Understanding and Predicting Size Selection in Diamond‐Mesh Cod Ends for Danish Seining: A Study Based on Sea Trials and Computer Simulations

Abstract

Danish 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

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

“…For complete model details, see Wileman et al (1996), Wienbeck et al (2014), and Herrmann et al (2016). To determine which model best described the data, we evaluated fit statistics for each model.…”

Fishing profiles of Danish seiners and bottom trawlers in relation to current EU management regulations

“…Shorter haul durations, shallower fishing grounds and smaller total catches were found in seines than in trawls. Besides the late entry of fish into the net and the corresponding short time within the gear (Herrmann et al., ; Noack et al., ), these are all factors that have positive impact on the survival of discarded fish (van der Reijden et al., ). Previous studies on discard survival focused on different types of trawling such as beam trawling (Depestele, Desender, Benoît, Polet & Vincx, ; van der Reijden et al., ; Uhlmann et al., ) and otter trawling (Methling, Skov & Madsen, ), but no studies have so far investigated discard survival probabilities for Danish seines.…”

“…lighter ground gear of seines) and particularly the fishing procedures (Eigaard et al., ; Herrmann, Krag, Feekings & Noack, ), this grouping of seines and trawls has been brought into question by fishers and other stakeholders in the EU. Fishers that operate seines claim a loss of more marketable fish than those using trawls when legal mesh sizes are used (see Herrmann et al., ). This highlights the need for more detailed information about the two gear types and their catches.…”

“…The objective of this landing-obligation system was to make fishers more selective (Condie, Grant & Catchpole, 2013) and to reduce bycatch instead of utilising quota for less commercial catches (Borges, Cocas & Nielsen, 2016). However, as previous studies found, indications of differences in the selectivity characteristics of seines and trawls as well as larger L 50 values (length at which 50% of the fish are retained) for seines for species such as cod Gadus morhua L. (Herrmann et al, 2016;Noack, Frandsen, Krag, Mieske & Madsen, 2017), proportions of fish below MCRS are likely different. Furthermore, differences in gear constructions (e.g.…”

Estimating escapement of fish and invertebrates in a Danish anchor seine

“…The codend is the part of towed fishing gears where the catch is collected and where the main selection of fish occurs (Wileman et al, 1996). Therefore, most studies on towed fishing gears, e.g., selectivity studies on trawls (e.g., Reeves et al, 1992;Graham et al, 2004;Frandsen et al, 2010) or Danish anchor seines (e.g., Herrmann et al, 2016;Noack et al, 2017), or survival studies (e.g., Uhlmann et al, 2016), focused on the individuals in or escaping from the codend. Previous studies on the selectivity of commercially valuable crustaceans in different types of trawls, however, found that a substantial part of the selection of Norway lobster (Nephrops norvegicus; Hillis and Earley, 1982), brown shrimp (Crangon crangon; Polet, 2000) and Antarctic krill (Euphausia superba; Krag et al, 2014a) takes place in the forward parts of a trawl net.…”