length based stock assessment of the white- spotted rabbitfish, siganus canaliculatus

LENGTH BASED STOCK ASSESSMENT OF THE WHITE-SPOTTED RABBITFISH, Siganus Canaliculatus

(PARK, 1797) FROM THE ARABIAN SEA OFF OMAN

(1) Marine Science and Fisheries CentreMinistry of Fisheries Wealth, P.O. Box 1546; P.C. 133, Muscat

Sultanate of Oman*E-mail: [email protected]

Thalassas, 29(2) · June 2013: 67-76An International Journal of Marine Sciences

Key words: Arabian Sea, Oman, Siganus canaliculatus, growth parameters, mortality, MSY.

Palabras clave: Mar Arábigo, Omán, Siganus canaliculatus, parámetros de crecimiento, mortalidad, MSY.

A. AL-MARZOUQI(1)

67Thalassas, 29(2) · June 2013

ABSTRACT

Whitespotted rabbitish, S. canaliculatus is the dominant species in the catches of siganids of Oman. In recent years, the fish-ing pressure on the stock of S. canaliculatus has increased considerably. No information on the stock parameters of the fish is available, the present study has conducted for sustainable harvest of the stock. The size of fish in commercial catches ranged between 15 and 38 cm of total length (TL). The VBG parameters estimated were: L∞ = 40.13 cm, K = 0.85 y-1 and t0 = -0.086 y. The life span of fish was around 3.5 years and commercial catch was mainly constituted by individuals of 1-2 years of age. The estimated annual Z, M and F coefficients were 2.66, 1.36 and 1.3 respectively. The E, U and M/K ratios were 0.49, 0.46 and 1.6 respectively. The growth performance index of 3.14 indicated the faster growth of the fish. The MSY calculated varied from 519 t to 618 t. While, the estimated average standing stock was 390 t, the total stock was 1,102 t. At the F equal to 1.0, the stock biomass decreased to 723 t. The Yw/R for the current F was estimated at 62.5 g. The study indicates that the present effort for the fishery of S. canaliculatus is optimum. Any alteration in the existing fishing pattern or increase of effort would affect recruitment and reduce MSY.

RESUMEN

Siganus canaliculatus es la especie dominante en las capturas de sigánidos de Omán. En los últimos años ha aumentado con-siderablemente la presión de pesca sobre la población de S. canaliculatus. No hay información disponible sobre los parámetros de las poblaciones de los peces, siendo el objetivo de este estudio conocer la pesca sostenible en esta población.El tamaño de los peces en las capturas comerciales oscilan entre los 15 y los 38 cm de longitud total (LT). Los parámetros estimados fueron VBG: L ∞ = 40.13 cm, K = 0,85 año-1 y t0 = -0.086 y. La vida de los peces fue de alrededor de 3,5 años y la captura comercial estuvo constituida principalmente por individuos de 1-2 años de edad. Los coeficientes estimados anuales Z, M y F fueron 2,66, 1,36 y 1,3 respectivamente. La E, U y tasa M / K fueron 0,49, 0,46 y 1,6, respectivamente. El índice de rendimiento de crecimiento de 3,14 indica un crecimiento más rápido de los peces. El Rendimiento Máximo Sostenible (RMS) calculado varió entre 519 y 618 t t. Mientras, el stock promedio estimado actual fue de 390 t, el stock total fue de 1.102 t. En F=1.0, la biomasa de la población se redujo a 723 t. El Yw / R para el F actual se estima en 62,5 g. El estudio indica que el esfuerzo actual de la pesquería de S. canaliculatus es óptima. Cualquier alteración en el patrón de pesca existente o aumento del esfuerzo afectaría al reclutamiento y reducir el RMS.

A. AL-MARZOUQI

INTRODUCTION

Fishes of the family Siganidae popularly known as rabbitfishes are moderate sized commercially important fishes and form an important constituent of the shallow coastal demersal fisheries in the Indo-West Pacific region from the Arabian Gulf to Western Australia and to Hong Kong and Taiwan (Randall, 1995). In the northern Arabian Sea coast of Oman, the siganids are commercially harvested by the artisanal fishermen using gillnets, traps, beach seines and by industrial trawlers. The progressive rise in the number of fishers of Oman has increased the fishing pressure on the siganid resources of the Arabian Sea. About seven-fold increase of the annual average catch of 126 t for the period 1994-2000 to 866 t for 2001-2006 indicates the fishers now target siganids more actively (GoSO, 2003; 2004; 2005; 2006).

