Population parameters of Lepturacanthus savala from the trawl catches in the north-eastern part of the Bay of Bengal, Bangladesh were investigated based on length frequency data, using complete ELEFAN computer program. The asymptotic length (Lα) and growth constant (K) were estimated to be 106.50 cm (total length) and 0.80/year respectively. Based on these growth parameters, the total mortality (Z) was estimated to be 1.89. The estimated values for natural mortality (M) and fishing mortality (F) were 1.08 and 0.81 respectively. The estimated value for the exploitation rate (E) using the length converted catch curve was 0.43. The recruitment pattern showed two peaks per year. The estimated sizes of L. savala at 25, 50 and 75% probabilities of capture were 57.49, 60.39 and 63.28 cm respectively. The estimated length weight relationship for combined sex was W=0.00093 TL(super)2.9

Amin, S.M.N.

Haque, M.A.

Mustafa, M.G.

Zafar, M.

Aquatic Commons

Bangladesh]. Fish. Res., 4(2), 2000:179-184 
Population dynamics of the ribbon fish, Lepturacanthus 
savala (Cuvier 1829) from the north-eastern part of the Bay 
of Bengal 
M.G. Mustafa1•*, M. Zafar, M.A. Haque and S.M. Nurul Amin1 
Institute of Marine Science, University of Chittagong, Chittagong4331, Bangladesh 
1 Bangladesh Fisheries Research Institute, Mymensingh 2201 
*Correspondiong author 
Abstract 
Population parameters of Lepturacanthus savala from the trawl catches in the north-
eastern part of the Bay of Bengal, Bangladesh were investigated based on length 
frequency data, using compleat ELEF AN computer program. The asymptotic length (L 
oo) and growth constant (K) were estimated to be 106.50 em (total length) and 0.80/year 
respectively. Based on these growth parameters, the total mortality (Z) was estimated to 
be 1.89. The estimated values for natural mortality (M) and fishing mortality (F) were 
1.08 and 0.81 respectively. The estimated value for the exploitation rate (E) using the 
length converted catch curve was 0.43. The recruitment pattern showed two peaks per 
year. The estimated sizes of L. savala at 25, 50 and 75 percent probabilities of capture 
were 57.49, 60.39 and 63.28 em respectively. The estimated length weight relationship for 
combined sex was W = 0.00093 TL 2·97 
Key words: Population dynamics, L. savala, Bay of Bengal 
Introduction 
Lepturacanthus savala (F. Trichiuridae) is the most abundant and commercially 
important fish in the Bay of Bengal. It is locally known as "Chari Mach". It forms about 
2.5% of the total demersal trawl catch (Lamboeuf 1987) and account for 0.83% of the 
estimated total shrimp trawl production for 1989-90 (Mustafa and Khan 1992). They feed 
on teleostean fishes, shrimps, other crustacean and cephalopods (Mustafa and Begum 
1994 ). Dried fish is very popular all over the country and also exported to the other 
countries like U.K., Singapore, Middle-East and SriLanka. 
There is no published information on population dynamics of Lepturacanthus savala 
in Bangladesh. In the present study, the population parameters of L. savala were 
estimated to assess its stock in the north-eastern part of the Bay of Bengal. 
M.G. Mustafa et al. 
Materials and methods 
Collection of data 
Length frequency data of L. savala were collected from trawler catches in the north-
eastern part of the Bay of Bengal during the period October 1996 to September 1997 by 
making regular fortnight field visits to the major fish landing centres in Firingibazar, 
Chittagong. More than eight trawlers of Sea Resources Group Companies Ltd. 
Bangladesh were sampled randomly. On each sampling day, total lengths of 100-200 fish 
obtained by random sampling were measured to the nearest 0.1cm using a measuring 
scale. 
Analysis of data 
Monthly length frequency distribution of L. savala for each month was analysed 
using compleat ELEFAN computer program (Gyanilo et al. 1989). The program was also 
used to estimate the parameters of the von Bertalanffy growth equation. The fitting of 
the best growth curve was based on the ELEFAN I program, which allows the line to 
pass through the maximum number of peaks of the length frequency distribution. With 
the aid of the best growth curve the growth constant (K) and the asymptotic length (Loo) 
were estimated. Additional estimate of Loo and Z/K value were obtained by plotting L 
