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

Abstract

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.

Performance of the Nordmøre Grid in Shrimp Trawling and Potential Effects of Guiding Funnel Length and Light Stimulation

“…To account for both within-and between-haul variations in selectivity (Fryer 1991) when estimating the uncertainty for the average size-dependent grid passage probability, we PERFORMANCE OF THE NORDMØRE GRID applied a double bootstrap method using the facilities in the software tool SELNET (Herrmann et al 2012). For each species analyzed, 1,000 bootstrap repetitions were conducted to estimate the 95% confidence limits (Efron percentiles) for the model parameters (C grid , L50 grid , and SR grid ) and for the grid passage probability curve (Herrmann et al 2012).…”

“…For each species analyzed, 1,000 bootstrap repetitions were conducted to estimate the 95% confidence limits (Efron percentiles) for the model parameters (C grid , L50 grid , and SR grid ) and for the grid passage probability curve (Herrmann et al 2012). The effects of shortening the guiding funnel and adding LEDs were evaluated based on plotting the estimated grid passage probability curve with confidence intervals for each of these "configurations" against the equivalent baseline configuration curve for the design mostly applied in the fishery.…”

Improving release efficiency of cod (Gadus morhua) and haddock (Melanogrammus aeglefinus) in the Barents Sea demersal trawl fishery by stimulating escape behaviour

“…Incorporating this combined model approach in each of the bootstrap repetitions enabled us to account for additional uncertainty in the release efficiency curve due to uncertainty in model selection . The release efficiency analysis was conducted using the software tool SELNET (Herrmann et al 2012). …”

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

“…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.…”

“…Selectivity analysis.-The statistical analysis software SELNET (SELection in trawl NETting) was used to analyze the data (Sistiaga et al 2010;Herrmann et al 2012). Average sizeselection curves were estimated by pooling length (l) data across tows for each cod end, r av (l).…”