Assessment of dual selection in grid based selectivity systems

Sistiaga, Manu Berrondo; Herrmann, Bent; Grimaldo, Eduardo; Larsen, Roger B.

doi:10.1016/j.fishres.2010.05.006

Cited by 105 publications

(91 citation statements)

References 16 publications

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“…Thus, an optimal selection device for this fishery should provide a sharp selection profile just above 44 cm so that the majority of fish above 44 cm would be retained and the majority below would be released from the gear. Sistiaga et al (2010) have shown that a 55-mm Sort-V grid combined with diamond mesh codends had L50 values in the range 51.6-55.9 cm, which are not significantly different from the results we have here for either the EW or T90 gears (at the 95% level). There is, however, a significant difference between the mean SR values of these two gears and, as shown in Figure 2C, the T90 codend is closer to the 44 cm minimum landing size and retains significantly more fish in the length range 55-76 cm.…”

Section: Discussioncontrasting

confidence: 75%

Estimating the selectivity of unpaired trawl data: a case study with a pelagic gear

et al. 2016

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Summary:Most selectivity experiments employ either the covered codend or paired gear methods. It is not always possible, however, to use these methods. Owing to operational, biological and/or environmental considerations, there may be no obvious way or it may be inappropriate to pair the test and control data. Hence, it will not be possible to estimate the selectivity of the gear and its uncertainty using standard statistical methods. This study presents a methodology for analysing the selectivity of fishing gears from unpaired test and control data. The uncertainty in the control and test population structures is accounted for by using a double bootstrapping procedure that takes into account both between-haul and within-haul variation. This bootstrapping approach is used to assess the selectivity of two different devices, a 139.5 mm T90 codend and a 135.9 mm codend with 140.9 mm lateral exit windows, in the Barents Sea pelagic cod trawl fishery. The purpose of the experiment was to test and compare the performance of the two devices in pelagic trawl fisheries, where high densities of fish can be encountered. Significant differences were detected between the T90 codend and the codend with the exit windows but only for sizes of cod between 55 and 76 cm.Keywords: trawl selectivity; pelagic fisheries; unpaired data; cod.Estimando la selectividad en redes de arrastre con lances no pareados: un caso de estudio con una red pelágica Resumen: La mayoría de los experimentos de selectividad emplean el método de copo cubierto o el de lances pareados. Sin embargo, la utilización de estos métodos no es siempre posible. En ocasiones, no se puede encontrar una manera lógica de emparejar los datos provenientes de lances de prueba y lances control, o esta puede ser inapropiada debido a consideraciones de tipo operacional, biológico o medioambientales. Por lo tanto, no sería posible estimar la selectividad de la red y la incertidumbre de los resultados obtenidos utilizando métodos estadísticos estandarizados. Este estudio presenta una metodología que facilita el análisis de la selectividad en artes de pesca en los que los datos provienen de lances no pareados. La incertidumbre en las estructuras poblacionales capturadas en los lances prueba y control se tiene en cuenta utilizando un método de doble "bootstrapping" que considera la variabilidad en cada lance y entre lances. Utilizamos este método de "bootstrapping" para estimar la selectividad de dos dispositivos diferentes en la pesca pelágica de bacalao del mar de Barents: un copo T90 con mallas de 139,5 mm y un copo con mallas romboidales de 135,9 mm con ventanas laterales de 140,9 mm. El propósito del experimento fue comparar el comportamiento de ambos dispositivos en la pesca de arrastre pelágico de bacalao, donde se pueden encontrar altas densidades de pescado. Se detectaron diferencias significativas entre el copo T90 y el copo con las ventanas pero solo para tallas de bacalao comprendidas entre 55 y 76 cm.

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Section: Discussioncontrasting

confidence: 75%

Estimating the selectivity of unpaired trawl data: a case study with a pelagic gear

et al. 2016

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“…This approach avoids underestimation of the confidence limits of the average selection parameters L 50 and SR, which according to Fryer (1991) would otherwise occur from simply estimating the average L 50 and SR values from pooled data without using bootstrapping to account simultaneously for both within-and between-haul variation in the selection process. The bootstrapping method used is similar to the method described in Sistiaga et al (2010) except that the model fitted to our data is much simpler. As in Sistiaga et al (2010), the data analysis was carried out with the software tool SELNET (developed by the first author of this study).…”

