Introduction

Seerfishes are considered as one of the high value resources due to high economic return and export markets (Muthiah, 2002). Among the five species of seer fishes the king seer fish, Scomberomorus commerson and Spotted seer fish, S. guttatus are commonly caught in the Indian coast. There was steady increase in the seerfish production from the Indian seas in the last five decades (1950s to 1990s). During 1980’s to 1990’s in seer fish production, India was placed third in the world and first among the countries bordering Indian Ocean (Devaraj, 1999). In the Eastern Indian Ocean, seerfish catch have doubled over the decade from 1989 to 1998 (Pillai, 2002). The spotted seerfish fishery is concentrated mainly in the northern parts of both west and east coast of India (Muthiah, 2003a). During the last two decades they are mostly exploited by bottom trawlers operating in the deeper waters beyond 50 to 300m depth (Muthiah, 2003b). Northeast coast of India offers one of the most diverse fishery resources in Indian Exclusive Economic Zone, (Somvanshi, 2003). The species Scomberomorus guttatus contributed 1.6% to the total marine fish landings of India, the average landing being 19,712 t (Prathibha Rohit and Subhadeep Ghosh, 2012). Information on the abundance, biology and population parameters of fishery resources are essential for their exploitation to an optimum level as well as for a sustainable fishery. A lot of work has been done on the fishery, distribution, biology and growth of seerfishes in Indian waters (Naik et al., 1998, Muthiah et al., 2002, 2003a and 2003b, Kasim et al., 2002, Ghosh et al., 2009, 11 and Prathibha Rohit et al., 2012). In the present paper an attempt has been made to study the biology of S. guttatus with special reference to the growth parameters by analyzing the exploratory survey data collected onboard the survey vessels of Fishery Survey of India (FSI).

Materials and Methods

Samples for our study was collected during the exploratory cruises of the FSI vessels Matsya Shikari (Combination Trawler, OAL - 39.5 m, GRT – 352 MT.) and Matsya Darshini (Purse-Seine cum Pelagic Trawler, OAL - 36.5M, GRT - 268.8 MT.) during the period 2006-2010. The gears used for survey were 12.92 x 12.92 fathom Mid water Trawl & 45.6 m Expo-model Fish Trawl, 34 m Fish Trawl, 36.2 m Cephalopod Trawl and 34 m Shrimp Trawl. The data collected from Lat. 16°N – 20°N to Long. 83°E -85°E was utilized for the study. The samples collected were subjected for morphometric measurements. The specimens were measured for total length (TL +/- 1cm, FL+/- 1cm) and weight was taken to the nearest gm. Specimens were dissected to study the maturity and gut contents. The data collected was analyzed for the morphometric relationship such as total length (TL) - fork Length (FL). The parameters for both the sexes were regressed with each other with the help of the linear equation Y= a +bX, ‘r’ being the correlation coefficient. The relationship W = aL ^b (Le Cren, 1951) was used for the length weight analysis where W is the weight of the fish in gm and L is the total length in cm. The relationship was expressed in the logarithmic form as: Log W = log a + b log L. The male to female ratio (M: F) was determined.  

A total of 1849 specimens collected during the period 2006-10 were taken for in depth analysis. Various methods in the FAO-ICLARM Stock assessment tool – FiSAT-II software (Ver.: 1.2.2, 2005) were used to analyze the length-weight relationship, growth parameters such as L∞ and K, natural mortality(M), fishing mortality(F) and total mortality Z, recruitment pattern, and virtual population analysis. Powell-Wetherall’s Method was also used for estimation of L∞ and Z/K by pooling a time series of length-frequency data (Wetherall, 1986). Pauly’s empirical equation (Pauly, 1980) was used for natural mortality (M) calculation. The total mortality (Z) was estimated from length converted catch curve by taking the mean habitat temperature as 28.5°C. The recruitment patterns – recruitment pulses from a time series of length frequency data was studied to ascertain the spawning and recruitment period (Pauly, 1983, Moreau & Cuende, 1991). Length structured Virtual Population Analysis (VPA) was used to ascertain the loss due to natural causes and fishing pressure at various length classes.

