Iranian Journal of Fisheries Sciences 19(2) 793-813 2020 DOI: 10.22092/ijfs.2018.119873. Comparative assessment of population biology of three popular species, argenteus, Pampus chinensis and Parastromateus niger in the Bay of Bengal, Bangladesh

Karim E.1,3; Liu Q.1*; Forruq Rahman M.1; Khatun M.H.1; Protim Barman P.1; Shamsuzzaman M.M.2; Mahmud Y.3

Received: November 2017 Accepted: November 2018

Abstract are one of the most ample high priced fisheries of the Bay of Bengal, Bangladesh. The present study featuring the comparison of the life history parameters of three Pomfrets i.e. Silver (), Chinese (P. chinensis) and Black (Parastromateus niger) is based on the monthly length frequency data from the commercial landings from July 2015 through June 2016. The length (TL) of all three Pomfrets ranged from 8 to 55cm and weight (W) varied from 24 to 1302g. An allometric growth pattern was found in all cases when estimating LWR. The VBGF -1 parameters for silver pomfret was L∞= 54.6cm, K= 0.39yr while it was 54.6cm, 0.62yr-1, 57.75cm, and 0.94yr-1 for both Chinese and black pomfrets, respectively. Based on LCCC analysis the total mortality (Z), natural mortality (M) and fishing mortality (F) for silver and Chinese pomfrets were found to be the lowest compared with some previous studies related to the , whereas black pomfret showed higher mortality rates to some extent. The exploitation ratio (E=F/Z) of silver and Chinese pomfrets were lower than the Gulland (1971) criterion of demarcation point of 0.5 and was higher for black pomfret which showed over-exploited stocks. The YPR analysis also showed the heavily exploited state of black pomfret fishery, therefore, immediate management approach should be required to maintain sustainable stocks.

Keywords: Bay of Bengal, Pomfrets, Growth, Mortality, Exploitation

1-College of Fisheries, Ocean University of , Qingdao 266003, China 2-School of Environmental and Natural Resources Law, Ocean University of China, Qingdao 266100, China 3-Bangladesh Fisheries Research Institute (BFRI), Mymensingh-2201, Bangladesh *Corresponding author's Email: [email protected] 794 Karim et al., Comparative assessment of population biology of…