Whitespotted rabbitfish, S. canaliculatus is dominant

in the landings of Oman (Park, 1797), and the estimated catches for the years 2005-2006 and 2006-2007 stood at 571 t and 443 t respectively (GoSO, 2005; 2006; MSFC, unpublished data).

Oman having jurisdiction over an ocean area of about 533,180 km2 of exclusive economic zone (EEZ) is empowered with great responsibility of developing and better managing the fisheries resources therein. The success of a fishery depends critically on the state of the fish stock. In spite of the commercial importance, no information is available on the population parameters of S. canaliculatus from Oman. Hence, the present study was undertaken to estimate the stock parameters of S. canaliculatus such as the size and age composition, growth, mortality and potential yield to help develop appropriate policy for sustainable harvest of the stock of S. canaliculatus in the Arabian Sea coast of Oman.

MATERIALS AND METHODS

For the length based stock assessment, monthly length frequency data were collected at random for two years between April 2005 and March 2007 from different artisanal gears such as gillnets of various sized meshes, traps and beach seines operated in the coastal waters of the Arabian Sea between Lakbi and Salalah, and demersal trawlers operated beyond 10 nautical miles from the shore or 50 m depth (Fig. 1).

68 Thalassas, 29(2) · June 2013

Figure 1:

Map showing the sampling sites along the Arabian Sea coast of Oman.

LENGTH BASED STOCK ASSESSMENT OF THE WHITE-SPOTTED RABBITFISH, SIGANUS CANALICULATUS (PARK, 1797) FROM THE ARABIAN SEA OFF OMAN

The pooled length frequency data were analyzed for the size frequency distribution. A total of 3,275 fish were measured for their total length (TL) to the nearest 1 mm.

Estimation of age and growth

For the estimation of age and growth based on length frequency data, a total of 3,275 fish from commercial landings were measured for their TL. The minimum and maximum sizes of fish ranged between 15 cm and 38 cm. The length frequency data were grouped into 1 cm class interval. The growth was estimated for the pooled unsexed length data.

To estimate the von Bertalanffy growth (VBG) parameters (L∞, K and t0) of fish, the pooled TL frequency data were grouped into 1 cm class interval to fit the equation,

Lt = L∞*[1 – e –K*(t – t0)]

using the LFDA version 5.0 of FMSP- Fish Stock Assessment Software (Hoggarth et al., 2006). Three alternative fitting techniques such as Shepherd’s Length Composition Analysis (SLCA), Projection Matrix (PROJMAT) and ELEFAN 1 with non-seasonal version of VBG curve were adopted to calculate VBG parameters. The routine Powell-Wetherall technique available with the FMSP-software was also used to estimate L∞ and Z/K. Length at age was estimated from the plots of SLCA, PROJMAT and ELEFAN 1, and the empirical method of Froese and Binohlan (2000).

Growth performance index (Ø’)

The overall growth performance index of S. canaliculatus was calculated empirically (Munro and Pauly, 1983) using the formula,

Phi prime (Ø’) = log10 K + 2*log10 L∞

where, K is expressed on annual basis and L∞ in cm.

Length at capture (Lc)

Length at first capture (Lc) was estimated from cumulative percentages of length against length classes.

Estimation of mortality

The instantaneous total mortality rate (Z) was estimated using the length converted catch curve method (Pauly, 1983) and Beverton-Holt method (Beverton and Holt, 1956) using the routines provided in the LFDA version 5.0 of FMSP software and the average of both the techniques was taken for subsequent analyses.

Natural mortality coefficient (M) of fish was estimated by three different empirical methods (Pauly, 1980; Rikhter and Efanov 1976; Alagaraja 1984) and the average M was taken for further analyses.

In the empirical method of Pauly (1980), the following equation was adopted.

ln M = -0.0152 - 0.279 * ln L∞ + 0.6543 log * k + 0.4634 * ln T

where ‘T’ indicates the annual mean temperature (oC) of the surrounding water in which the fish lives. In the present study, the T value was taken as 24°C as this value represents the mean bottom water temperature in the Arabian Sea off Oman (Thangaraja, 1995).

