ReseaRch PaPeR

Journal of Agricultural and Marine Sciences Vol. 21 (1):  19 – 24
DOI: http://dx.doi.org/10.24200/jams.vol21iss0pp19-24
Received 15 Aug. 2014  Accepted 19 Feb 2015

An assessment of longnose trevally (Carangoides chrysophrys) (Cuvier, 1833) 
fishery in the Arabian Sea, Oman

Issam H. Al-Rasady1  and Anesh Govender2

1 Issam H. Al-Rasady ( ) Marine Sciences and Fisheries Center, 
Ministry of Agriculture and Fisheries Wealth PO Box 427, Muscat 100, 
Sultanate of Oman. Email: asamrasadi@hotmail.com
2 Department of Marine Science and Fisheries, College of Agricultural and 
Marine Sciences, Sultan Qaboos University, PO Box 34, Al-Khod 123, 

Sultanate of Oman.

Introduction

The rapid increase in fishing efforts and improved fishing efficiency in the last two decades have resulted in depletion of many fisheries stocks in 
the world (FAO, 2007). This trend also applies to Omani 
fisheries. For example, kingfish (Scomberomorus com-
merson) catch in Omani waters has declined from above 
20000 mt in the late 1980’s to around 6000 mt in recent 
years, although the maximum yield was reported in 
1988 at 27000 mt (GoSO, 2003). The catch of spiny rock 
lobster (Panulirus homarus) declined from above 1900 
mt in 1988 to only 180 mt in 1999 (GoSO, 2000).

The Ministry of Agriculture and Fisheries Wealth 
plans to protect the economically important fish stocks 
from overfishing and longnose trevally Carangoides 

chrysophrys belong to this category. Carangoides chrys-
ophrys is found in the Indian Ocean from the Red Sea 
and Arabian Gulf to the western of the Pacific Ocean 
from New South Wales to the Ryukyu Islands (Lieske 
and Myers, 1994). Insular localities for the species in 
the Indian Ocean include Madagascar, Comoros and 
the Seychelles (Smith-Vaniz, 1984). Longnose trevally 
Carangoides chrysophrys, abundant in Omani waters 
(Al-Abdessalaam, 1995), has a high economic value and 
supports both the commercial industrial and commer-
cial traditional fisheries. Oman is one of the countries 
in the world that contributes significantly to the report-
ed global capture production of Carangids (FAO, 2005). 
Though no separate catch statistics are available for C. 
chrysophrys in Oman, large jacks catch data include nine 
commercially important species of the family Carangi-
dae, including longnose trevally and reported landings 
of 2359 mt were estimated for a value of 1.822 million 
Omani rials (1 OR = 2.6 USD) (GoSO, 2008). The cur-
rent fishing regulations in Oman apply only to the mesh 
size of the demersal trawler, which operate in coastal 
shallow and deep water of more than 50 m depth with-

تقييم املصائد السمكية للصال يف حبر العرب املطل على سلطنة عمان 
عصام محيد الرصادي1  . أنيش جوفندر2

Abstract: The present study assessed the fishery state of longnose trevally (Carangoides chrysophrys) in the North 
West Arabian Sea. Key population parameters were estimated, and yield and spawning stock biomass per recruit anal-
yses were conducted. The equation presented by Alagaraja (1984) for estimating natural mortality resulted in M = 0.29 
year-1 and lead to the best estimate of longevity. Hence this value was used in the yield and spawning stock biomass per 
recruit analyses. The total mortality (Z) was estimated as 0.39 year-1, based on a catch curve analysis. Length-at-50% and 
age-at-50% captures were 38.21cm and 4 years respectively. The yield and spawning biomass per recruit analyses indi-
cate that the current fishing mortality rate (Fcurr) was lower than the fishing mortality corresponding to the maximum 
yield per recruit (Fmax) and was also higher than the target reference point (F0.1) , suggesting that overfishing, currently, 
does not occur. However, any increase in the fishing effort in the future may lead to overfishing. 