minus L' on L (Wetherall1986 as modified by Pauly 1986), i.e. 
L- L' =a+ bL' 
where, L oo =-alb and Z/K = - (1 + b)/b 
where L is defined as the mean length, computed from L' upward, in a given 
length-fre_guency sample while L' is the limit of the first length class used in computing a 
value of L. 
The growth performance of L. savala population in terms of length growth was 
compared using the index of Pauly and Munro (1984). i.e. 
<j>' = Log 10 K + 2 Log10 Loo. (Where L oo is the asymPtotic length in em and K is the 
growth constant per year}. 
The instantaneous total mortality coefficient (Z) was estimated using the length 
converted catch curve method which has been incorporated into the compleat ELEFAN 
computer program (Gayanilo et al. 1989). Natural mortality rate (M) was estimated using 
Pauly's empirical relationship (Pauly 1980) i.e. · 
Log10 M = - 0.0066 - 0.279 Log10 L= + 0.6543 Log10 K + 0.4634 Log10 T 
where L= is expressed in em and T, the mean annual environmental water 
temperature in ac (here it was 28°C). 
Fishing mortality (F) was obtained by subtracting M (natural mortality) from Z 
(total mortality) and exploitation rate (E) was obtained from F/Z (Gulland 1971). 
Recruitment pattern was obtained by backward projection on the length. 
Using Pauly's empirical equation for theoretical age at length zero (Pauly 1979) a 
very approximate estimate of theoretical age at length zero was obtained. The equation 
used as follows: 
Log 10 ( -t0 ) = - 0.3922 - 0.2752 log10 Loo- 1.038 log10 K 
180 
Population dynamics of L. savala 
The recruitment pattern was also derived using the compleat ELEF AN computer 
program (Gayanilo et al. 1989). 
The probabilities of capture by length (Pauly 1984) of L. savala were estimated by 
calculating the ration between the points of the extrapolated descending arm and the 
corresponding assending arm of the length converted catch curve. 
Relative yield-per-recruit Y/R and biomass-per-recruit B/R were obtained from the 
estimated growth parameters and probabilities of capture by length (Pauly and Soriano 
1986). The calculations were carried out using the compleat ELEF AN package 
developed at ICLARM (Ingles and Pauly 1984). 
Length weight relationship was estimated for combined sex using simple linear 
regression (Zar 1984). For this purpose 352 specimens of L. savala were measured and 
varied from 12.0 em to 32.0 em in total length and 25g to 340g in body weight during one 
year samples. 
Results and discussion 
Growth parameters 
The length range obtained in the fishery was 32-104 em. In addition, the length 
range, which contributed significantly to the fishery, was within 56-70 em. The length 
frequency distribution of L. savala for one year study period are shown in Fig. 1. The 
best growth curves estimated by the compleat ELEFAN computer program (Gayanilo et 
al. 1989) are shown in this figure. The values for asymptotic length (Loo) and the von 
Bertalanffy growth co-efficient (K) estimated for the stock were 106.50 em and 0.80/year 
respectively. The powell-wetherall plot is shown in Fig. 2. The corresponding estimates 
of Loo and Z/K for L. savala are 106.90 em and 2.38 respectively. This additional estimate 
of Loo is slightly higher than the estimated through ELEF AN I. 
GROWTH CURVE 
OCT NOV DEC JAN FEB MAR APR MAY JUN JUL AUG SEP 
1996 1997 
Fig. 1. Monthly length frequency distribution of Lepturacanthus savala 
during the study period with the estimated growth curves. 
181 
M.G. Mustafa et al. 
16 
0 
0 
12 0 
0 
< 
0 
" 
0 
z B 
0 
0 
l) 
0 
0 
"--' 
I 
I-' 
Z6 POWELL -WETHERALL PLOT 
0 
0 
0 
0 
0 
0 
13 
• 
.. 
0~--------~----------_. 0~--------~~--------~ 
"8.5 76.5 104.5 47.5 75.5 1035 
0 0 
Fig. 2. Powell-wetherall plot ofLepturacanthus savala (Lex:= 106.90cm and Z/K=2.38). 
Mortality and exploitation rate 
The length converted catch curve of L. savala is shown in Fig. 3. The values for 
instantaneous total mortality co-efficient (Z), natural mortality co-efficient (M), Fishing 
mortality co-efficient (F) and the exploitation rate (E) calculated form the data points of 
figure were 1.89, 1.08, 0.81 and 0.43 respectively. It appears that the stock of L. savala of 
the investigated area is not under fishing pressure. 
CATCH CURVE 
10 
2 ] 
R11lall' .. e age! y!'.ars- tO) 
