Population parameters of the catfishes, Arius caelatus (Valenciennes, 1830) and Arius tenuispinis (Day, 1877) from Mumbai waters

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1 Indian Journal of Geo-Marine Sciences Vol. 42(6), October 2013, pp Population parameters of the catfishes, Arius caelatus (Valenciennes, 1830) and Arius tenuispinis (Day, 1877) from Mumbai waters *Bhawesh T. Sawant, S K Chakraborty, A K Jaiswar, Debabrata Panda, S K Bhagabati & Paramita B. Sawant Central Institute of Fisheries Education, Versova, Andheri (West), Mumbai , India [ address: bhweshsawant@gmail.com] Received 22 March 2012; revised 23 August 2012 The population parameters like growth, mortality, exploitation rate and length at first capture of Arius caelatus and A. tenuispinis from Mumbai waters were investigated to derive information required for their management. Asymptotic length (L ) and growth coefficient (K) were calculated as 520 mm and 0.70 year -1 for A. caelatus and 550 mm and 0.73 year- 1 for A. tenuispinis, respectively. Instantaneous rate of total, natural and fishing mortalities were estimated to be 2.37, 1.18 and 1.19 for A. caelatus and 2.42, 1.19 and 1.23 for A. tenuispinis, respectively. Size at first capture was estimated as 274 mm for A. caelatus and 268 mm for A. tenuispinis. Exploitation ratio (E) was found to be at optimum level for both A. caelatus (0.5) and A. tenuispinis (0.51), indicating the stocks are exploited at optimum level and can be fished sustainably in years to come. [Keywords: catfish, species, mortality, landings, capture] Introduction Exploitation of marine fishes demand studies directed towards understanding the population of the exploited stocks in space and time. The catfishes are demersal in habit and widely distributed in the Indo- Pacific region more preciously on the west and east coasts of India to Bangladesh, Myanmar, Singapore, Malacca, Indonesia, Brunei, Darussalam, Malaysia and Pakistan. Marine catfishes are generally bottom living, preferring a muddy habitat and that makes them a suitable target for bottom trawling,. Generally, they have been observed to be most dense over inshore muddy areas, particularly in depths up to m. However, their low fecundity and wanton destruction of eggs, juveniles and incubating males by purse seines has caused the catfish population to be under severe stress. Landings of catfishes follow ebb and tide pattern with some species ebbing and totally disappearing from the fishery at certain times, followed by resurfacing of the same, after a period. This observation calls for updated knowledge of its population parameters for regular assessment of its stock dynamics and recruitment so as to draw valid conclusions regarding the renewability and revival of + Formed part of the work for the award of PhD thesis by the Central Institute of Fisheries Education *Corresponding author: its fishery at any point of time. This aspect is important in the context of multispecies fishery in India and more prominently in Maharashtra, wherein impact of fishing is not only on target groups but also on associated species/groups caught as by-catch. The importance of catfish in Indian fishery is highly significant as its contribution to fishery of Maharashtra to the total catfish catch of the west coast of India is 23.5%, which is about 0.39% to the total marine fish catch of India 1. Among the 21 species of catfishes, a dozen are caught along the coasts of the country 2, out of which the two species under investigation form a sizable fishery along the Mumbai coast. Studies on these two species (Arius caelatus and Arius tenuispinis) of catfishes from Indian waters are scanty. Growth, mortality, recruitment and maximum sustainable yield of A. caelatus have been studied by Chakraborty et al. 3 from Maharashtra. Available information on its biology is mainly due to the work of Sekharan and Mojumder 4 from Vishakhapatanam, Menon 5 and Menon and Muthiah 6 from Mandapam and Raje 7 from Mumbai. Dan 8 worked on the population parameters of Tachysurus tenuispinis along Visakhapatnam coast and Shekharan 9 worked on its distribution in the north western Bay of Bengal. Considering the increase in fishing pressure along Mumbai coast, a detailed study on population

