Economic Performance Efficiency of Gillnet Based on Mesh Size and Net Color  

Fatemeh Radfar1 , Houshang Ansari2 , Mohammad Hasan Gerami3,4 , Mehdi Dastbaz1
1. Gorgan University of Agricultural and Natural Resources, Gorgan Iran
2. Iranian Fisheries Research Organization, South Iran Aquaculture Research Center, Ahvaz, Iran
3. Gonbad Kavous University, Gonbad Kavous Iran
4. Young Researchers & Elite Club, Shiraz Branch of Islamic Azad University, Shiraz, Iran
Author    Correspondence author
International Journal of Marine Science, 2015, Vol. 5, No. 7   doi: 10.5376/ijms.2015.05.0007
Received: 10 Dec., 2014    Accepted: 25 Jan., 2015    Published: 04 Feb., 2015
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This is an open access article published under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
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Radfar et al., 2015, Economic performance efficiency of gillnet based on mesh size and net color, International Journal of Marine Science, Vol.5, No.7 1-4 (doi: 10.5376/ijms.2015.05.0007)


Increasingefficiency of fishing is one of major goals of fisheries researchers. The aim of this study was to evaluate the efficiency of gillnet with three different colors of green, blue and white, and three different mesh size 3.75, 6 and 10 cm (STR) in Khuzestan waters. Data were recorded from three fishing harbor Arvand, Choobedeh of Abadan and Khoramshahr during 2008-2009. Simpson diversity and economic diversity index were used to analyze data. Results showed that economical index of green net was more than the other colors. In addition, the efficiency of 10 cm (STR) mesh size was higher than two treatments. In conclusion, results demonstrated that using green net with 10 cm (STR) mesh size is more economical.

Gillnet; Mesh size; Color; Efficiency

Optimizing and improving efficiency of fishing gears is one of the important issues that fisheries and environmental sciences emphasize to. Gillnet is a wall structure of net that lied in water column and catch the fish school. Less requirements of gillnet fishing rather than other fishing methods (like trawl and purse seine) made it as a popular method in Iran (Dastbaz, 2011). Scombridae, Clupeidae, Carcharhinidae, Carangidae and Rachycentridae are the main groups of pelagic fish that found in catch composition of gillnet (Gerami and Dastbaz, 2013). There are 740 fishing vessels and more than 1200 fishing boats using gillnet (pelagic and bottom) in Khouzestan waters.

36 species (70% total catch) of gillnet catch are bycatch (Ansari, 2013). Therefore it is necessary to improve efficiency of gillnet for reducing bycatch. Several studies about catch composition of gillnet were done in Persian Gulf (Dastbaz, 2011; Parsa et al., 2014). Efficiency of stable gillnet with 170 cm (STR) mesh size due to reduce catching Persian sturgeon (Acipenser persicus) was also investigate (Behrooz Khoshgalb, 2010). Determining standard mesh size of gillnet for Yellowfin tuna(Thunnus albacares) in Oman Sea was another investigation done by Hosseini (2003).

The aim of present survey is to evaluate the efficiency of gillnet according to mesh size and color. Net color is one of the important factor affecting gillnet catch. The more net color fading in water the more out of sight of fish, then the operation of this net is successful. Fish are myopic animal and they can see 10 m at a 20 m depth from the surface (Balık and Çubuk, 2001). This creatures have color detection ability, thus different net color can affect catch (Backiel and Welcomme, 1980). Gillnets are used in various color in and fishermen don’t have any knowledge of its great function, so the present tries to introduce basic information of gillnet with three different colors and mesh size and state best economical one.
1 Materials and Methods
Gillnets catch data were recorded from fishing vessels of three harbors Arvand, Choobedeh of Abadan and Khoramshahr (Khouzestan Province, Iran) during 2008-2009 in Khouzestan waters, Persian Gulf (Figure 1). Because of different sunlight that radiate to water during a day, we try to assimilate hanging up (remaining) and setting time of net. Thus data were classified and outlined data were removed. Simpson and economic diversity indexes were used to analyzing the efficiency of nets.

