Fig 1.
Illustration of the working principle of a sorting system built from a Nordmøre grid and a subsequent selective codend with curves representing the corresponding size dependent grid passage probability, codend retention probability and the combined size selectivity.
Table 1.
Overview of the hauls carried out and number (n) of individuals measured in each haul during the sea trials.
Fig 2.
Grid passage probability for Northern shrimp (a-c). Circles illustrate experimental rates, solid curves represent the fitted model, and stippled curves are the 95% CI’s. Green lines and circles represent the data for grid with 17 mm bar spacing, red– 21 mm grid spacing, and blue line–grid with 19 mm grid spacing. Dotted green and red lines represent total population size structure retained by the gear. Plots d-f show the difference in the length-dependent grid passage probability (delta) between the different grids with 95% CI’s (stippled lines).
Table 2.
Selectivity parameters and fit statistics for Northern shrimp describing the grid passage probability for the three different grids considered in this study.
Fig 3.
Grid passage probability for cod (a-c). Circles illustrate experimental rates, solid curves represent the fitted model, and stippled curves are the 95% CI’s. Green lines and circles represent the data for grid with 17 mm bar spacing, red– 21 mm grid spacing, and blue line–grid with 19 mm grid spacing. Dotted green and red lines represent total population size structure retained by the gear. Plots d-f show the difference in the length-dependent grid passage probability (delta) between the different grids with 95% CI’s (stippled lines).
Table 3.
Selectivity parameters and fit statistics for cod describing the grid passage probability for the three different grids considered in this study.
Fig 4.
Grid passage probability for American plaice (a-c). Circles illustrate experimental rates, solid curves represent the fitted model, and the stippled curves are the 95% CI’s. Green lines and circles represent the data for grid with 17 mm bar spacing, red– 21 mm grid spacing, and blue line–grid with 19 mm grid spacing. Dotted green and red lines represent total population size structure retained by the gear. Plots d-f show the difference in the length-dependent grid passage probability (delta) between the different grids with 95% CI’s (stippled lines).
Table 4.
Selectivity parameters and fit statistics for American plaice describing the grid passage probability for the three different grids considered in this study.
Fig 5.
Combined (grid and codend) selectivity curves (a-c) and delta plots (d-f) obtained with different grid bar spacing for Northern shrimp. In plots a-c, the green curve shows results for 17 mm, blue– 19 mm, and red– 21 mm grid spacing. Stippled lines are the 95% CI’s.
Fig 6.
Number of retained Northern shrimp and the entry population (grey line) when using grid with 17 mm (green), 19 mm (blue) and 21 mm (red) bar spacing.
Stippled lines represent the 95% CI’s.
Table 5.
Catch efficiency indicators nP+ (in %) for Northern shrimp with carapace lengths >15 mm and >20 mm, respectively, and bycatch species (cod and American plaice) and fraction of undersized shrimp (nDiscardRatio) (in %) when using the 17, 19 and 21 mm bar spacing grids combined with the 35 mm codend for the population encountered.
Table 6.
Change in the catch efficiency indicator nP+ (in %) for Northern shrimp with carapace lengths >15 mm and >20 mm, respectively and bycatch species (cod and American plaice) and fraction of undersized shrimp (nDiscardRatio) (in %) when using the 17 and 21 mm bar spacing with respect to the 19 mm bar spacing (baseline) for the population encountered.
Fig 7.
Combined (grid and codend) selectivity curves (a-c) and delta plots (d-f) obtained with different grid bar spacing for cod. In plots a-c, the green curve shows results for 17 mm, blue– 19 mm, and red– 21 mm grid spacing. Stippled lines are the 95% CI’s.
Fig 8.
Number of retained cod and the entry population (grey line) when using grid with 17 mm (green), 19 mm (blue) and 21 mm (red) bar spacing.
Stippled lines represent the 95% CI’s.
Fig 9.
Combined (grid and codend) selectivity curves (a-c) and delta plots (d-f) obtained with different grid bar spacing for American plaice. In plots a-c, the green curve shows results for 17 mm, blue– 19 mm, and red– 21 mm grid spacing. Stippled lines are the 95% CI’s.
Fig 10.
Number of retained American plaice and the entry population (grey line) when using grid with 17 mm (green), 19 mm (blue) and 21 mm (red) bar spacing.
Stippled lines represent the 95% CI’s.