Thalassas, 3(1) January 214: 67-73 An International Journal of Marine Sciences Growth, mortality and yield per recruit of the Randall s threadfin bream Nemipterus randalli (Russell, 1986) from the Arabian Sea off Oman Fatma Al-Kiyumi, Sahar Mehanna* & Nabila Al-Bulush *Marine Science and Fisheries Centre sahar_mehanna@yahoo.com ABSTRACT Growth, mortality, population and yield parameters of Nemipterus randalli were studied based on the data collected during the trawl survey for demersal fisheries along the Arabian Sea coast of Oman. Total specimen lengths ranged from 4 to 2.2 cm and weights from 1.5 to 15 g. Maximum age was 2 years for both sexes. The length weight relationship was described as W =.135 L 3.642 (r 2 =.94). The VBGF parameters in length for this species were estimated as follows. L = 22.12 cm and K =.64 y -1. The total, natural and fishing mortalities were calculated as 3., 1.4 & 1.6 respectively. The exploitation ratio and rate were calculated as.53 &.51 respectively. The yield per recruit study shows that it can be raised by increasing the length at first capture and fishing efforts. The results of stock assessment show that though there is scope to increase the exploitation level by 31.3% to get the maximum Y /R, the increase in yield will be marginal (6.7%). Key words: Arabian Sea, Nemipteridae, Nemipterus randalli, growth, mortality, yield per recruit. RESUMEN Se estudian los parámetros relacionados con el crecimiento, mortalidad, población y rendimiento de Nemipterus randalli utilizando los datos obtenidos durante la campaña de estudio de pesquerías demersales a lo largo de la costa del Mar Arábigo en Omán. Las longitudes totales de los especímenes variaron entre 4 y 2,2 cm y los pesos entre 1,5 y 15 g. La edad máxima encontrada fue de 2 años en ambos sexos. La relación peso-longitud se describió como W =.135 L 3.642 (r 2 =.94). Los parámetros VBGF sobre longitud para la especie citada se estimaron como sigue: L = 22,12 cm y K =,64 año -1. Las mortalidades total, natural y por pesca se calcularon en 3,, 1,4 y 1,6 respectivamente. La tasa de explotación y su razón se estimaron en,53 y,51 respectivamente. El estudio demuestra que es posible incrementar el rendimiento por reclutamiento incrementando la longitud en primera captura y el esfuerzo pesquero. El estudio de la población muestra que aunque todavía hay campo para incrementar el nivel de explotación un 31,3% para obtener el máximo en Y /R, el incremento en rendimiento sería pequeño (6.7%). Palabras clave: Mar Arábigo, Nemipteridae, Nemipterus randalli, crecimiento, mortalidad, rendimiento por reclutamiento. Thalassas, 3(1) January 214 67
Fatma Al-Kiyumi, Sahar Mehanna & Nabila Al-Bulush Introduction The threadfin breams of the genus Nemipterus (family Nemipteridae) are widespread throughout the tropical and subtropical Indo-West Pacific region and more than 2 species are recognized (Russell, 199). They are small to moderate-sized fishes and most inhabit shallow sand or mud bottoms, and are taken commercially by hook-and-line and bottom trawl. They most abundant in depths of 2 to 5 m and feed mainly on small shrimps, squid, small fishes and benthic animals (Russell, 1993). Many biological studies have been done for the genus Nemipterus as those species are commercially important in many parts of the world. Therefore, stock parameters such as for age, growth and mortality have been examined to manage them properly. Randall s threadfin bream, Nemipterus randalli is distributed in the Western Indian Ocean including the east and southwest coast of India, Pakistan, Arabian Gulf, Arabian Sea, Red Sea, Gulf of Aden, east African coast, Seychelles and Madagascar (Randall, 1995). This species has been previously misidentified as Nemipterus mesoprion. It is a common fish in Oman waters and locally named as Ghazwan. Nemipterus randalli is caught in a multigear and multispecies demersal fisheries in Arabian Sea. Unfortunately, since there is no catch statistics for threadfin bream, accurate estimates of neither the yield nor fishing effort of this species are available. Since there is no any information about threadfin bream species in Oman waters, an evaluation of the stock status of this species is urgently needed. The objective of this study was to provide information