Figure 1 Studied area and fishing vessels locations

Simpson index
Simpson index is based on the number of species in sample. Using this index in fishing requires to change basis of measurement from the number to biomass (Goda and Matsuoka, 1986; Gupta, 2010). Accordingly, The Simpson index (biodiversity) represented is:

Yit is the catch of species “i” at the time of “t”, Ytis the total of catch during “t” period and “S” is the number of species caught during “t” period. In 2010, Gupta introduced a modified formula of Simpson index to exploit commercial fish that the values of each commercial fish were defined. Indeed, demand rate and fish price are the coefficient to valuing of these species. The equation is:

TR = Σ Pi Yi
In this equation Pi , is valuation coefficient of species ”i”; “TR”, is value of total species and “B” is bio-economy diversity index.
2 Results
When the economic value of total species is similar together, the economic diversity index is equal to bio-diversity index (Table 1). If the population of total catch belongs to commercial species, the economic diversity index is larger than bio-diversity index and vice versa. Analyzed colors for three experimental nets were white, blue, and green. Three mesh sizes 3.75, 6 and 10 cm (STR) were also examined. Total catch of experimental nets were 25794.15 kg during sampling period that were valued in terms of demand and market price (Table 3).analysis of diversity index showed that white net and green net had lowest and highest efficiency respectively. Mesh with 10 cm (STR) and 3.75 cm (STR) also had maximum and minimum efficiency (Table 1 and 2). Catch rate and trapped species have been shown in Figures 2 to 7.

Table 1 Sipmson and Economic diversity index in nets with different colors


Table 2 Sipmson and Economic diversity index in nets with different mesh sizes


Table 3 species caught with gillnets during sampling period (2008-2009)


Figure 2 Fish species trapped by gillnet with 3.75 cm stretched mesh size


Figure 3 Fish species trapped by gillnet with 6 cm stretched mesh size


Figure 4 Fish species trapped by gillnet with 10 cm stretched mesh size


Figure 5 Fish species trapped by green gillnet


Figure 6 Fish species trapped by blue gillnet


Figure 7 Fish species trapped by white gillnet

3 Discussion
Fish have different reaction to net against various colors (Hamley, 1975). An investigation had been done in aquarium and shown that when Cod encounter to net, swim parallel to net and tend to go to the region of net that not seen (Stewart, 1984). Narayanappa et al, (1977) reported that the highest catch of gillnets in Burla water (India) was related to white net and then yellow, gray, green and blue nets. According to Steinberg (1985) the most effect catch of Baltic cod is belonged to dark green net. In Beyúehir lake (Turkey) most of fishermen usually used green nets and dark green nets have high efficiency to catch carp pike fish and then light green (Balık and Çubuk, 2001). In this study analysis showed that green net had high economic diversity index versus Simpson index. Thus we concluded that green net has the best economic efficiency and catch the more valuable species. According to Figures 5, 6 and 7 net with green color allocate highest catch composition. The appearance of green net is less visible in aquarium rather than other colors (Wardle et al, 1991). It is important to know that depth and trophy condition of region can affect the net color efficiency; it’s because of shallow waters are usually transparent and have low production and it’s obvious that light colors are less visible in this waters. This condition is taken place for dark color in trophic and deep waters.
Mesh size is an important issue in gillnet efficiency. A specific mesh size catch specific length group more than the others (Hosseini, 2003). Determining an appropriate and efficient mesh size to catching various species in water reservoirs seems to be impossible. Gillnet has high diversity and by-catch (Gerami et al., 2014). Local fishermen believe that nets with smaller meshes have the best efficiency in catching. Result showed that economic diversity index of 10 cm (STR) mesh has the best condition in relation to Simpson diversity index versus the two other mesh size in this study. When mesh size changed from 5.1 to 15.2 cm (STR), catching valueless species is reduced and selectivity is optimized (Jester, 1977). Hosseini (2003) reported that among 4 experimental mesh sizes (237, 215, 197 and 170 mm STR), net with 237 mm (STR) mesh size has more better efficiency of catching Yellowfin tuna (Thunnus albacares) in Sistan and Balouchestan waters. In addition, Faife (2003) stated that the mean lengths of cod increased with mesh size of gillnet (6, 7, 8 and 9cm STR). Figure 4 also showed that 10 cm (STR) mesh size has the highest diversity and catch composition rather than the other meshes.
Results show that catch with green net with 10 cm (STR) mesh size in Khouzestan waters is more economic than blue, white, 3.75 and 6 cm (STR) mesh sizes nets. It’s important to note that frequency of various species in this study was ignored and catchability of fishing gears for all species was assumed equal. In addition, the process of catch such as wedging, snagging, and entangling was not considered in this study. Future researches can evaluate behavior of various species against different colors of net in experimental condition.
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