2 776 INDIAN J. MAR. SCI., VOL. 42, NO. 6, OCTOBER 2013 parameters of A. caelatus and A. tenuispinis has become important for the management of the resource, as the previous studies happen to be carried out at a time when the fishing pressure was relatively less. Materials and Methods The length frequency data was collected from commercial catches landed at three major landing centres of Mumbai i.e. New Ferry Wharf, Sassoon Docks and Versova (Fig. 1) from August, 2008 to June, Samples were obtained at landing sites from catches of shrimp trawlers, which have a cod end mesh size of about 15 mm. Fishes were selected at random from landings and recorded to nearest mm of total length using a measuring board. Sample weight and total catch of the species on the day of observation were recorded. Length frequency data was grouped into 10 mm class interval and raised for the day and subsequently for the month using the method of Sekharan 10 for analysis of growth and mortality parameters. The raised data were pooled for one year by using FiSAT programme developed by Gayanilo et al. 11. The von Bertalanffy parameters L and K were estimated by ELEFAN-I technique. The total instantaneous mortality (Z) was estimated by length converted catch curve method 12. Fig. 1 Map of Mumbai showing sampling sites Estimate of natural mortality rate (M) was obtained using the empirical equation derived by Pauly 13 : ln (M) = * ln(l ) *ln(K) *ln(T) where, L and K are von Bertalanffy parameters in cm and year -1 respectively and T is the mean annual water temperature which was taken as 28.2 C 14. Annual instantaneous rate of fishing mortality (F) was calculated by subtracting the natural mortality rate (M) from the total mortality rate (Z) (F = Z M). Present exploitation ratio (E) was calculated as the proportion of the fishing mortality relative to total mortality (E = F/Z) and exploitation rate (U) were calculated by the relationship: U = (F/Z) * (1 e z ) as given by Beverton and Holt 15. Sizes at which fish had a probability of capture of 25, 50, 75 and 100% were estimated from trawl selection curve generated from the probability of capture employing FiSAT programme. Results Length frequency data were collected in the length range of 180 to 490 mm for A. caelatus and 190 to 530 mm for A. tenuispinis, respectively. VBGF parameters L and K estimated by ELEFAN-I were 520 mm and 0.70 year -1 for A. caelatus, while 550 mm and 0.73 year -1 for A. tenuispinis, respectively (Fig. 2). Taking these values, the average lengths at different age groups were calculated for both the species by using von Bertalanffy s growth equation 16. Average length attained by A. caelatus was 258, 388, 453, 486, 502 and 510 mm at the end of 1, 2, 3, 4, 5 and 6 th years of its life span, respectively, while the same in case of A. tenuispinis were 287, 429, 500, 535, 553 and 561 mm at the end of 1, 2, 3, 4, 5 and 6 th years, respectively (Fig. 3). Maximum size of A. caelatus recorded during the period of study was 486 mm at which the corresponding age was estimated at 3.5 years which can be taken as the fishable life span of the fish. The L max was reported as 523 mm and the corresponding t max was estimated to be 4.0 years in case of A. tenuispinis, indicated its fishable life span in Mumbai waters. The annual instantaneous rates of fishing induced mortality (F), natural mortality (M) and total mortality (Z) are given in Table 1. Total instantaneous mortality coefficient was obtained from length converted catch curve were 2.37 and 2.46 for A. caelatus and A. tenuispinis, respectively (Fig. 4). Using Pauly s

