Jul 3, 2000 - Abstract.- This study gives age composition, growth and mortality of the mullet, Liza carinata collected from the shallow waters of the tidal creek ...
Pakistan J. Zool., vol. 33(1), pp. 1-5, 2001.
Age, Growth and Mortality of the Mullet, Liza carinata (Pisces: Mugilidae) in the Backwaters of Bhanbhore, Sindh (Pakistan: Northern Arabian Sea) GHULAM ABBAS Centre of Excellence in Marine Biology, University of Karachi, Karachi-75270, Pakistan Abstract.- This study gives age composition, growth and mortality of the mullet, Liza carinata collected from the shallow waters of the tidal creek of Bhanbhore, located 72 km southwest of Karachi during monthly sampling conducted from JUly, 1998 to June, 1999. Total length of the specimens ranged from III to 205 mm and the weight from 21 to GO g. The length-weight relationship indicated positive allometric growth (b=3.123). Based on daily scale growth increment formation, it was observed that fish aged from 129 to 330 days. Thus the lifespan of L. carinata in the study area seems to be 1 year. Growth in length was expressed for the whole sample with von BertalanfTy's equation. The theoretical maximum length was Loo = 172.5 mm. The growth coefficient was K = 0.22. Total and natural mortality were found to Z = 1.14/month and M = 0.30/month. The exploitation ratio (E = 0.737) suggests that the fishing pressure on L. carinata was high in the region investigated, Key words: Age, growth, mortality, scale, backwaters of Bhanbhore, Sindh cost, Liza carinata.
INTRODUCTION Mullet, Liza carinata of the family Mugilidae is a pelagic species which usually lives in inshore waters associated with mangrove swamps (Macintohs, 1982; Kraljevic and Dulcie, 1996). Locally, this species is known as boi and is the target of a commercial fishery along the Arabian Sea coast of Pakistan. It forms a significant component of the coastal catches (Anonymous, 1992). Published information on its biology and ecology in its natural environment is limited. Qureshi (1987) was the first worker who made a fairly detailed study of the maturation and fecundity of some common grey mullets from Karachi coast. Subsequently, Khatoon and Hussain (1997) determined the spawning seasons of Liza carinata and L. subviridis on the basis of the abundance of their eggs with description of early developmental stages. Abbas (2000) recently presented view of the annual recruitment of L. carinata and Coilia dussumieria in the backwaters of Bhanbhore. Prior to that, Ahmed and Abbas (1999) while studying the abundance of finfish and shellfish juveniles in the same area, found that L. subviridis and L. carinata exhibited fair abundance. The present study seeks to examine the age, growth and mortality of the mullet Liza carinata from the backwaters of Bhanbhore along Sindh coast, based on the examination of daily scale growth increments. 0030-9923/200I/000I-0001 $ 04.00/0 Copyright 2(101 Zoological Society of Pakistan.
MATERIALS AND METHODS Mullet, Liza carinata were collected from the backwaters of Bhanbhore (240 45'N and 66° 55'E) along Sindh coast, Karachi. In these backwaters three stations (1, 2, 3) located 100 m apart were selected for sampling, which was conducted by a gillnet (length 19 m; width 3 m and mesh size 33 mrn) from July, 1998 to June 1999. At each of these sampling stations the gill-net was operated once a month by the boat for 40-60 min. All the fishes obtained from the stations were weighed separately to represent three samples per month and thus 36 samples were collected in all during the experiments. Total length of the fishes were measured to the nearest mm, from the tip of the snout to the tip of the caudal fin. Fishes were identified with the help of FAO identification sheets (Fischer and Bianchi, 1984). The maturity stages were identified (Griffiths, 1996). Age determination was done by reading scale rings under a stereomicroscope at 400-fold magnification. Scale samples (10 to 15 scales) were removed from the base of the pectoral fin and from the flanks below the first dorsal fin. They were cleaned in 5% sodium peroxide. To establish a length-weight relationship all individuals (N = 500) were measured for total length to the nearest 1.0 mm and weighed to the nearest 0.1 g. The commonly used length-weight relationship W = aLb was applied (Ricker, 1975), where W is the weight, L is the total length, and a and b are constants. The condition factor was calculated by the usual formula
G.ABBAS
2
K = 100 W/L3, where K is condition factor, W is body weight and L is the total length of the fish, suggested by Hile (1936). The programme Statgraphics version 3.0 was used to estimate the growth parameters Lom K and to in the von Bertalanffy equation: L, = Loo(l-e·K ({.to,). Where, L, is length at time t, Loo is asymptotic maximum length, K is a growth constant and to is an initial time. The instances mortality rates (Z) were calculated through least-square regression of the natural log of the number in an age group on age (Sparre and Venema, 1989). Natural mortality (M) was estimated using estimates of Loo, K and annual mean water temperature (29.50 C; Deggobis, 1988) based on the empirical equation of Pauly (1983). From Z and M estimates, fishing mortality was computed as F = Z-M. The exploitation ratio was calculated by the equation E = F/Z.