Section: Discussionmentioning

confidence: 99%

“…The bootstrapping method used is similar to the method described in Sistiaga et al (2010) except that the model fitted to our data is much simpler. As in Sistiaga et al (2010), the data analysis was carried out with the software tool SELNET (developed by the first author of this study). Further information on SELNET can be found in Frandsen et al (2011), Wienbeck et al (2011 and Sistiaga et al (2010) or can be obtained by contacting the corresponding author.…”

Section: Discussionmentioning

confidence: 99%

“…As in Sistiaga et al (2010), the data analysis was carried out with the software tool SELNET (developed by the first author of this study). Further information on SELNET can be found in Frandsen et al (2011), Wienbeck et al (2011 and Sistiaga et al (2010) or can be obtained by contacting the corresponding author. To be able to estimate the 95% confidence bands for the retention likelihood along the entire selection curve, SELNET was further developed as part of this study.…”

Section: Discussionmentioning

confidence: 99%

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Understanding the Size Selectivity of Redfish (Sebastes spp.) in North Atlantic Trawl Codends

Herrmann¹,

Sistiaga²,

Nielsen³

et al. 2012

J. Northw. Atl. Fish. Sci.

214

140

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The majority of trawl selectivity studies for the three redfish species of particular commercial importance in North Atlantic fisheries: Sebastes marinus, Sebastes mentella and Sebastes fasciatus, are based on data collected from diamond mesh codends with mesh sizes ranging from 88 mm to 147 mm. We demonstrate how results from these studies can be understood by morphological characteristics of the species. We predict codend size selection based on morphological data collected from golden redfish (S. marinus) individuals. Further, consistent with previously reported morphological similarities between the three redfish species, we show the predictions for S. marinus may successfully be extrapolated to understand experimental codend size selectivity results reported for S. mentella and S. fasciatus. In addition to the comparison with previously reported data, we present new experimental results for a codend applied in Northeast Atlantic redfish trawl fishery.

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“…Fit statistics indicating that a model could adequately describe the data included P-values greater than 0.05 and a deviance value no greater Efron 1982) for L 50 and SR based on 1,000 bootstrap repetitions using a double-bootstrapping method implemented in SELNET to account for both within-tow and between-tow variation. This is the same approach that was used by Sistiaga et al (2010) and Herrmann et al (2012) to avoid underestimating confidence limits for selectivity curves when pooling tow data. To determine whether the selectivity curves for a given species differed significantly between any two of the three cod end types, the P-value was calculated as the number of times out of the 1 million pairs of bootstrap L 50 values that the L 50 for net A was less than the L 50 for net B.…”

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Improving Catch Utilization in the U.S. West Coast Groundfish Bottom Trawl Fishery: an Evaluation of T90‐Mesh and Diamond‐Mesh Cod Ends

et al. 2017

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The limited-entry bottom trawl fishery for groundfish along the U.S. West Coast operates under a catch share program, which is implemented with the intention of improving the economic efficiency of the fishery, maximizing fishing opportunities, and minimizing bycatch. However, stocks with low harvest guidelines have limited the ability of fishermen to maximize their catch of more abundant stocks. Size-selection characteristics of 114-mm and 140-mm T90-mesh cod ends and the traditional 114-mm diamond-mesh cod end were examined by using the covered cod end method. Selection curves and mean L 50 values (length at which fish had a 50% probability of being retained) were estimated for two flatfish species (Rex Sole Glyptocephalus zachirus and Dover Sole Microstomus pacificus) and two roundfish species (Shortspine Thornyhead Sebastolobus alascanus and Sablefish Anoplopoma fimbria). Mean L 50 values were smaller for flatfishes but larger for roundfishes in the 114-mm T90 cod end compared to the diamond-mesh cod end. For Rex Sole, Dover Sole, and Shortspine Thornyheads, selectivities of the 140-mm T90 cod end were significantly different from those of the other cod ends; the 140-mm T90 cod end was most effective at reducing the catch of smaller-sized fishes but with a considerable loss of larger-sized marketable fishes. Findings suggest that T90 cod ends have potential to improve catch utilization in this multispecies fishery.

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Assessment of dual selection in grid based selectivity systems

Cited by 105 publications

References 16 publications

Estimating the selectivity of unpaired trawl data: a case study with a pelagic gear

Estimating the selectivity of unpaired trawl data: a case study with a pelagic gear

Understanding the Size Selectivity of Redfish (Sebastes spp.) in North Atlantic Trawl Codends

Improving Catch Utilization in the U.S. West Coast Groundfish Bottom Trawl Fishery: an Evaluation of T90‐Mesh and Diamond‐Mesh Cod Ends

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