on the biology, population dynamics, and stock assessment of N. randalli in the Arabian Sea waters. The results obtained in this study will help the decision makers to identify the reference point for randall s threadfin bream management. Material and Methods The data used for this analysis was obtained off the Arabian Sea coast of Oman during the period from September 27 to September 28. Samples were taken during five trawl surveys of 47 days for each using RV Al-Mostakila I. The total lengths of 368 fish were measured and a subsample of 1749 specimens (83 males and 919 females) was taken for biological analysis (length, weight, sex and maturity stage). As there is no significant difference in size distribution between sexes, length frequency distributions for the sexes combined (Fig. 1) were used for the analysis. Three methods were used to study age and growth of N. randalli; ELEFAN programme (Gayanilo et al., 1988), By Bhattacharya (1967) and the Wetherall et al. (1987) plot which gives an estimate of L and Z/K. Length-weight relationship was computed for males, females and pooled data following LeCren (1951). Total mortality coefficient Z was estimated using the length converted catch curve (Pauly, 1983) method, and the natural mortality coefficient M was estimated by Pauly s empirical formula (198), while the fishing mortality coefficient F was calculated by subtracting M from Z. The exploitation ratio E was calculated by the formula E = F/(M+F) (Gulland, 1971) and the exploitation rate U was calculated as U = F(1-e -z )/M+F (Beverton and Holt, 1957; Ricker, 1975). Frequency The mid-point of the smallest length group in the 12 1 8 6 4 2 n= 368 Sep Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep 27 28 Months Figure 1: Monthly length frequency distribution for Nemipterus randalli. catch during the survey period was taken as length at recruitment (L r ). The length corresponding to the first value in the descending limb of the length converted catch curve was taken as the length at first capture (L c ). For studying the effects of change in the exploitation pattern, Beverton and Holt s (1966) relative yield per recruitment analysis was done by using different values of E. Results and Discussion Length composition and Sex ratio Males (n = 83) were not significant larger than females (n = 919) in total length (P >.5; Fig. 2). Length frequency distributions showed no significant differences in the range of sizes between sexes; most females ranged from 1 to 15 cm TL and males from 1 to 14 cm TL. The highest mean length was recorded in August and September and the lowest during January-March with a length range of 4-2.2 68 Thalassas, 3(1) January 214
Growth, mortality and yield per recruit of the Randall s threadfin bream Nemipterus randalli (Russell, 1986) from the Arabian Sea off Oman Frequency 16 14 12 1 8 6 4 2 Male Female 7.5 8.5 9.5 1.5 11.5 12.5 13.5 14.5 15.5 16.5 17.5 18.5 19.5 2.5 Mid-length (cm) Fig. 2. Length frequency distribution for males and females Nemipterus randalli Figure 2: Length frequency distribution for males and females Nemipterus randalli. 16 14 12 Mean length 1 8 6 4 2 Sep Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep Month Fig. 3. Monthly mean lengths for Nemipterus randalli Figure 3: Length frequency distribution for males and females Nemipterus randalli. Frequency 45 4 35 3 25 2 15 1 5 Male Female Sep Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep Month Figure 4: Monthly mean lengths for Nemipterus randalli. cm for pooled data (Fig. 3). The mean length of N. randalli off Oman is larger during monsoon due to the movement of larger fish from relatively deeper water into shallower areas. The same finding was observed by Murty et al., 1992 and Joshi, 25. Females were outnumbered males with an overall sex ratio 1:1.11 male:female, this ratio is significantly different from the ideal ratio 1:1 (χ 2 = 4.53; P <.5). Monthly male:female ratio showed a fluctuation from month to month, where females outnumbered males in November, April and May. Also, while the most months didn t show a significant difference in sex ratio, May, October and November showed a highly significant difference between sexes. The highest percent of males and females was recorded during April and May (Fig. 4). Thalassas, 3(1) January 214 69