Results

Abundance

During the period 2006 – 2010, S. guttatus was the major species of seerfish landed by the survey vessels, forming 62.24% of the total landings of the seerfishes. Catch was more by pelagic trawling, in comparison with the demersal gear. Although S. guttatus was represented in the catch throughout the year, the period August-October and January-February yielded better catch (fig.1). It could be seen that the females were dominant during the month of August followed by October, whereas male population was more during August followed by January. The depth strata 30-100 m yielded a better  catch rate  than the depth zone 101-200 m. Latitude 17°N of the east coast was more productive followed by 16°N, 18°N and 19°N.

Morphometry

The morphometric measurements such as TL, FL, weight and the mean, SD value and morphometric relationship are given in table 1 for both male and female. In the case of male the TL ranged between 21.5 cm and 67.1 cm. The fork length was between 16.1 and 63.5 cm and the weight was in between 150 and 1750 gm. The linear relationship between TL and FL was worked out to be FL = -1.49 + 0.88 TL(r = 0.98). In the case of female the TL ranged between 26 and 63.1 cm and fork length 21-59 cm. The weight observed was between 200 and 2150 gm. The linear relationship between TL and FL was observed to be FL = 1.16 + 0.82 TL(r = 0. 99).

Sex ratio

A total of 1849 specimens consisting of 725 males and 1124 females were taken for sex ratio analysis. During the period of study the male to female ratio was found to be 1:1.6(table 2). All the length groups from 15.1 to 66 were represented by male however only 14 length groups i.e from 21.1-24.0 to 60.1-63.0 were represented by female. Among the males it was noticed that the length group 39.1-42.0 cm contributed maximum followed by 36.1-39.0. In the case of female also similar result was obtained. The length group 39.1-42 contributed maximum to the population followed by 36.1-39.0. In the overall sex distribution in different length groups, one interesting pattern could be noticed. Up to 33 cm fork length (i.e immature specimens) the males were more than females. From 33.1 cm onwards and up to 45 cm (i.e maturing specimens) female population was exactly one and half of the male population in all the length groups. However 48 to 54 cm (i.e matured specimens) the female population completely outnumbered the male population and the rate of enhance of female than male decreased gradually up to 63 cm.

Length frequency study

The male specimens were recorded from 16.1 cm to 63.5 cm fork length and the percentage of male was more at 39.1-42.0 cm and 36.1-39.0 cm respectively, whereas the female specimens were recorded from 21 – 61.5 cm fork length and the dominance was at 39.1-42.0 cm and 36.1-39 cm respectively (fig.2).

Length - weight relationship

The length – weight relationship for both sexes of Scomberomorus guttatus was analyzed and presented. The equations derived are

Female:  Log W= -1.1285 + 2.4644 Log L (r= 0.92)…………………………… (1)

Male:    Log W= - 0.8331+2.2683 Log L (r = 0.91)…………………………… (2)

The ‘r’ value for both the sexes showed high degree of correlation.

The ANOVA was applied and it revealed that there is no significant difference between the regression coefficients of females and males. Hence the data for females and males were pooled together and a common length weight relationship was fitted.

The equation in respect of pooled data is

Log W = -1.1283 + 2.4627 Log L(r = 0.91)………………………………….. (3)

Gonadal stages and maturity studies

A total of six stages were encountered during the study period viz, immature (stage I), maturing (stage II and III), mature (stage IV), ripe (stage V) and spent (fig. 3). From the figure it could be noticed that the matured and ripe specimens were observed almost round the year. The peak spawning activity was during December to April. The juvenile must be recruited to the fishery during January to June.

Growth parameters

The electronic length frequency analysis I (ELEFAN I) was used to estimate the asymptotic length (L∞), growth constant K and t₀. The observed parameters i.e., L∞, K and t₀ were found to be 64.6, 0.97 and -0.1329 respectively. The Von Bertalanffy growth equation for the species can be written as follows

Lt = 64.6 [1- e ^{-0.97(t+0.1329)}]

The Von Bertalanffy growth curve is shown in figure 4.