3 SAWANT et al.: POPULATION PARAMETERS OF THE CATFISHES FROM MUMBAI WATERS 777 Fig. 2 Growth curve fitted by ELEFAN-I method for (a) A. tenuispinis, (b) A. tenuispinis Table 1 Mortality and exploitation rates for A. caelatus and A. tenuispinis A. caelatus A. tenuispinis Fishing mortality rate (F) Year -1 Natural mortality rate (M) Year -1 Fishing mortality rate (Z) Year -1 Exploitation ratio (E) Exploitation rate (U) was equal to 1.0, was 325 mm and 335 mm for A. caelatus and A. tenuispinis, respectively. Sizes, at which fish had a probability of capture of 25, 50 and 75% were estimated at 251, 274 and 296 mm for A. caelatus, and the same was estimated at 241, 268, 296 mm for A. tenuispinis respectively (Fig. 5). Fig. 3 The von Bertalanffy growth function fit to size at age relationship for (a) A. caelatus, (b), A. tenuispinis formula, the natural mortality rate M was estimated at 1.18 for A. caelatus and 1.19 for A. tenuispinis. Fishing mortality rate was estimated by subtracting the M from Z as 1.19 and 1.28 for A. caelatus and A. tenuispinis. Values of E (exploitation ratio) and U (exploitation rate) were calculated as 0.50, 0.51 and 0.45, 0.48 for A. caelatus and A. tenuispinis, respectively. Size, at which fishes were fully vulnerable to fishery, when the probability of capture Discussion Several workers have investigated the growth parameters of catfishes. However, information available related to A. caelatus and A. tenuispinis is limited. Age and growth of the A. tenuispinis was studied by Dan 8 based on length frequency data and skeletal parts like opercular bone and otolith from Waltair waters. Estimated growth parameters by Alagaraja and Srinath 17, based on trawl catch data were L = 560 mm, K = 0.78 year 1 and W = 3230 g. Menon and Bande 18 reported that A. caelatus grows to a maximum size of 600 mm in Indian waters, the annual fluctuation of water temperature in summer and winter months is not more than 5 C. Thus, there

4 778 INDIAN J. MAR. SCI., VOL. 42, NO. 6, OCTOBER 2013 Fig.5 Probability of capture by trawl selection analysis for (a) A. caelatus, (b) A. tenuispinis Fig. 4 Length converted catch curve for estimation of Z for (a) A. caelatus, (b) A. tenuispinis is little chance of stress resulting in formation of rings and even if the rings are formed the periodicity is difficult to ascertain. Most vital parameters i.e. VBGF parameters, L and K for A. caelatus estimated as 520 mm and 0.70 year 1, respectively in the present study have not been worked upon earlier. The L max observed during present investigations was 486 mm for A. caelatus and 523 mm for A. tenuispinis. It appears that the fishing pressure in recent years have affected the growth of the fish as it is evident by the low value of L max observed in the present study in case of both the species compared to some of the earlier reports. As a thumb rule, L max is considered as 95% of L, in that case L for A. caelatus and A. tenuispinis was calculated as mm and mm, respectively. The estimates thus obtained are closer to the estimates made by other computer based methods for L. In the present study, the growth rate K was found as 0.70 year -1 for A. caelatus and 0.73 year -1 for A. tenuispinis. Estimate seems to be reasonable as catfishes are typically carnivorous and voracious in feeding habit and are likely to grow at a faster rate. The present study has established the key population parameters of the two representatives of the family Ariidae, which are optimally exploited in Mumbai waters. Age and growth studies were based on the collected length frequency data. In the tropical waters the researchers are totally dependent on length frequency data for age determination. Other methods like use of hard parts, though shows rings cannot be specified for periodicity. It is for that reason, with subjectivity and limitations, length frequency data remains the most utilized tool for age determination in tropical fishes. During the present investigation a number of methods were used for the estimation of growth of which except Modal Progression Analysis by Devaraj 19 and using the data read at monthly intervals from that fitted in Ford-Walford plot 20,21, all the methods are computer based. Selection of growth parameters from such a wide variety of methods was again difficult. Thus, in present study, linking of means, (combination of Bhattacharya 22 ; Gulland and Holt 23 methods) was selected as the correlation