Fatma Al-Kiyumi, Sahar Mehanna & Nabila Al-Bulush Weight (g) 16 14 12 1 8 6 4 2 Male y =.66x 3.3247 R 2 =.9314 5 1 15 2 Length (cm) 16 14 Female Weight (g) 12 1 8 6 4 2 y =.19x 3.1569 R 2 =.9272 5 1 15 2 Length (cm) Figure 5: Length weight relationship for males and females Nemipterus randalli. Length-weight relationship A sample of 83 males ranging from 8 to 2.2 cm TL and from 3 to 15 g total weight and 919 females with length range 7-19.7 cm and weight range of 3-145 g were used to estimate the length weight relationship. As a considerable part of the catch were unsexed, the length-weight relationship was also estimated for all data pooled (length range was 4-2.2 cm with weights of 1.5-15 g). The obtained equations (Fig. 5) were: Male: W =.66 L 3.3247 Female: W=.19 L 3.1569 Pooled: W=.135 L 3.642 An allometric growth was observed for males and females while an isometric growth was noticed for pooled data. This may be due to consider the small specimens in the calculations. The significance of variation between b values of the sexes was tested by ANOVA and the difference was not significant at 5% level. Age and growth Plotting of the histogram and obtaining the modes was done using the method of Bhattacharya (1967). Two discernible cohorts appear to be present in the sample (Fig. 6). The mean lengths of the two cohorts were 14.5 and 19.6 cm TL. The Von Bertalanffy plot was used to obtain the growth parameters and the L estimate was 22.12 cm and the curvature constant K estimate was.64 per year. The asymptotic length obtained by the three methods (Figs. 6, 7 & 8) do not vary much and the growth coefficient K obtained by the three methods was more or less same (L = 21.53 cm and K =.67 by ELEFAN and L = 22.19 cm and K =.61 by Wetherall et al. plot). Also these results are agreeing with those reported for N. mesoprion the most similar nemipterid species for N. randalli. At Kakinada the estimated L and K of N. mesoprion were 21.9 cm and.83 year -1 respectively (Murty, 1981). At Chennai the estimated L was 2.7 cm and K= 1.8 (Vivekanandan, 1991). Using the ELEFAN programme Murty et al. (1992) estimated L and K off Cochin as 24.4-27.3 cm and.51-.62 year -1. At Mumbai, N. mesoprion grows to 14.7, 21.5 and 25.2 cm at the end 7 Thalassas, 3(1) January 214
Growth, mortality and yield per recruit of the Randall s threadfin bream Nemipterus randalli (Russell, 1986) from the Arabian Sea off Oman same author gave L value as 27.4 cm and K as.85 per year. Fig. 6. Bhattacharya method Figure 6: Bhattacharya method. Fig. 7. ELEFAN plot Figure 7: ELEFAN plot. Fig. 8. Wetherall plot Figure 8: Wetherall plot. Fig. 9. Length converted catch curve Figure 9: Length converted catch curve. of I-III years of life and the estimated L was 27.4 cm and K was.76 year -1 (Chakraborty, 22). In Cochin, N. mesoprion reaches 15.8, 22.4 and 25.3 cm at the end of first, second and third year respectively and the length obtained by LFSA package was 15.9, 21.8, 24.4 and 25.4 cm at the end of I-IV years (Joshi, 25). The same author gave L value as 27.4 cm and K as.85 per year. Mortality and exploitation ratio The catch curve analysis based on length distributions as described in Pauly (1983) was applied and the estimate obtained for the total mortality coefficient was Z = 3. per year. Using Pauly s formula, (Pauly, 198) a natural mortality M = 1.4 per year was obtained. Accordingly Thalassas, 3(1) January 214 71
Fatma Al-Kiyumi, Sahar Mehanna & Nabila Al-Bulush Fig. 1. Relative yield per recruit analysis Figure 1: Relative yield per recruit analysis. the fishing mortality estimate was 1.6 per year (Fig. 9). The exploitation ratio and rate were estimated as.53 and.51 respectively indicating that this species was in its optimum status. Estimation of relative yield per recruit Relative yield Y /R and biomass B /R per recruit were estimated using the Beverton and Holt (1966) method. The relative yields and biomass determined relative to a range of values for the exploitation rate are plotted in Figure 1. A maximum Y /R was obtained at E =.68 but the raising fishing effort to such level will be associated with a negligible increase in Y/R (6.7%) and a slight decrease in B /R (4%). Also, the exploitation rate which maintain 5% of the spawning stock