Introduction associated with other over the Pomfrets belong to the family muddy bottoms with coarse sands and Stromatidae (Pampus argenteus and P. feed mainly on zooplankton, salps, chinensis) and ctenophores, jellyfish, medusa and (Parastromateus niger) have been small benthic organisms (Last, 1997). widely distributed in coastal, estuarine Mean annual landings of Bay of and marine habitats ranging from 5-105 Bengal, Bangladesh indicate that meters in depth in the Bay of Bengal, pomfrets are abundant in the month of Bangladesh coast (Shahidhullah, 1986), November to April (FRSS, DoF). Some and are an extremely relished table previous studies of pomfrets of this in domestic and export markets. region by Pati (1982, 1985), Hussain et Pomfrets fishery of Bangladesh is al. (1977), Mustafa (1999), mainly mainly based on three popular species focused on the biology, feeding habit i.e. silver pomfret (P. argenteus), and breeding or spawning including Chinese pomfret (P. chinensis) and some demographic properties as well. black pomfret (P. niger) that comprises Significant writings on the fishery and more or less 95% of the total catches stock estimates especially of silver among the all pomfret fisheries (DoF, pomfrets of Bay of Bengal, Bangladesh 2016). Over the last 15 years, the belong to the fishery that existed over a annual average catch was about 21,890 couple of decades ago (Khan, 1982; t. Less than 4% of this came from Khan et al., 1992; Khan and Latif, industrial trawl landings of Bangladesh, 1997; Khan, 2000; Sivakami et al., comprising silver pomfrets (42.4%), 2003). Despite their commercial value, black pomfrets (29.7%) and Chinese detailed research on the recent pomfret pomfrets (23.4%). The remaining 98% fishery with special reference to the of landings was through artisanal population dynamics of these areas are captures which was mainly based on scanty and scattered. This study mainly both mechanized and non-mechanized deals with the assessment of population boats-capture fish from 10-50m depth characteristics of three commercially contributing to about 35%, 29% and important pomfrets of Bay of Bengal, 27% of black, silver and Chinese Bangladesh with special consideration promfrets, respectively (FRSS, DoF). to the comparison of their life history Most of this catch came from parameters too. Sundarban Mangrove Forest (SMF), Length-structured data for assessing adjacent coastal and marine areas in the stock and population dynamics study south and the Cox’s Bazar and were commonly used where age- Chittagong, southeast coast of structure data are limited (Sparre and Bangladesh. Venema, 1998). Age determination of Pomfrets are mostly inshore species pomfrets has not been possible, so that are also entitled amphidromous and length-based methods are applied to benthopelagic fish (Riede, 2004). They assess stocks in these areas usually form small schools or shoals (Parsamanesh et al., 1998; Morgan, Iranian Journal of Fisheries Sciences 19(2) 2020 795 1985). Age data are more tough and which is basically used to catch Hilsa painstaking to collect because the bends (sardine), set bag nets (SBN) and seine on the otolith were indistinct and not nets (TN) (Mustafa, 1999). For this easy to interpret (Morale-Nin and reason, the whole study was conducted Panfili, 2005). The dissimilarity in in three important marine landing spots parameters evaluated for pomfrets throughout the coastal belt of depends on many factors such as Bangladesh including Cox’s Bazar, temperature, geographical area, type of Chittagong, Kuakata and Pathorghata ecosystem and the approaches deployed (Figure 1). All of the biological data of for the assessment of parameters. silver, Chinese and black Pomfrets of Nevertheless, for the Bay of Bengal both sexes were collected between July area, it seems that the approaches used 2015 and June 2016 (12 months) from for the assessments are the key factor in different artisanal fishing vessels that the detected differences in the estimated captured fishes by using several gear parameters, which somewhat reflects like SBN, gill net, seine net etc. from the difference of the results acquired by the above mentioned landing stations applying the length-based methods. that were visited monthly. Best efforts This work is the first attempt to provide were given to sample identification and data on the parameters of growth and data was recorded together with their standing stocks of three pomfret species specific catch in weight and size in of the Bay of Bengal, Bangladesh, length. The total length (TL) of fish which will shed light on future research samples was measured to the nearest for fisheries scientists and researchers 0.1 cm and body weight (W) to the of various agencies for the sustainable nearest 0.1g. Fish were placed ventral management and production of pomfret side down and the upper lobe of the fishery. caudal fin depressed in line with the body axis (Compagno, 1984a). Length Materials and methods frequency and length-weight data of a Sampling total of 1472, 1402 and 1022 At present, artisanal fishery of individuals of silver pomfret, Chinese Bangladesh contributed to more or less pomfret and black pomfret, respectively 91% of total marine captures, the rest of both sexes’ were measured and data coming from industrial trawls. In were recorded in 3cm class intervals on artisanal catches, the maximum species the excel sheet. are caught with drift gill nets (DGN), 796 Karim et al., Comparative assessment of population biology of…

Figure 1: Visited Fish landing centers (red arrows) of Bangladesh for collecting data from July 2015 to June 2016.

Data analysis log10-transformed data (Le Cren, 1951) In this study, a computer software then calculated by using the power package named FiSAT II (FAO- function: W aLb where a is a constant ICLARM stock assessment tool, condition factor and b is slope or Gayanilo et al., 2005) was used to allometric growth parameter. After analyze the length frequency data. that, Actually, this software was developed  Evaluating initial value of mainly for analyzing length-frequency asymptotic length (L∞) and growth but also enables related analyses like constant (K) using the von size at age, growth, mortality rate, Bertalanffy growth function (VBGF) biological reference points, growth parameters of the method ELEFAN-I performance index, virtual population (Electronic Length Frequency analysis and so on. Analysis). The von Bertalanffy equation for growth in length

Steps of the procedure according to Haddon (2011) is: Lt =

Firstly, in order to assess length-weight L∞ (1–exp (-K (t– t0)), where Lt was relationship (LWR), TL and W of three the length at time t, L∞ was the species were calculated separately with asymptotic length, K was the growth Iranian Journal of Fisheries Sciences 19(2) 2020 797

coefficient and t0 was the carried out with the input values of hypothetical age or time where LWR parameters i.e. intercept (a), length was equal to zero. Additional slope (b) and growth parameters

estimated value of t0 was obtained by values e.g. asymptotic length (L∞), the empirical equation by Pauly growth coefficient (K) and mortality

