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Population dynamics of the green mussel Perna viridis from the high spat-fall coastal water of Malacca, Peninsular Malaysia
Fisheries Research 84 (2007) 147–152
Population dynamics of the green mussel Perna viridis from the high spat-fall coastal water of Malacca, Peninsular Malaysia S.M. Al-Barwani ∗ , A. Arshad, S.M. Nurul Amin, S.B. Japar, S.S. Siraj, C.K. Yap Biology Department, Faculty of Science, University Putra Malaysia, 43400 UPM Serdang, Selangor, Malaysia Received 30 March 2006; received in revised form 16 September 2006; accepted 1 October 2006
Abstract Population parameters such as asymptotic length (L∞ ), growth coefficient (K), mortality rates (Z, F and M), exploitation level (E) and recruitment pattern of green mussel Perna viridis were estimated using length–frequency data from the coast of Malacca, Peninsular Malaysia. Asymptotic length (L∞ ) was 102.38 mm and growth coefficient (K) was estimated at 1.50 year−1 . Total mortality (Z) for P. viridis was 2.48 year−1 , while natural mortality (M) and fishing mortality (F) were 1.69 and 0.79 year−1 , respectively. The growth performance index was (ϕ ) 4.197 and the exponent “b” of the length–weight relationship was 2.602 (±0.02) during the study period. The asymptotic wet weight estimated from length–weight relationship was 40.81 g. Exploitation level (E) of P. viridis was 0.32 while the maximum allowable limit of exploitation (Emax ) was 0.43. The recruitment pattern was continuous with one major peak in the months of July–August. The exploitation level (0.32) and lower fishing mortality (0.79 year−1 ) indicate that the green mussel is under-exploited from Malacca coastal waters. © 2006 Elsevier B.V. All rights reserved. Keywords: Population dynamics; Perna viridis; Malacca; Malaysia
1. Introduction The green mussel, Perna viridis (Siddall, 1980; Vakily, 1989) occurs widely in shallow waters along the west coast of Peninsular Malaysia (Ismail et al., 2000; Yap et al., 2002). World wide, P. viridis is known to be native to the coastal marine waters of the Indo-Pacific region, extending from the Arabian Gulf to the southern province of Guangdong and Fujian in China and southern Japan (Siddall, 1980). In the recent years, P. viridis was introduced to Australia, Caribbean, North America and South America through fouling on boat hulls or ballast-water traffic (Benson et al., 2001; Chapman et al., 2003). The culture activity of this species in Malaysia was mainly confined to southern Johor in the early 1980s (Kamal Zaman, 2000) (Fig. 1). At present, culturing of green mussels has extended from Kedah in the north to Johor in the south and east coast of Peninsular Malaysia because of transplantation of mussel seeds. The coastal community of Sebatu, Malacca is involved
∗ Corresponding author at: Sultan Qaboos University, Marine Sciences, College of Agriculture and Marine, Sultan Qaboos University, Seeb, Muscat, Oman. Tel.: +968 24415246. E-mail address: [email protected] (S.M. Al-Barwani).
0165-7836/$ – see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.fishres.2006.10.021
in fishing and bivalve culture of various species, to include consumption and sale of P. viridis. Bivalve culture is recognized as a valuable food resource in many parts of Asia (Angell, 1986; Chonchuenchob et al., 1980; McCoy and Chongpeepien, 1988; Vakily, 1989). Throughout the world, bivalve exploitation plays an important role in the national economy of many countries (Vakily, 1992). Several works have been conducted on green mussel in Malaysia (Sivalingam, 1977; Sivalingam and Bhaskaran, 1980; Choo and Speiser, 1979; Kamal Zaman, 2000; Ismail et al., 2000; Yap et al., 2002, 2003, 2004). There is however no report regarding the population dynamics and exploitation status of mollusc fishery in Malaysia. For the management of mollusc resources, knowledge of various population parameters and exploitation level (E) of that population is required. There are many tools for assessing exploitation levels and population dynamics of a stock. Of those, FAO-ICLARM Stock Assessment Tools (FiSAT) has been most frequently used for estimating population parameters of fin-fish and shell-fish (Amin et al., 2001a,b, 2002; Mancera and Mendo, 1996; Tuaycharden et al., 1988; Vakily, 1992) because it needs only length–frequency data. The advantage of this technique is that within 1 year it is possible to assess any fish stock if sufficient length–frequency data is available. The objective of the present study was to estimate the population parameters and
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To establish the length–weight relationship, the commonly used relationship W = aLb was applied (Ricker, 1975; Quinn and Deriso, 1999), where W is the weight (g), L the total length (mm), a the intercept (condition factor) and b is the slope (growth coefficient, i.e. fish relative growth rate). The parameters a and b were estimated by least squares linear regression on log–log transformed data: log10 W = log10 a + b log10 L. The coefficient of determination (r2 ) was used as an indicator of the quality of the linear regression (Scherrer, 1984). Additionally, 95% confidence limits of the parameters a and b and the statistical significance level of r2 were estimated. The inverse von Bertalanffy growth equation (Sparre and Venema, 1992) was used to find the lengths of the P. viridis at various ages. Then VBGF was fitted to estimates of length-atage curve using non-linear squares estimation procedures (Pauly et al., 1992). The VBGF is defined by the equation: Lt = L∞ [1 − e−k(t−t0 ) ] where Lt is the mean length at age t, L∞ the asymptotic length, K the growth coefficient, t the age of the P. viridis and t0 is the hypothetical age at which the length is zero (Newman, 2002). The total mortality (Z) was estimated by a length converted catch curve method (Pauly, 1984). Natural mortality rate (M) was estimated using the empirical relationship of Pauly (1980): log10 M = −0.0066 − 0.279 log10 L∞ + 0.6543 log10 K + 0.4634 log10 T Fig. 1. Sampling locations (triangle) in the coastal water of Malacca, Malaysia.
