Multi-monofilament Gillnet Selectivity for Capoeta trutta (Heckel
Transkript
Multi-monofilament Gillnet Selectivity for Capoeta trutta (Heckel
ISSN: 2148-0273 Cilt 2, Sayı 1, 2014 / Vol. 2, Issue 1, 2014 Multi-monofilament Gillnet Selectivity for Capoeta trutta (Heckel, 1843) in Keban Dam Lake, Elazig, Turkey Ali Ekber ÇAT*, Fahrettin YÜKSEL** Abstract In this study, by benefiting from indirect estimation method developed by Holt (1963), multimonofilament gillnets with different mesh size used in fishing of Capoeta trutta (Heckel, 1843) that have selective properties were determined. Field studies were carried out between November 2011 and May 2012 in Pertek Region of Keban Dam Lake (Elazig-Turkey). In experiments, five pieces of gillnets with 35, 40, 45, 50 and 55 mm mesh sizes and 3 x 0.12 mm diameter multi-monofilament polyamide material were used. A total of 720 samples of Capoeta trutta were caught in 24 fishing attempts. It was determined that optimum catch length of Capoeta trutta caught by gillnets with 35, 40, 45, 50, and 55 mm mesh size as 28.57; 32.65; 36.73; 40.81 and 44.89 cm, respectively, common selectivity factor (SF) as 8.16 and common standard deviation (SD) as 3.51. Length at first maturity of female C. trutta (29.07 cm) was compared to the optimum selection lengths of gillnets with mesh sizes of 35, 40, 45, 50 and 55 mm. Results indicate that gillnets with mesh size of greater than or equal to 40 mm would be appropriate for catching C. trutta in the Keban Dam Lake. The use not of smaller mesh sizes are considered to be extremely important for the sustainable catching of C. trutta in Dam Lake. Key words: Keban Dam Lake, Capoeta trutta, gillnets, selectivity, mesh size _________________________________________________________ *Yüksek lisans öğrencisi, Tunceli Üniversitesi, Su Ürünleri Fakültesi, Tunceli **Yrd. Doç. Dr., Sorumlu Yazar, Tunceli Üniversitesi, Su Ürünleri Fakültesi, Tunceli, e-mail: [email protected] Multi-monofilament Gillnet Selectivity for Capoeta trutta (Heckel, 1843)…| 16 Keban Baraj Gölü (Elazığ-Türkiye)’ndeki Capoeta trutta (Heckel, 1843) İçin Multimonofilament Galsama Ağı Seçiciliği Özet Bu çalışmada, Holt (1963) tarafından geliştirilen indirekt tahmin yönteminden yararlanılarak, Capoeta trutta (Heckel, 1843) avcılığında kullanılan farklı göz büyüklüklerine sahip multi monofilament galsama ağlarının seçicilik özellikleri belirlenmiştir. Arazi çalışmaları, Kasım 2011 ile Mayıs 2012 tarihleri arasında Keban Baraj Gölü Pertek Bölgesi’nde gerçekleştirilmiştir. Araştırmada 0,50 donam faktörüne göre donatılmış, 3 x 0,12 mm kalınlığında multi monofilament poliamid materyalden yapılmış, 100 m uzunluğunda, 100 göz derinliğinde 35, 40, 45, 50 ve 55 mm göz genişliğinde (iki düğüm arası mesafe) 5 adet galsama ağı kullanılmıştır. Yapılan 24 avcılık denemesinde 720 adedi hedef tür (Capoeta trutta) olmak üzere toplam 1134 adet balık yakalanmıştır. Araştırmada kullanılan 35, 40, 45, 50 ve 55 göz genişliğindeki ağlarla yakalanan Capoeta trutta (Heckel, 1843) balıklarının optimum yakalama boyları sırasıyla 28,57; 32,65; 36,73; 40,81 ve 44,89 cm, ağların ortak seçicilik faktörü (SF) 8,16 ve ortak standart sapması (SD) 3,51 olarak tespit edilmiştir. Keban Baraj Gölü’nde, Capoeta trutta (Heckel, 1843) balıklarının ilk üreme boyu (29,07 cm) ile avcılıkta kullanılan ağların optimum yakalama boyları karşılaştırıldığında, Keban Baraj Gölü’nde C. trutta avcılığında 40 mm ve üzeri göz genişliğindeki galsama ağlarının uygun olduğu belirlenmiştir. Baraj gölündeki C. trutta populasyonunun geleceği açısından daha küçük gözlü ağların kullanılmamasının son derece önemli olduğu sonucuna varılmıştır. Anahtar kelimeler: Keban Baraj Gölü, Capoeta trutta, galsama ağları, seçicilik, göz genişliği Introduction Keban Dam Lake is the second largest dam lake in Turkey (measured by surface area). The surface area of Keban Dam Lake is 687.31 km2. It has some species and subspecies of Cyprinidae, Bagridae, Cobitidae, Mastacembelidae and Salmonidae (Harlıoğlu et al., 2004). Capoeta trutta belonging to family Cyprinideae has a wide distribution as well as it has important economical value in fisheries of Keban Dam Lake. It was reported that nearly 14.1% of the fish caught from Keban Reservoir