Improving fishing effort descriptors: Modelling engine power and gear-size relations of five European trawl fleets

Eigaard, Ole Ritzau; Rihan, Dominic; Graham, Norman; Sala, Antonello; Zachariassen, Kristian

doi:10.1016/j.fishres.2011.03.010

Cited by 36 publications

(29 citation statements)

References 24 publications

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“…A study linking vessel size and fish mortality in Danish fisheries suggested a logarithmic increase for gear size [61]; this would be interesting to study in greater detail, as no data were available on individual trawl width. Less secrecy regarding fuel consumption in fisheries would also foster improvement.…”

Section: Conclusion and Future Recommendationsmentioning

confidence: 99%

Integrated environmental assessment of fisheries management: Swedish Nephrops trawl fisheries evaluated using a life cycle approach

et al. 2012

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Section: Conclusion and Future Recommendationsmentioning

confidence: 99%

Integrated environmental assessment of fisheries management: Swedish Nephrops trawl fisheries evaluated using a life cycle approach

et al. 2012

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“…This type of rigging was developed to enable an increase in the horizontal fishing area covered by the ground gear without increasing the vertical opening and towing resistance, and hence a greater catch efficiency for certain demersal species can be achieved by the same towing power (Sainsbury, 1996;Eigaard et al, 2011). The highest efficiency increase is achieved for species closely associated to the bottom which are not necessarily herded by the sweeps, and due to their sedentary behavior are not likely to escape over the headline of the trawl.…”

Section: Introductionmentioning

confidence: 99%

“…Species such as Norway lobster and monkfish (Lophius spp.) fall into this category (Sangster and Breen, 1998;Eigaard et al, 2011 and sweeps, the area swept by the total gear (door spread) will determine the catch. This is the case for species such as plaice (Pleuronectes platessa), haddock (Melanogrammus aeglefinus) and cod (Eigaard et al, 2011).…”

Section: Introductionmentioning

confidence: 99%

“…fall into this category (Sangster and Breen, 1998;Eigaard et al, 2011 and sweeps, the area swept by the total gear (door spread) will determine the catch. This is the case for species such as plaice (Pleuronectes platessa), haddock (Melanogrammus aeglefinus) and cod (Eigaard et al, 2011). Hence, if the swept area of the ground gear is doubled, when shifting from e.g., a single-rig cod trawl to a twin-rig Nephrops trawl one can in theory expect catches of Norway lobster to double, and similar when doubling the herding area (door spread) for more active species (Fig.…”

Section: Introductionmentioning

confidence: 99%

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Influence of twin and multi-rig trawl systems on CPUE in the Danish Norway lobster (Nephrops norvegicus) fishery

et al. 2016

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a b s t r a c tOne of the most effective ways to alter catch and length compositions in trawls is to adjust the mesh size or add selective devices such as sorting grids and selective netting panels. These changes are often introduced into the fishery in a top down manner whereby fishermen are forced to comply with specific legislation. However, fishermen have also introduced gear modifications that have contributed to improving species selectivity in trawls. One of the simplest and most effective modifications that came from industry was the development and introduction of twin and multi-rig trawls. Here we analyse catch rates of four target species, Norway lobster (Nephrops norvegicus), cod (Gadus morhua), plaice (Pleuronectes platessa) and haddock (Melanogrammus aeglefinus), to try and understand how the use of multi-rig trawls have altered catch rates within the Danish demersal trawl fishery over the last 16 years (1997)(1998)(1999)(2000)(2001)(2002)(2003)(2004)(2005)(2006)(2007)(2008)(2009)(2010)(2011)(2012). Results showed that catch rates of Nephrops in multi-rig trawls were significantly higher (1.89-2.03) than those in single trawls. For cod, haddock and plaice there was no significant effect of gear type. The results are discussed in relation to the Common Fisheries Policy reform and the increasing importance of industry introduced gear modifications.