(1983) as log10 (-t0) = -0.3922 – parameters values e.g. natural

0.275 log10 L∞ - 1.038 log10K. mortality (M) and fishing mortality  Estimation of instantaneous total (F) to evaluate the fishing mortalities mortality (Z) through length per length class by using the formula

converted catch curve method by of Sparre and Venema (1998). The t0 Pauly (1983) was used. Additional value was taken as zero. parameters of M and F (natural  Then the optimal fishing mortality

mortality and fishing mortality) were rate Fopt = M was determined as the also calculated. The regression limit of biological reference points

formula for Z is Ln (Nt) =Ln(N0)– Zt, for pomfrets in the Bay of Bengal,

where Nt is the population size at age Bangladesh following methods of

t and N0 is population size at zero Gulland (1969). (Pauly, 1980). The equation by  Estimation of yield per recruit (Y R-1) Pauly (1980) was used for natural values by using the model of

mortality (M) from log10 Beverton and Holt (1957)

M=0.0066–0.279 log10 L∞ +0.654 incorporated into the FiSAT-II

log10 K + 0.4634 log10 T. Where T= program (Gayanilo et al., 2005) 23oC was average annual surface through the formula

3 nK() tc t0 temperature of the water in the Bay M( t  tF )(M nK Qe t )( t  ) Y/(1 R FW ee c rc ) n  w   F M nK of Bengal, Bangladeshi waters in n0 were done. In which Y R-1 was which the stock of pomfrets occurs. w yield per recruit, t was the average The F (Fishing mortality) was c age of first capture, t was the evaluated by using the relationship λ asymptotically ages, t was the age of subtracting F=Z-M. The r exploitation ratio (E) was evaluated of recruitment, Ǫn was the constant by using the relationship of Gulland and equal to 1, -3,3 and -1 when n (1971a): E = F/Z = F/(F+M). was 0, 1, 2 and 3 correspondingly (Pitcher and Hart, 1982).  Estimating probabilities of capture by detailed analysis of the left  Lastly, estimating growth ascending part of the catch curve, performance index (Phi prime Φ') and by constructing a selection curve through following equations by by using Z (total mortality) and M Pauly and Munro (1984) Φ'= log10 K (natural mortality) including + 2 log10 L∞ and Φ= log10 K + 2/3 log10 W∞. asymptotic length (L∞) and growth coefficient (K).

 Length-structured virtual population

analysis (VPA) of three species were 798 Karim et al., Comparative assessment of population biology of…

Results parameter a and b for the three pomfret Length–weight relationship parameters species i.e. silver, Chinese and black (LWRPs) were described by the power equation The length-weight relationships of three as W= 0.1101 L2.4248 where R2=0.9879 pomfret species silver, Chinese and (n=1472), W=0.393L2.07 where R2= black are shown in Figure 2 where 0.9848 (n=1402) and W= 0.3539L2.1113 length ranged between 10 and 52 cm at where R2= 0.9887 (n=1022). Dominant average length 26.7 cm with lengths were found between 20 and SD±5.26cm for silver pomfret, between 31cm for P. argenteus, between 22 and 8 and 50 cm with SD±4.67cm for 30 cm for P. chinensis and between 23 Chinese and between 11 and 54 cm and 30 cm for P. niger, respectively with SD±5.56cm for black pomfret. (Table 1). The length–weight relationship

Table 1: Estimated key parameters of growth, mortality, exploitation and yield of three pomfret species of the Bay of Bengal, Bangladesh during July 2015 to June 2016. Population parameters Silver Pomfret Chinese Pomfret Black Pomfret

Intercept (a) 0.11 0.393 0.3539

Exponent (b) 2.4248 2.07 2.1113

Coefficient of determination (R2) 0.9879 0.9848 0.9887

Asymptotic length (L∞) 54.6cm 54.6cm 57.75cm

Growth coefficient (K) 0.39 yr-1 0.62 yr-1 0.94 yr-1

Theoretical age (t) at zero length (t0) - 0.44545 years -0.65443 years -0.84873 years

Goodness of fit (Rn) 0.197 0.118 0.246 -1 -1 -1 Total mortality (Z) 0.95yr at CI95% 1.53yr at CI95% 2.89yr at Cl 95% at 0.33 – 2.12 0.42 – 3.76 -0.31 – 7.21 Mean annual water temperature of Bay of 240C 240C 240C Bengal, Bangladesh Natural mortality (M) 0.72895 yr-1 0.98725 yr-1 1.2761 yr-1 Fishing mortality (F) F= Z-M 0.22105 yr-1 0.54275 yr-1 1.6139 yr-1