exploitation level of P. viridis to assess the stock position of the species from Malacca coastal waters. 2. Materials and methods The study was conducted at Sebatu in Malacca coastal waters (02◦ 06.002 N, 102◦ 28.004 E), straits of Malacca (Fig. 1). Random sampling was done monthly between February 2004 and December 2004. Specimens of P. viridis were kept in a freezer until ready to be analyzed. Upon being ready, the mussels were cleaned of all encrusting organisms and their byssus were removed. In the laboratory, total shell length of 1000 individuals was measured using a Vernier caliper to the nearest 0.1 mm and total weight was taken by an electronic balance of 0.001 g accuracy. The data were then grouped into shell length classes by 5 mm intervals. Subsequently the data were analyzed using the FiSAT software as explained in detail by Gayanilo et al. (1996). Asymptotic length (L∞ ) and growth coefficient (K) of the von Bertalanffy growth function (VBGF) were estimated by means of ELEFAN-1 (Pauly and David, 1981). K-scan routine was conducted to assess a reliable estimate of the K value. The estimates of L∞ and K were used to estimate the growth performance index (ϕ ) (Pauly and Munro, 1984) of P. viridis using the equation: ϕ = 2 log10 L∞ + log10 K
where M is the natural mortality, L∞ the asymptotic length, K refers to the growth coefficient of the VBGF and T is the mean annual habitat temperature (◦ C) of the water in which the stocks live. Once Z and M were obtained, then fishing mortality (F) was estimated using the relationship: F =Z−M where Z is the total mortality, F the fishing mortality and M is the natural mortality. The exploitation level (E) was obtained by the relationship of Gulland (1965): E=
F F = Z F +M
The recruitment pattern of the stock was determined by backward projection on the length axis of the set of available length–frequency data as described in FiSAT. This routine reconstructs the recruitment pulse from a time series of length–frequency data to determine the number of pulses per year and the relative strength of each pulse. Input parameters were L∞ , K and t0 (t0 = 0). Normal distribution of the recruitment pattern was determined by NORMSEP (Pauly and Caddy, 1985) in FiSAT. 3. Results 3.1. Growth parameters Asymptotic length (L∞ ) of the VBGF was 102.38 mm and the growth coefficient (K) was 1.5 year−1 for P. viridis. The
S.M. Al-Barwani et al. / Fisheries Research 84 (2007) 147–152
Fig. 2. Restructured length–frequency distribution with growth curves superimposed using ELEFAN-1 (L∞ = 102.38 cm and K = 1.50 year−1 ).
computed growth curve using these parameters is shown over the restructured length distribution in Fig. 2. The observed maximum length was 97.50 mm and the predicted maximum length was 111.00 mm (Fig. 3). The confidence interval was 90.90–131.11 mm (95% probability of occurrence). The best estimated value of K was 1.5 year−1 (Fig. 4). The growth performance index (ϕ ) was 4.197. 3.2. Length–weight relationship The length of individuals ranged from 11.02 to 98.97 mm and the weight from 0.11 to 36.42 g. The length–weight relationship curve is presented in Fig. 5. The calculated length–weight equation was log W = −3.61818 + 2.602 log L, in exponential form the equation is W = 0.00024L2.602 (r2 = 0.99; P < 0.01). The computed growth coefficient (b) was 2.602 (±0.02). The b values ranged from 2.54 to 2.87 at 95% confidence limit. 3.3. Age and growth It was assumed in the age and growth analysis that the value of the third parameter of the von Bertalanffy growth function t0 be zero (Pauly and David, 1981). Therefore, the sizes attained by P. viridis were 22.65, 40.28, 54.02, 64.72, 73.05 and 79.53 at the end of 2, 4, 6, 8, 10 and 12 months of age, respectively.
Fig. 4. Estimation K of P. viridis in the coast of Malacca.
Fig. 3. Estimation of maximum length of P. viridis.
Fig. 5. Length–weight relationship of P. viridis.
