Evaluation of sorting grids for deepwater rose shrimp (Parapenaeus longirostris) in the Eastern Mediterranean demersal trawl fishery

Abstract

The study aimed to evaluate sorting grids of 10 and 15 mm bar spacing specifically for separation of deep water rose shrimp, but including other species, in a Mediterranean multispecies demersal trawl fishery. Data were collected 15-25 October 2008 in Sıg˘acık Bay, Eastern Aegean Sea with the commercial trawler, ÔHapulog˘luÕ, using a modified bottom trawl net. A total of 22 valid hauls (12 with 10 mm, ten with 15 mm grids) were obtained. The separation rate of anglerfish was highest, with 100% for weight and number in both codends among all species. Grid elimination of broadtail short-fin squid showed differences between 95.3 and 80.3% in terms of weight, and 89.7 and 66.2% in terms of number for 10 and 15 mm, respectively. Separation ratios for hake, silver scabbard fish, and horse mackerel were between 96.3 and 100% in terms of weight, and 92.2 and 100% in terms of number in both codends. Shrimp separation was in total calculated as 60.8 and 37.0% by number, and 70.7 and 44.4% by weight in 10 and 15 mm bar spacing trawl grids, respectively, demonstrating that substantial improvement in species selectivity (deep water rose shrimp from others) is possible to achieve by adding sorting grids in the Mediterranean demersal trawl fishery. To optimize the overall selection performance in such fisheries, a variety of grid systems, bar spacings and materials as well as the economic consequences need to be evaluated.

How Can We Reduce the Overexploitation of the Mediterranean Resources?

“…Since undersized fishes of many large-sized species, such as M. merluccius, are highly vulnerable to the minimum mesh size enforced in the Mediterranean (40 mm square or 50 mm diamond) (Brčić et al, 2018;Mytilineou et al, 2018) and a further increase of the mesh size would lose shrimps, cephalopods, and medium-sized fish, the exploitation pattern can be enhanced through: (i) increasing the trawl net selectivity by adopting grids and separators that allow the undersized fish to escape (Coll et al, 2008;Massutí et al, 2009;Aydın and Tosunoglu, 2011;Vitale et al, 2018b); (ii) delaying the size/age of the first capture of juveniles through spatial and/or temporal closures to fisheries when and where the juveniles aggregate in order to improve the fraction of fish reaching sexual maturity (Caddy, 1999(Caddy, , 2009Fiorentino et al, 2003;Garofalo et al, 2011;Colloca et al, 2015;Despoti et al, 2020;Mytilineou et al, 2020;Milisenda et al, 2021); or (iii) a combination of the two approaches.…”

Towards more selective Mediterranean trawl fisheries: are juveniles and trash excluder devices effective tools for reducing undersized catches?

“…In particular, the studies carried out on sorting grids have revealed clear advantages associated with their use in mixed trawl fisheries, such as improved selectivity and by-catch reduction (e.g. Massutí et al 2009, Aydın andTosunoğlu 2011), a stable selection pattern during the tow (Suuronen and Sardà 2007), and a higher survival rate of specimens escaping from the grid bars compared with a conventional cod-end mesh (e.g. Brčić et.…”

“…Although all these studies point to the positive impact of sorting grids on the size at first capture of commercial fish and crustaceans (e.g. Massutí et al 2009, Aydın andTosunoğlu 2011), their adoption in Mediterranean trawl fisheries is still very low. Lack of sorting grid implementation could be linked to several causes, including fishers' resistence to changing fishing traditions and customs, and, consequently their unwillngness to modify their fishing gear substantially.…”

Isolation By Distance (IBD) signals in the deep-water rose shrimp Parapenaeus longirostris (Lucas, 1846) (Decapoda, Panaeidae) in the Mediterranean Sea

“…The exploitation of this species takes place all year round, even if peak landings occur from March to July (Levi et al, 1995;Abdel Razek et al, 2006). Studies regarding the deep-water rose shrimp have primarily focused on its distribution, biology (Bombace, 1975;Lembo et al, 2000;Mori et al, 2000;Abelló et al, 2002;Bayhan et al, 2005;Arculeo, 2009), and fishery aspects (Sbrana et al, 2003;Sobrino et al, 2005;Sbrana et al, 2006;Ligas et al, 2011;Aydın and Tosuno glu, 2012). The population dynamics has been studied, in particular regarding the link between population abundance and environmental factors (Guijarro et al, 2009;Ligas et al, 2011).…”