Exploitation rate (E) E= F/Z 0.2327 0.355 0.55844 M/K ratio 1.87 1.59 1.36

-1 -1 -1 Fmax 1.2 yr 2.0 yr 2.85 yr

-1 -1 -1 F0.1 1.0 yr 1.5 yr 1.6 yr Maximum mortality range (cm) 34-38 47-50 49-52

GPI Φ' (phi prime) 3.065 3.267 3.496

Dominant Length range (cm) 20-31 22-30 23-30

Dominant weight range (g) 191-478 302-423 304-545g

Sample size (n) 1472 1402 1022

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Silver Pomfrets Chinese Pomfrets

Black Pomfret

Figure 2: Length-weight relationship of three pomfret species i.e. Silver (n= 1472), Chinese (n= 1402) and Black (n= 1022) from the Bay of Bengal, Bangladesh.

Estimation of growth parameters (GPs) 0.62yr-1 and 0.94 yr-1 for P. argenteus, The method of ELEFAN-I in FiSAT II P. chinensis and P. niger, respectively. packages (Pauly, 1983) was used to The goodness fit index values (Rn) from estimate the L∞ (asymptotic length) and the ELEFAN-I routine (0.197 for silver, K (growth coefficient). Size distribution 0.118 for Chinese and 0.246 for black of length frequency data of the three pomfret) were constructed by the pomfret species were arranged at 3 cm totality of observation in this function. interval. The estimated values of L∞ and The hypothetical age of the three

K were obtained as L∞= 54.6cm, species at zero length was estimated as -1 54.6cm and 57.75cm while K= 0.39yr , t0= -0.44545 years for silver, -0.65443 800 Karim et al., Comparative assessment of population biology of… for Chinese and -0.84873 for black graphical representations of the output pomfret, respectively (Table 1). The VBGF curves are shown in Figure 3.

Silver Pomfrets

Chinese Pomfrets

Black Pomfrets

Figure 3: Comparative analysis of growth curves (restructured) for three pomfret species of the Bay of Bengal, Bangladesh with model of von Bertalanffy growth function (VBGF).

Iranian Journal of Fisheries Sciences 19(2) 2020 801

Mortality (M) and exploitation ratio equation, the value of natural mortality (ERs) was found (M= 0.72895yr-1, 0.98725yr- Rapid total mortality values for the 1 and 1.2761yr-1) and the fishing three pomfret species of the Bay of mortality (F= 0.22105yr-1, 0.54275yr-1 Bengal, Bangladesh Z=0.95yr-1, 1.53yr- and 1.6139yr-1) was obtained by the 1 and 2.89yr-1 for silver, Chinese and subtracting Z from M values of three black pomfret, respectively accordingly species silver, Chinese and black were constructed from the input values pomfret, respectively. The exploitation of VBGF growth parameters (L∞ and K) ratio (E= F/Z eg. 0.2327 for silver, in the length converted catch curve 0.335 for Chinese and 0.558 for black model described by Pauly (1983) (Fig. pomfret) was also achieved (Table 1). 4). Whereas by using Pauly (1980)

Silver Pomfrets Chinese Pomfrets

Black Pomfrets

Figure 4: Length converted catch curve of the three pomfret species from Bangladeshi waters.

Virtual population analysis (VPA) length weight relationship parameters

The value of growth parameters (L∞ and (a and b) were used to shape the length K), mortality parameters (M and F) and structured virtual population analysis 802 Karim et al., Comparative assessment of population biology of…

(LVPA) for the three pomfret species of indicated the higher fishing mortality of Bangladesh from the output graphics of the three pomfret species. LVPA by FiSAT (Figure 5) which

Silver Pomfrets Chinese Pomfrets

Black Pomfrets

Figure 5: Comparative study of Length structured virtual population analysis cohort (LVPA) for the three pomfret species of Bay of Bengal, Bangladesh.