In Rikhter and Efanov’s method (1976), the following formula was adopted

M = 1.521 / tm0.72 – 0.155


29

Fig. 2. Frequency distribution of S. canaliculatus in the commercial

Catches during 2005-2007

0

2

4

6

8

10

14 19 24 29 34 39

Per

cent

age

Total length (cm)

n=3275

Figure 2:

Frequency distribution of S. canaliculatus in the commercial Catches during 2005-2007.

A. AL-MARZOUQI

where, tm = the age at which 50% of the population matures.

Alagaraja’s (1984) method assumes that 99% of a cohort had died if it had been exposed to natural mortality only. The formula used was:

M1% = -ln (0.01)/Tm

where Tm indicates longevity and M1% indicates natural mortality corresponding to 1% survival.

The value of fishing mortality (F) was computed by subtracting natural mortality from total mortality as, F = Z – M.

Exploitation rate (E)

The ratio between fish caught and the total mortality (Ricker, 1975) or the exploitation rate (E) (Sparre and Venema, 1992) was computed as,

E =F/Z = F / (M+F)

Exploitation Ratio (U)

To estimate the fraction the fish present at the start of a year that is caught during the year, the equation given by Beverton and Holt (1957) and Ricker (1975) as,

U = F / Z (1-e-z) was adopted.

Yield

The annual catches of S. canaliculatus for the years 2005-06 and 2006-07 were considered as yield (Y) for the respective years.

Standing stock

The standing stock was estimated by weight (t) using the formula,

Standing stock = Y/F

where Y is the yield and F, the fishing mortality

Biomass

The biomass estimated using the relation between yield and exploitation ratio as

Biomass = Y/U

where Y was the annual yield and U, the exploitation ratio.

Maximum Sustainable Yield (MSY)

The maximum sustainable yield (MSY) was calculated by the equation suggested by Cadima (in Traodec, 1977) as,

MSY = 0.5 (Y+MB¯)

where Y is the total catch in a year B¯ is the average biomass in that year and M the natural mortality. The MSY was also estimated by Thompson and Bell technique using the yield software (Hoggarth et al., 2006).

Yield-per-recruit and Biomass-per-recruit

The routine available with the ‘Yield’ package incorporated in the FMSP Software (Hoggarth et al., 2006) was employed. All the input parameters used for Yield software were obtained from the present


30

Fig. 3. VBG curve of S. canaliculatus by SLCA

Figure 3: VBG curve of S. canaliculatus by SLCA.


study. The length-weight parameters and length at maturity were taken from a separate study of the authors. For length-weight parameters, the input ‘a’ and ‘b’ values were 0.00005 and 2.7364 respectively. The length at first maturity was calculated as suggested by King (1995) and taken as 23.3 cm. Beverton and Holt stock recruitment relationship was applied (Pilling et al., 1999). The estimations of equilibrium yield-per-recruit (Yw/R), total biomass-per-recruit (TB/R), stock spawning biomass-per-recruit (SSB/R) and fishable biomass-per-recruit (FB/R) for a range of F-values were made in this study.

Optimum length of capture (Lopt)

The optimum length of exploitation was estimated empirically from the equation (Froese and Binohlan, 2000) as,

Lopt = 3*L∞/ 3+M/K

where Lopt denotes the optimum length of exploitation, L∞, the asymptotic length, M, the

natural mortality and K, the growth coefficient.

RESULTS

Size frequency distribution

The size range of S. canaliculatus in the commercial catches ranged between 15 cm and 38 cm of TL (Fig. 2) and the smaller sized individuals (15-17 cm) represented less than 1% of the total fish measured (N = 3275). About 24.2% of fish were caught up to the size group 24 cm. Fish measuring up to 28 cm contributed to 51.4% in the total catch and fish measuring between 29 and 38 cm TL represented by 48.6% of the catch.Estimation of VBG parameters and age

For the monthly length frequency data of S. canaliculatus during 2005-2007, growth curves were fitted


31

Fig. 4. VBG curve of S. canaliculatus by PROJMAT method

Figure 4: VBG curve of S. canaliculatus by PROJMAT method.

