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Öğe ALTERNATIVE CODEND DESIGNS TO IMPROVE SIZE SELECTIVITY FOR NORWAY LOBSTER (NEPHROPS NORVEGICUS) AND ROSE SHRIMP (PARAPENAEUS LONGIROSTRIS) IN THE AEGEAN SEA(Brill Academic Publishers, 2009) Tokac, Adnan; Ozbilgin, Huseyin; Kaykac, HakanRose shrimp (Parapenaeus longirostris) and Norway lobster (Nephrops norvegicus) are the two main target crustaceans for the demersal trawl fleet in the international waters of the Aegean Sea. In the present study, selectivity data were obtained for these two species in commercial codends (300 MC is 40 mm polyethylene codend with 300 meshes on its circumference) and two newly designed types, known as a narrow codend (200 MC is 40 mm polyethylene codend with 200 meshes on its circumference - 33% reduced) and square mesh top panel codend (SMTPC is constructed as 150 diamond meshes on the lower and 75 square meshes on the top panel), respectively. These three types of codends were tested using the covered codend method. Trawling was carried out at depths ranging from 269 to 426 m onboard a commercial vessel in August 2004. Selection parameters were obtained by fitting a logistic equation using the maximum likelihood method. The rose shrimp, in terms of weight, was the most abundant marketable species, with catch per hour values of 19.1, 16.0, and 15.0 kg in 300 MC, 200 MC, and SMTPC, respectively. Results of the selectivity analysis indicate that the commercially used 40 mm nominal mesh size PE codend is rather unselective for these species. In general, narrow and square mesh top panel codends have relatively higher L(50) values than the commercial codend. However, the differences are significant only for rose shrimp, but not for Norway lobster. It is concluded that despite the improvements in selectivity, the codend modifications 'narrow' and 'square mesh top panel' were not sufficient to release immature specimens of either species, at least not when using the 40 mm PE standard netting.Öğe EFFECTS OF MESH CONFIGURATION ON THE SELECTIVITY OF DEMERSAL TRAWL CODENDS FOR NEPHROPS NORVEGICUS (LINNAEUS, 1758) (DECAPODA, NEPHROPHIDAE)(Brill Academic Publishers, 2009) Kaykac, Hakan; Ozbilgin, Hueseyin; Tokac, AdnanIn the present study, we have compared the selectivity of a diamond mesh codend (40D), currently used by Turkish trawl fishermen, and a square mesh codend (40S), which is in the legislation for EU Mediterranean countries (EC 1967/2006). Trawling was carried out onboard the commercial trawler "Niyazi Reis" in the international waters between Turkey and Greece, at depths ranging from 158 to 264 m, in August 2005. Selectivity data were obtained by using the covered codend technique. Selection parameters were estimated by fitting a logistic equation using the maximum likelihood method. Nephrops norvegicus escaped from the codends with retention ratios of 0.98 and 0.91 for 40D and 40S codends, respectively. The selection curves of the two codends are found to be significantly different (p < 0.01). For combined sexes, L(50) values of 16.03 (s.e. 0.41) and 19.38 mm (s.e. 0.51) were estimated in 40D and 40S codends, respectively. The results of this study clearly demonstrate that N. norvegicus took advantage of the increase in escape area provided by the change in mesh configuration from diamond to square.Öğe How fish populations in Lake Bafa (Western Anatolia) respond to ecological shifts(Wiley, 2024) Kurtul, Irmak; Kaya, Cueneyt; Kaykac, Hakan; Ilhan, Ali; Duzbastilar, F. Ozan; Tosunoglu, Zafer; Sari, Hasan M.Long-term biodiversity monitoring is crucial for freshwater ecosystems as it enables the detection of even subtle changes and biodiversity trends, guiding conservation efforts and ensuring the sustainability of these vital habitats. Despite becoming more commonly considered in the field of freshwater ecology and biological invasions, studies using long-term time series from T & uuml;rkiye's freshwater resources have remained scarce. To assess the availability of data and ultimately present a baseline for future efforts, we combined published museum records and samples from recent field studies from the highly anthropogenically-altered Lake Bafa in Western Anatolia covering the period 1958-2019. Lake Bafa has a very diverse aquatic ecosystem, providing habitat for both freshwater and saltwater species, and is one of the allottees in T & uuml;rkiye's inland fish production. In the current study, we investigated how fish populations in Lake Bafa were affected by environmental changes and examined changes in taxonomic and functional