Biological reference points (Yield per for Chinese pomfret and Fmax was -1 -1 recruit and probability of capture) 2.85yr and F0.1 was 1.6yr for black The relative yield per recruit (Y'/R) and pomfret. Since the current age at the biomass-per-recruit (B'/R) were first capture in case of silver pomfret determined as a function of Lc/L∞ and was approximately 1 year and Fcurrent

M/K of the three pomfret species by was 0.221, which was smaller than Fmax using the model of Beverton-Holt yield and F0.1 represented the stock was in per recruit with the knife-edge selection safe condition while safer stock result in FiSAT-II (Figure 6). When tc was 1 were also found from the analysis of the -1 the Fmax was estimated at 1.2yr and values of Fcurrent 0.543 for Chinese -1 F0.1 was 1.0yr for silver pomfret. On pomfret, which was less than Fmax and the other hand, when tc was 1 Fmax was F0.1. In the case of black pomfret, -1 -1 estimated at 2.0yr and F0.1 was 1.5yr Fcurrent was 1.614, which was less than Iranian Journal of Fisheries Sciences 19(2) 2020 803

-1 Fmax but greater than F0.1 indicating and 1.28yr for black pomfret and the over exploited stocks. When using current fishing mortality rates were low biological reference point, Fopt = M for silver and Chinese pomfret but high (Patterson, 1992), it was 0.73yr-1 for for black pomfret. silver pomfret, 0.987yr-1 for Chinese

Silver Pomfret Chinese Pomfret

Black Pomfret

Figure 6: Relative yield per recruitment model with the knife edge selection option for three pomfret species of the Bay of Bengal, Bangladesh (yellow line: Emax, Red line: E50 ).

Probabilities of capture (Figure 7) of recruit. The highest captured length the three pomfret species were also class values ranged from 46 cm and figured by projecting the down part of above for black pomfret whereas it was the catch curve backward and the length 37cm and lower for silver and 43cm at 50% catch was calculated from a plot and above for Chinese pomfret. of probabilities of capture which was integrated in calculating yield per 804 Karim et al., Comparative assessment of population biology of…

Silver Pomfrets Chinese Pomfrets

Black Pomfrets

Figure 7: Comparative study of probability of capture of Silver Pomfret, Chinese Pomfret and Black Pomfret of the Bay of Bengal, Bangladesh.

Growth Performance index (GPI) the monsoon as it was proved as the The von Bertalanffy growth parameters peak of the breeding season (Pati, of L∞ and K were used for the 1982). Nevertheless artisanal fishers estimation of growth performance roam for fishing to nearby littoral indices (phi prime or index Φ') of waters of 10–40 m depth and pomfret silver, Chinese and black pomfret of the are the major targeted fish in that Bay of Bengal, Bangladesh as 3.065, period, when they start their spawning 3.267 and 3.496, respectively. migration to their suitable spawning grounds with muddy-sandy bed rock Discussion (Pati, 1982). Hence this time is called In Bangladesh, banning of industrial lean period which is reflected in this trawl fishing activities started from the study too. Fishing not only shrinks middle of May to middle of July by the populations but also creates variations Department of Fisheries (DoF) when in the species inter-relations (Nikolskiii, fishing was postponed coinciding with 1980). Iranian Journal of Fisheries Sciences 19(2) 2020 805 LWR negative allometric growth as it will According to Gayanilo and Pauly grow differently in three dimensions (1997), length frequency distribution (Ricker, 1973; Wootton, 1998; analysis can be used for the resource Gayanilo et al., 2003). Comparative evaluation and management of the fish studies of slope values (b) acquired populations and this study was from various areas of these species are completely based on length composed presented in Table 2. Apart from the data. Length-weight relationship is the studies of Gujrat, Maharastra and basic parameter in fishery biology and Veraval of the Indian waters by Khan, stock assessment of fish (Abdurahiman 2000, most of the studies agree with the et al., 2004) which is also helpful to above observations. As the fish grows, estimate gonad maturity, changes in weight are relatively greater metamorphosis and feeding rate of fish than changes in length, due to (Le Cren, 1951). The value of a and b approximately cubic relationships from the LWR study, according to between weight and length. The LWR Ricker (1973) may be dissimilar parameter a, may vary daily, between the calculations done using the seasonally, and/or between habitats, grouped and individual data. The slope unlike the parameter b, which does not value b from the LWR study of the three vary significantly all through the year pomfret species were estimated at 2.425 (Bagenal and Tesch, 1978). for silver pomfret, 2.07 for Chinese Differences in LWR parameters may pomfret and 2.113 for black pomfret. represent spatial variation (Sparre et al., All of these values show negative 1989) due to the influence of water allometric growth because b value quality or food availability on fish equal to 3 indicates isometric growth growth as sandy-muddy shallow waters (that the fish holds the same proportion are the most favorable conditions for of its shape throughout the life). Larger pomfrets (Pati, 1982). or smaller than 3 indicates positive or