The L∞ and (Z/K) obtained by the Powell- Wetherall method were found to be 45.51 and 0.404 respectively. The mortality parameters such as natural mortality (M), fishing mortality (F) and Total mortality (Z) were 1.43, 1.27 and 2.70 respectively. The longevity of the species was worked out to be 2 years. Taking the L∞ = 64.6, K = 0.97 and t₀ = -0.1329 the length of the species after 0.5 year, 1 year, 1.5 year and 2 years was estimated to be 29.6 cm, 43.1 cm, 51.3 cm and 56.4 cm respectively(fig.5). It could be observed that during the first six months the growth rate of the species was the maximum (4.9 cm/month). It decreased henceforth, 2.2cm/month during the seventh - twelfth month, 1.4cm/month during twelfth- eighteen months and 0.9 cm/year during eighteen to twenty four months period. Some biological parameters of the species are given in table 3.

Recruitment pattern

The recruitment pattern (fig.6) indicated that the species spawns throughout the year with peak spawning during January to June.

Virtual population analysis

The virtual population analysis (VPA) has shown that the mortality due to natural causes alone was up to 28cm (fig.7). The fishing pressure started at 28.1cm and increased steadily thereafter up to 58.1 cm midlength. The maximum fishing mortality of 2.4 was recorded at size of 43.5 cm.

Food and feeding

The feeding intensity showed that 56.2% stomachs were empty followed by half full (18.3%), full stomach (11.8%), quarter full (8.6%) and three fourth full (5.1%), fig.8. The gut content analysis revealed that these fishes are piscivorous in nature and the dietary composition in the order of preferences are anchovies (45%), sardines (45%), shrimps (3%), upenoids (3%), squid (2%), lizard fish (1%) and silverbellies (1%), fig.9.

Discussion

The trawls are the major gears and they land the juvenile seerfish and contribute 10.1% to the total catch and rest of the catch was landed by the indigenous gears (Prathibha Rohit & Shubhadeep Ghosh, 2012). The seerfishes contribute about 2.3% of the total marine fish landings in India (Pandian, 2005). The catch of the seerfish in northeast coast of India has increased to considerable level during recent past. The monthly production trends indicated that peak catches were during March – April at Visakhapatnam (Muthiah, 2002). The exploratory survey data indicates that there is a marginal increase in catch of spotted seerfish during the period from 2006 to 2010.

Naik et al., 1998 reported the total length range of the species in the west coast as 25-72 cm. Muthiah et al., 2002 recorded the length of spotted seerfish in the range of 16 - 62 cm in the west coast of India. Ghosh et al., 2009 recorded the range was between 20 to 58 cm from the west coast. The size range of spotted seerfish was between 20.1 and 66.0 cm in the upper east coast of India as reported by Pandian et al., 2005. They were also of the opinion that the size group of the species which supported the commercial fishery was in the length range of 32 – 42 cm and the size at first maturity was 34 cm. The fork length of S.guttatus landed by gillnets ranged between 20 cm and 60 cm all over India as per the studies conducted by Prathibha Rohit & Shubhadeep Ghosh, 2012. In the present study the size range was from 16.1 to 63.5 cm fork length (FL) which is more or less the same sizes as recorded in the east coast as well as west coast.

Naik et al., 1998 reported the male to female ratio of the species as 1:1.2 in the west coast of India. In the present study also similar result was obtained with dominance of female in the population. The dominance of female was observed as the fish grows and it was more in the higher length groups. Very less study has been done on the morphometric relationship of seer fish in Indian waters. The relationship between the total length and fork length was attempted in the present paper and it yielded a linear relationship with higher degree of correlation between both the parameters. Naik et al. (1998) studied the L-W relationship of S guttatus in the mid-west coast of India and reported the ‘b’ value as 2.7506 and 2.9071 for male and female respectively and the pooled value as 2.8226. Pandian et al. (2005) reported the ‘b’ value in the L-W relationship as 2.7499 in the upper east coast of India. Pratibha Rohit and Subhadeep Ghosh (2012) studied the relationship for both the west coast and east coast of India and obtained the ‘b’ value as 2.8884 suggesting an allometric growth. All these studies indicated that the ‘b’ value is less than 3. From this it can be said that the rate of increase of weight is less in comparison to the length increase for the S. guttatus spp. and it is lesser than 3. In the present study the ‘b’ value obtained is 2.2633 for male and 2.4644 for female which is in agreement with the previous studies and suggests a negative allometric growth of the species in the north east coast of India. Also the lesser ‘b’ value (2.2683) of male specimens than the female specimens (2.4644) indicates that the rate of increase of weight in relation to length is less for male than the females and for a particular length group the corresponding females will be heavier than the males.