Keywords:  Mortality, length-at-50% capture, yield per recruit, longnose trevally

املســتخلص:  قامــت هــذه الدراســة بتقييــم مصائــد مسكــة الصــال (Carangoides chrysophrys) يف الشــمال الغــريب لبحــر العــرب. وأجريــت التحاليــل 
ملوشــرات مصائــد األمســاك الرئيســية. وقــد أســفرت املعادلــة الــي قدمهــا Alagaraja )1984( لتقديــر الوفيــات الطبيعيــة مبعــدل 0.29 يف الســنة وأعطــت 
أفضــل مؤشــر ألقصــى عمــر. وبالتــايل مت اســتخدام هــذه القيمــة يف تقديــر الكتلــة احليويــة للمخــزون البيــاض. وقــدر جممــوع الوفيــات )Z( مبعــدل 0.39 
يف الســنة. اســتنادا إىل حتليــل منحــى الصيــد فقــد كانــت أطــول 50٪ مــن األمســاك املعرضــة للصيــد حــوايل 38.21ســم اي يف عمــر 4 ســنوات. وتشــر 
حتليــات الكتلــة احليويــة للمخــزون البيــاض إىل أن معــدل وفيــات الصيــد احلــايل (Fcurr) أقــل مــن وفيــات الصيــد املقابلــة ألقصــى قــدر مــن احملصــول الــذي 
ميكــن حتصيلــه (Fmax). وكان أيضــاً أعلــى مــن النقطــة املرجعيــة املســتهدفة )F0.1(، ممــا يشــر إىل أن هــذا النــوع مــن األمســاك ال يتعــرض حاليــا للصيــد 

اجلائــر. ومــع ذلــك فــإن أي زيــادة يف جهــد الصيــد يف املســتقبل قــد تــؤدي إىل اإلفــراط يف صيــد هــذا النــوع مــن األمســاك.
الكلمات املفتاحية: معدل الوفيات. الطول عند 50٪ من النضج اجلنسي. االنتاج لكل عنصر جديد. الصال  



20 SQU Journal of Agricultural and Marine Sciences, 2016, Volume 21, Issue 1

An assessment of longnose trevally (Carangoides chrysophrys) fishery in the Arabian Sea, Oman

in the continental shelf and enforce a minimum mesh 
size for the main net of 210 mm and 110 mm in the cod 
end (RRWFMCS, 1999). Minimum landing size limits 
in Oman fishing regulations are applied only on crus-
taceans (lobster) and  molluscs (abalone) (RRWFMCS 
1999) because they represent an unreasonable amount 
of additional labour for the fleet if applied to commercial 
fisheries where catches are large (King, 1995).

Yield per recruit models are widely used in fisheries 
management. In this study we developed an age-struc-
tured yield per recruit (YPR) and spawner biomass per 
recruit (SPR) models for the Carangoides chrysophrys 
stock in the northwestern Arabian Sea to provide scien-
tific advice to the fisheries managers.

Methods

Sampling
Freshly landed fish were randomly selected and pur-
chased from commercial fishermen at two landing sites 
on the Arabian Sea coast of the Sultanate of Oman: Al 
Lakbi (18011’1” N; 56032’56” E) and Raysut (16057’37” 
N; 53059’52” E). Sampling took place from April 2005 
to September 2006. Specimens were caught with hand-
lines, gillnets and traps. Annual strong southwest mon-
soon winds (between May and September) result in poor 
weather conditions forcing fishing activity in Al Lakbi to 
cease; hence, all biological sampling took place at Ray-
sut (Al-Rasady et al., 2012;  Al-Rasady et al., 2013) for a 
more detailed description of the sampling programme).

Population parameters
Various models were used in this study for estimating 
the instantaneous natural mortality rate (M) for each sex 
and combined sexes (Table 1).

where 
   K      = coefficient of von Bertalanffy growth model,
   Tm   = maximum age or fish life span, and
   tm50%  = the age at 50% maturity.

