Abstract
This study investigates the effects of trap selectivity of various mesh size on escape success of the blue crab (Callinectes sapidus). The study was carried out Camlik Lagoon of Yumurtalik Gulf in the Mediterranean Sea and total of 1051 blue crabs were caught by rectangular baited trap. Using traps constructed with 30, 35, 40, 45 and 50 mm square mesh the proportion of crabs escaping through each mesh size was measured for each half centimetre carapace width (CW) class. A logistic model was fitted to the size frequency data of the retained and escaped blue crabs for each mesh size in the experiment. L50 and selection range (SR) for the 30, 35, 40, 45 and 50 mm (bar length) square meshes tested in this study was 8.47 cm and 0.85 cm; 9.31 cm and 0.39 cm; 10.40 cm and 0.31 cm; 11.72 cm and 1.17 cm; 13.17 cm and 0.89 cm respectively. The 50 mm square mesh of the trap showed relatively better selectivity considering the size at 50% sexual maturity of blue crab Callinectes sapidus, and the high rate of immature escapers. Keywords: Blue crab Callinectes sapidus; Trap; Size selectivity; Mediterranean Sea
Highlights
The blue crab is an important commercial species that inhabits coastal areas, estuaries, and lagoons throughout the southern part of Turkey (Enzenross et al 1997; Türeli 1999)
This study investigates the trap mesh selectivity of five different square mesh (30, 35, 40, 45 mm and 50 mm bar length) size on the escape success of blue crabs
The number of specimens caught in the traps was 1051 blue crabs during the selectivity study, with sizes ranging from 6 to 16 cm carapace width (CW)
Summary
The blue crab is an important commercial species that inhabits coastal areas, estuaries, and lagoons throughout the southern part of Turkey (Enzenross et al 1997; Türeli 1999). The maximum Carapace Width (CW) of blue crab reported in Turkey is 18.1 cm and mean CW is 12 cm for both female and male crabs (Türeli 1999; Atar & Seçer 2003). Reported size at first maturity is 6.05 cm for female and 4.48 cm for male individuals (Türeli 1999). Hexagonal or square mesh wire traps with a small mesh size are currently used by commercial fishermen to catch blue crabs in Turkish lagoons. There is no required mesh shape, nor a minimum mesh size limit for traps, which constitute the most commonly, used fishing gear in crab fisheries. Unacceptable numbers of sub-legal blue crab and immature fish, which are commonly abundant in lagoons, will be retained if the mesh size is too small; the legal catch of blue crabs will be reduced if the mesh is too large
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