Fig. 3. Length-converted catch curve of Lepturacanthus savala. 
Theoretical age of length zero (t0 ) 
The estimated value for t0 using Pauly's empirical equation (Pauly 1979) was 
0.0708/year. 
Recruitment pattern 
Recruitment pattern of L. savala during the study period are shown in Fig. 4. The 
recruitment pattern showed two peaks, one around in March and the other around in 
July. The means oftwo pluses of recruitment are separated by an interval of four months. 
The first pulse produced 11.39% of the recruits while the other produced 16.56%. 
182 
Population dynamics of L. savala 
RECRUITMENT PATTERN 
20 
Fig. 4. Recruitment patter of Lepturacanthus savala. 
Probabilities of capture 
The probabilities of capture of L. savala is shown in Fig. 5. The estimated sizes of L. 
savala at 25%, 50% and 75% probabilities of capture were 57.49 em, 60.39cm and 63.28 em 
respectively. 
PROBABILITY OF CAP7URE ANALYSIS 
"' ~ 6 
8 
48.5 64.5 
l.engthclasses (em) 
Fig. 5. Probabilities of capture pattern of Lepturacanthus savala. 
The yield-per,-recruit and biomass-per-recruit 
The relative yield-per-recruit and biomass-per-recruit were determined as a function 
of Lc/Loo and M/K are 0.567 and 1.35 respectively. Fig. 6 shows that the present 
exploitation rate (E = 0.43) not exceeds the optimum exploitation rate (E max = 0.64). 
0o -~2s·---s-~ 
~ ,6 
' 
' ~ ,., 
] 
~ .2 
.15 ~ .H 
r~ploJt~I•Dn ra!t 
Fig. 6. Relative yield-per-recruit and biomass- per-recruit 
of L. savala (Lc /Loo=0.567, M/K=l.35). 
Length-weight relationship 
The estimated length weight relationship for the species was Log W = - 3.03 + 2.97 Log 
TL, in exponential form this equation is W = 0.00093TL 2·97 The log length and log 
183 
M.G. Mustafa et al. 
weight of the fish linearly related with a co-efficient of correlation (r = 0.996, p 
<0.001, t cal. = 22.08, n = 37 size range). 
References 
Gulland, J.A., 1971. The fish resources of the ocean west of fleet survey. Fishing News (Books). 
Ltd, FAO. 225 pp. 
Gayanilo, F. C. Jr., M. Soriono and D. Pauly, 1989. A draft guide to compleat ELEFAN. ICLARM 
Software 2. 70pp. 
Ingles, J and D. Pauly, 1984. An atlas of the growth, mortality and recruitment of Philippine 
fishes. ICLARM Teach. Rep., 13: 127pp. 
Lamboeuf, M., 1987. Bangladesh fish resources of the continental shelf, R!V Anushandhani 
trawling survey result. (Sept. 1984-June, 1986) FI: DP/DGD/80/025, 1: 26pp. 
Mustafa, M. G. and M. Begum, 1994. Some aspect of the biology of the ribon fish, Lepturacanthus 
savala in the Bay of Bengal. Proc. Ninth Nat. Zool. Conf. Bangladesh. pp. 23-30. 
Mustafa, M.G. and MG. Khan, 1992. Bottom trawl fishery studies on interactive marine fisheries 
of Bangladesh BOBP/WP/89, 89-105p. 
Pauly, D., 1979. Theory and management of tropical multi-species stocks. A review, with emphasis 
on the South-east Asian Demersal Fisheries. ICLARM Studies and Reviews 1. 35pp. 
Pauly, D., 1980. On the inter-relationships between natural mortality, growth performance and 
mean environmental temperature in 175 fish stocks. J, Cons. ClEM. 39(3): 175-192. 
Pauly, D., 1984. Fish population dynamics in tropical waters. A manual for use with 
programmable calculators. ICLARM Stud. Rev. 8. 325pp. 
Pauly, D., 1986. On improving operation and use of the ELEFAN programs. Part II. Improving 
the estimation of Loc. Fishbyte 4(1): 18-20. 
Pauly, D and J. L. Munro, 1984. Once more, on the composition of growth in fish and 
invertebrates Fishbyte 2(1): 21. 
Pauly, D and M.L. Soriano, 1986. Some practical extensions to Beverton and Holts relative yield-
per-recruit model. In: Ist Asian Fisheries Forum (eds. J.L. Maclean, L.B. Dizon and L.V. 
Hosillos). Asian Fisheries Society, Manila, Philippines. pp. 149-495. 
Wetherall, J. A., 1986. A new method for estimating growth and mortality parameters from length 
frequency data. Fishbyte, 4(1): 12-15. 
Zar, J.H., 1984. Biostatistical analysis. Prentice-Hall Inc. Englewood Cliffs, N.J. 718 pp. 
(Manuscript received 2 May 1999) 
184 


Population dynamics of the ribbon fish, Lepturacanthus savala (Cuvier 1829) from the north-eastern part of the Bay of Bengal

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Population dynamics of the ribbon fish, Lepturacanthus savala (Cuvier 1829) from the north-eastern part of the Bay of Bengal

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