Lokasinya ialah di sekitar Sungai Batang Lupar. Hanya inilah ... ikan,
pencemaran ..... in salinities ranging from 5.9 to 52.5 parts per thousand (ppt).
During the ...
BULETIN PERI KANAN FISHERIES BULLETIN
No. 53
SOME ASPECTS OF THE BIOLOGY OF IKAN TERUBOK, Hilsa loti (Valenciennes) (FAMILY: CLUPEIDAE) AT THE LOWER BATANG LUPAR RIVER, SARAWAK
BY
ALBERT C. GAMBANG FISHERIES RESEARCH INSTITUTE BINTA WA, SARA W AK
Mr Albert C. Gambang was born on the 15th July 1955 in Kg. Kepayang, Simunjang, Sarawak. He graduated from the University of Malaya with a B. Sc (Hons) in Botany. He joined the Fisheries Department as a Fisheries Officer on the 21st August 1978. He has attended courses on Fisheries subjects in and outside the country. He is now with the research section of the Marine Fisheries Department, is experienced in demersal fish resources research and has published fisheries resources in Sarawak.
Sarawak. He 5 articles on
SOME ASPECTS OF THE BIOLOGY OF IKAN TERUBOK, Hilsa tali (Valenciennes) (FAMILY: CLUPEID AE) AT THE LOWER BATANG LUPAR RIVER, SARAWAK
BY
ALBERT C. GAMBANG FISHERIES RESEARCH INSTITUTE BINTAWA, SARAWAK
DEPARTMENT OF FISHERIES MINISTRY OF AGRICULTURE. MALAYSIA 19RR
OICETAK
OLEH
JABATAN
HAJI MOKHTAR SHAMSUODIN.
PERCETAKAN J.S.D., KETUA
NEGARA.
S.M.r .•• S.M.S., PENGARAH
1988
ICUALA S.M.P.,
LUMPUR IC.M.N.,
P.I.S.,
CONTENTS Page
ABSTRACT
1. INTRODUCTION
1
2. MATERIALSAND METHODS: 2.1 Study Area .. 2.2 Trips .. 2.3 Fishing Methods and Gear .. 2.4 Fish Movement .. 2.5 Fish Catch .. 2.6 Reproductive Biology .. 2.7 Length-weight Relationship 2.8 Estimated Growth Curve
3 3 3 3 3 3 4 4
3. OBSERVATIONSAND RESULTS: 3.1 Fishing Methods, Gear and Catch 3.2 Fish Movement .. 3.3 Fishing Season of Hilsa toli .. 3.4 Length Frequency of the Catch
6 7 7 8
3.5 Length-weight Relationship 3.6 Estimated Growth Curve 3.7 Reproductive Biology .. 3.7.1 3.7.2 3.7.3 3.7.4 3.7.5
9 10
10
Sex Ratio ..
10
Length at First Maturity Spawning Season
10
Frequency Fecundity
13 13
of Spawning
10
4. DISCUSSION
15
5.
17
ACKNOWLEDGEMENT
6. REFERENCES..
18
ApPENDIX
20
The present study is an attempt to cover some aspects of the biology of Ikan Terubok, Hilsa toli. at the lower Batang Lupar river as this is the main river left where the fish is believed to go for spawning. Results of the study showed that fishing season is directly related to spawning activity of Hilsa toli starting from August to early November, with a peak in September. The fish spawns once during the year and migrates as far as 30 miles upriver from the sea to spawn. A single female fish produces between 327,731 to 591,224 eggs. The fish mature when they reach 28-30 cm in size and grow to as large as 59 em. Ratio of female to male fish is 2: 1. The decline of the fish stock is due to several causes of which the increase in fishing pressure and chemical preservatives and dust from timber logs along the river are probably some of the main ones.