biomass (E=.34) was found to lower than the current E (.51) Conclusion Nemipterus randalli appears to be exploited under its optimum level and there is a scope for a considerable extension of the fishery. But any recommendation to increase the effort in a multi-species gear should consider all the components of the fishery by that gear. Also, before any advice to increase the fishing effort, a more precise assessment would be required and a sampling programme for the commercial landings should be established to provide total catches by size groups. Also, an investigation for the impact of the fishery independent factors like upwelling, predation and other changes in environmental parameters on the growth and recruitment should be done. Finally, improving the catch statistics recording system to cover all species caught from Oman coasts should be considered. References Beverton, RJH, Holt, SJ, 1957. On the dynamics of exploited fish populations. Fish. Invest. Minist. Agric. Fish Food. G.B. (2 Sea Fish), 19: 533pp. Bhattacharya, CG, 1967. A simple method of resolution of a distribution with Gaussian components. Biometrics, 23: 115-135. Chakraborty, SK, 22. Growth, mortality and stock assessment of Nemipterus mesoprion (Bleeker) from Mumbai waters. Indian J. Fish., 49 (4): 389-396. Erguden, D, Turan, C, Gurlek, M, Yaglioglu, D, Gungor, M, 21. Age and growth of the Randall s threadfin bream Nemipterus randalli (Russell, 1986), a recent Lessepsian migrant in Iskenderun Bay, northeastern Mediterranean. J. Appl. Ichthyol., 26 (3): 441 444. Gayanilo, FCJr, Soriano, M, Pauly, D, 1988. A draft guide to COMPLEAT ELEFAN. ICLARM Software Project 2: 65pp. Gulland, JA, 1971. The fish resources of the oceans. West by fleet. Survey, Fishing News (Books) Ltd. For FAO: 255pp. Joshi, KK, 25. Biology and population dynamics of Nemipterus mesoprion (Bleeker) off Cochin. Indian J. Fish., 52 (3) : 315-322. Le Cren, E.D., 1951. Length-weight relationship and seasonal cycle in gonad weight and condition of the perch (Perca fluviatilis). J. Anim. Ecol., 2: 21-219. Murty, VS, 1981. Observations on some aspects of biology of the threadfin bream Nemipterus mesoprion (Bleekeri) from Kakinada along the east coast of India. Indian J. Fish., 28: 199-27. Murty, VS, 1982. Observations on some aspects of biology of threadfin bream Nemipterus mesoprion (Bleeker) from Kakinada. Indian J. Fish. 28(1/2): 199-27. Murty, VS, Rao, TA, Srinath, M, Vivekanandan, E, Somasekharan Nair, KV, Chakraborty, SK, Raje, SG, Zacharia, PU, 1992. Stock assessment of threadfin breams (Nemipterus spp.) of India. Indian J. Fish., 39 (1&2). 72 Thalassas, 3(1) January 214
Growth, mortality and yield per recruit of the Randall s threadfin bream Nemipterus randalli (Russell, 1986) from the Arabian Sea off Oman Randall, JE, 1995. Coastal Fishes of Oman. University of Hawaii Press, Honolulu, Hawaii. 217 pp. Ricker, WE, 1975. Computation and interpretations of biological statistics of fish populations. Bull. Fish Res. Bd.Can., 191: 382 pp. Russell, BC, 199. Nemipterid fishes of the world (threadfin breams, whiptail breams, monocle breams, dwarf monocle breams, and coral breams). Family Nemipteridae. An annotated and illustrated catalogue of nemipterid species known to date. FAO Fisheries Synopsis no. 125, 12. FAO, Rome. Russell, BC, 1993. A review of the threadfin breams of the genus Nemipterus (Nemipteridae) from Japan and Taiwan, with description of a new species. Japanese J. Ichthyol., 39: 295 31. Vivekanandan, E, 1991. Spawning and growth of three species of threadfin breams off Madras. Indian J. Fish., 38 (1) : 9-12. Vivekanandan, E, James, DB, 1986. Population dynamics of Nemipterus japonicus (Bloch) in the trawling grounds of Madras. Indian. J. Fish., 33: 145-154. Wetherall, JA, Pavovina, JJ, Ralston, S, 1987. Estimating growth and mortality in steady state fish stocks from length frequency data. In : Theory and application of length based methods in fisheries research. D. Pauly and G.Morgan (Eds.)., 13: 53-74. Zacharia, PU, Nataraja, GD, 23. Fishery and biology of threadfin bream, Nemipterus mesoprion from Mangalore Malpe. Indian J. Fish., 5 (1): 1-1. (Received: July, 7, 213; Accepted: October, 24, 213) Thalassas, 3(1) January 214 73
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