32

Fig. 5. VBG curve of S. canaliculatus by ELEFAN method

Figure 5: VBG curve of S. canaliculatus by ELEFAN method.

A. AL-MARZOUQI

by SLCA (Fig. 3), PROJMAT (Fig. 4) and ELEFAN (Fig. 5) techniques. The L∞ calculated by Wetherall technique was 38.6 cm. All the techniques gave comparable values of L∞ (SLCA = 41.2 cm; PROJMAT = 41.7 cm; ELEFAN = 39 cm) (Table- 1). The average L∞ estimated by the first three techniques (i.e. 40.13 cm) was considered for analysis of stock assessment. The growth coefficient (K) values ranged between 0.8 and 0.9 y-1 with the average being 0.85 y-1. There was difference in the estimated t0 values between the methods and the average t0 calculated was -0.086 y.

The age distribution of S. canaliculatus in the commercial catches (Fig. 6) indicated that individuals of 1-2 years of age were dominant.

The length converted age for S. canaliculatus using different methods are shown in Table- 2. The growth estimated at the end of one year ranged from 26 cm to 28 cm and at the end of two years from 33 cm to 36 cm. However, the growth during the third year of life of S. canaliculatus was estimated differently by different methods.

The life span estimated by the equation 3/K (Pauly, 1983a) using the average K was found to be about 3.5 years. Estimation of length at age by empirical method of Froese and Binohlan is shown in Fig. 7.

Growth performance index (Ø’)

The overall growth performance index for S. canalicu-latus from the Arabian Sea coast of Oman was 3.14.

Length at capture

Though individuals measuring 15 cm were encountered in the catches, fish measuring up to 18 cm of TL contributed <1% of the total number of fish (Fig. 2). However, the length at which 50% of fish were caught was 27.8 cm (Fig. 8).

Population dynamics and stock assessment

Estimation of total mortality (Z) The instantaneous total mortality coefficient (Z) of

S. canaliculatus estimated for the pooled data of both the years by the length converted catch curve method (Pauly, 1983) was 2.66 (SE=0.079). However, the Beverton-Holt method (Beverton and Holt, 1956) gave a lower value (1.65, SE=0.168). Hence, considering the natural mortality (M) estimated in the present study, the Z calculated by length converted catch curve method (2.66) was taken for further analysis.

Estimation of natural mortality (M) Natural mortality coefficient (M) of S. canaliculatus

estimated by three different empirical methods gave comparable values. The values were 1.38 by Pauly’s empirical formula, 1.32 by Alagaraja’s technique and 1.37 by Rikhter and Efanov method. The average of the above three values calculated as 1.36 was taken as M of S. canaliculatus in the Arabian Sea coast of Oman.

Estimation of fishing mortality (F)The fishing mortality (F) computed for S. canaliculatus

in the present study by subtracting natural mortality from total mortality (F = Z – M) was 1.3.

Exploitation rate (E) and Exploitation Ratio (U)The exploitation rate (E) and exploitation ratio (U) were

0.49 and 0.46 respectively for the pooled data of two years.

Yield, Standing stock, Biomass and MSYThe yield for the year 2005-2006 was 565 t and for the

year 2006-2007 was 449 t. The average annual yield for both the years worked out to 507 t. Based on this yield, the estimated average annual standing stock stood at 390 t with the annual average total stock of 1102 t.

The MSY estimated by Cadima’s formula was 519 t. However, the Thompson and Bell analysis (Fig. 9),


33

Fig. 6. Age distribution of S. canaliculatus

34

Fig. 7. Estimation of length at age in S. canaliculatus by Froese

and Binohlan (year) method

0

10

20

30

40

0 0.5 1 1.5 2 2.5 3 3.5

Age (y)

Leng

th (c

m)

Figure 6: Age distribution of S. canaliculatus. Figure 7: Estimation of length at age in S. canaliculatus by Froese

and Binohlan (year) method.


indicated higher MSY (618 t). The biomass which stood at 2,1,79 at F=0 decreased to 1,637 at F 0.2 and to723 t at F 1.0 which further decreased to 55 t at F 3.