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Perna viridis
Asymptotic length (L∞ ) in mm Growth coefficient, K (year−1 ) Natural mortality, M (year−1 ) Fishing mortality, F (year−1 ) Total mortality, Z (year−1 ) Exploitation level (E) Allowable limit of exploitation (Emax ) Length range (mm) Weight range (g) Sample number (N)
102.38 1.5 1.69 0.79 2.48 0.32 0.43 11.02–98.93 0.11–36.42 1000
Fig. 6. Plot of age and growth of P. viridis based on computed growth parameters.
Fig. 8. Recruitment pattern of P. viridis.
Fig. 7. Length converted catch curve of P. viridis.
The absolute increase has been presented in Fig. 6. The calculated average growth rate of P. viridis for the first 6 months was 9.00 (±1.48) mm/month and in the following 6 months was 4.25 (±0.70) mm/month. 3.4. Mortality and exploitation Length converted catch curve analysis produce total mortality estimates value of Z = 2.48 year−1 for P. viridis (Fig. 7). Natural
mortality (M) was 1.69 year−1 and fishing mortality (F) was 0.79 year−1 for the species (Table 1). Exploitation level (E) of P. viridis was 0.32 and the maximum allowable limit of exploitation (Emax ) value was 0.43 (Table 1). 3.5. Recruitment pattern The recruitment pattern of P. viridis was continuous throughout the year and the only major peak observed was during July–August (Fig. 8). The peak pulse produced 44.55% of the observed recruitment during the study period.
Table 2 Parameters of von Bertalanffy growth function of P. viridis from different countries Location
Species
L∞ (cm)
K (year−1 )
ϕ
T (◦ C)
Source
Malaysia Malaysia Hong Kong Thailand India USA India Colombia Venezuela Korea
P. viridis P. viridis P. viridis P. viridis P. viridis C. virginica C. madrasensis C. rhizophorae C. rhizophorae C. gigas
102.38 89.4 101.9 112.0 184.6 125.8 119.0 149.0 76.0 103.7
1.5 2.14 0.30 1.00 0.25 0.50 0.77 0.90 3.96 2.35
– – – – – 3.90 4.04 4.30 4.34 4.40
29.4 – – – – 11.0 28.0 30.0 – 16.0
Present study Choo and Speiser (1979) Lee (1985) Tuaycharden et al. (1988) Narasimham (1981) Vakily (1992) Vakily (1992) Mancera and Mendo (1996) Angell (1986) Vakily (1992)
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Table 3 Previously published values of the coefficients “a” and “b” for Perna from various locations Species
Location
a
b
Length units
Source
P. viridis P. viridis P. viridis P. viridis P. viridis P. viridis P. viridis P. canaliculus
Malaysia, Malacca Hong Kong India, Goa India, Kakinada Bay Malaysia, Penang Singapore Thailand, upper Gulf New Zealand, Ahipara
0.0002 1.12E−03 5.13E−04 1.63E−04 2.22E−04 9.81E−02 7.07E−02 2.14E−04
2.602 2.37 2.50 2.88 2.76 2.79 2.78 2.80
mm mm mm mm mm cm cm mm
Present study Lee (1985) Parulekar et al. (1982) Narasimham (1981) Choo and Speiser (1979) Cheong and Chen (1980) Chonchuenchob et al. (1980) Hickman (1979)
4. Discussion The comparison with growth parameters obtained in other studies show differences in P. viridis from the different areas in the world (Table 2). The highest value of L∞ (184.60 mm) is from India waters (Narasimham, 1981) and the lowest value (89.4 mm) is in Malaysia (Choo and Speiser, 1979). The highest (2.14 year−1 ) and lowest (0.25 year−1 ) value of K is observed in India waters (Narasimham, 1981). It is observed that the present L∝ value (102.38 mm) of P. viridis from Malaysia coastal waters is very close to Thailand and Hong Kong (Table 2) but K value is not similar with other countries except for India. The growth coefficient b generally lies between 2.5 and 3.5 and the relation is said to be isometric when it is equal to 3 (Carlander, 1977). In the present case, estimated b (2.602) lies between the values mentioned by Carlander (1977) and significantly smaller then isometric value (3) at 5% level. Table 3 summarizes previously published values of the coefficients “a” and “b” for Perna. The values of “b” show considerable variation, ranging from 2.37 (Lee, 1985) to 2.86 (Narasimham, 1981). The exponent “b” of the size–weight relationship in P. viridis is generally different from 3 as shown in Table 3. This might partly be explained through the influence of ecological factors such as mussel density, shore level, etc. Such ecological differences were demonstrated by Hickman (1979) who compared wild stocks and raft-grown populations of Perna canaliculus. The overall average growth rate of P. viridis showed 6.95 (±2.01) mm/month which enable it to attain a total length of around 76.49 mm in 11 months. This indicates that culture of P. viridis could be a successful industry in the area due to its better growth rate than that is usually obtained for other bivalve species (Mendo and Jurado, 1993). Similar