Research Report

Stock Assessment of Heavybeak Parrotfish Scarus gibbus (Ruppell, 1829) (Family: Scaridae) off Tuticorin Coast, India (08°53.6’N, 78°16’E and 08°53.8’N, 78°32’E) – 36M  

Thiruvengadam Vaitheeswaran , V.K. Venkataramani
1 Tilapia Project-Hatchery Technical and Head Victoria Treasures Limited, Bugabo Bay Garuga on Victoria Lake, Kampala, Uganda, East Africa
2 Former Dean, Fisheries College and Research Institute, Tamil Nadu Fisheries University, Tamil Nadu, India
Author    Correspondence author
International Journal of Aquaculture, 2017, Vol. 7, No. 24   doi: 10.5376/ija.2017.07.0024
Received: 17 Nov., 2017    Accepted: 20 Dec., 2017    Published: 29 Dec., 2017
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Vaitheeswaran T., and Venkataramani V.K., 2017, Stock assessment of heavybeak parrotfish Scarus gibbus (Ruppell, 1829) (Family: Scaridae) off Tuticorin coast, India (08°53.6’N, 78°16’E and 08°53.8’N, 78°32’E) - 36M, International Journal of Aquaculture, 7(24): 159-165 (doi: 10.5376/ija.2017.07.0024)


The commercial important coral reef fishes viable source, re-aggregating, have been exploited coral reef parrot fish in pears coast of Gulf of Mannar. Its beautifully colour parrot fish reported between ranges 08°53.6’N, 78°16’E and 08°53.8’N, 78°32’E at a depth of 36 m. The parrot fishing of natural mortality (M), fishing mortality (F) and total mortality (Z) was calculated at 0.47, 0.40 and 0.87, respectively. Growth equation based on modified von Bertalanffy’s equation and Ford-Walford graph was arrived. The growth parameters such as L∞ = 104.50 cm and K = 0.23 was estimated combining both sexes. Length and weight frequency data obtained from the growth equation, has been dealing with S. gibbus attains the length of 21.96, 39.21, 51.76, 62.74, 70.58, 77.64 and 83.13 mm during first and seventh year respectively. The spawning peaks one in December and another in April could be observed. The life span of S. gibbus was estimated for seven years. The exploitation ratio of 0.46 indicated that the resource of S. gibbus is currently exploited along the Tuticorin coast. Heavy fishing pressure on the length group 6 to 81 cm revealed that S. gibbus in Tuticorin waters suffer due to recruitment overfishing. The present level of exploitation rate and exploitation ratio (F/Z) is estimated at 0.46 and 0.5 respectively. The average length of parrot fish, the beginning capture (Lc) was calculated as 20.0 cm. The total stock, average annual stock and maximum sustainable yield were estimated as 35.150 tonnes, 9.385 tonnes and 10.206 tonnes respectively. Virtual Population Analysis have been assessing the mortality ranges from 85 cm. The parrot fish study shows that the further stressed that strict management measures need to be undertaken to conserve this species from further to avoid exploitation and to restore the biodiversity of heavybeak parrotfish population of Gulf of Mannar in general and Tuticorin coast in particular.

Scarus gibbus; Population dynamics; Age and growth; Thoothukudi coast; Recruitment pattern; India

1 Background

The nest building of parrotfish is always a unique group of parrot fish (Family: Scaridae) in pearl coast of India.  Parrot fish have been found in tropical, sub-tropical, Indo-Pacific, partial temperate countries and Indian Oceans, its habitat only for coral associate fishes, have been reported that the herbivorous food and feeding habit. Streelman and Alfaro (2002) have been reported that the 90 species of parrotfish in the group of (Family: Scaridae). Randall (1974) has been revealed that the parrot fish feeds on coral polyps and algae. Study revealed that the marine ornamental fish has been reported in the Gulf of Mannar, 113 species of fish from 24 families (Venkataramani et al., 2005). Tamil Nadu ranks 5th in total fish production of the country and the total fish production of the Tamil Nadu State during 2014-15 were 6.97 lakhs tonnes. The export of marine products of 93,477 MT and earned a foreign exchange of Rs. 5,308.17 crores during 2014-15 (Rupees). The fisheries sector of Tamil Nadu has contributed 0.7 percent of the total Gross State Domestic Product (GSDP) of the State (Policy note, 2015-2016). The present investigation, to estimate asymptotic length (L∞), growth coefficient (K), natural mortality (M), fishing mortality (F), total mortality (Z), exploitation ratio (E) and recruitment pattern (Lc/L∞); where Lc is length at first capture) and M/K and length-weight relationship of S. gibbus off Tuticorin coast of Gulf of Mannar, India.