RESULTS AND DISCUSSION The length frequency distribution of the mullet Liza carinata during the study is shown in Figure 1. The total length of individuals ranged from 111 to 205 mm and the weight from 21 to 60 g. Age, for the above named mullet species, was from 129 to 330 days (Table I). These observations are in conformity with those of Andaloro (1983) and Arruda et al. (1991). Having gone through this couple of studies, it may be possible to speak that L. carinata, in this study, is considered to have one year lifespan. Such conclusions are based on the spawning activity of the mullet (Abbas, 2000). According to him, L. carinata spawns earlier in the month of January and extends to March. Khatoon and Hussain (1997) mentioneed that L. carinata spawned from February to March and again from June to September. Qureshi (1987) while studying the spawning of L. carinata and Valamugii cunnesius from offshore waters, it was suggested a prolong spawning period with two peaks during March and December. These observations were advocated by Luther (1973) and Chan (1977) who observed that mullets breed year-round in mangrove estuaries along the coasts of Peninsular Malaysia and India. In the present study, the females out numbered the males by a big margin of 73 to 27% (X2 = 47.52; P>0,05). Percentage of the maturity in both males and females being 86-100 during December, January and February, is suggestive of the spawning time of L. carinata. This
general abundance of the species was related to somewhat low salinities (34 to 35°100) and good concentration of oxygen (4 to 5 ml/Iitre) in January, February, April and May. Specimens measuring 120140 mm were less abundant and their peak occurred in September 1993. Few specimens measuring 100120 mm were found in August 1991 and November 1992, followed by 17.24% in March 1992 (n=85). Table
1.-
Minimum,
maximum
Liza carinata caught Bhanbhore, June 1999.
Length intervals (rnrn)
during
and mean age (days) of from the backwaters of the period, July 1988 to
Age (days) Number
Mini.
Maxi.
Mean±SD
241±6.72
110-129.9
86
129
271
130-149.9
324
137
295
255±9.11
150-169.9
61
158
321
283±6.79
170-189.9
19
149
330
298±7.00
190-209.9
10
171
285
251±9.50
Total
500
The parameters of van Bertalanfy's equation were estimated as: Loo = 172.5 mm (± SE = 1.37), K = 0.22 (± SE = 0.071) and to = 0.655 (± SE = 0.462) (r2 = 0.997), yieldingL, = 172.5 (l_e·J22,tt0655) (Fig. 2). The asymptotic length and intrinsic growth values strongly correlated (r2 = 0.99) may contribute to a better understanding of good growth for the mullet in Bhanbhore backwaters, when this area was rich in food availability. The calculated lengthweight regression in combined sexes was W = 1.813. V123 (R2 = 0.988). Weight increased allometrically with size since the value of the slope b (SD = 0.772; SE = 0.049) had a significant (P < 0.05) difference from the value 3.0 (an ideal slope) (Fig. 3). The value of b from the present study corresponds with the one estimated by Kraljevic and Dulcie (1996) for Liza aurata (b = 3.161, R2 = 0.99) and Tursi et al. (1996) for Mullus barbatus (b = 3.2, R2 = 0.99). Little variation in the exponents at different stages of the growth of fishes reported by these authors could also be attributed to different stages in ontogenetic development, as well as to differences in age, maturity and sex. Geographic location and associated environmental conditions, such as
AGE, GRo\\,'TH AND MORTALITY OF LlZA CARINATA
100
15July1998 N = 17
17 August 1998 N = 13
3
21 September N = 10
1998
80 Fomal._ Malo
Fomalo_ Malo
0
60
Fomalo_ Malo
0
0
40 20 0 100
19 October N=7
1998
16 November 1998 N = 42
22 December 1998 N = 63
80 Fomalo_ Male
60
~ 0 C Q)
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20 0
Q)
100
0-
16 January 1999 N = 29
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Length interval (mm) Fig. 1. Size-frequency distribution Bhanbhore during the study period.