Pandian et al., 2005 obtained high value L∞ (75.05) and K (0.96) in the upper east coast of India. Prathibha Rohit & Shubhadeep Ghosh, 2012 studied the growth parameters in the Indian waters and reported the L∞ and K as 61.27 and 1.4 per year respectively by ELEFAN I. The same data was analyzed by Powell and Wetherall plot too and it gave a similar value for L∞ 60.19 cm. Present values of L∞ and K estimated by ELEFAN I were 64.2 and per 0.7/ years respectively and by Powell-Wetherall plot 45.51 and 0.4/year respectively. Observed mid length of the specimens recorded was 58.5 cm and the predicted extreme length is 62.5 cm, hence the value obtained for L∞ by Powell-Wetherall plot i.e., 45.51 cm appears unrealistic. The value obtained by ELEFAN I appears to be more appropriate.

Kasim and Abdussamad (2002) studied the mortality parameters of the species in the east coast of India and reported the mean natural mortality as 1.50, fishing mortality as 5.02 and total mortality as 6.52. Pandian et al. (2005) obtained the natural mortality as 1.32 /year. Pratibha Rohit and Subhadeep Ghosh (2012) obtained the M, F and Z values as 1.79, 2.92 and 4.71 respectively. All these studies indicate that the fishing pressure is more on the species in both the coasts. In the present study, the natural mortality was 1.43, fishing mortality was 1.28 and total mortality was 2.71 which suggests that the present exploitation level is optimum, however more fishing effort will have an adverse effect on the fishery. Pratibha Rohit et al., 2012 reported the longevity of the species as 2 years. Taking Z = 2.71 the t_max (Hoenig’s, 1983) was computed to be 2 years in the present study. In the first six month period the growth rate of the species was maximum (4.1 cm/ year) and it decreased in the subsequent six month period indicating maximum growth of the species in the first six month period itself in the north east coast of India.

Kasim et al., (2002) reported the peak recruitment period for the species during March-April followed by December in the east coast of India. Previous studies (Kasim et al., 2005) indicated the recruitment period of the species in the east coast from October to June with peak period during February - May. Pratibha Rohit and Subhadeep Ghosh (2012) reported a unimodal recruitment pattern with the young ones being recruited to the fishery for most of the months of the year. They indicated the peak recruitment during February to July. In the present study six stages of maturity for the species was obtained and it could be seen that the recruitment period was between January-July with peak during May. The smallest length of recruit was 16.1cm. The present observation agrees well with the previous studies.

VPA was studied by various researchers and it indicates that loss in the stock was due to natural causes alone was up to 34cm (Kasim, 2002). In the present study however indicated that the natural cause of mortality alone in the stock was up to 28cm. The fishing pressure started at 28.1cm midlength and it increased steadily up to 58.1cm midlength. The fishing pressure was intense at 37-49cm and 55-58cm. The present observation is indicative of exploitation of smaller specimens in the fishery.

Naik et al., 1998 studied the gut contents of the seer fish in the mid-west coast and found that 46.1% of the fishes were empty stomach and these species are piscivorous in nature with Stolephorus spp. as the dominant item in the gut. Pratibha Rohit and Subhadeep Ghosh (2012) recorded anchovies, scads and sardines in the gut in almost all the months. In the present study also similar observations were made. 56.2 % of the stomachs were empty and the preferred food items were mainly anchovies, sardines and shrimps etc.

The present study indicates an unusual sex ratio i.e dominance of female in the higher length groups need to be studied more elaborately. Also the fishing mortality is less than the natural mortality which could be due to predation, starvation etc. 56% of the specimens studied was found to be empty stomach is supportive of this. Present trend in fishery in northeast coast is mainly multispecies and also resource specific gear for seerfish is not operated here. Hence to arrive at the stock structure of the species the biological as well as the growth parameters need to be taken as inputs in various methods and models duly taking into consideration the environmental parameters and other natural causes affecting the fishery.

Acknowledgement

The special thanks to Director General, Fishery Survey of India for his encouragements. The Authors are expressing thanks to all of the Scientist participants, Skippers and crew of the survey vessels of Fishery Survey of India, Visakhapatnam for collection of the data.

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