Kajian sekarang ini ialah satu usaha meliputi beberapa aspek kajihayat Ikan Terubok, Hilsa toli. Lokasinya ialah di sekitar Sungai Batang Lupar. Hanya inilah sungai utama yang masih tinggal dan dipercayai ikan datang ke sini untuk -bertelur. Keputusan kajian menunjukkan bahawa musim menangkap ikan ada hubungan dengan musim bertelur Ikan Terubok, Hilsa toli. Musimnya bermula dari bulan Ogos hingga ke awal November. Kemuncak musimnya ialah pada bulan September. Ikan ini bertelur sekali sahaja dalam setahun. Untuk bertelur, ikan ini berhijrah dari laut ke hulu sungai sejauh 30 batu. Seekor ikan betina boleh mengeluarkan telur antara 327,731 hingga 591,224 biji. Ikan ini matang apabila ukurannya mencapai ke tahap 28-30 cm panjang dan boleh membesar sehingga 59 em. Nisbah saiz ikan betina dan jantan ialah 2: 1. Kekurangan stok ikan ini adalah kerana beberapa sebab. Antara sebab utamanya ialah bertambahnya aktiviti penangkapan ikan, pencemaran dari bahan kimia dan sisasisa habuk dari perusahaan balak qi sepanjang sungai.
In the early sixties, Ikan Terubok (Hilsa spp., Family Clupeidae) was caught in large quantities during the peak periods in the coastal waters and estuaries of rivers in Malaysia such that sometimes they oversupplied the market (Chua & Mathias 1978). This fish was once very common in Peninsular Malaysia especially in the coastal areas of Johore. Chua & Mathias reported that during peak seasons the market price dropped to such an extent that it was more economical to use the fish as fertilizers in the rubber plantations. The price then was 40 sen per kilogram. In Sabah, the fish was formerly found along the Northwest coast and formerly occurred in immense shoals in the coastal waters around Labuan but now the fish is rarely found here. In Sarawak the fish was formerly found in all the coastal waters and all estuaries of river. The fishermen reported that in a few hours of fishing, hundreds of kilograms of the fish could be caught (Personal communication with the fishermen). Now the "Terubok" is very rarely found in Peninsular Malaysia and Sabah. Presently the fish is found in only a few river estuaries and coastal areas of Sarawak and in smaller quantities. The estuaries and lower part of rivers include Sematan,Lundu, Sadong, Bako, Saribas, Batang Lupar and Muara Lassa (Fig. 1). The coastal areas are off Tanjong Sirik. Pulau Burong, off Oya, Mukah, Balingian, Bintulu and Miri. The main areas where the fish is presently found in relative abundance are the Batang Lupar river, and the coastal area around Pulau Burong. Ikan Terubok is very popular among both local and overseas consumers (more now, that the fish is getting scarce) for its tasty flesh (though bony) and eggs. Fish with eggs can now fetch a price of M$1O.00/kg while the salted eggs alone can fetch as much as M$90.00/kg. This has encouraged th fishermen to exploit the fish irrationally, without thinking of the consequences of overfishing. The fish is believed to spawn seasonally. Delsman (1921-1938) reported that in the west coast of Peninsular Malaysia the fish migrated into estuaries and further upstream during the spawning season. According to Delsman, the "Terubok" produced pelagic eggs and the young hatched out within twenty-four hours. Young and juvenile "Terubok" were then found in large numbers in mangrove fringed estuaries in the southern part of Peninsular Malaysia. There are two main species of "Ikan Terubok" (or "Shad" in English) found in Sarawak. The species Hilsa macrura (Bleeker) has a small mouth and is locally called "Terubok", whereas the second species Hilsa toli (Valenciennes) has a large mouth and is locally called "Bekawal". Of the two species, Hilsa macrura is usually caught in coastal areas especially around Pulau Burong. Hilsa toli is mostly caught around the estuary and lower region of Batang Lupar river. The lower Batang Lupar river is one of the few rivers left in Sarawak where Hilsa toli is believed to go upriver in large numbers tospawn. Because of the decline in the stock. there is a possibility that the stock may become extinct. There is therefore considerable interest in Sarawak to protect this fish, such as through rational exploitation. However, there is very little information about the fish in this part of Malaysia. The present study covers the lower Batang Lupar area and its estuary (Fig. 2). The aim of this study is to describe the reproductive biology, fishing and fishing gear used, fishing season, movement and growth of the fish.
