Abstract
AbstractDanish seining is an important fishing method used to harvest demersal species. Knowledge about the size selectivity of different demersal species with this type of fishing gear is therefore of importance for managing the exploitation of marine resources. However, there are only limited data on size selection in cod ends in this fishery. Sea trials were therefore carried out to collect size selectivity data for Atlantic Cod Gadus morhua, Haddock Melanogrammus aeglefinus, and Witch Flounder Glyptocephalus cynoglossus for a diamond‐mesh cod end. For all three species, the data were best described by a double logistic selection curve, implying that two different size selection processes occur in the cod end. The double selection process could be explained by an additional selection process occurring through slack meshes. The results imply that the escapement of 46% and 34% of the larger Atlantic Cod and Haddock (those above 48 cm), respectively, would be through wide‐open or slack meshes. Since these mesh states are only likely to be present in the latest stage of the fishing process (e.g., when the cod end is near the surface), a large fraction of the bigger fish probably escaped near the surface, which might influence their likelihood of survival. Furthermore, based on the models established for explaining the experimental size selection, we were able to predict the effect of changing the mesh size on cod end size selection in the Danish seine fishery.Received December 9, 2015; accepted February 18, 2016
Highlights
The Danish or anchor seine is an active demersal fishing technique which was invented by the Danish fisherman Jens Væver in 1848, and in the first half of the 20th century it became one of the most important fishing gears used in Denmark (Thomson 1981)
The formulas for the four selection models, together with additional information, can be found in Wileman et al (1996). In addition to these four classical size selection models, which assume that all fish entering the cod end are subject to the same size selection process, we considered a model that we refer to as the double logistic model (DLogit)
Lengths were obtained from 7,307 Atlantic Cod, 6,901 Haddock, and 5,462 Witch Flounder, and these form the basis for the size selectivity analysis
Summary
The Danish or anchor seine is an active demersal fishing technique which was invented by the Danish fisherman Jens Væver in 1848, and in the first half of the 20th century it became one of the most important fishing gears used in Denmark (Thomson 1981). After dropping an anchor attached to a set of marker buoys, the fishing vessel starts encircling the fishing area by laying out the first lead-filled rope (Figure 1A), which can be up to 4,000 m long. The end of this rope is attached to one wing tip of the seine net. Danish seines are towed at considerably lower speeds, especially in the early phases of the operation, and the global geometry of the gear gradually goes from being overspread in the setting phase to completely closed at the end of the collecting and closing phases. With the considerable differences in the operations of the two gear types, the selectivity of these two gears can be expected to differ
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