In order to choose the best estimate of natural mor-
tality, the criterion proposed by Alagaraja (1984) was 

used as suggested by Gonçalves et al. (2003):
(Tm)=4.605/M
The method which gave the best estimate of longevity 

was applied and evaluated by a sensitivity analysis which 
varied M by ±10% in the per recruit analysis. Instanta-
neous total annual mortality rates (Z) was estimated us-
ing numbers at age data for each sex and combined with 
a pooled regression equation where the Z value was esti-
mated according to Ricker (1975) from the right desend-
ing limb of a linearized age catch curve excluding age 
groups older than 14 yrs and those not fully recruited to 
the fishery (2 yrs old fish and younger for females and 3 
yrs old fish and younger for males and sex combined) as 
suggested by Sparre and Venema (1989). The instanta-
neous fishing mortality (F) was estimated by subtracting 
the instantaenous natural mortality rate (M) from the 
instantaneous total mortality rate (Z).

Length at 50% capture (LC) was estimated from the 
length frequency data by the method as suggested by 
Griffiths et al. (2006). Selectivity curves were generated 
by fitting a logistic function to the plot of probability of 
capture (Chen et al., 1992)  i.e. numbers in a particular 
size class divided by the total number of fish sampled 
(expressed as percentage) against size class (L), from 
which the value of the parameter (LC), the smallest size 
class at which 50% of the fish were fully recruited to the 
fishery was obtained. The logistic equation was:

P
L
=

100
1+exp −r L−L

c( )( ) (1)
 where PL = percentage of capture in length class L 

and
  r   = the width of the ogive.
The von Bertalanffy (1934) equation was used to con-

vert LC to an age- at- 50% capture (tc):

t
c
=t

0
−
1
K
ln 1−

L
c

L
∞

⎛

⎝
⎜

⎞

⎠
⎟ (2)

where  LC = length-at-50% capture
   L∞ = the asymptotic length.9

Table 1. Emprical equations used to calculate natural mortality (M) for Carangoides chrysophrys in the Arabian Sea. (K) 
growth coefficient of the von Bertalnaffy growth model, (tmax) maximum age or fish life span, and (tm 50%)  the age at 50% maturity.

References Equation Assumpation

Rikhter and Efanov (1976): M = 1.52
t
m50%( )

0.72

⎛

⎝
⎜
⎜

⎞

⎠
⎟
⎟
−0.155 Close association between M and tm 50%

Hoenig (1983): ln M( )=1.44−0.982ln Tm( ) Relation between M and tmax
Alagaraja (1984): M = −ln 0.01( )/Tm Relation between M and tmax
Ralston (1987): M =0.0189+2.06K Relation between M and  growth rate



21Research Article

Al-Rasady , Govender

Per recruit analysis
Two variables, the spawner biomass per recruit (SBR) 
and yield per recruit (YPR) (Beverton and Holt, 1957), 
were calculated for various estimates of fishing mortal-
ities ranging from 0 to 1 yr−1. The SBR was calculated 
using the following equation:

SBR =
SB
R

= exp − FS
t
−M( )t( )

t=0

tmax

∑ a Lt( )
b
G
t

(3)

where
SB     = the total spawner biomass (in g),
R       = the number of recruits (set to 1, by        

definition),
F      = instantaneous fishing mortality rate,

M      = instantaneous natural mortality rate,
a and b     = constants of the length–weightrelation-

ship of combined sexes,

 Lt        = the predicted von Bertalanffy mean 
length-at-age t and 

tmax = the maximum observed age in the fish-
ery (year)

Gt        = the fraction of mature fish at age t and-
was assumed to be knife-edged i.e.