consisted of C. trutta (Celayir et al., 2006). For sustainable fishery, selectivity of the target species is very important in the point of getting maximum product and protecting young individuals. Thanks to the use 17 | Ali Ekber ÇAT, F a h r e t t i n Y Ü K S E L of fishing gear in scientific studies, the determination of the length distributions of caught species has importance with regard to knowing the stock. Gillnets are mostly used fishing tools in this direction. It is known that selectivity of gillnets can be arranged with their mesh size and that they are a fishing tool having high selectivity (Hamley, 1975; Gulland, 1983; Petrakis and Stergiou, 1995; Ayaz et al., 2009). Gill nets are chiefly used to catch fish with an almost uniform body size since the mesh size must match the fish’s girth; the mesh size used depends on the species and size range being targeted. The selection curve is often assumed to be bell shaped (Karakulak and Erk, 2008). Several studies have been carried out to estimate the selectivity parameters for different species in inland waters of Turkey (Çetinkaya et al., 1995; Balık, 1999; Balık and Çubuk, 2001; Özekinci et al., 2003; Özyurt and Avşar, 2005; Özekinci et al., 2007). Since ecological factors affect the biological characteristics of fish species, gillnet selectivity parameters change for different species and different populations (Özekinci et al., 2007). The purpose of this study is to estimate selectivity parameter of multimonofilament gillnets with mesh size of 35, 40, 45, 50 and 55 mm, many of which are utilized by the commercial fisheries for Capoeta trutta in Keban Dam Lake. The results are of major importance for improving the management of fisheries resources in Dam Lake. Materials and Methods The study was realized in Pertek fishing Area of Keban Dam Lake (ElazigTurkey) from November 2011 to May 2012. It was performed 24 fishing attempts in the period of seven months. Samples were collected with multi-monofilament gillnets that had mesh sizes of 35, 40, 45, 50 and 55 mm, and the length of each gillnet was 100 m as well as depth of them was 100 mesh. They were made of multi-monofilament polyamide twine. The twine diameter sizes of all nets were 3 × 0.12 mm. The nets were rigged on a float-line and a lead-line with a hanging ratio of 0.50. In terms of length, hanging ratio, twines and colors, all nets were the same, differing only in mesh size. Multi-monofilament Gillnet Selectivity for Capoeta trutta (Heckel, 1843)…| 18 The nets were set at sunset and retrieved in the early hours, next day. After the fishing operations, the total lengths (TL) of fish were measured with millimetric measurement board and the weights (W) of them were taken on the scales having 1 g sensitivity. Classification of fish species was made according to Geldiay and Balık (2007). The fish caught were segregated according to the mesh size of gillnets and grouped in length groups at 1 cm interval. Selectivity parameters of gillnets in respect of C. trutta fishing were estimated according to the indirect method proposed by Holt (1963). This method allows the estimation of selectivity parameters by comparing the catches in terms of quantity according to two different mesh sizes for the same length class. This method was modified by Sparre et al. (1989) and expressed as follows (Özekinci et al., 2007); The natural logarithms of the number caught per length group, Ca and Cb, by two slightly different mesh sizes, ma and mb, are linearly related to fish lengths; ln (Cb/Ca) = a+bL, Where L is the length class of caught fish, a and b are the intercept and slope of the linear regression, respectively. The optimum lengths (Lma and Lmb) for mesh sizes ma and mb, the selection factor (Sf) and standard deviation (Sd) were then estimated from the following equations: Lma = -2 [ama/b (ma+ mb)] Lmb = –2 [amb/b (ma+ mb)] = Lma. mb/ma and Sf = -2 a/b (ma+ mb) Sd = {-2 a (mb – ma)/b(ma+mb)}½ If the numbers of mesh sizes used are more than two, the common selectivity factor will be calculated as fallows (Sparre et al., 1989), 19 | Ali Ekber ÇAT, F a h r e t t i n Y Ü K S E L SF = -2 Σ [(ai/bi) (mi + mi+1)]/Σ[(mi+mi+1)2] for I = 1 to n-1 The common standard deviation (SD) was calculated