2 Materials and Methods

The length frequency data, catch and effort data have been collected from Tuticorin coast of Gulf of Mannar from January 2004 to December 2004. S. gibbus the catch and effort data have been assessing for the estimation growth parameters by ELEFAN Programme (Gayanilo, 1995), mortality, exploitation rates and recruitment pattern by using FiSAT programme (Gyanilo and Pauly, 1997). ‘L∞’ and ‘K’ was calculated by Ford-Walford plot (Ford, 1933; Walford, 1946) of Lt against Lt + 1 on mortality basis and ‘t0’ was calculated by Gulland and Holt’s (1959) plot. The growth was expressed using von Bertalanffy’s (1938) equation given as



Where L∞ is the asymptotic length ‘K’ Growth coefficient


3 Results and Discussion

Scarus gibbus, the wide range of variety of length group of fishes are characterized by proliferate of growth (depends upon tropical or temperate continent), age-at-first maturity spawning capability, in which are characteristic of r and k theory of perciform the selected species. The conservation of scarid species, off Tuticorin coast of India, is to avoid overfishing in this geographical zone.


3.1 Growth parameters

Figure 1 shows restructured length distribution for the computed growth curve. The von Bertalanffy growth equation for S. gibbus was estimated as L∞ = 104.50 and K = 0.23. Choat and Axe (1996) has been revealed that the bumphead parrotfish (Bolbometopon muricatum) to attain to the maximum reach at 1000 mm at Solomon Islands (Hamilton, 2004). S. gibbus is relatively moderate in growth K = 0.23. According to Sparre and Venema (1993) has suggested that the same genus group and related the species level was K and natural mortality, and it is related to same age and the length and weight of the fish. The M value was calculated 0.47 and the M/K ratio of S. gibbus was estimated 2.04. The M/K value is found to be in close proximity limit among the closely associated species (Beverton and Holt, 1956). The M/K ration, S. gibbus have been decreasing within the range of 2.0-3.0. Genus Scaridae, the species level was closely associated group, the result shows that the similar K and L∞ values have life-span varying by a factor of 2-4, Chlorurus microrhinos (K = 0.307, L∞ = 428, Tmax = 15), Chlorurus sordidus (K = 1.117, L∞ = 193, Tmax = 9), Hipposcarus longiceps (K = 0.282, L∞ = 350, Tmax = 12), Bolbometpon muricatum (K = 0.136, L∞ = 693.81, t0 = -0.11), Cetoscarus bicolor (K = 0.255, L∞ = 420.56, t0 = -0.09), Chlorurus microrhinos (K = 0.301, L∞ = 429.89, t0 = -0.08), Scarus frenatus (K = 0.844, L∞ = 232.36, t0 = -0.05), Scarus niger (K = 0.736, L∞ = 238.01, t0 = -0.06), Scarus psitticus (K = 1.190, L∞ = 172.10, t0 = -0.05), Scarus rivulatus (K = 0.220, L∞ = 308.50, t0 = -0.15), Scarus schlegeli (K = 0.403, L∞ = 238.81, t0 = -0.11), Sparisoma atomrium (K = 1.828, L∞ = 101.08, t0 = -0.06), Sparisoma aurofrenatum (K = 1.163, L∞ = 170.89, t0 = -0.05), Sparisoma chrysopterum (K = 1.176, L∞ = 237.97, t0 = -0.04), Sparisoma rubripinne (K = 0.811, L∞ =237.57, t0 = -0.05) and Sparisoma viride (K = 0.498, L∞ = 318.96, t0 = -0.06) (Choat and Robertson, 2002).


Figure 1 Estimation of growth parameter through ELEFAN I programme of Scarus gibbus


The total mortality (Z) and fishing mortality (F) was calculated 0.87 and 0.40, respectively. Figure 2 showing the catch curve was estimated by Z. In the present study deal with exploitation ratio (E) was estimated as 0.53. As the E is <0.5, it was estimated stock of S. gibbus along southeast coast is under much fishing pressure. The asymptotic length (L∞) and growth coefficient (K) have been calculated from the Ford-Walford plot was L∞ = 157.75 cm and K = 0.06. The estimated was t0 = -0.47 year. Total mortality (Z = F + M) was calculated using the method of Beverton and Holt (1956) and natural mortality (M) using Pauly's formula (Pauly, 1978). Bolbometopon muricatum the estimated growth rate was (K = 0.063) and, life span of S. gibbus was estimated for seven years. According to Gulland (1971), if the E is >0.5 the stock may be considered as overfished. The results of Virtual Population Analysis showed the F increases to a maximum at 40 cm (Figure 3).