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“…For the purpose of monitoring demersal fish stocks, bottom trawl surveys are most commonly used (Bertrand et al 2002. As trawl efficiency is constantly improving and fishing practice is continuously changing (Lucchetti and Sala 2012, Eigaard et al 2011, Lucchetti and Sala 2010, Fiorentini et al 2004, this type of standardized survey provides reliable data for describing and quantifying changes in the exploited fish populations (Jukic-Peladic et al 2001). The most common method used for relative biomass estimation is the swept area method (Saville 1977, Sparre andVenema 1998).…”

Section: Introductionmentioning

confidence: 99%

Influence of sea-bottom temperature and depth on swept area estimation from trawl surveys

Brčić¹,

Grilli²,

Sala³

2014

Sci. Mar.

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Summary:The methodological approach to data collection and analysis in Mediterranean bottom trawl surveys has changed considerably since their beginnings in the mid-1980s. The introduction of new technologies in surveys greatly improved knowledge on trawl underwater geometry, but also raised a question on the reliability of the data obtained. The most commonly used trawl monitoring systems in the Mediterranean use the constant speed of sound when calculating horizontal distance from one sensor to another. However, the speed of the sound in seawater is not constant because it depends on water temperature, pressure, and salinity. This is known to affect the performance of the horizontally transmitting sonars, and it is reasonable to assume that unless it is properly compensated for, the readings from trawl monitoring systems can be incorrect, resulting in biased swept area estimates, and hence potentially producing bias in abundance estimates. In the knowledge that speed of sound depends on temperature, salinity and pressure, the Del Grosso (1974) equation was used to calculate the compensation coefficient for a series of theoretical depth and temperature data. A simple model is proposed in the current paper for the manual correction of the horizontal net opening and swept area estimates. Temperature and depth data obtained from the MEDATLAS project are used to show seasonal and spatial variation in the near-bottom speed of sound, and the results demonstrate that, unless compensated for properly, the error in the horizontal net spread ranges from -1.5% to 2.9%.Keywords: swept area; bottom trawl survey; net opening; Mediterranean Sea.Influencia de la temperatura del fondo del mar y profundidad en la estimación del área de barrido en sistemas de arrastre Resumen: El enfoque metodológico para la recopilación de datos y análisis en estudios de arrastre de fondo del Mediterráneo ha cambiado considerablemente desde sus inicios en los años ochenta. La introducción de nuevas tecnologías en los estudios ha mejorado enormemente el conocimiento de la geometría de los artes de pesca de debajo del agua, pero, al mismo tiempo, surge la pregunta de la fiabilidad de los datos obtenidos. Los sistemas de seguimiento más comúnmente utilizados en los artes en el Mediterráneo usan la velocidad constante del sonido cuando calculan la distancia horizontal de un sensor a otro. Sin embargo la velocidad del sonido en el agua marina no es constante ya que depende de la temperatura del agua, de la presión y la salinidad. Se sabe que esto afecta al rendimiento de los sonares que transmiten en horizontal, y es razonable suponer que si se compensan adecuadamente, las lecturas de los monitores de seguimiento del arte pueden ser incorrectos, dando lugar a estimaciones sesgadas del área barrida por el arte, y en consecuencia potencialmente producir sesgo en bastantes estimaciones. Conociendo que la velocidad del sonido depende de la temperatura, salinidad y presión, se ha usado la ecuación de Del Grosso (1974) para calcular el coeficiente de compe...

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Improving fishing effort descriptors: Modelling engine power and gear-size relations of five European trawl fleets

Cited by 36 publications

References 24 publications

Integrated environmental assessment of fisheries management: Swedish Nephrops trawl fisheries evaluated using a life cycle approach

Integrated environmental assessment of fisheries management: Swedish Nephrops trawl fisheries evaluated using a life cycle approach

Influence of twin and multi-rig trawl systems on CPUE in the Danish Norway lobster (Nephrops norvegicus) fishery

Influence of sea-bottom temperature and depth on swept area estimation from trawl surveys

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