as the mean value of the individual estimates for each consecutive pair of mesh sizes, SD = {1/(n-1) Σ [(2ai (mi+1 - m I)]/[bi2 (mi+mi+1)]}½ The optimum length (corresponding to a 100% of probability of retention) for each mesh-sizes m was obtained as: Lm = (SF) x m The probability of capture (P) for a given length L in a gill net with mesh size m was determined from the following equation: P = exp [-(L-Lm)2/(2SD2)] Results In 24 fishing attempts conducted in Pertek Fishing Area of Keban Dam Lake, a total of 1134 specimens were captured and 720 of total number were the target species (C. trutta). In the operations realized, 235, 175, 122, 102 and 86 numbers of C. trutta were caught by gillnets with a mesh size of 35, 40, 45, 50 and 55 mm, respectively. Distribution of total length the fish was in the range of 24-50 cm. The use of larger mesh sizes resulted in increased mean length of captured fish. Length frequency values and natural logarithms of catch rate of C. trutta caught by the different mesh sizes are given in Table 1 and Fig. 1. Multi-monofilament Gillnet Selectivity for Capoeta trutta (Heckel, 1843)…| 20 Table 1. Length frequency values and natural logarithms of catch rate of C. trutta caught by the different mesh sizes (35, 40, 45, 50 and 55 mm) Mesh size (mm) TL (cm) Frequency (%) 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 Total Logarithmic correction 35 (a) 40 (b) 45 (c) 50 (d) 55 (e) Ln (b/a) Ln (c/b) Ln (d/c) Ln (e/d) 1 3 14 22 60 39 31 24 18 12 8 1 1 1 1 6 9 24 29 28 24 19 17 7 6 3 2 10 16 17 16 13 14 9 8 6 4 3 2 2 1 1 235 175 122 2 6 8 4 6 5 7 5 11 14 12 10 4 3 1 2 2 7 3 5 4 3 4 8 7 5 9 12 13 -2.6391 -1.2993 -1.8971 -0.4855 -0.0667 0.1542 0.2877 0.4595 0.7538 1.9459 -2.6741 -1.0296 -0.4055 -0.1112 -0.0606 0.6190 0.8473 1.0986 -1.4469 -0.9808 -0.9555 -0.6931 -0.5878 0.3185 0.8473 1.0986 1.2040 -1.2993 -1.2528 -0.4055 -0.3567 0.2231 1.0986 2.4849 1 3 2 86 102 30 35 mm n=235 25 40 mm n=175 45 mm n=122 20 50 mm n=102 15 55 mm n=86 10 5 0 24 26 28 30 32 34 36 38 40 42 44 46 48 50 Figure 1. Length frequency distribution of C. trutta(cm) caught in gillnets with 35, 40, 45, 50 and 55 mm Total legth mesh sizes. 21 | Ali Ekber ÇAT, F a h r e t t i n Y Ü K S E L A plot of fish length versus different mesh size combinations indicated a linear relation. Therefore a linear regression was fitted to the data of catch ratios (Fig. 2). The figure shows the linear relationships that were obtained for different mesh size combinations (35-40 mm combination, 40-45 mm combination, 45-50 mm combination and 50-55 mm combination). Catch rates of gillnets for each mesh size were calculated in correspondence with the length groups of the fish caught. Selectivity curves were plotted using these values (Fig. 3). It was observed that the selection range of gillnets increased gradually with increasing mesh size. 3 A 0 -1 -2 -3 20 25 30 35 Total length (cm) 2 Catch ratios (Ln) Catch ratios (Ln) y = 0.424x - 13.63 R² = 0.905 1 y = 0.463x - 16.19 R² = 0.872 0 -1 -2 30 35 Total length (cm) 3 y = 0.357x - 13.72 R² = 0.946 0 1 25 C 1 B 40 Catch ratios (Ln) Catch ratios (Ln) 2 2 -1 40 D 2 y = 0.595x - 24.95 R² = 0.908 1 0 -1 -2 -2 30 35 40 Total length (cm) 45 35 40 45 50 Total length (cm) Figure 2. Plots of logarithm of catch ratios for different mesh size combinations versus total length (A: 35-40 mm combination, B: 40-45 mm combination, C: 45-50 mm combination, D: 50-55 mm combination). Multi-monofilament Gillnet Selectivity for Capoeta trutta (Heckel, 1843)…| 22 Figure 3. Selection curves of the 35, 40, 45, 50 and 55 mm gillnets for C. trutta The calculations of the selectivity parameters were based on the nets pairs of 3540, 40-45, 45-50 and 50-55. The regression slope, intercept and coefficient for optimum lengths and selectivity parameters such as selection factors and standard deviation were assessed from length frequency distributions for each mesh size combination (Table 2). The r2 values given in the table are statistically analyzed. According to this, it is determined that there is a linear relationship between the natural logarithm of the capture rates and the lengths of the fish and this relationship is statistically significant (P<0.05). The common selectivity factor, standard