Species selectivity in the Eastern Mediterranean demersal trawl fishery using grids to reduce non-target species

Abstract

Summary Scientific studies have been conducted on size selectivity of trawls with grids in the Mediterranean; however, none has focused on species selectivity. The aim of the present study was to analyze the value of sorting grids with 20 mm bar spacing for species separation, in a demersal trawl fishery mainly targeting deep water rose shrimp (Parapenaeus longirostris) in the Eastern Mediterranean. Fishing trials were carried out 17–24 August 2008 onboard the commercial trawler ‘Hapuloglu’, using a modified bottom trawl net. The separation rate for silver scabbard fish (Lepidopus caudatus) was highest among all species with 98% by weight and 97% by number in 44 mm diamond (44D) and 40 mm square mesh (40S) codends, respectively. The exclusion of European hake (Merluccius merluccius) by the grid shows differences between 85 and 93%, in weight and 64 and 83% in number for codends of 44D and 40S, respectively. Excluding the ratio for greater forkbeard (Phycis blennoides), the angler fish (Lophius piscatorius) and broadtail short fin squid (Illex coindetii) varied between 93 and 97% in weight, and 81 and 86% in number in both codends. Losses of legal sized rose shrimp were determined as 23 and 25% in 44D and 40S, respectively. The results obtained in the present study demonstrate that substantial separation of fish and shrimp can be achieved in this Mediterranean demersal trawl fishery. However, further developments should be explored; for this purpose the behaviour of species has to be studied in relation to trawl and grid design and where commercial consequences of changes in gear technology need to be considered.