2 research outputs found
Bycatch in 36 and 40 mm PA Turkish twin rigged beam trawl codends
The Turkish twin rigged beam trawl which has two identical nets rigged side by side on the same beam targets mainly the Parapenaeus longirostris, although some bycatch fish species have also become target species. Thus, landings of the shrimp beam trawling fleet also include some commercially valuable fishes. Our study focused on the bycatch commercial species which are caught by the beam trawl fishery with nominal mesh sizes 36 and 40 mm PA (diamond) codend in the Sea of Marmara (Turkey) and also on the minimum landing size (MLS) established for Merluccius merluccius, Merlangius merlangus euxinus, Mullus surmuletus, Trachurus trachurus and Pomatomus saltatrix. Since there was no MLS value for Spicara smaris, the length at first maturity (LFM) was used for this species. Experiments were carried out onboard the commercial beam trawler. In 20 hauls, the average codend catch weight was 63.12 kg for 36 mm PA and 66.51 kg for 40 mm PA. On the other hand, for 36 mm PA, 83.5% of M. merluccius, 74.3% of M. merlangus euxinus, 29.7% of T. trachurus, 10.8% of P. saltatrix and 8.6% of M. surmuletus were below the MLS. For 40 mm PA, 88.9% of M. merlangus euxinus, 87.7% of M. merluccius, 42.5% of T. trachurus, 7.2% of P. saltatrix and 6.7% of M. surmuletus were below MLS. In addition, 7.5% of S. smaris were below length at first maturity (LFM) for 36 PA codends.Key words: Beam trawl, rose shrimp, Parapenaeus longirostris, bycatch, discards, minimum landing size, Sea of Marmara, Turkey
Recommended from our members
Holocene Climatic Optimum centennial-scale paleoceanography in the NE Aegean (Mediterranean sea)
Combined micropaleontological and geochemical analyses of the high-sedimentation gravity core M-4G provided new centennial-scale paleoceanographic data for sapropel S1 deposition in the NE Aegean Sea during the Holocene Climatic Optimum. Sapropel layer S1a (10.2–8.0 ka) was deposited in dysoxic to oxic bottom waters characterized by a high abundance of benthic foraminiferal species tolerating surface sediment and/or pore water oxygen depletion (e.g., Chilostomella mediterranensis, Globobulimina affinis), and the presence of Uvigerina mediterranea, which thrives in oxic mesotrophic-eutrophic environments. Preservation of organic matter (OM) is inferred based on high organic carbon as well as loliolide and isololiolide contents, while the biomarker record and the abundances of eutrophic planktonic foraminifera document enhanced productivity. High inputs of terrigenous OM are attributed to north Aegean borderland riverine inputs. Both alkenone-based sea surface temperatures (SSTs) and δO18G. bulloides records indicate cooling at 8.2 ka (S1a) and ~7.8 ka (S1 interruption). Sapropelic layer S1b (7.7–6.4 ka) is characterized by rather oxic conditions; abundances of foraminiferal species tolerant to oxygen depletion are very low compared with the U. mediterranea rise. Strongly fluctuating SSTs demonstrate repeated cooling and associated dense water formation, with a major event at 7.4 ka followed by cold spells at 7.0, 6.8, and 6.5 ka. The prominent rise of the carbon preference index within the S1b layer indicates the delivery of less degraded terrestrial OM. The increase of algal biomarkers, labile OM-feeding foraminifera and eutrophic planktonic species pinpoints an enhanced in situ marine productivity, promoted by more efficient vertical convection due to repeated cold events. The associated contributions of labile marine OM along with fresher terrestrial OM inputs after ~7.7 ka imply sources alternative/additional to the north Aegean riverine borderland sources for the influx of organic matter in the south Limnos Basin, plausibly related to the inflow of highly productive Marmara/Black Sea waters