studies have been reported by Amin et al. (2001b), Amin and Zafar (2004) and Blaber et al. (1998) on fish species through length converted age method which also been followed in this study. Higher natural mortality (1.69 year−1 ) observed than fishing mortality (0.79 year−1 ) of P. viridis seen in the present study indicates the unbalanced position in the stock. The lower value of E (E = 0.32) indicates the ‘under-fishing’ condition of P. viridis in the study area. According to Gulland (1965), the yield is optimized when F = M; therefore, when E is more than 0.5, the stock is over-fished. The recruitment pattern suggests that annual recruitment consist of one seasonal pulse (Fig. 8), i.e. one cohort is produced
per year and the highest peak occurs in July–August. There is no published report on recruitment of P. viridis in Malaysia. However, it has been reported that the P. viridis spawn mainly during September–December from east coast of India (Rajagopal et al., 1998). In the present study, it is observed that the major spawning occurs in the months of January–February in the study area (Fig. 2). The major recruitment peak (July–August) detected in this study should correspond to the major spawning season. 5. Conclusion From the present study, it could be concluded that the stock of the green mussel shows the potential for exploitation in Sebatu coast of Malacca. More exploitation is possible and could be an option for the livelihood of the coastal communities of the area. Acknowledgements The authors would like to express their sincere gratitude to Malaysian Technical Cooperation Program (MTCP) for financial support of the study. In addition, thanks go to Mr. Khyrul Amri for the assistance during field sampling. We sincerely extend our thankful appreciation to the two anonymous reviewers of the manuscript for the valuable comments and constructive criticisms. References Amin, S.M.N., Haroon, A.K.Y., Alam, M., 2001a. A study on the population dynamics of Labeo rohita (Ham.) in the Sylhet basin, Bangladesh. Indian J. Fish. 48, 291–296. Amin, S.M.N., Rahman, M.A., Haldar, G.C., Mazid, M.A., 2001b. Studies on age and growth and exploitation level of Tenualosa ilisha in the coastal region of Chittagong, Bangladesh. J. Inland Fish. Soc. India 33, 1–5. Amin, S.M.N., Rahman, M.A., Haldar, G.C., Mazid, M.A., Milton, D., 2002. Population dynamics and stock assessment of Hilsa shad, Tenualosa ilisha in Bangladesh. Asian Fish. Sci. 15, 123–128. Amin, S.M.N., Zafar, M., 2004. Studies on age, growth and virtual population analysis of Coilia dussumieri from the neritic water of Bangladesh. J. Biol. Sci. 4, 342–344. Angell, C.L., 1986. The biology and culture of tropical oysters. ICLARM Stud. Rev. 12, 37. Benson, A.J., Marelli, D.C., Frischer, M.E., Danforth, J.M., Williams, J.D., 2001. Establishment of the green mussel, Perna viridis (Linnaeus 1758) (Mollusca: Mytilidae) on the west coast of Florida. J. Shellfish Res. 20, 21–29. Blaber, S.J.M., Staunton-Smith, J., Milton, D.A., Fry, G., Velde, T.V., Pang, J., Wong, P., Boon-Teck, O., 1998. The biology and life-history strategies
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Pauly, D., 1980. On the interrelationships between natural mortality, growth parameters and mean environmental temperature in 175 fish stocks. J. Cons. Int. Explor. Mer. 39, 175–192. Pauly, D., David, N., 1981. ELEFAN-I BASIC program for the objective extraction of growth parameters from length–frequency data. Meeresforschung 28 (4), 205–211. Pauly, D., 1984. Fish population dynamics in tropical waters: a manual for use with programmable calculators. ICLARM Contrib. 143, 325. Pauly, D., Caddy, J.F., 1985. A modification of Bhattacharya’s method for the analysis of mixtures of normal distributions. FAO Fisheries Circular, vol. 781. FAO, Rome, p. 16. Pauly, D., Munro, J.L., 1984. Once more on the comparison of growth in fish and invertebrate. Int. Cent. Living Aquat. Resour. Manage. Fish. Byte 2 (1), 21. Pauly, D., Soriano-Bartz, M., Moreau, J., Jarre, A., 1992. A new model accounting for seasonal cessation of growth in fishes. Aust. J. Mar. Freshwater Res. 43, 1151–1156. Quinn II, T., Deriso, R.B., 1999. Quantitative Fish Dynamics. Oxford University Press, New York, p. 542. Rajagopal, S., Venugopalan, V.P., Nair, K.V.K., Van Der Velde, G., Jenner, H.A., den Hartog, C., 1998. Reproduction, growth rate and culture potential of the green mussel, Perna viridis (L.) in Edaiyur backwaters, east coast of India. Aquaculture 162, 187–202. Ricker, W.E., 1975. Computation and interpretation of biological statistics of fish populations. Bull. Fish. Res. Board Can. 191, 382. Scherrer, B., 