Yield-per-recruit and Biomass-per-recruitThe yield-per recruit (Yw/R) and total biomass-

per-recruit (TB/R), stock spawning biomass-per-recruit (SSB/R) and fishable biomass-per-recruit (FB/R) of S. canaliculatus were calculated for F-values ranging from 0-3 (Fig. 10). The Yw/R at the current F value of 1.3 was 62.46 g. By testing various F-values, it was found that the MSY/R was 65.3g at the F of 2.2 and beyond this F, the Yw/R decreased with increased F. The initial estimated values of TB/R, SSB/R and FB/R were 129.9g, 155.7g and 172.2g respectively which decreased with increase of F.

Optimum length of capture (Lopt)From the empirical equation (Froese and Binohlan,

2000), the optimum length of exploitation (Lopt) estimated was 24.9 cm with the range being 21.1 – 29.5 cm. The Lopt/L∞ value was 0.62.

DISCUSSION

The size range of fish in the commercial catches in the present study ranged between 15 cm and 38 cm of TL. The calculated length at first maturity for male and female fish was 22.6 cm and 23.9 cm respectively. As the fish measuring above 24 cm of TL contributed to about 75.8% of the total fish caught and fish measuring 28 cm and above constituted about 51.4% of the total catch (Fig. 3), the present harvest pattern is ideal to maintain the stock and no specific management strategy is needed at present.

S. canaliculatus is a candidate species for aquaculture due to its fast growth performance as one of the straits (Lam, 1974). The fish fed with pelleted diet grew faster and reached 20 cm of fork length in 6 months in the culture systems in Tanzania (Bwathondi, 1982). In the present study, the growth estimated by different methods indicated that the fish may attain 26 -28 cm of TL at the end of first year, 33-36 cm at the end of second and 38 cm


35

Fig. 8. Length at first capture of S. canaliculatus

0

20

40

60

80

100

10 15 20 25 30 35 40

Cum

ulat

ive

%

Total length (cm)

n=3275

Lc=27.8 cm

36

Fig. 9. Predicted total biomass and yield for a range of fishing strategies

0

500

1000

1500

2000

2500

0

100

200

300

400

500

600

700

0 0,2 0,4 0,6 0,8 1 1,2 1,4 1,6 1,8 2 2,2 2,4 2,6 2,8 3

Bio

mass (t)

Yie

ld (

t)

F-factor

Yield (tonnes)

MSY

Figure 8: Length at first capture of S. canaliculatus. Figure 9: Predicted total biomass and yield for a range of

fishing strategies.

37

Fig. 10. Equilibrium yield-per-recruit and biomasses-per-recruit against F

(Yw/R, yield-per-recruit; SSB/R, stock spawning biomass-per-recruit;

FB/R, fishable biomass-per-recruit; TB/R, total biomass-per-recruit)

(Received: June, 29, 2012; Accepted: April, 2, 2013)

0

0,02

0,04

0,06

0,08

0,1

0,12

0,14

0,16

0,18

0,2

0 0,5 1 1,5 2 2,5 3

Yiel

d (k

g)

Fishing mortality

Yw/R SSB/R FB/R TB/R

Figure 10: Equilibrium yield-per-recruit and biomasses-per-recruit against F

(Yw/R, yield-per-recruit; SSB/R, stock spawning biomass-per-recruit;

FB/R, fishable biomass-per-recruit; TB/R, total biomass-per-recruit)

A. AL-MARZOUQI

during the third year of its life (Table-8). The empirical methods (Pauly, 1983; Froese and Binohlan, 2000) also indicated that the maximum age of S. canaliculatus might be around 3.5 years. In the Palau waters, the longevity of S. canalicualtus was estimated to be about 2 years (Hasse et al., 1977). However, the average annual growth estimated for S. canaliculatus from Abu-Dhabi is lower than the values obtained in the present study and the life span of the fish has been reported to be 7.8 years (Grandcourt et al., 2007) which appears to be a higher estimate. A comparison of the VBG parameters of S. canaliculatus showed that the higher K values were obtained mostly in the culture systems than in the present study which was the lowest (Table- 3).

The growth performance index (phi prime index, Ø’) for S. canaliculatus from the Arabian Sea coast of Oman was 3.14. It is generally seen that the in fishes is distributed around 3 (Zacharia, 2003). No earlier report is available on the growth performance of S. canaliculatus from any other area, it was not possible to compare the growth performance in this species from the Arabian Sea coast of Oman.

