Selectivity of commercial and experimental codends for the demersal trawl fishery of the deep-water rose shrimp, Parapenaeus longirostris (Lucas, 1846), in the Aegean Sea

Abstract

In this study, the selectivity of commercial and alternative (experimental) codends for the deep-water rose shrimp, Parapenaeus longirostris, in the Aegean Sea demersal trawl fishery was investigated. Tested were the 44-mm diamond mesh codend as used in commercial fisheries (D44), in addition to a 50 mm diamond (D50), a 40 mm square (S40), and a 40 mm 90° turned mesh (T40), respectively. Sea trials were carried out in the eastern Aegean Sea, with a local commercial trawler using a modified trawl net with 620 meshes circular mouth opening. A total of 35 valid daytime hauls (8 with D44, 9 with D50, 8 with S40 and 10 with T40) were carried out. Selectivity data were collected using the covered codend method and analysed by means of a logistic equation with the maximum-likelihood method. Mean selection curves were estimated and compared using the between-haul variations model. The mean 50% retention carapace length values (LC50) were estimated as 21.2 ± 0.1, 23.2 ± 0.3, 20.8 ± 0.2 and 20.5 ± 0.4 mm CL for D44, D50, S40, and T40, respectively. Selection range (SR) values were determined as 4.9 ± 0.1 mm in D44, 8.7 ± 0.3 mm in D50, 4.0 ± 0.3 mm in S40, and 10.1 ± 0.3 mm in T40. While haul duration and total catch among the parameters did not affect the LC50 values for the investigated codends, the value of the parameter describing the weight of P. longirostris caught in that codend showed an effect for the D50 and T40 codends. Consequently, all investigated codends yielded sufficient LC50 results when considering the minimum landing size (MLS) value imposed by the EU (20 mm CL). In conclusion, the legally allowed S40, which gave an LC50 value close to that of D44, and which would be the preferable codend in terms of its releasing characteristics for individuals under the MLS value (89%), can be used as a good alternative for the D44 (preferred by the fishermen) in the deep-water rose shrimp fishery.