G
t
=

0,if		t <t
m

1,if		t ≥t
m

⎧
⎨
⎪

⎩⎪
(4)

where tm = the age at 50% maturity. 
St  is the gear selectivity at age t and is also assumed to be 
knife-edged i.e.

S
t
=

0,if		t <t
c

1,if		t ≥t
c

⎧
⎨
⎪

⎩⎪
(5)

where tc= the age at 50% capture.

Yield per recruit in number (YPRS) was calculated as:

YPR
S
=
YP

S

R
S

=

F
S ,t

F
S ,t
+M

St=0

tmax

∑ e− FSSS ,t −MS( )t 1−e− FSSS ,t −MS( )( )
(6)

where YPs is the total yield in numbers for a cohort 
throughout its lifespan. 

Yield per recruit (YPR) in mass was calculated from 
the following equation: 

YPR
mass( ) = YPRta Lt( )

b

t=0

tmax

∑ (7)

where a and b are  parameters of the length–weight rela-

Table 2. Natural mortality rates (M) estimated from different 
equations (Table 1) for Carangoides chrysophrys in the Arabi-
an Sea. Te= predicted longevity in years.

Method
M (year -1)

Te
(yr)Male Female

Com-
bined

Rikhter and Efanov 
(1976):

0.40 0.40 0.40 11.65

Hoenig (1983): 0.28 0.28 0.28 16.61

Alagaraja (1984): 0.29 0.29 0.29 16.00

Ralston (1987): 0.49 0.54 0.53 08.63

y = 4.71 + − 0.35 ⋅ x,  R 2 = 0.83

−2

0

2

4

4 8 12 16

Age (years)

Lo
g 

of
 F

re
qu

en
cy

Figure 1. Age-based catch curves for males (top) , females 
(middle) and combined sex (bottom) for Carangoides 
chrysophrys in the Arabian Sea.

y = 4.98 + − 0.35 ⋅ x,  R 2 = 0.82

−2

0

2

4

4 8 12 16

Age (years)

Lo
g 

of
 F

re
qu

en
cy

y = 5.83 + − 0.39 ⋅ x,  R 2 = 0.86

0

2

4

6

4 8 12 16

Age (years)

Lo
g 

of
 F

re
qu

en
cy



22 SQU Journal of Agricultural and Marine Sciences, 2016, Volume 21, Issue 1

An assessment of longnose trevally (Carangoides chrysophrys) fishery in the Arabian Sea, Oman

tionship of combined sexes. Biological references point 
(Fmax) and (F0.1) were estimated in order to compare them 
to the current fishing mortality and determine the status 
of the longnose trevally stock.  

Results
The von Bertalanffy growth model parameters (L∞ , K, 
to and tmax) were obtained from Al-Rasady (2013) and 
the length-weight relationships constants (a sex combined ,b 
sex combined ) were obtained from Al-Rasady (2012). Natural 
mortality and longevity, calculated for each sex and for 
the combined sexes, are shown in table 2.

Hoenig’s and Alagaraja’s equations gave the best esti-
mates of longevity, while the rest of the methods under-
estimated the longevity of longnose trevally.

Total mortality rates (Z) for each sex and combined 
sexes are shown in figure 1. The total mortality rate for 
the combined sexes was higher than for each sex sep-
arately but the difference between Z for each sex was 
small. Fishing mortality (F) is presented in table 3. The Z 
for the combined sexes was only used for estimating the 
fishing morality. Fishing mortality had positive values 
when based on Hoenig’s and Alagaraja’s equations, but 
negative values based on the other models. Fishing mor-

tality estimated by Hoenig was higher than the Alaga-
raja method. The total length at which 50% of longnose 
trevally were caught in the fishery was 38.2 cm (Fig. 2). 
This translates to an age of about 4 years using the von 
Bertalanffy growth model. Parameters used to assess the 
status of longnose trevally stock in the Arabian Sea using 
a per recruit analysis are given in table 4.  