diversity of non-native species over time. The analyses revealed-concomitant to an increase in native marine and freshwater species richness-an increase in non-native species richness over time. Non-native species did not interfere with native species' niche space, whereas applied models indicate that in this highly altered ecosystem, foremost temperature and salinity shaped the fish community over time, limiting the impacts of non-native species. These results have implications for the fishery of the lake, which includes highly valuable catadromous fish species, highlighting the value and importance of collecting long-term data in T & uuml;rkiye to better understand both invasion dynamics and changes in the naturality of Turkish ecosystems. These findings further underline the importance of long-term data to create new management strategies for the lake and to start restoration processes, thus improving fisheries management.Öğe Predictive models and comparison of the selectivity of standard (TO) and turned mesh (T90) codends for three species in the Eastern Mediterranean(Elsevier Science Bv, 2014) Tokac, Adnan; Herrmann, Bent; Aydin, Celalettin; Kaykac, Hakan; Unluler, Arcan; Gokce, GokhanThe main objective of this study was to compare and predict the size selective properties of 900 turned mesh codends (T90) with those of similar standard diamond mesh codends (TO) without other design changes. In particular, we wanted to investigate whether a T90 codend can be a simple way to improve size selectivity in the multi-species Mediterranean demersal trawl fisheries. Data were collected and analyzed for three species, while considering the codend design parameters mesh size (m) and netting direction (TO or T90) as potential fixed effects for size selection parameters 50% retention length (L50) and selection range (SR). A special model was constructed and model choice was performed separately for red mullet (Mullus barbatus), common pandora (Pagellus erythrinus) and annular sea bream (Diplodus annularis) based on the AIC value (Akaike, 1974) while considering every possible simpler sub-model following the procedure described in Wienbeck et al. (2011). L50 and SR predictions were made based on this model for TO and T90 codends with mesh sizes from 38 mm to 52 mm for each species separately. The findings revealed that T90 codends significantly improve size selectivity of red mullet and common pandora compared to conventional TO codends of the same mesh size. However, L50 and SR values for TO and T90 codends were found to be similar for annular sea bream. This difference in codend size selectivity between species with regard to turning codend netting orientation by 900 may be related to the difference in body shape. Red mullet and common pandora have rounded shapes while annular sea bream has a laterally compressed body shape. Increase in mesh size was found to increase L50 for all three species for both codend types. (C) 2013 Elsevier B.V. All rights reserved.Öğe Selectivity of commercial, larger mesh and square mesh trawl codends for deep water rose shrimp Parapenaeus longirostris (Lucas, 1846) in the Aegean Sea(Inst Ciencias Mar Barcelona, 2009) Kaykac, Hakan; Tokac, Adnan; Ozbilgin, HuseyinWe investigated the differences between size selectivity of a commercial codend (40 mm, diamond mesh - 40D), a larger mesh codend (48 mm diamond mesh - 48D), and a Square mesh codend (40 mill square mesh - 40S) for Parapenaeus longirostris in international waters of the Aegean Sea. Selectivity data were collected by using a covered codend method and analysed taking between-haul variation into account. The results indicate significant increases in L-50 values in relation to an increase in mesh size and when the square mesh is used in the commercial trawl codend. The results demonstrate that the commercially used codend (40D) is not selective enough for P. longirostris in terms of length at first maturity. Changing from a 40D to a 48D codend significantly improves selection, with an increase of about 15% in the L-50 values (carapace length 14.5 mm for 40D and 16.6 mm for 48D). Similarly, 40 mm square mesh, which has recently been legislated for EU Mediterranean waters, showed a 12.4% higher mean L-50 value (16.3 mm) than 40 mm diamond mesh for this species. However, despite these improvements, the 48D and 40S codends still need further improvements to obtain higher selectivity closer to the length at first maturity (20 mm carapace length).