Catching efficiency and selectivity of entangling nets

Size selectivity of trammel nets in southern European small-scale fisheries

“…Trammel nets are generally considered to be less size selective than gill nets, with size frequency distributions frequently skewed to the right (Millner, 1985;Dickson, 1989;Fabi et al, 2002;Fitzhugh et al, 2002). The selectivity curve of trammel nets is domed but has a flatter shape than that for fin-fish caught with gill nets, as reported by authors who used the same methodology to fit the selectivity curve (Koike and Matuda, 1988;Losanes et al, 1992a). If a significant proportion of individuals, especially the larger ones, are pocketed or trammelled, then the selectivity curve may not fall to zero or even have a descending limb, implying that very few fish escape after coming into contact with the trammel net (Salvanes, 1991;Losanes et al, 1992b).…”

“…Hanging ratios for the inner net generally range between 0.3 and 0.5, while hanging ratios of the larger mesh outer panels are typically greater. Vertical slack, the ratio of the depth of the small-meshed inner panel to that of the large-meshed outer panels (Losanes et al, 1992a), is commonly between 1.5 and 2.0.…”

“…In contrast, size selectivity was clearly a function of the smaller mesh of the inner panels, with modal length generally increasing with inner panel mesh size for many species. Other authors also report that the catches and the size selectivity of trammel nets depends primarily on the mesh size of the inner net (e.g., Kitahara, 1968;Koike and Takeuchi, 1985;Koike and Matuda, 1988;Salvanes, 1991;Purbayanto et al, 2000;Losanes et al, 1992a).…”

Ichthyofaunal survey of rivers within Ewekoro cement manufacturing operational areas

“…Fish samples were collected on each river once a month using a combination of the gillnetting method (Udolisa et al 1994;Petrokis and Stergiou 1996) and double chambered fish traps set in tandem overnight (Olaleye and Akinyemiju 1996) on sampling days. The methods of sample collection were found appropriate for the study because the fish population was unknown and the fish net encountering rate could not be determined (Losanes et al 1992).…”

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“…It has been reported that the inner-panel mesh size is responsible for the size selectivity of trammel nets (Losanes et al, 1992;Erzini et al, 2006;Stergiou et al, 2006). Results of the present study confirmed this fact and indicated that a slight increase in the inner-panel mesh size resulted in a significant difference in length distributions of both A. sohal and S. rivulatus (Table 2), with the overlapping over the majority of length classes (Figure 3), and the mean observed total length of the retained fish increased from 20.4 to 23.9 cm for A. sohal and from 19.1 to 21.2 cm for S. rivulatus with the slight increase in the inner-panel mesh size from 50 to 62 mm (Table 1).…”