deviation, and optimum selection length of fish for each mesh size of gillnets used in the study were given in Table 3. Table 2: Parameters of the regressions of log-transformed C. trutta catch ratios on length-class midpoints for various gillnet combinations (mesh sizes 35, 40, 45, 50 and 55 mm). r2 Lm1 Lm2 SF SD 0.4240 0.049 0.905 30.01 34.30 8.58 3.18 -16.199 2.50 0.4633 0.072 0.873 32.91 37.02 8.23 2.98 5.0 -13.724 1.23 0.3577 0.032 0.946 36.35 40.39 8.08 3.36 5.5 -24.956 3.56 0.5959 0.085 0.908 39.89 43.88 7.98 2.59 m1 m2 a SE(a) 3.5 4.0 -13.635 1.54 4.0 4.5 4.5 5.0 b SE(b) 23 | Ali Ekber ÇAT, F a h r e t t i n Y Ü K S E L Table 3: Common selection factor (SF), common standard deviation (SD) and estimated optimum selection lengths (Lopt) of C. trutta for gillnets of 35, 40, 45, 50 and 55 mm mesh sizes, respectively. SF SD L35 L40 L45 L50 L55 8.16 3.51 28.57 32.65 36.73 40.81 44.89 Discussion Fishing gear selectivity studies are important tools for fisheries management; by regulating the mesh size of gillnet, the approximate minimum catch sizes of the target species can be recognized (Sparre et al., 1989). Hence, selectivity of gillnets has received wide attention in various parts of the world (Özekinci et al., 2007). In present study, selectivity parameters of gillnets with different mesh sizes used C. trutta catching in Keban Dam Lake was determined. The selection ranges for mesh sizes of 35, 40, 45, 50 and 55 mm show that large mesh sizes catch a greater size range of fish. Selectivity factor is directly related with the body structure of fish as well as design properties of fishing material in selectivity of nets. While, this value is high in thin and long body shaped namely fusiform fish, this value decreases as far as the body thickens (stubby form) (Hovgard and Lassen, 2000; Altinagac et al., 2009). The selectivity estimates for C. trutta in this study showed that individual selection factors range between 7.98 and 8.58 (Table 2), a fact consistent with findings of Andreev (1962), who maintains that selection factors generally range between 5 and 10. The value of the common selection factor and common standard deviation of gillnets were determined as 8.16 and 3.51, respectively. Özekinci et al. (2003) used gillnets with mesh size of 22, 28, 36 and 44 mm for Capoeta trutta in Keban Dam Lake and calculated common selection factor and common standard deviation as 8.40 and 2.46, respectively. The finding of both studies is show similarity although mesh sizes used are different. Nevertheless, the observed selectivity factor change in body proportions due to sexual maturity, time and depth of setting nets (Dayaratne, 1988; Özekinci et al., 2007). To be not caught fish being under first reproduction length has great importance for sustainable fishery. Catching those being under the first reproduction length will make pressure on population and so will cause the population to become smaller and to Multi-monofilament Gillnet Selectivity for Capoeta trutta (Heckel, 1843)…| 24 vanish in time (Ayaz et al., 2009). Sexual maturity for C. trutta females in the Keban Dam Lake was reported as ages of III and as 29.07 cm total length (Düşükcan, 2005). Length at first maturity of female C. trutta when compared to the optimum selection lengths of gillnets with mesh sizes of 35, 40, 45, 50 and 55 mm, indicate that gillnets with mesh size of greater than or equal to 40 mm would be appropriate for catching C. trutta in the Keban Dam Lake, as the optimum selection length (32.65 cm) is greater than length at first maturity. Acknowledgements This study was summarized from Ali Ekber ÇAT’s master thesis that funded by the Scientific Research Projects Coordination Unit of Tunceli University (Project Number: YLTB011-01) References Andreev, N.N., (1962). Handbook of Fishing Gear and its Rigging. Pishchepromizdat, Moscow. 454P. (Translated from Russian by Israel Progr. Sci. Transl., 1966). Altinagac, U., Kara, A., Ozekinci, U., Ayaz, A., Ismen, A., Altin, A. and Begburs C.R., (2009). Selectivity of Fishhooks Used in Blotched Picarel (Spicara maena) in Artisanal Fishery in Dardanelles. Journal of Animal and Veterinary Advances, 8(8): 1646-1652. 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