1984. Biostatistique. Morin, Montreal, Paris. Siddall, S.E., 1980. A clarification of the genus Perna (Mytilidae). Bull. Mar. Sci. 30 (4), 858–870. Sivalingam, P.M., 1977. Aquaculture of the green mussel, Mytilus viridis Linnaeus, in Malaysia. Aquculture 11, 297–312. Sivalingam, P.M., Bhaskaran, B., 1980. Experimental insight of trace metal environmental pollution problems in mussel farming. Aquaculture 20, 291–303. Sparre, P., Venema, S.C., 1992. Introduction to Tropical Fish Stock Assessment, Part 1—Manual. FAO Fisheries Technical Paper 306/1, p. 376. Tuaycharden, S., Vakily, J.M., Saelow, A., McCoy, E.W., 1988. Growth and maturation of the green mussel (Perna viridis) in Thailand. In: McCoy, E.W., Chongpeepien, T. (Eds.), Bivalve Mollusc Culture Research in Thailand, pp. 88–101. Vakily, J.M., 1989. The biology and culture of mussels of the genus Perna. ICLARM Stud. Rev. 17, 63. Vakily, J.M., 1992. Determination and comparison of bivalve growth, with emphasis on Thailand and other tropical areas. In: ICLARM Technical Report 36, p. 125. Yap, C.K., Ismail, A., Tan, S.G., Omar, H., 2002. Correlations between speciation of Cd, Cu, Pb and Zn in sediment and their concentrations in total soft tissue of green-lipped mussel Perna viridis from the west coast of Peninsular Malaysia. Env. Int. 28 (1–2), 117–126. Yap, C.K., Ismail, A., Tan, S.G., Rahim, I.A., 2003. Can the shell of the greenlipped mussel Perna viridis from the west coast of Peninsular Malaysia be a potential biomonitoring material for Cd, Pb and Zn? Estuar. Coast. Shelf Sci. 57 (4), 623–630. Yap, C.K., Ismail, A., Tan, S.G., 2004. Heavy metal (Cd, Cu, Pb and Zn) concentrations in the green-lipped mussel Perna viridis (Linnaeus) collected from some wild and aquacultural sites in the west coast of Peninsular Malaysia. Food Chem. 84, 569–575.
Population dynamics of the green mussel Perna viridis from the high spat-fall coastal water of Malacca, Peninsular Malaysia S.M. Al-Barwani ∗ , A. Arshad, S.M. Nurul Amin, S.B. Japar, S.S. Siraj, C.K. Yap Biology Department, Faculty of Science, University Putra Malaysia, 43400 UPM Serdang, Selangor, Malaysia Received 30 March 2006; received in revised form 16 September 2006; accepted 1 October 2006
Abstract Population parameters such as asymptotic length (L∞ ), growth coefficient (K), mortality rates (Z, F and M), exploitation level (E) and recruitment pattern of green mussel Perna viridis were estimated using length–frequency data from the coast of Malacca, Peninsular Malaysia. Asymptotic length (L∞ ) was 102.38 mm and growth coefficient (K) was estimated at 1.50 year−1 . Total mortality (Z) for P. viridis was 2.48 year−1 , while natural mortality (M) and fishing mortality (F) were 1.69 and 0.79 year−1 , respectively. The growth performance index was (ϕ ) 4.197 and the exponent “b” of the length–weight relationship was 2.602 (±0.02) during the study period. The asymptotic wet weight estimated from length–weight relationship was 40.81 g. Exploitation level (E) of P. viridis was 0.32 while the maximum allowable limit of exploitation (Emax ) was 0.43. The recruitment pattern was continuous with one major peak in the months of July–August. The exploitation level (0.32) and lower fishing mortality (0.79 year−1 ) indicate that the green mussel is under-exploited from Malacca coastal waters. © 2006 Elsevier B.V. All rights reserved. Keywords: Population dynamics; Perna viridis; Malacca; Malaysia
1. Introduction The green mussel, Perna viridis (Siddall, 1980; Vakily, 1989) occurs widely in shallow waters along the west coast of Peninsular Malaysia (Ismail et al., 2000; Yap et al., 2002). World wide, P. viridis is known to be native to the coastal marine waters of the Indo-Pacific region, extending from the Arabian Gulf to the southern province of Guangdong and Fujian in China and southern Japan (Siddall, 1980). In the recent years, P. viridis was introduced to Australia, Caribbean, North America and South America through fouling on boat hulls or ballast-water traffic (Benson et al., 2001; Chapman et al., 2003). The culture activity of this species in Malaysia was mainly confined to southern Johor in the early 1980s (Kamal Zaman, 2000) (Fig. 1). At present, culturing of green mussels has extended from Kedah in the north to Johor in the south and east coast of Peninsular Malaysia because of transplantation of mussel seeds. The coastal community of Sebatu, Malacca is involved
∗ Corresponding author at: Sultan Qaboos University, Marine Sciences, College of Agriculture and Marine, Sultan Qaboos University, Seeb, Muscat, Oman. Tel.: +968 24415246. E-mail address: [email protected] (S.M. Al-Barwani).
