Gill net and trammel net selectivity in the northern Aegean Sea, Turkey

Hakan Erk,F. Saadet Karakulak

doi:10.3989/scimar.2008.72n3527

Abstract

Fishing trials were carried out with gill nets and trammel nets in the northern Aegean Sea from March 2004 to February 2005. Four different mesh sizes for the gill nets and the inner panel of trammel nets (16, 18, 20 and 22 mm bar length) were used. Selectivity parameters for the five most economically important species, bogue (Boops boops), annular sea bream (Diplodus annularis), striped red mullet (Mullus surmuletus), axillary sea bream (Pagellus acarne) and blotched picarel (Spicara maena), caught by the two gears were estimated. The SELECT method was used to estimate the selectivity parameters of a variety of models. Catch composition and catch proportion of several species were different in gill and trammel nets. The length frequency distributions of the species caught by the two gears were significantly different. The bi-modal model selectivity curve gave the best fit for gill net and trammel net data, and there was little difference between the modal lengths of these nets. However, a clear difference was found in catching efficiency. The highest catch rates were obtained with the trammel net. Given that many discard species and small fish are caught by gill nets and trammel nets with a mesh size of 16 mm, it is clear that these nets are not appropriate for fisheries. Consequently, the best mesh size for multispecies fisheries is 18 mm. This mesh size will considerably reduce the numbers of small sized individuals and discard species in the catch.

Highlights

Artisanal fisheries play a significant role in Turkish fisheries
The SELECT method was used to estimate the selectivity parameters of a variety of models
The length frequency distributions of the species caught by the two gears were significantly different

Summary

Introduction

Artisanal fisheries play a significant role in Turkish fisheries. Eighty-nine percent (16460) of 18396 vessels belong to the artisanal fishery (TUIK, 2005).The length of the boats ranges from 6 m to 10 m, engine power ranges from 5 to 100 HP, and crew from 1 to 3. Artisanal fisheries play a significant role in Turkish fisheries. Eighty-nine percent (16460) of 18396 vessels belong to the artisanal fishery (TUIK, 2005). Gill nets are used to catch fish with an almost uniform body size since the mesh size must match the fish’s girth; the mesh size used depends on the species and size range being targeted. Trammel nets are specially designed gill nets that are constructed by joining three parallel sheets of netting. The two outer sheets are made of netting with a very large mesh size. The trammel net design enables catching fish by two different processes; (a) gilling and entangling, like conventional gill nets, and (b) trapping large fish in the bags of the inner netting (FAO, 2000). Trammel nets are generally considered to be less size selective than gill nets (FAO, 2000; Fabi et al, 2002). The selection curve is skewed or multimodal and may be more appropriate than the normal curve (Hamley, 1975)

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Discussion

Conclusion