5 SAWANT et al.: POPULATION PARAMETERS OF THE CATFISHES FROM MUMBAI WATERS 779 Table 2 Estimation of growth parameters by different methods Methods Arius caelatus Arius tenuispinis L K L K (mm) (year -1 ) (mm) (year -1 ) Modal Progression Analysis by Scattegram Technique (Devaraj, 1983) 12 Ford-Walford plot ( , ) Bhattacharya Method (FiSAT, 1967) Gulland and Holt Plot (1959) ELEFFAN Method (FiSAT) (Gayanilo et al., 1996) 11 coefficient was relatively better by this method and also it is combination of two methods. First the separation of Gaussian components by Bhattacharya 22 was done and refining the same by Gulland and Holt 23 plot. Though a fair estimate of growth parameters can be obtained by using the length frequency data, the subjectivity part of it is always criticized. With these limitations in mind, still we find a good degree of acceptance at present of the estimates of growth parameters. This has been further strengthened by the introduction of application of computer based programmes which has, to a greater extent, popularized studies in the field of population dynamics. Conclusion The A. caelatus and A. tenuispinis are the two dominant species in the catfish catches along the west coast of India. Average length attained at the end of first year was estimated at 270 mm and 276 mm for A. caelatus and A. tenuispinis, respectively. Estimated K values, 0.70 year -1 for A. caelatus and 0.73 year -1 for A. tenuispinis indicated that both the species grow at a moderately faster rate. The exploitation ratio (E) estimated for A. caelatus was 0.50 and 0.51 for A. tenuispinis. This indicated that both the resources were exploited optimally leaving no chance for change in fishing efforts from present level, but a marginal increase in the efforts may be undertaken to increase their production. Though they appears as bycatch of shrimp trawling, results also ascertain increase of cod end mesh size of trawl in order that fish can achieve their full growth potential, as smaller species are being exploited. Acknowledgements Authors are thankful to the Director, Central Institute of Fisheries Education (CIFE), Mumbai for providing facilities for carrying out the work. References 1 Anon, Annual Report. Central Marine Fisheries Research Institute, Cochin, 133p, Mukundan C, Marine catfish resources of India: Exploitation and prospects: CMFRI Bulletin 40, Cent. Mar. Fish. Res. Inst., Cochin. 94p. 3 Chakraborty S K, Deshmukh V D, Khan M Z, Kuber Vidyasagar & Raje S G, Estimates of growth, mortality, recruitment pattern and maximum sustainable yield of important fishery resources of Maharashtra coast. Indian J. Mar. Sci., 26, Sekharan K V & Mojumder P, On the size of eggs found in the mouth of two males of catfish Tachysurus caelatus (Val.). J. Mar. Biol. Asso. India, 15 (1), Menon N G, Observation on the intraovarian ova of a few Tachysurids from Indian waters. Indian J. Fish., 32 (2), Menon N G & Muthiah C, Marine catfish resources of India. Biology of the important species of catfish. Bull. Cent. Mar. Fish. Inst., Kochi, 40, Raje S G, Some aspects of biology of catfishes Tachysaurus caelatus (Valenciennes) and Osteogeneiosus milataris (Linnaeus) from Mumbai. Indian J. Fish., 53 (3), Dan S S, Age and growth in the catfish, Tachysurus tenuispinis (Day) Indian J. Fish., 27(1&2): Shekharan K V, The depth distribution of catfishes T. thalassinus (Rupell) and T. tenuispinis (Day) in the northwestern Bay of Bengal. Indian J. Fish., 20 (1), Sekharan K V, On oil sardine fishery of the Calicut area during the year to Indian J. Fish., 9A (2), Gayanilo F C Jr, Sparre, P & Pauly D, FAO-ICLARM Stock Assessment Tools (FiSAT) users guide, FAO Computerized Information Series (Fisheries) No. 8, FAO, Rome, 3 diskettes and 124p. 12 Pauly D, Length-converted catch curves: a powerful tool for fisheries research in the tropics (Part I). ICLARM Fishbyte, 1(2), Pauly D, A selection of simple methods for the assessment of tropical fish stocks. FAO Fish., Circ. No. (729), 54p. 14 Bapat S V, Deshmukh V D, Krishnamorti B, Muthiah C, Kagwade P, Ramamirtham C P, Mathew K J, Pillai S K & Mukundan C, Fishery resources of exclusive economic zone of northwest coast of India. Bull. Cent. Mar. Fish. Res. Inst., 33, 86 p.

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