At the current fishing mortality rates (Fcurr) the 
spawning biomass per recruit (SBR) was at 46.85% of 
that at the absence of fishing mortality for the base case 
of and 36.95% and 59.02% for the -10% M and +10% M 
respectively (Fig. 3). YPR curves, in mass suggests that 
a maximum yield can be attained at an Fmax value equal 
to 0.147 year-1, 0.143 year-1 and 0.151 year-1 for the base 
case of M and -10% M and +10% M respectively (Table 
5). The estimates of F0.1 were nearly identical to the esti-
mates of Fmax (Table 5).

Discussion
Equations of Hoenig (1983) and Alagaraja (1984) pro-

vide reasonable estimates of M for longnose trevally in 
the Arabian Sea. Griffiths et al. (2006) used various equa-
tions to estimate the natural mortality, including Hoe-
nig’s (1983) equation, for the Talang queenfish, Scomb-
eroides commersonnianus (Carangidae).  However, they 
excluded Hoenig’s (1983) M estimate from the yield per 

Table 3. Populations dynamic parameters of Carangoides 
chrysophrys in the Arabian Sea used in the per recruit anal-
ysis.

Parameter Value

a 0.0291

b 2.7702

L∞ 73.01 cm

K 0.25 yr-1

t0 -1.21 yr

tmax 16 yrs

tc 3.85 yrs

tm 4.83 yrs

M 0.29 yr-1

-10% M 0.26 yr-1

+10% M 0.32 yr-1

Fcurr M 0.0976 yr
-1

Fcurr -10% M 0.1264 yr
-1

Fcurr +10% M 0.0688 yr
-1

Table 4. Estimates of biological reference points for longnose 
trevally Carangoides chrysophrys captured in the Arabian 
Sea for varying values of natural mortality (M). Estimates of 
fishing mortality (F) are in the unit yr-1.

Base Case -10% of M  +10% of M

F0.1 0.146 0.142 0.15

Fmax 0.147 0.143 0.151

0

25

50

75

100

20 40 60 80

Total length (cm)

Fr
ac

tio
n 

re
ta

in
ed

Figure 2. Selectivity curve for Carangoides chrysophrys in 
the Arabian Sea showing the mean size at 50% capture. 

Table 5. Fishing mortality estimates for Carangoides chryso-
phrys in the Arabian Sea. Z = instantaneous total mortality 
rate and M is the instantaneous natural mortality rate and are 
given for the combined sexes. F = instantaneous fishing mor-
tality rate. Negative value of fishing mortality are unrealistic.

Method Z (yr-1) M (yr-1) F (yr-1)
Rikhter and Efanov (1976): 0.39 0.40 -0.01

Hoenig (1983): 0.39 0.28 0.11

Alagaraja (1984): 0.39 0.29 0.10

Ralston (1987): 0.39 0.53 -0.14



23Research Article

Al-Rasady , Govender

recruit analysis due to the large uncertainty and the fact 
that it tends to underestimate the maximum age (Grif-
fiths et al., 2006). In our study Hoenig’s (1983) equation 
overestimated the maximum age and hence we choose 
the estimate of M from the Alagaraja (1984) equation.

The estimate of natural mortality in this study was 
0.29 year−1 which is near the higher limit of natural mor-
tality estimated for Talang queenfish, S. commerson-
nianus, in northern Australia (0.16–0.26 yr−1) (Griffiths 
et al., 2006) and substantially lower than that observed 
for the fast growing species Carangoides bajad and Gna-
thanodon speciosus in the Arabian Gulf (Grandcourt et 
al., 2004). 

Total mortality rate in this study was 0.39 yr-1. Values 
of the total mortality rate (Z) were 1.16 and 1.83 yr−1 for 
C.bajad and G.speciosus from the Arabian Gulf, respec-
tively which is high, possibly due to high growth rates 
and/or higher fishing effort (Grandcourt et al. 2004). 
Natural mortality estimates other than those based on 
Hoenig’s (1983) and Alagaraja’s (1984) equations lead to 
negative values of F which are unrealistic. 