Öğe Selectivity of commercial, larger mesh and square mesh trawl codends for deep water rose shrimp Parapenaeus longirostris (Lucas, 1846) in the Aegean Sea(Inst Ciencias Mar Barcelona, 2009) Kaykac, Hakan; Tokac, Adnan; Ozbilgin, HuseyinWe investigated the differences between size selectivity of a commercial codend (40 mm, diamond mesh - 40D), a larger mesh codend (48 mm diamond mesh - 48D), and a Square mesh codend (40 mill square mesh - 40S) for Parapenaeus longirostris in international waters of the Aegean Sea. Selectivity data were collected by using a covered codend method and analysed taking between-haul variation into account. The results indicate significant increases in L-50 values in relation to an increase in mesh size and when the square mesh is used in the commercial trawl codend. The results demonstrate that the commercially used codend (40D) is not selective enough for P. longirostris in terms of length at first maturity. Changing from a 40D to a 48D codend significantly improves selection, with an increase of about 15% in the L-50 values (carapace length 14.5 mm for 40D and 16.6 mm for 48D). Similarly, 40 mm square mesh, which has recently been legislated for EU Mediterranean waters, showed a 12.4% higher mean L-50 value (16.3 mm) than 40 mm diamond mesh for this species. However, despite these improvements, the 48D and 40S codends still need further improvements to obtain higher selectivity closer to the length at first maturity (20 mm carapace length).Öğe Size selectivity of commercial (300 MC) and larger square mesh top panel (LSMTPC) trawl codends for blue whiting (Micromesistius poutassou Risso, 1826) in the Aegean Sea(Academic Journals, 2010) Kaykac, HakanIn the present study, size selectivity of a commercial (300 MC) and a larger square mesh top panel (LSMTPC) codend for blue whiting (Micromesistius poutassou) were tested on a commercial trawl net in the international waters between Turkey and Greece. Trawling, performed during daylight was carried out at depths ranging from 124 to 230 m, and towing speed changed between 2.2 and 2.3 knots for a 13-day sea trial in August 2005. Selectivity data were obtained by using the covered codend technique. Selection parameters were estimated by fitting a logistic equation using the maximum likelihood method. The results show that mean L(50) values of 16.98 (s.e. 0.22) and 22.84 (s.e. 0.51) cm were estimated for 300 MC and LSMTPC, respectively. These values show that the LSMTPC codend has higher L(50) values than the 300 MC codend. In view of the length value of blue whiting at first maturity (15 to 18 cm), mean L(50) value of LSMTPC codend is remarkably higher than 300 MC codend.Öğe Understanding the size selectivity of red mullet (Mullus barbatus) in Mediterranean trawl codends: A study based on fish morphology(Elsevier, 2016) Tokac, Adnan; Herrmann, Bent; Gokce, Gokhan; Krag, Ludvig A.; Nezhad, Davod S.; Lok, Altan; Kaykac, Hakan; Aydin, Celalettin; Ulas, AliRed mullet (Mullus barbatus) is one of the most important commercial species for the multi-species Mediterranean demersal trawl fisheries. Several experimental studies have been carried out to assess the codend size selectivity for red mullet in the last two decades. However, while the number of experiment-based selectivity studies on red mullet are considerable, very little theoretical work exists which tries to understand and explain the size selectivity for this species in trawl codends. Therefore the main objective of this study was to establish a theoretical framework to explain and predict the size selection of red mullet in bottom trawl codends of different mesh size and configuration. We identified the important morphological characteristics of red mullet which determine the size selection in towed fishing gears using the FISHSELECT methodology and further used this methodology to predict size selection for a wide range of mesh configurations through simulations. For example we predicted the 50% retention length for red mullet to be in the range 9.2-15.8 cm for the legal 50 mm mesh size diamond mesh codend and in the range 10.6-14.2 cm for the legal 40 mm mesh size square mesh codend. The simulated size selection was found to agree well with previously published results for codend size selection of red mullet obtained from sea trials. Thus based on fish morphology we were able to understand and explain previous results leading to a better understanding of the codend size selection for this species. Further the morphologically based results enable predictions of size selection of red mullet in codend designs not previously tested experimentally. (C) 2015 Elsevier B.V. All rights reserved.