Table 2: Comparative study of estimated LWR parameters of Pomfret from studies in various areas of the world. Species Name Location Slop “b” Source Silver Pomfret Combined 2.4248 Current study (P. argenteus)

Chinese Pomfret Combined 2.07 Bay of Bengal, Bangladesh Do (P. chinensis)

Black Pomfret Combined 2.113 Do (P. niger) Chinese Pomfret Bay of Bengal, Bangladesh Combined 2.983 Mustafa, 1999 (P. argenteus) Silver Pomfret Bay of Bengal, Bangladesh Combined 2.929 Mustafa, 1999 (P. argenteus) Chinese Pomfret Karachi, Pakistan Combined 1.438* Quratulan, 2015 (P. chinensis) Silver Pomfret Maharastra State, India Combined 3.0058 Khan, 2000 (P. argenteus) Silver Pomfret Combined 3.0789 Gujrat, India Khan, 2000 (P. argenteus) Silver Pomfret Combined 3.0848 Karnataka, India Khan, 2000 (P. argenteus) 806 Karim et al., Comparative assessment of population biology of…

Table 2 continued: Black Pomfret Combined 2.792 Kerala, India Khan, , 2000 (P. niger) Black Pomfret Taiwan Strait Combined 2.9811* Tao et al., 2012 (P. niger) Silver Pomfret Verabal, India Combined 3.0504 Ghosh et al., 1995* (P. argenteus) b = slope, * using fork length (FL)

Growth parameters expected growth curve for adults while

Von Bertalanffy growth function positive values of t0 indicates slower (VBGF) parameters were evaluated by growth (King, 1997). The coefficient of ELEFAN-I method using FiSAT II natural mortality M is proportional with (Gayanilo et al., 2005) software the growth coefficient K of a fish and package, which is fundamentally inversely proportional to the asymptotic unintended and does not rely on length (L∞) and longevity (Beverton and assessing the parameters of cohort Holt, 1956). In this study, asymptotic distribution directly. Therefore, it length (L∞) was slightly higher provides a merely weak assumption compared with the estimated values by about the distribution of sizes within the Khan (2000) from the Indian waters, as cohorts. The length models of each well as by Haque (1998) and Mustafa cohort are permanent to lie upon a (1999) from the Bay of Bengal (Table curve labelled by growth models i.e. 3) which may be due to the use of total von Bertalanffy growth model results in length of the species. However, the the provision of a strong assumption calculated growth coefficient (K) value about growth (Pitcher & Hart, 1982). for silver pomfret in this study were The estimated asymptotic length of lower as compared to the values from the three pomfret species, L∞= 54.6cm different areas whereas the K value of for silver, 54.6cm Chinese and 57.75cm black pomfret was higher. Conversely, for black pomfret were found in the the goodness of fit (Rn) of the model present study which are within the estimated in this study was between 0 acceptable range compared with the and 1 and when it is close to 1, it shows maximum length of 52cm for both a better fit (Gayanilo et al., 2003). The silver and Chinese pomfret and 55 cm score of Rn can be used for the for black pomfret (Table 1). The seasonally oscillating growth curves estimated L∞ parameter of the VBGF that fits best in the length frequency should be quite close to the maximum data to find the K values for the growth length of the fish, while t0 should be analysis through the ELEFAN-I less than zero so that the fish may have method. However slight differences a positive length at zero age (Moreau et found in asymptotic length from al., 1986). The t0 value quantifies the different areas maybe because of the growth rate in adults and adolescents, effect of physico-chemical and negative values of t0 mean higher biological factors on fishing practice. percentage of juveniles than the

Iranian Journal of Fisheries Sciences 19(2) 2020 807

Table 3: Summary of estimated growth parameters of Pomfret in different regions.

