal level they started around sunrise. On a haul level, haul duration decreased from haul to haul, with the longest hauls taking place at the time of highest... |
| Tipo: Text |
Palavras-chave: Time of day; Fishing strategy; Diel activity patterns; Catchability. |
| Ano: 2008 |
URL: http://archimer.ifremer.fr/doc/2007/publication-2618.pdf |
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| Trenkel, Verena; Skaug, Hans. |
| We propose a random effects model for disentangling population abundance and capture efficiency effects on bottom-trawl catches. The spatial distribution of individual fish is assumed random leading to a Poisson distribution for the number of individuals in the trawl path (no schooling). Capture efficiency, i.e. the proportion of individuals in the trawl path being retained by the gear, is modelled as a random variable. We propose model extensions that include the effects of body size on haul efficiency. We applied the models to several species from the Celtic Sea groundfish community based on small-scale repetitive hauls. The resulting abundance estimates allowed us to study population abundance ratios; the estimated capture efficiencies were comparable... |
| Tipo: Text |
Palavras-chave: Trawl survey; Poisson distribution; Celtic Sea; Catchability; Abundance. |
| Ano: 2005 |
URL: http://archimer.ifremer.fr/doc/2005/publication-828.pdf |
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| Eigaard, Ole Ritzau; Marchal, Paul; Gislason, Henrik; Rijnsdorp, Adriaan D.. |
| Many marine fish stocks are overexploited and considerable overcapacity exists in fishing fleets worldwide. One of the reasons for the imbalance between resource availability and fishing capacity is technological development, which continuously increases the efficiency of the vessels—a mechanism referred to as “technological creep.” We review how the introduction of new and more efficient electronic equipment, gear design, engines, deck equipment, and catch-handling procedures influences the capture efficiency (catchability) of commercial fishing vessels. On average, we estimate that catchability increases by 3.2% per year due to technological developments, an increase often ignored in fisheries management. The documentation and quantification of... |
| Tipo: Text |
Palavras-chave: Catchability; Fishing mortality; Fishing power; Fisheries management; Fleet capacity; Technological development. |
| Ano: 2014 |
URL: https://archimer.ifremer.fr/doc/00222/33368/35784.pdf |
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| Mahevas, Stephanie; Trenkel, Verena; Doray, Mathieu; Peyronnet, Arnaud. |
| Several factors affect trawl catchability: (i) gear and vessel technical characteristics, (ii) anthropogenic factors, and (iii) biological factors. The objectives of this study were to assess the relative contribution of each factor to variations in hake (Merluccius merluccius) landings by the French trawler fleet operating on the shelf of the northern Bay of Biscay (ICES Subdivision VIIIa). Using generalized linear models, the impact of technical and anthropogenic factors was evaluated using landings per unit effort (lpue) obtained from logbooks. Variations in hake lpue were explained primarily by anthropogenic factors. For studying the biological components of catchability, the results of a scientific trawl survey in July 2006 involving three similar... |
| Tipo: Text |
Palavras-chave: Accessibility; Beam trawl; Catchability; Fishing power; GLMM; Spatial distribution. |
| Ano: 2011 |
URL: http://archimer.ifremer.fr/doc/00021/13244/10287.pdf |
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| Perrotta, R.G.. |
| Analyzed in this paper is the structure of the fleet applied to mackerel fishing based at Mar del Plata Port (38° LS); an attempt is also made at establishing the best system for measuring the fishing effort; the changes in catch capability (availability and vulnerability)are duly analyzed. Sampling vessels that allow greater data, particulary by in relation to the fishing effort, are available since the 1983/84 fishing season. |
| Tipo: Journal Contribution |
Palavras-chave: Catch/effort; Catchability; Fishing fleet. |
| Ano: 1988 |
URL: http://hdl.handle.net/1834/1959 |
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| Campbell, R.A.; Tuck, G.N.. |
| Due to the general lack of targeted fisheries on billfish, the resource status of these species within the Indian Ocean has not been analysed in any previous study and currently remains unknown. Nevertheless, significant quantities of billfish are caught annually in the Indian Ocean and, being generally long lived, these species remain vulnerable to overfishing. In this paper preliminary indices of stock availability are presented for the main billfish species based on the catch and effort data pertaining to the Japanese and Taiwanese Indian Ocean longline fisheries. While the indices need to be treated with some caution (due to problems relating to the accuracy of the catch and effort data, and the fact that changes in catchability have not been factored... |
| Tipo: Proceedings Paper |
Palavras-chave: Catch/effort; Stock assessment; Overfishing; Catchability; Fishing gear. |
| Ano: 1998 |
URL: http://hdl.handle.net/1834/58 |
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| Registros recuperados: 13 | |
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