0165-7836/$ – see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.fishres.2006.10.021
in fishing and bivalve culture of various species, to include consumption and sale of P. viridis. Bivalve culture is recognized as a valuable food resource in many parts of Asia (Angell, 1986; Chonchuenchob et al., 1980; McCoy and Chongpeepien, 1988; Vakily, 1989). Throughout the world, bivalve exploitation plays an important role in the national economy of many countries (Vakily, 1992). Several works have been conducted on green mussel in Malaysia (Sivalingam, 1977; Sivalingam and Bhaskaran, 1980; Choo and Speiser, 1979; Kamal Zaman, 2000; Ismail et al., 2000; Yap et al., 2002, 2003, 2004). There is however no report regarding the population dynamics and exploitation status of mollusc fishery in Malaysia. For the management of mollusc resources, knowledge of various population parameters and exploitation level (E) of that population is required. There are many tools for assessing exploitation levels and population dynamics of a stock. Of those, FAO-ICLARM Stock Assessment Tools (FiSAT) has been most frequently used for estimating population parameters of fin-fish and shell-fish (Amin et al., 2001a,b, 2002; Mancera and Mendo, 1996; Tuaycharden et al., 1988; Vakily, 1992) because it needs only length–frequency data. The advantage of this technique is that within 1 year it is possible to assess any fish stock if sufficient length–frequency data is available. The objective of the present study was to estimate the population parameters and
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To establish the length–weight relationship, the commonly used relationship W = aLb was applied (Ricker, 1975; Quinn and Deriso, 1999), where W is the weight (g), L the total length (mm), a the intercept (condition factor) and b is the slope (growth coefficient, i.e. fish relative growth rate). The parameters a and b were estimated by least squares linear regression on log–log transformed data: log10 W = log10 a + b log10 L. The coefficient of determination (r2 ) was used as an indicator of the quality of the linear regression (Scherrer, 1984). Additionally, 95% confidence limits of the parameters a and b and the statistical significance level of r2 were estimated. The inverse von Bertalanffy growth equation (Sparre and Venema, 1992) was used to find the lengths of the P. viridis at various ages. Then VBGF was fitted to estimates of length-atage curve using non-linear squares estimation procedures (Pauly et al., 1992). The VBGF is defined by the equation: Lt = L∞ [1 − e−k(t−t0 ) ] where Lt is the mean length at age t, L∞ the asymptotic length, K the growth coefficient, t the age of the P. viridis and t0 is the hypothetical age at which the length is zero (Newman, 2002). The total mortality (Z) was estimated by a length converted catch curve method (Pauly, 1984). Natural mortality rate (M) was estimated using the empirical relationship of Pauly (1980): log10 M = −0.0066 − 0.279 log10 L∞ + 0.6543 log10 K + 0.4634 log10 T Fig. 1. Sampling locations (triangle) in the coastal water of Malacca, Malaysia.
exploitation level of P. viridis to assess the stock position of the species from Malacca coastal waters. 2. Materials and methods The study was conducted at Sebatu in Malacca coastal waters (02◦ 06.002 N, 102◦ 28.004 E), straits of Malacca (Fig. 1). Random sampling was done monthly between February 2004 and December 2004. Specimens of P. viridis were kept in a freezer until ready to be analyzed. Upon being ready, the mussels were cleaned of all encrusting organisms and their byssus were removed. In the laboratory, total shell length of 1000 individuals was measured using a Vernier caliper to the nearest 0.1 mm and total weight was taken by an electronic balance of 0.001 g accuracy. The data were then grouped into shell length classes by 5 mm intervals. Subsequently the data were analyzed using the FiSAT software as explained in detail by Gayanilo et al. (1996). Asymptotic length (L∞ ) and growth coefficient (K) of the von Bertalanffy growth function (VBGF) were estimated by means of ELEFAN-1 (Pauly and David, 1981). K-scan routine was conducted to assess a reliable estimate of the K value. The estimates of L∞ and K were used to estimate the growth performance index (ϕ ) (Pauly and Munro, 1984) of P. viridis using the equation: ϕ = 2 log10 L∞ + log10 K
where M is the natural mortality, L∞ the asymptotic length, K refers to the growth coefficient of the VBGF and T is the mean annual habitat temperature (◦ C) of the water in which the stocks live. Once Z and M were obtained, then fishing mortality (F) was estimated using the relationship: F =Z−M where Z is the total mortality, F the fishing mortality and M is the natural mortality. The exploitation level (E) was obtained by the relationship of Gulland (1965): E=
F F = Z F +M
The recruitment pattern of the stock was determined by backward projection on the length axis of the set of available length–frequency data as described in FiSAT. This routine reconstructs the recruitment pulse from a time series of length–frequency data to determine the number of pulses per year and the relative strength of each pulse. Input parameters were L∞ , K and t0 (t0 = 0). Normal distribution of the recruitment pattern was determined by NORMSEP (Pauly and Caddy, 1985) in FiSAT. 3. Results 3.1. Growth parameters Asymptotic length (L∞ ) of the VBGF was 102.38 mm and the growth coefficient (K) was 1.5 year−1 for P. viridis. The
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Fig. 2. Restructured length–frequency distribution with growth curves superimposed using ELEFAN-1 (L∞ = 102.38 cm and K = 1.50 year−1 ).