Species Name Location L∞ (cm) K Source

Silver Pomfret 54.6 0.39 -0.44455 Present Study (P. argenteus)

Chinese Pomfret Bay of Bengal, 54.6 0.62 -0.6544 Do (P. chinensis) Bangladesh

Black Pomfret 57.75 0.94 -0.8487 Do (P. niger) Black Pomfret Bay of Bengal, 41.0 0.59 - Mustafa, 1999* (P. niger) Bangladesh Silver Pomfret North-eastern Bay 29.8 0.53 - Haque, 1998* (P. argenteus) of Bengal Chinese Pomfret North-eastern Bay 38.1 0.67 - Haque, 1998* (P. chinensis) of Bengal Silver Pomfret Maharastra, India 39 0.7 - Khan, 2000 (P. argenteus) Silver Pomfret Gujrat, India 39.5 0.75 - Khan, 2000 (P. argenteus) Silver Pomfret Karnataka, India 36 0.69 - Khan, 2000 (P. argenteus) Black Pomfret Kerala, India 56 0.73 - Khan, 2000 (P. niger) Silver Pomfret Veraval 41.57 0.64 -0.0315 Ghosh et al., 2009 (P. argenteus) Silver Pomfret Parsamanesh et al., 40 1.1 -0.45 (P. argenteus) 1998 Chinese Pomfret Parsamanesh et al., Persian Gulf 36.8 0.8 -0.52 (P. chinensis) 1998 Black Pomfret Taiwan Strait 34.11 0.3157 -1.7045 Tao et al., 2012 (P. niger) Silver Pomfret East China Sea & 38.44 (F) 0.26 -0.96 Lee et al., 1992 (P. argenteus) Korean Waters 33.57 (M) 0.24 -1.10

* Fork length, L∞= asymptotic length (cm -TL), K = growth rate/yr, t0 = hypothetical age (yr) at which length of the fish is equal to zero

Mortality rate and Chinese pomfret, which may be Mortality parameters are natural due to the high market demand, mortality, total mortality and fishing therefore, resulting in the higher fishing mortality ratio which may not stop at a mortality and some other environmental constant level, but may change from issues that may effect on natural time to time (Sparre and Venema, mortality. Comparatively, the estimated 1989). The estimated total mortality natural mortality was the lowest among rate of the three pomfret species of the the other reported values of different present study was lower in the case of areas in case of silver pomfret and also silver and Chinese pomfret compared lower to some extent for Chinese with some previous studies and higher pomfret. The analyzed fishing mortality for Black pomfret except in the study in rate of silver and Chinese pomfret were Kerala, India by Khan (2000) that are also smaller to some extent in the shown in Table 4. Those plotted values present study compares to that in other (Table 4, Fig. 4) were overall higher studies. Nevertheless, for black than that in the current study for silver pomfret, except in the study in 808 Karim et al., Comparative assessment of population biology of…

Karnataka, Indian waters by Khan pomfret, the exploitation value (F/Z) of (2000), both the values were found to silver and Chinese pomfret were also be slightly higher because of its higher recorded as the lowest in the current market demand and moderately less findings as the observed values of cost compared with other pomfret exploitation from the other studies. species that are suitable for mass Exploitation ratio is a measure to consumption in Bangladesh. The lower estimate the level of utilization of the values of natural mortality of silver and fishery. According to Gulland (1971) Chinese pomfret may be different due criteria, when the exploitation ratio is to the water temperature (24⁰C in the above 0.5 then the stock is considered Bay of Bengal, Bangladesh) and higher as overfished or over-exploited. In this fishing mortality rate is only influenced study, only black pomfrets showed the by increasing fishing efforts in the case exploitation ratio of E= 0.558 indicating of black pomfret. Natural mortality that the stock is over-exploited. mostly depends on some factors, i.e. Increased fishing pressure persisted on predation, old age, environmental stress the black pomfret population in the Bay and parasitic effects or diseases (King, of Bengal, Bangladesh, and it can thus 1997). According to Beverton and Holt be asserted that the population in this (1957), in most of the fish species the area has not been managed properly. M/K ratio ranging from 1.12 to 2.50 Therefore, effective management plans were observed. M/K ratio of the current are urgently needed to maintain the study (1.87 for silver pomfret, 1.59 for stocks of this fish in the Bay of Bengal, Chinese pomfret, and 1.36 for black Bangladesh. pomfret) were within the above range (Table 1). Similarly, except for black

Table 4: Estimated mortality rates of Pomfrets from different regions and comparisons with the current study. Species Name Area Z M F Source Silver Pomfret 0.95 0.729 0.221 Current study (P. argenteus)

