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.
Ayaz, A., Kale, S., Cengiz, O., Altinagac, U., Ozekinci, U., Oztekin, A. and Altin, A.,
(2009). Gillnet Selectivity for Bogue Boops boops Caught by Drive-in Fishing
Method from Northern Eagean Sea, Turkey. Journal of Animal and
Veterinary Advances, 8 (12): 2537-2541.
Balık, İ., (1999). Investigation of the Selectivity of Monofilament Gillnets
Used in Carp Fishing (Cyprinus carpio L. 1758) in Lake Beyşehir.
Turkish Journal Zoology, 23: 185-187.
Balık, İ. and Çubuk, İ., (2001). Selectivity of Gillnet Used for Catching Rudd
(Scardinius erytrophtalmus L. 1758) and White Bream (Blica björkna L.
25 | Ali Ekber ÇAT, F a h r e t t i n Y Ü K S E L
1758) in Lake Ulubat (Apolyont). XI. National Fisheries Symposium, Hatay,
1: 1-10.
Celayir, Y., Pala, M. and Yüksel, F., (2006). Fisheries of Keban Dam Lake. Proceedings
of the Fisheries and Reservoir Management Symposium, Feb. 7-9, Aquademi.net
Electronic Publishing, Antalya, Turkey, 259-267.
Çetinkaya, O., Sarı, M. and Arabacı, M., (1995). A Preliminary Study on Catch
Composition and Selectivity of the Trammel Net Used in Fishing of
Chalcalburnus tarichi (Pallas 1811) in Lake Van (Turkiye). Journal of Fisheries
and Aquatic Science, 12: 1-13.
Dayaratne, P., (1988). Gill-net Selectivity for Amblygaster (Sardinella) sirm. Asian
Fisheries Science, 2: 71-82.
Düşükcan, M., (2005). Reproduction Biology of Capoeta trutta (Heckel, 1843)
Populations from Keban, Karakaya and Atatürk Dam Lakes. Master thesis, Fırat
University, Institute of Science, Elazığ.
Geldiay, R. and Balık, S., (2007). Freshwater Fishes of Turkey. Ege University Faculty
of Fisheries Publications, 16, Bornova, İzmir, Turkey.
Gulland, J.A., (1983). Fish stock assessment. A manual of basic methods. FAO/Wiley
Series on Food and Agriculture, Chichester, UK Wiley Interscience, 255 p.
Hamley, J. M., (1975). Review of Gillnets Selectivity. Journal of the Fisheries
Research Board of Canada, 32: 1943-1969.
Harlıoğlu, M.M., Barım, Ö., Türkgülü, İ. and Harlıoğlu, A.G., (2004). Potential
fecundity of an introduced population, Keban Dam Lake, Elazığ, Turkey, of
freshwater
crayfish,
Astacus
leptodactylus
leptodactylus
(Esch.,
1852).
Aquaculture, 230: 189-195.
Holt, S. J., (1963). Methods of determining gear selectivity and its application. Int.
Comm. Northwest Atlantic Fish. Spec. Publ., 5: 106-115.
Hovgard, H. and Lassen, H., (2000). Manuel on Estimation of Selectivity for Gillnet
and Longline Gears in Abundance Surveys. FAO Fish. Tech. Pap., 397, 84P.
Karakulak, F.S. and Erk, H., (2008). Gill net and trammel net selectivity in the northern
Aegean Sea, Turkey, Scientia Marina, 72 (3): 527-540.
Özekinci, U., Altınağaç, U., Ayaz, A., Cengiz, Ö., Ayyıldız, H., Kaya, H. and Odabaşı,
D. (2007). Monofilament gillnet selectivity parameters for European Chub
Multi-monofilament Gillnet Selectivity for Capoeta trutta (Heckel, 1843)…| 26
(Leuciscus cephalus L. 1758) in Atikhisar Reservoir, Canakkale, Turkey.
Pakistan Journal of Biological Sciences, 10(8): 1305-1308.
Özekinci, U., Beğburs, C. B. and Tenekecioğlu, E., (2003). An investigation of gill nets
selectivity used in Capoeta capoeta umbla (Heckel, 1843) and Capoeta trutta
(Heckel, 1843) (Siraz fish) fishery in Keban Dam Lake. E.Ü. Journal of
Fisheries & Aquatic Sciences, 20, (3-4): 473-479.
Özyurt, C.E. and Avşar, D., (2005). Investigation of the selectivity parameters for carp
(Cyprinus carpio L. 1758) in Seyhan Dam Lake. Turkish Journal of Veterinary
and Animal Sciences, 29: 219-223.
Petrakis, G. and Stergiou, K.I., (1995). Gill net selectivity for Diplodus annularis and
Mullus surmuletus in Greek waters. Fisheries Research, 21, 455-464.
DOI:
10.1016/0165-7836(94)00293-6
Sparre, P., Ursin, E. and Venema, S. C., (1989). Introduction to Tropical Fish Stock
Assessment, Part I. Manuel, FAO Fish. Tech. Rome. Pap. No. 306.1, 337 p.