Trawl cod-end selectivity for deepwater red shrimp ( Aristaeomorpha foliacea, Risso 1827) in the Strait of Sicily (Mediterranean Sea)

• Published in: Fisheries research 2002-08, Vol.57 (2), p.131-144
• Main Authors: Ragonese, S., Bianchini, M.L., Di Stefano, L.
• Format: Article
• Language: English
• Subjects: Animal, plant and microbial ecology; Applied ecology; Aristaeomorpha foliacea; Biological and medical sciences; Bottom trawl; Exploitation and management of natural biological resources (hunting, fishing and exploited populations survey, etc.); Fundamental and applied biological sciences. Psychology; Marine; Mediterranean Sea; Red shrimp; Selectivity
• ISSN: 0165-7836; 1872-6763
• DOI: 10.1016/S0165-7836(01)00342-3

The results of two trawl surveys carried out in the Strait of Sicily (Central Mediterranean Sea) aiming at evaluating the retention coefficients and the selectivity of the commercial gear used in the fishery of the deepwater giant red shrimp, Aristaeomorpha foliacea, are presented and discussed. The study is based on the covered cod-end method (cover of 14 mm mesh) and illustrates the selectivity of three different cod-ends, with mesh of 20, 24 and 28 mm (nominal side dimension). Data were collected in spring and summer 1993, from about 2 weeks of experimental trawling in each season on three fishing grounds. The total number of valid hauls (3 h each) was 31 and 42 in the first and second period, respectively. The two chosen periods allowed the whole dimensional span of the red shrimp (from 12 to 70 mm of carapace length, CL) to be covered. The 20 mm mesh cod-end (the minimum legal size by Italian by-laws) catches all the adult red shrimps ( CL>35–40 mm) , with only a minimal fraction of the juveniles passing through (CL 50=18–19 mm; SF =0.9) . The 24 mm mesh cod-end permits the greater fraction of the juvenile component (CL 50=21 mm; SF =0.9) to escape, whereas the 28 mm mesh cod-end still captures the greatest majority of the adults, while allowing a substantial part of the juveniles (CL 50=23–24 mm; SF =0.83–0.87) to escape. The main conclusions are: (1) neither the mesh presently in use in the Strait of Sicily (16–18 mm) nor the legal mesh (20 mm) are satisfactory in the biological sense; (2) the introduction of a cod-end with a mesh of 28 mm (side) is strongly recommended; (3) management interventions other than mesh regulation are required, given that not even the 28 mm cod-end achieves a CL 50 near the size at onset of maturity estimated for the red shrimp of the Strait of Sicily (about 40 mm CL).