| Summary: | Gillnet selectivity curves for North Sea Atlantic cod (Gadus morhua) were fitted to catch data obtained with six different mesh sizes. The selectivity curves investigated included frequently used selectivity models following the normal, lognormal, and gamma distributions. Another group of selectivity models that take the method of capture (gilled, maxillae, or "randomly" enmeshed) into consideration was also included. The best description of the selection data was found for the latter models. Therefore, the capture processes and girth measurements should be recorded as a matter of routine and such data used when constructing and evaluating gillnet selectivity models. The shape of the selectivity curve for those size intervals where there were satisfactory catch information was well defined, while the selection curve was ambiguous outside the interval with adequate data. Ambiguities in the shape of the selectivity curve can be diminished by choosing an appropriate range in mesh sizes and ensuring that the mesh sizes match the size distribution of the population fished. It is furthermore suggested that the estimated length distribution of the fish encountering the nets be robust to misspecification of the selectivity model Gillnet selectivity curves for North Sea Atlantic cod (Gadus morhua) were fitted to catch data obtained with six different mesh sizes. The selectivity curves investigated included frequently used selectivity models following the normal, lognormal, and gamma distributions. Another group of selectivity models that take the method of capture (gilled, maxillae, or "randomly" enmeshed) into consideration was also included. The best description of the selection data was found for the latter models. Therefore, the capture processes and girth measurements should be recorded as a matter of routine and such data used when constructing and evaluating gillnet selectivity models. The shape of the selectivity curve for those size intervals where there were satisfactory catch information was well defined, ...
|
|---|