computed growth curve using these parameters is shown over the restructured length distribution in Fig. 2. The observed maximum length was 97.50 mm and the predicted maximum length was 111.00 mm (Fig. 3). The confidence interval was 90.90–131.11 mm (95% probability of occurrence). The best estimated value of K was 1.5 year−1 (Fig. 4). The growth performance index (ϕ ) was 4.197. 3.2. Length–weight relationship The length of individuals ranged from 11.02 to 98.97 mm and the weight from 0.11 to 36.42 g. The length–weight relationship curve is presented in Fig. 5. The calculated length–weight equation was log W = −3.61818 + 2.602 log L, in exponential form the equation is W = 0.00024L2.602 (r2 = 0.99; P < 0.01). The computed growth coefficient (b) was 2.602 (±0.02). The b values ranged from 2.54 to 2.87 at 95% confidence limit. 3.3. Age and growth It was assumed in the age and growth analysis that the value of the third parameter of the von Bertalanffy growth function t0 be zero (Pauly and David, 1981). Therefore, the sizes attained by P. viridis were 22.65, 40.28, 54.02, 64.72, 73.05 and 79.53 at the end of 2, 4, 6, 8, 10 and 12 months of age, respectively.
Fig. 4. Estimation K of P. viridis in the coast of Malacca.
Fig. 3. Estimation of maximum length of P. viridis.
Fig. 5. Length–weight relationship of P. viridis.
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Perna viridis
Asymptotic length (L∞ ) in mm Growth coefficient, K (year−1 ) Natural mortality, M (year−1 ) Fishing mortality, F (year−1 ) Total mortality, Z (year−1 ) Exploitation level (E) Allowable limit of exploitation (Emax ) Length range (mm) Weight range (g) Sample number (N)
102.38 1.5 1.69 0.79 2.48 0.32 0.43 11.02–98.93 0.11–36.42 1000
Fig. 6. Plot of age and growth of P. viridis based on computed growth parameters.
Fig. 8. Recruitment pattern of P. viridis.
Fig. 7. Length converted catch curve of P. viridis.
The absolute increase has been presented in Fig. 6. The calculated average growth rate of P. viridis for the first 6 months was 9.00 (±1.48) mm/month and in the following 6 months was 4.25 (±0.70) mm/month. 3.4. Mortality and exploitation Length converted catch curve analysis produce total mortality estimates value of Z = 2.48 year−1 for P. viridis (Fig. 7). Natural
mortality (M) was 1.69 year−1 and fishing mortality (F) was 0.79 year−1 for the species (Table 1). Exploitation level (E) of P. viridis was 0.32 and the maximum allowable limit of exploitation (Emax ) value was 0.43 (Table 1). 3.5. Recruitment pattern The recruitment pattern of P. viridis was continuous throughout the year and the only major peak observed was during July–August (Fig. 8). The peak pulse produced 44.55% of the observed recruitment during the study period.
Table 2 Parameters of von Bertalanffy growth function of P. viridis from different countries Location
Species
L∞ (cm)
K (year−1 )
ϕ
T (◦ C)
Source
Malaysia Malaysia Hong Kong Thailand India USA India Colombia Venezuela Korea
P. viridis P. viridis P. viridis P. viridis P. viridis C. virginica C. madrasensis C. rhizophorae C. rhizophorae C. gigas
102.38 89.4 101.9 112.0 184.6 125.8 119.0 149.0 76.0 103.7
1.5 2.14 0.30 1.00 0.25 0.50 0.77 0.90 3.96 2.35
– – – – – 3.90 4.04 4.30 4.34 4.40
29.4 – – – – 11.0 28.0 30.0 – 16.0
Present study Choo and Speiser (1979) Lee (1985) Tuaycharden et al. (1988) Narasimham (1981) Vakily (1992) Vakily (1992) Mancera and Mendo (1996) Angell (1986) Vakily (1992)
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Table 3 Previously published values of the coefficients “a” and “b” for Perna from various locations Species
Location
a
b
Length units
Source
P. viridis P. viridis P. viridis P. viridis P. viridis P. viridis P. viridis P. canaliculus
Malaysia, Malacca Hong Kong India, Goa India, Kakinada Bay Malaysia, Penang Singapore Thailand, upper Gulf New Zealand, Ahipara
0.0002 1.12E−03 5.13E−04 1.63E−04 2.22E−04 9.81E−02 7.07E−02 2.14E−04
2.602 2.37 2.50 2.88 2.76 2.79 2.78 2.80
mm mm mm mm mm cm cm mm
Present study Lee (1985) Parulekar et al. (1982) Narasimham (1981) Choo and Speiser (1979) Cheong and Chen (1980) Chonchuenchob et al. (1980) Hickman (1979)