The annual instantaneous total mortality coefficient (Z) of S. canaliculatus estimated by length converted catch curve method in the present investigation was 2.66. However, a lower estimate of Z (1.51) based on

age based catch curve has been reported from the Arabian Gulf (Grandcourt et al., 2007). The natural mortality rate (M) estimated by the empirical methods gave an average M of 1.36 in the Arabian Sea coast of Oman. The high M value in S. canaliculatus can be explained as when the fish grow fast (high K) are likely to attain higher natural mortality rate as compared to fishes that grow slow and consequently with lower M (Gulland, 1969). Since, M is linked with the longevity and the latter to the growth coefficient K, the M/K ratio is found to be constant among closer related species and sometimes within the similar taxonomic groups (Beverton and Holt, 1959; Banerji, 1973). The M/K ratio usually ranges between 1 and 2.5 (Beverton and Holt, 1959). In the present study, the M/K ratio for S. canaliculatus was calculated to be 1.6. The estimated fishing mortality (F = 1.3) was close to the value of M during the study period.

The exploitation rate (E) generally indicates the state of exploitation of a stock under exploitation assuming that the optimal value of E≈0.5, which in turn assumes that the sustainable yield is optimized when F≈M (Gulland, 1971) In the present study, as the estimate of F was is slightly lower than the M and the calculated E was 0.49 which is almost close to the optimum level. Along the Arabian Sea coast of Oman, while the average total stock (Y/U) of S. canaliculatus during the study period was 1,102


25

Table- 1. VBG parameters estimated by different methods based on length data

Method L∞ (cm) K (yr-1) t0 (yr)

SLCA 41.19 0.90 -0.035

PROJMAT 41.73 0.856 -0.064

ELEFAN 1 39.043 0.801 -0.160

Average parameter values 40.13 0.852 -0.086

Table- 2. Age-length-key in S. canaliculatus

Method Age in years

1 2 2.25 2.75 3

Length (cm)

SLCA 28 35 - 38 -

Projmat 28 36 38 - -

ELEFAN 26 33 - - 38

25

Table- 1. VBG parameters estimated by different methods based on length data

Method L∞ (cm) K (yr-1) t0 (yr)

SLCA 41.19 0.90 -0.035

PROJMAT 41.73 0.856 -0.064

ELEFAN 1 39.043 0.801 -0.160

Average parameter values 40.13 0.852 -0.086

Table- 2. Age-length-key in S. canaliculatus

Method Age in years

1 2 2.25 2.75 3

Length (cm)

SLCA 28 35 - 38 -

Projmat 28 36 38 - -

ELEFAN 26 33 - - 38

Table 1:

VBG parameters estimated by different methods based on length data.

Table 2:

Age-length-key in S. canaliculatus.


t, the average standing stock (Y/F) worked out to 390 t. The Yw/R for the current F was estimated as 62.5 g and MSY/R was 65.3 g at the F of 2.2.

The estimated MSY for S. canaliculatus from the Arabian Sea coast of Oman for the period of study was 569 t which was the average of the values calculated by Cadima’s formula (519 t) and yield analysis (618 t). Hence, the speculation on the annual average landings of about 200 t of S. canaliculatus from the entire coast of Oman (Al-Abdessalaam, 1995) is an underestimate. Though, the annual estimated landings of all siganids in Oman for the period from 1994 to 2000 was less than 300 t, catches started to increase from 2001. The average annual catch for the period 2001-2006 was 866 t with the highest catch being 1,155 t during 2005 (GoSO, 2006).

The estimated catches of S. canaliculatus from the Arabian Sea declined from 565 t during 2005-2006 to 449 t during 2006-2007, about 20.5% reduction (MSFC, unpubl. data). In a fishery, there may be a long term average MSY about which catches may fluctuate in response to environmental changes (Hoggarth et al., 2006). The drop in the catch during 2006-07 from the previous year may be viewed as a fluctuation due to fishery independent causes. However, this assumption needs validation. The catches during 2005-06 though not exceeded MSY level, they were close to it. This indicates that the effort level in this fishery has reached maximum limit. At the current F (=1.3), the estimated exploitation ratio E is 0.49. Hence, there is no scope for further increase in catches of S. canaliculatus from the Arabian Sea and the current effort is optimum for this fishery.