Chinese Pomftret Bay of Bengal, 1.53 0.987 0.543 Do (P. chinensis) Bangladesh

Black Pomfret 2.89 1.276 1.614 Do (P. niger) Black Pomfret Bay of Bengal, 2.42 1.16 1.26 Mustafa, 1999 (P. niger) Bangladesh Silver Pomfret North-eastern Bay of 1.97 1.18 0.79 Haque, 1998 (P. argenteus) Bengal Chinese Pomfret North-eastern Bay of 2.12 1.29 0.83 Haque, 1998 (P. chinensis) Bengal Silver Pomfret Maharastra, India 4.033 1.49 2.984 Khan, 2000 (P. argenteus) Silver Pomfret Gujrat, India 3.165 1.05 2.114 Khan, 2000 (P. argenteus) Silver Pomfret Karnataka, India 5.054 2.52 2.527 Khan, 2000 (P. argenteus) Iranian Journal of Fisheries Sciences 19(2) 2020 809

Table 4 continued: Black Pomfret Kerala, India 4.4 0.88 3.52 Khan, 2000 (P. niger) Silver Pomfret Veraval, India 3.31 1.2 2.11 Ghosh et al., 2009 (P. argenteus) Black pomfret Taiwan Strait 1.82 0.74 1.09 Tao et al., 2012 (P. niger) Silver Pomfret East China Sea & 1.5 0.76 0.74 Lee et al., 1992 (P. argenteus) Korean Waters Z = total mortality, M = natural mortality, F = fishing mortality

Growth performance index (Phi prime Biological reference points (BRPs) Φ') BRPs are now widely used for the GPI compare the growth performance conservation and management of of the fish species with different fisheries resources as the level of populations of the same or different fishing mortality (Haddon, 2011). F0.1 environmental fish populations and and Fmax are the most familiar points higher values indicate higher growth which are frequently used in fisheries (Pauly and Munro, 1984). The management (Hilborn and Walters, comparison of the growth rates is a 1992). The target biological reference matter of multiple factors of the growth point Fmax is the F, which produces the rate (K) and the asymptotic length (L∞). maximum value of yield-per-recruit

According to the Pauly and Munro (YPR). F0.1 is another target reference (1984), parameter Phi prime (Φ') acts as point at which the marginal gain in an indicator of the inconsistency on the YPR decreased to an arbitrary 10% accuracy of the estimated growth from that at F=0. (Hilborn and Walters, parameters of the same or related 1992). species of stocks. This index is also Biological reference points (BRPs) endorsed by the von Bertalanffy growth from the procedures Fopt =M, by parameters (L∞ and K) because it Patterson (1992) which are Fopt= 0.73 facilitates the program between the for silver pomfret, 0.987 for Chinese species and growth (Pauly and Munro, pomfret, and 1.28 for black pomfret. 1984). In this study, the estimated value The YPR (Figure 6 and Table 1) of GPI of the three pomfret species indicated the values of Fmax and F0.1 of were 3.065 for silver, 3.267 for Chinese the three pomfret species when tc was and 3.496 for black pomfret which are assumed to be 1. Since the age of first considered to specify slow growth. capture during the current study was Apart from the genetic structure, approximately one year, the current determining the growth potential of a fishing mortality rate (Fcurrent) of species, overfishing, dietary patterns 0.221yr-1 for silver pomfret and 0.543 and their utilization may affect the yr-1 for Chinese pomfret were lower growth performance of a specific than Fopt, Fmax and F0.1. Hence, the species. status of silver pomfret and Chinese pomfret stocks are now in safer 810 Karim et al., Comparative assessment of population biology of… conditions and it is recommended to Administration) for sponsorship during strictly maintain the current fishing his doctoral degree because this work is efforts of the Bay of Bengal, supported by the special research fund Bangladesh. Because of limited of Ocean University of China information and available data, it is (201022001). very hard to compare the life history parameters with the others i.e. that what References biological and ecological differences Abdurahiman, K.P., Harishnayak, contribute to this process. In case of T., Zacharia, P.U. and Mohamed, black pomfret, current fishing mortality K.S., 2004. Length-weight -1 (Fcurrent) was 1.61yr which was higher relationship of commercially than Fopt and F0.1 indicating that the important marine fishes and stocks of this fish are now over- shellfishes of the Southern Coast of exploited, therefore, immediate steps Karnataka, Indian Journal of should be taken for its sustainable Fisheries, 27, 9-14. management. In comparison with some Bagenal, T.B. and Tesch, P.W., 1978. other studies on silver and Chinese Age and growth. In: Bagenal, T. pomfret from the Arabian and Indian (ed.). 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