Abstract: The kingfish, Scomberomorus commerson is an epipelagic and migratory species found across the coastal waters of tropical region. It is a commercially important species in the North of Persian Gulf. The population parameters of species are important in fishery management. So, this study investigated some population characteristics of S. commerson, in the northern coasts of the Persian Gulf (Bushehr waters). Fish were selected at random from three namely landing stations during April 2010 to March 2011. The Length-Weight Relationship (LWR) was estimated by using the equation W = aLb and the FiSAT software was used to analyse the growth parameters. Length-weight relationship indicated isometric growth with b = 2.93. The growth parameters of the Von Bertalanffy equation were estimated as: L∞ =143.85 cm, K = 0.31, t0 = -0.63 years with a growth performance index (ø') of 3.81. These findings can be used as biological input parameters in further stock evaluations in this region.
INTRODUCTION
The kingfish, Scomberomorus commerson is an epipelagic and migratory species found across the coastal waters of tropical regions. It is distributed in the Indo-Pacific area, from the Red Sea and South Africa to Southeast Asia, North to China, Japan and South to Australia (Randall, 1995). This species occurs from the edge of the continental shelf to coastal waters where it is found along drop-offs, gently sloping reefs and lagoon waters from depths of 10-70 m (McPherson, 1985; Myers, 1991). Scomberomorus commerson is a commercially important species which is caught with a variety of gears including nets, bamboo stake traps, mid-water trawls and longlines in coastal waters around its distribution (Collette, 2001). In the North of Persian Gulf it is mainly caught using gillnets, hook and long lines. Juveniles and young fish occur in small schools, While adults may be individually (Collette, 2001). The diet mainly includes variety of small fishes such as clupeids, anchovies (Blaber et al., 1990) and carangids, though squids and penaeid shrimps are also consumed. For the management of fish resources, knowledge of various population parameters is an essential prerequisite. In this context, the objective of this study was to estimate length-weight relationships and growth parameters of S. commerson from Northern coasts of the Persian Gulf for fishery management.
MATERIALS AND METHODS
Size frequency data was collected monthly during April 2010 to March 2011 from the Northern coast of Persian Gulf. Fish were selected at random from three namely landing stations (Deylam, Bushehr and Dayyer) in the Bushehr Province (Fig. 1).
| Fig. 1: | Map of Persian Gulf, showing the location of the three regions where Scomberomorus commerson were sampled |
Fork Length (FL) was measured in centimeters for all fish by using a measurement board. The Length-Weight Relationship (LWR) was estimated by using the equation W = aLb, where a is the intercept of the regression and b is the regression coefficient (Pauly, 1984). Additionally, in order to verify if the b value was significantly different from the isometric (b = 3), the Student’s t-test with a confidence level of ±95% (α = 0.05) was employed.
The FAO-ICLARM Stock Assessment Tools, FiSAT software (Gayanilo and Pauly, 1997) was used to analyze the monthly length-frequency data. The ELEFAN procedure in FISAT was employed to estimate L∞ and K of the Von Bertalanffy equation: Lt = L∞{1-exp[-K(t-t0)]}, where L∞ is the asymptotic length that an average fish would achieve if it continued to live and grow, K is the growth coefficient which determines how fast the fish approaches L∞ and t0 is the hypothetical age for Lt = 0.
t0 was estimated by using Pauly’s empirical equation (Pauly, 1979):
log (-t0) = -0.3922-0.275 log L∞-1.038 K
The estimated growth parameters were compared with other studies using the growth performance index, Φ'{Formatting Citation} {Formatting Citation} (Munro and Pauly, 1983):
Φ' = ln K+2 ln L∞
RESULTS
The total length of 3982 fish ranged from 20-139 cm (Fig. 2). The length-weight data for 250 specimens showed a relationship of W = 0.016 F.L2.93 with a regression coefficient R2 = 0.969 (Fig. 3). The growth parameters were as follow: L∞ = 143.85 cm, K = 0.31, t0 = -0.63. The yearly growth curve is shown in Fig. 4. These results gave a growth performance index (Φ') of 3.81.
| Fig. 2: | Length frequency distribution of Scomberomorus commerson in the Persian Gulf, Bushehr waters (2010-2011) |
| Fig. 3: | Length-weight relationship of Scomberomorus commerson collected in Persian Gulf, Bushehr waters (2010-2011) |
| Fig. 4: | Growth curve of Scomberomorus commerson collected in Persian Gulf, Bushehr waters (2010-2011) |
DISCUSSION
In this study the "b" parameter value, has not shown any significant difference with 3 and it is close to 3 for the S. commerson in Area 51, indicating isometric growth (King, 2007) (Table 1). Differences in growth patterns can be the result of fluctuations in environmental parameters, physiological conditions of the fish at the time of collection and sex of fish (Biswas, 1993).
| Table 1: | Regression coefficients of length-weight relationship for Scomberomorus commerson from different areas |
| Table 2: | Comparison of the estimates of growth parameters for Scomberomorus commerson from different areas |
| *Fork length | |
Because of the difficulty in determining age of fish in tropical and subtropical waters, the length-based stock assessment methodologies, have been developed (Pauly, 1984; Pauly and Morgan, 1987). Many researchers (Ahmed et al., 2008; EL-Ganainy and Sabra, 2008) have successfully studied population parameters of fish species using length-frequency data. So, in the present study the length frequency was used to estimate growth parameters of Scomberomorus commerson. The value of L∞ and K obtained were 143.85 cm FL and 0.31 years–1, respectively. The estimates of growth parameters reported by different researchers from the Persian Gulf and other areas have a variety of ranges (Table 2). It may be due to the differences in genetic structure and/or differences in temperature, density of food and diseases (Pauly, 1994; Wootton, 1990) and other factors (e.g., area, season, number of observed individuals, sampling techniques or analytical methods) (Le Cren, 1951). The growth performance index value (3.81) obtained in this study was similar to the values of other studies (3.61-4.22) (Table 2). This indicates that the estimation of growth parameters for S. commerson using the length-frequency method in this study was reliable.