The current study was aimed to investigate the bycatch in commercial beam trawls used in the rapa whelk (Rapana venosa) fishery during September 1, 2015, and April 30, 2016. Four commercial boats using beam trawls were chartered and catch data were recorded from a total of 87 hauls. The hauls were performed at a depth of 7.1-28.3 meters for a duration of 20-77 min and the hauling speed varied between 1.4-2.7 knots. About 28 species were identified as bycatch, on an average this amounted to 11.4% of the total number of specimens. There were identified two different groups in the bycatch (G1: 7-18 m, G2: 19-26 m) based on the depth. Although there was noticed a decline in the volume of bycatch in group G2, it was not significant between the groups (p>0.05). According to the results of the Generalized Additive Models (GAM), the variables affecting the by-catch amount were identified as a fishing area, depth, haul duration, and the amount of captured rapa whelk (p<0.01). In addition, a large proportion of immature individuals of striped venus clams (Chamelea gallina), blood cockles (Anadara kagoshimensis), Mediterranean mussels (Mytilus galloprovincialis) and wedge clams (Donax trunculus) were caught as bycatch during the exploration. The current piece of work discusses the impact of commercial beam trawls on the demersal macrofauna.

In this study, factors (depth, season and mesh size) influencing the catch and discards of whiting (Merlangius merlangus euxinus) gillnet fishery on the Black Sea coasts of Turkey were investigated. A total of 19 species were identified and the target species, whiting (Merlangius merlangus euxinus), dominated 87.56% of the total catch and followed by red mullet (Mullus barbatus) with 6.32%. While 82.02% of the total catch had commercial value, 17.98% was discarded. The percentage of the discarded red mullet and whiting under MLS (<13 cm) were found to be 16.03% and 13.27%, respectively. The highest discard amount was observed in winter and the lowest one in summer. The discard rate was highest in the 55-74 m depth group and the 32 mm mesh size. One-way analysis of similarity (ANOSIM) showed that there were significant differences in the discard species compositions between spring and summer, as well as 32 and 40 mm, 32 and 44 mm mesh sizes (P<0.05). These results on the discard information in gillnet fishery can contribute to the literature on ecosystem-based sustainable fisheries management by highlighting relevant results on the protection of species and ecosystem.

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In the present study, the selectivity properties of trammel nets used in red mullet fishery by local fishermen were investigated. Trammel nets with five different mesh sizes (16, 17, 18, 20 and 22 mm bar length) in the inner panels and 100 mm mesh size in outer panel were used for fishing trial in the eastern Black Sea coast of Turkey between June 2010 and June 2011. Selectivity parameters for the target species Mullus barbatus, as well as Scorpaena porcus and Solea solea were estimated. Five different selectivity models (normal scale, normal location, gamma, log-normal and bi-modal) in the SELECT method were fitted to data sets. The bi-modal model gave the best fit for three species studied as it had the lowest deviance value. The optimum lengths for red mullet for the Bi-Modal model corresponding to 16, 17, 18, 20 and 22 mm mesh sizes were found as 15. 49, 16.46, 17.42, 19.36 and 21.30 cm, respectively. The minimum mesh size of the trammel nets especially used in red mullet fishery must be 18 mm in order to protect fish stocks and to secure a profitable fisheries and optimum catch efficiency for the future.Keywords: Mullus barbatus, selectivity, trammel net, SELECT, Black Sea. Doğu Karadeniz'de Barbunya Balığı (Mullus barbatus) Avcılığında Kullanılan Fanyalı Uzatma Ağların Seçiciliğinin Araştırılması ÖzetBu çalışmada, bölge balıkçıları tarafından barbunya avcılığında kullanılan fanyalı uzatma ağlarının seçicilik özellikleri incelenmiştir. Türkiye'nin Doğu Karadeniz kıyılarında Haziran 2010 ve Haziran 2011 tarihleri arasında beş farklı tür ağ göz açıklığına (16, 17, 18, 20 ve 22 mm kenar uzunluğu) ve 100 mm göz açıklığına sahip fanyalı ağlar avcılık denemeleri için kullanılmıştır. Hedef tür barbunyanın yanı sıra, iskorpit ve dil balığı için de seçicilik parametreleri tahmin edilmiştir. SELECT metodunda değerlendirilen beş farklı seçicilik modelinin (normal scale, normal location, gamma, log-normal ve bi-modal) verilere uygunluğu değerlendirilmiştir. Her üç balık türü için de en düşük sapma değerine sahip olan Bi-Modal modelin, uygun model olduğu belirlenmiştir. Bi-Modal modele göre barbunya için 16, 17, 18, 20 ve 22 mm göz açıklıklarına göre optimum boylar sırasıyla 15,49, 16,46, 17,42, 19,36 ve 21,30 cm olarak bulunmuştur. Balık stoklarını korumak, gelecek için sürdürülebilir balıkçılık ve optimum av verimliliğini sağlamak için özellikle barbunya avcılığında kullanılan fanyalı ağların minimum göz açıklığı 18 mm olmalıdır.