ACKNOWLEDGEMENTS

We are thankful to the Ministry of Agriculture and Fisheries Wealth, Government of Sultanate of Oman for providing the opportunity to carry out this study and to the Agriculture and Fisheries Development Fund, Oman for financial support. Our thanks are also due to H.E. Dr. Hamed Al-Oufi, the Under-secretary, Ministry of Agriculture and Fisheries Wealth – Fisheries sector and to all our colleagues in the Marine Science and Fisheries Centre and the Fisheries Laboratory at Salalah for technical support.

REFERENCES

Ahmed K.K.U., Amin S.M.N., Haldar G.C., Diwan S., Hossain, M.M(2005). Population dynamics and stock assessment of Labeo rohita (Hamilton) in the Kaptai Reservoir, Bangladesh. Asian Fisheries Science 18: 1-14.

Al-Abdessalaam, T.Z.S(1995). Marine species of the Sultanate of Oman. Ministry of Agriculture and Fisheries, Sultanate of Oman, Publication No. 46/95, 412 pp.

Alagaraja, K(1984). Simple methods for estimation of parameters for assessing exploited fish stocks. Indian Journal of Fisheries 31: 177-208.

Banerji, S.K(1973). An assessment of the exploited pelagic fisheries of the Indian seas. Proceedings of the Symposium on the Living Resources of the Seas around India, CMFRI Special Publication, Cochin. 176-183 p.

Beverton, R.J.H. and Holt, S. J(1956). A review of methods for estimating mortality rates in exploited fish populations, with special reference to sources of bias in catch sampling. Rapports et Proces verbaux des Réunions, Conseil


26

Table- 3. Growth parameters reported in the literature for S. canaliculatus

Country/Region L∞ (cm) K t0 Reference

Southern Negros, 25.2 1.872 0.02 Lam, 1974

Philippines

Aquaria 30.8 1.548 -0.08 Tsuda, et al., 1974

Aquaria 16.1 3.3 -0.09 von Westernhagen &

Rosenthal, 1976

Sea cages, Mactan Island, 31.6 1.978 -0.15 Horstmann, 1975

Philippines

Arabian Gulf, UAE 24.8 (FL) 1.0 -0.1 Grandcourt et al., 2007

Arabian Sea, Oman 40.13 0.852 -0.086 Present study

Table3:

Growth parameters reported in the literature for S. canaliculatus

A. AL-MARZOUQI

International pour L’Exploration de la Mer 17A: 1-153.Beverton, R.J.H. and Holt, S.J (1957). On the dynamics of

exploited fish populations. Fish. Invest. Minist. Agric. Fish. Food G.B. (2 Sea Fish)., 19: 533 pp.

Beverton, R. J. H. and Holt, S. J (1959). A review of the life spans and mortality rates of fish in nature, and their relation to growth and other physiological characteristics. In: Wolstenholme, G. E.W. and O’Connor, M. (Eds), CIBA Found. Colloq. on Ageing. 5: 142-180.

Bwathondi, P.O.J(1982). Preliminary investigations on rabbitfish, Siganus canaliculatus cultivation in Tanzania, Aquaculture 27: 205-210.

Froese, R. and Binohlan, C (2000). Empirical relationships to estimate asymptotic length, length at first maturity and length at maximum yield per recruit in fishes with a simple method to evaluate length frequency data. J. Fish. Biol., 56: 758-772.

GoSO (Government of Sultanate of Oman)(2003). Fisheries Statistics Book 2003, Directorate General of Planning and Investment Promotion, Statistics and Information Dept., Sultanate of Oman.




Grandcourt, T., Al Abdessalaam T., Francis F., Al Shamsi A(2007). Population biology and assessment of the white-spotted spinefoot, Siganus canaliculatus (Park, 1797) in the southern Arabian Gulf. Journal of Applied Ichthyology 23: 53-59.

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(Received: June, 29, 2012; Accepted: April, 2, 2013)

length based stock assessment of the white- spotted rabbitfish, siganus canaliculatus

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