of the mullet Liza carinata caught by gill-net from the backwaters of
G.ABBAS
seasonality (date and time of capture), stomach fullness, disease and parasite loads (Le Cren, 1951; Bagenal and Tesch, 1978), can also affect the value of b. The condition factor (K) varied from 0.20 to 1.31 with a mean of 0.881 in the males and from 0.252 to 1.150 with a mean of 0.613 in the females of L. carinata. High K values for males and females of L. carinata, hint at their well-being and gonadal maturation during February and May. Evidence to support this is available in another study of the spawning of mullet (Abbas, 2000). He mentioned that L. carinata spawns earlier in the month of January and extends to March.
210
E
190
E ~
170
~
150
~
•
•... 130 110
10
6 7 Ale (month)
11
12
Fig. 2. Von BertallanfTy growth curve of the mullet Liza carinata in the backwaters of Bhanbhore.
70 60
calculation
of fishing mortality gave F With the values of M and F available, the exploitation ratio was computed as E = 0.737. The mortality of the mullet was estimated from ages ~ 125 mm. Since there is no evidence of juvenile mortality (because the gear used had a mesh size of 33 mm), the estimated mortality rates represent only adult mortality. This is an indicator of the potential of L. carinata juveniles in the backwaters for future exploitation due to their wide distribution (Abbas, 2000). Being aware of the time when the world's attention has focussed on aquaculture as a food producing activity, it would be worthwhile to stock them in man-made ponds at the study site. The high stocking density of such ponds will, of course, be advantageous in a thriving fingerling producing industry development, thereby improving the national aquaculture production as well as providing an opportunity in fisheries to the poorer segments of society. Leasing out of the land along Sindh, Balochistan and Karachi coasts for seawater fish-pond construction is urgently appealing for this culture-based fisheries also. 0.84jmonth.
ACKNOWLEDGEMENTS The author is thankful to Prof. Dr. Viqar Uddin Ahmed (Ex. Director) of the Centre of Excellence in Marine Biology, University of Karachi, for the facilities provided .
E" 1..'3 L'''' • O.Q8 " 500
350 ~
40
REFERENCES
~3O 20
•
10
110
120
130
140
150 160 170 Totallcn,lh (mm)
180
190
200
210
220
Fig. 3. Length-weight relationship of the mullet Liza carinata in the backwaters of Bhanbhore.
In the present study, total mortality was 1.141/ month. Inserting in the equation the growth parameters (K, Loo) and the mean water temperature of the study area (T = 29.50 C; Deggobis, 1988), natural mortality (M) was 0.30/month, which is nicely in coincidence with the modal mortality (0.2-0.3; Pauly, 1980). Then, the
ABBAS, G., 2000. Abundance, spawning and growth of the anchovy, Coilia dussumieria (Engraulidae) and mullet, Liza carinata (Mugilidae) in Bhanbhore backwaters along Sindh coast (Pakistan: Northern Arabian Sea). Pakistan J. Zool., 32: 123-130. AHMED, M. AND ABBAS, G., 1999. Abundance of finfish and shellfish juveniles in the tidal backwaters of Bhanbhore, Sindh (Pakistan). Pakistan J. Zool., 31: 129-140. ANDALORO, F., 1983. Contribution on the knowledge of the age and growth of the Marsala lagoon golden mullet, Liza aurala (Risso, 1810). Rap. Commisso Internat. Mer Mediterr., 28: 81-82. ANON, 1992. Handbook of fisheries statistics of Pakistan. A publication of Marine Fisheries Department, Government of Pakistan. Ministry of Food, Agriculture and Cooperatives (Livestock Division), 1990, vol., 16, pp. 144. ARRUDA, L., AZEVEDO, J.N. AND NETO, A.I., 1991. Age and growth of grey mullet (Pisces, Mugilidae) in Ria de Aveiro (Portugal). Sci. Mar., 55: 497-504.
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BAGENAL,
T.B. AND TESCH,
AND MORTALITY
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