The estimates of Fmax and F0.1 were nearly identical in 
value. This is not surprising as the ascending limbs of 
the yield per-recruit curves (Fig. 4) show little curvature 
(other than at the top of the curve) i.e. the ascending 
limbs are generally linear with a constant slope which 
abruptly changes at the top over a very short range of 
fishing mortality increase and then rapidly declines. 

The current fishing mortality rate (Fcurr), by traps and 
handline, is well below the maximum fishing mortality 
Fmax and F0.1 estimates. However, any future increase in 
fishing effort will lead to overfishing of the stock because 
Carangoides chrysophrys has a slow growth rate coupled 
with a high longevity. Stocks with low growth rates gen-

erally require low fishing effort to maximize the yield 
(King, 1995) and species with low population growth 
rate have a greater tendency to be overfished (Nowlis 
and Roberts, 1999). Maximum fishing mortality (Fmax) 
is usually greater than the fishing mortality at the maxi-
mum sustainable yield (Fmsy), and exploiting the stock at  
Fmax over an extended period may deplete the spawn-
ing stock and reduce future recruitment (Clarke, 1991).   
Harvesting at Fmax, may in fact, lead to commercial ex-
tinction (Doubleday, 1976; Beddington and May, 1977; 
Beverton, 1994; Caddy and Mahon, 1995)

At the current fishing mortality rates (Fcurr), for all the 
three cases of the natural mortality, the spawning bio-
mass per recruit (SBR) is between (36.95 – 59.02) when 
compared to an unexploited stock. Values of SBR lower 
than 20% is a source for concern as there would be high 
possibility of future recruitment failure (Caddy, 1998). 

Values of length and age at 50% capture are lower 
than the length and age at 50% maturity which results 
in immature fish being caught. The current fishing mor-
tality rate (Fcurr), for Carangoides chrysophrys from the 
Arabian Sea is at an optimum level and should be main-
tained. However, any increase in the fishing effort may 
lead to overfishing of this fishery.

References
Al-Abdessalaam, T. Z.  1995. Marine species of the Sul-

tanate of Oman, Identification Guide. Ministry of 
Agriculture and Fisheries, Marine Science and Fish-
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Alagaraja, K. 1984. Simple methods for estimation of pa-
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Journal of Fisheries, 31: 177-208.

0

1000

2000

3000

0.0 0.1 0.2 0.3 0.4 0.5

Fishing mortality

S
pa

w
ni

ng
 b

io
m

as
s 

pe
r r

ec
ru

it 
(g

) Model
F0.1
Fcurr
Fmax

Figure 3. Spawning biomass per recruit curves for Ca-
rangoides chrysophrys in the Arabian Sea using different 
natural mortality rates. The current estimated mortality 
rate (M = 0.2878) is the continuous line. The dotted line 
corresponds to current mortality -10%, whereas the 
dashed line corresponds to M +10%. The black triangles 
are Fcurr, the open circles are Fmax and the black squares 
are the target reference point F 0.1.

0

50

100

150

0.0 0.1 0.2 0.3 0.4 0.5

Fishing mortality

Y
ie

ld
 p

er
 re

cr
ui

t (
g)

Model
F0.1
Fcurr
Fmax

Figure 4. Yield per recruit (g) curves for Carangoides 
chrysophrys in the Arabian Sea using different natural 
mortality rates. The current estimated mortality rate (M 
= 0.2878) is the continuous line. The dotted line corre-
sponds to current mortality -10%, whereas the dashed 
line corresponds to M +10%.The triangles are Fcurr, the 
circles are Fmax and the squares are the target reference 
point F0.1.



24 SQU Journal of Agricultural and Marine Sciences, 2016, Volume 21, Issue 1

An assessment of longnose trevally (Carangoides chrysophrys) fishery in the Arabian Sea, Oman

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