4. Discussion The comparison with growth parameters obtained in other studies show differences in P. viridis from the different areas in the world (Table 2). The highest value of L∞ (184.60 mm) is from India waters (Narasimham, 1981) and the lowest value (89.4 mm) is in Malaysia (Choo and Speiser, 1979). The highest (2.14 year−1 ) and lowest (0.25 year−1 ) value of K is observed in India waters (Narasimham, 1981). It is observed that the present L∝ value (102.38 mm) of P. viridis from Malaysia coastal waters is very close to Thailand and Hong Kong (Table 2) but K value is not similar with other countries except for India. The growth coefficient b generally lies between 2.5 and 3.5 and the relation is said to be isometric when it is equal to 3 (Carlander, 1977). In the present case, estimated b (2.602) lies between the values mentioned by Carlander (1977) and significantly smaller then isometric value (3) at 5% level. Table 3 summarizes previously published values of the coefficients “a” and “b” for Perna. The values of “b” show considerable variation, ranging from 2.37 (Lee, 1985) to 2.86 (Narasimham, 1981). The exponent “b” of the size–weight relationship in P. viridis is generally different from 3 as shown in Table 3. This might partly be explained through the influence of ecological factors such as mussel density, shore level, etc. Such ecological differences were demonstrated by Hickman (1979) who compared wild stocks and raft-grown populations of Perna canaliculus. The overall average growth rate of P. viridis showed 6.95 (±2.01) mm/month which enable it to attain a total length of around 76.49 mm in 11 months. This indicates that culture of P. viridis could be a successful industry in the area due to its better growth rate than that is usually obtained for other bivalve species (Mendo and Jurado, 1993). Similar studies have been reported by Amin et al. (2001b), Amin and Zafar (2004) and Blaber et al. (1998) on fish species through length converted age method which also been followed in this study. Higher natural mortality (1.69 year−1 ) observed than fishing mortality (0.79 year−1 ) of P. viridis seen in the present study indicates the unbalanced position in the stock. The lower value of E (E = 0.32) indicates the ‘under-fishing’ condition of P. viridis in the study area. According to Gulland (1965), the yield is optimized when F = M; therefore, when E is more than 0.5, the stock is over-fished. The recruitment pattern suggests that annual recruitment consist of one seasonal pulse (Fig. 8), i.e. one cohort is produced
per year and the highest peak occurs in July–August. There is no published report on recruitment of P. viridis in Malaysia. However, it has been reported that the P. viridis spawn mainly during September–December from east coast of India (Rajagopal et al., 1998). In the present study, it is observed that the major spawning occurs in the months of January–February in the study area (Fig. 2). The major recruitment peak (July–August) detected in this study should correspond to the major spawning season. 5. Conclusion From the present study, it could be concluded that the stock of the green mussel shows the potential for exploitation in Sebatu coast of Malacca. More exploitation is possible and could be an option for the livelihood of the coastal communities of the area. Acknowledgements The authors would like to express their sincere gratitude to Malaysian Technical Cooperation Program (MTCP) for financial support of the study. In addition, thanks go to Mr. Khyrul Amri for the assistance during field sampling. We sincerely extend our thankful appreciation to the two anonymous reviewers of the manuscript for the valuable comments and constructive criticisms. References Amin, S.M.N., Haroon, A.K.Y., Alam, M., 2001a. A study on the population dynamics of Labeo rohita (Ham.) in the Sylhet basin, Bangladesh. Indian J. Fish. 48, 291–296. Amin, S.M.N., Rahman, M.A., Haldar, G.C., Mazid, M.A., 2001b. Studies on age and growth and exploitation level of Tenualosa ilisha in the coastal region of Chittagong, Bangladesh. J. Inland Fish. Soc. India 33, 1–5. Amin, S.M.N., Rahman, M.A., Haldar, G.C., Mazid, M.A., Milton, D., 2002. Population dynamics and stock assessment of Hilsa shad, Tenualosa ilisha in Bangladesh. Asian Fish. Sci. 15, 123–128. Amin, S.M.N., Zafar, M., 2004. Studies on age, growth and virtual population analysis of Coilia dussumieri from the neritic water of Bangladesh. J. Biol. Sci. 4, 342–344. Angell, C.L., 1986. The biology and culture of tropical oysters. ICLARM Stud. Rev. 12, 37. Benson, A.J., Marelli, D.C., Frischer, M.E., Danforth, J.M., Williams, J.D., 2001. Establishment of the green mussel, Perna viridis (Linnaeus 1758) (Mollusca: Mytilidae) on the west coast of Florida. J. Shellfish Res. 20, 21–29. Blaber, S.J.M., Staunton-Smith, J., Milton, D.A., Fry, G., Velde, T.V., Pang, J., Wong, P., Boon-Teck, O., 1998. The biology and life-history strategies
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