Figure 2 Total mortality estimates by-catch curve method of Scarus gibbus


Figure 3 Virtual population analyses


3.2 Age and growth

S. gibbus, the large 264 trawlers in Tuticorin coast, the length ranges from 8.1 to 81 cm. The estimated of asymptotic length (L∞) was obtained by Powell and Wetherall (1986) was calculated L∞ = 104.50 and K = 0.23 (Figure 2). Randall and Bruce (1983) has been studied reveal that the green humphead parrotfish, Bolbometopon muricatum, estimated was 117 cm and weight was 46 kg. Family Pomacentridae, the related group of species, the length group was 60 mm and age was 16-18 years (Fowler and Doherty, 1992). The following growth parameters have been estimated by ELEFAN I method and it was L∞ = 104.50 cm and K = 0.23. S. gibbus the growth was calculated 21.96 and 39.21 mm, the first and second year respectively (Figure 1).


Total mortality coefficient (Z) estimated was 0.87 (Figure 2). Natural mortality was calculated 0.47 (M) and fishing mortality was 0.40. The exploitation rate (F/Z) estimated was 0.5 (Figure 4). Two peak spawning seasons was calculated during the month of December and April (Figure 5). The total potential resource is being over exploited from Tuticorin coast of Gulf of Mannar.


Figure 4 Relative yield-per-recruit and biomass-per-recruit Scarus gibbus (Lc /L∞ = 0.032. M/K = 2.04)


Figure 5 Recruitment pattern of Scarus gibbus


Length calculated for different years using von Bertalanffy’s growth equation was plotted along with the observed length of the same period which showed a general agreement in the growth pattern. This also showed high degree of agreement with other methods employed. Ford-Warlford graph was constructed for S. gibbus by plotting Lt + 1 against Lt where Lt is the height of the animal at a particular age. Lt + 1 when intersected by a 45º diagonal from the origin, L (length at infinity) was obtained and it was found to be 83.13 cm for this species. In the present study, age and growth were studied through different methods. However, von Bertalanffy’s equation showed agreement and gave reliable results. This heavy-beak parrot fish was found to have two recruitment seasons, one major season, during December and a minor season during April (Figure 5).


3.3 Yield per recruit and biomass per recruit 

S. gibbus, the length at first capture (Lc) was 21.96. The relative yield per recruit and biomass per recruit was calculated 0.03 and 2.4. The plot of yield per recruit (Y/R) against E is shown in Figure 6. The maximum Y/R was at E = 0.014. The present E (0.53) has not exceeded the optimum exploitation rate (Emsy = which maintain the 50% of the stock biomass). The optimum yield per recruit is 0.017 g. It is suggested that for attaining the maximum yield the fishing pressure could be increased by 0.53% from the present level L50/L∞ value are given in the Figure 7. S. gibbus, the studies showed that the urgent need to conserve parrot fish stocks of Tuticorin coast, India. Robertson et al. (1999) study revealed that the all coral reef fishes to extended life-spans, slow growth rates (tropical/temperate region), low natural mortality rates that the indication of marine species vulnerable to extinction through man-kind activities, to alarm of overexploitation.


Figure 6 Yield/Recruit and Biomass/Recruit of Scarus gibbus


Figure 7 Yield isopleth of Scarus gibbu


Authors’ contributions

Dr. V.K. Venkataramani, Dean and Principal Investigator, ICAR/NATP/CGP Mode project, and Dr. Vaitheeswaran Thiruvengadam, Senior Research Fellow, ICAR/NATP/CGP Mode project, he has been working as Senior Researcher of this project, he was involving and dedication of the project, sixteen species of stock assessment of marine ornamental finfishes and length frequency data collection, catch and effort data assessment, various parameters has been analysis and  biodiversity assessment of marine ornamental of Gulf of Mannar, India, FiSAT package analysis in this coast.



The authors are thankful to Indian Council of Agricultural Research, National Agricultural Technology Project, New Delhi, India, for providing funding facilities. I wish to thank Vice Chancellor, TamilNadu Veterinary and Animal Sciences University, Chennai, TamilNadu, India for providing all facilities and laboratory instruments, encouragements and supports.



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