FIG. 1: SHOWING NAMES OF PLACES WHERE THE SHAD (TERUBOKIBEKAWAL) IS FOUND.
LAUT
CHINA
SELATAN
FIG. 2: SHOWING THE BATANG LUPAR RIVER SYSTEM WHERE THE STUDY IS CARRIED OUT.
2
2.1
Study Area
The area studied covered the lower Batang Lupar river extending from the estuarine river mouth (Pulau Triso) to as far as Tanjong Bijat (Fig. 2) upstream. This is where most of Hilsa tali is still found in relative abundance in Sarawak. Fish caught within the river area were sold to the fish dealers in Lingga, a small village town and at Sebuyau, a small coastal town. 2.2
Trips
Monthly trips were planned to Lingga. Lingga was selected as our sampling site because most of the fishermen sold their catch here and besides, Lingga is situated almost at the centre of the study area. Sebuyau abundance. 2.3
was visited occasionally to check on the species sold there and their However, in 1985, we could make only six trips to Lingga and Sebuyau.
Fishing Methods and Gear
During fishermen
the trips, observations were interviewed.
on the fishing method
and gear were made and the
Fishermen were interviewed and observations were made on' the catch so as to ascertain how far upriver Hilsa tali was caught. This is to give us a rough picture about the migratory habit of the fish during the spawning season.
Landings were recorded from one fish dealer who had connections with a large number of fishermen in the Lingga area. The fish dealer kept records of the fish landings everyday for each fisherman and also separate records of fish with eggs (full belly) and fish without eggs (flat belly) as ascertained from fish samples, because the price of fish with eggs was double the price of fish without eggs. 2.6
Reproductive Biology
For making observations of gonads, two sorts of samples were utilized. Since the fish dealers remove'the ovarit;s from the fish, advantage is taken of the practice to make observations in the field. Up to 50 fish could be examined this way. Up to 20 specimens of both sexes were purchased and examined in the laboratory. For the field observation, each fish was measured for total length (which is also used in the length frequency analysis) and weight. As the stomach was cut open by the fish dealer, the maturity of eggs was noted using the Seven Point Maturity Stage (Appendix 2). The gonads were taken out and weighed. The distal end of the gonad was cut and preserved in 2% formalin for later use. Sexes of the fish were noted. The fish samples purchased were taken to the laboratory for analysis. Total length measured from the tip of the mouth to the tip of the upper caudal fin in centimeters and weight in grams of each fish were recorded. The stomach was cut open to observe the gonads for sex determination. The maturity of the gonads was determined using the Seven Point Maturity State Keys (Appendix 2). The gonads were weighed. Samples of
ova (taken from the middle section of the gonads) of up to 60 in number were measured for diameter. The ovaries of each fish were placed in modified Gilson's fluid (Appendix 3) for up to one week for egg counts using the gravimetric sampling method. While in the Gilson's fluid, the bottle containing the ovary was shaken to loosen the ova. After a week, the eggs were washed, spread on blotting paper, dried in air and weighed. Random samples of 500 eggs were counted and weighed. Total number of eggs in an ovary was given by F
=
nG g
where "F" is the fecundity, "n" is the number of eggs in subsample, weight of ovary and "g" is the weight of the subsample. The gonadosomatic index (GSI) which is the percentage body weight with gonads was calculated accordingly.
2.7
Length-weight
The functional
"G" is the total
of gonads weight over total
Relationship
relationship
between total body length and body weight of fish is given
by
where the weight (W) is proportional to a certain power (b) of the length (L) and "a" is a constant. Through the logarithmic transformation the above equation could be fitted into the line of best fit drawn by linear regression as: LoglOW
2.8
=
b 10glOL
+ log lOa
Estimated Growth Curve
The growth curve to express the growth of fish folIowed that of Von Bertalanffy Growth Formula (VBGF), which has the form: Lt
=
Lx [1 -
e-K(t-t..)j
where "Lx" is the maximum mean length the fish would reach if they were to grow to a very old age, "K" is growth coefficient, "to" is the "age" the fish would have had length zero if they had always grown according to the equation and "Lt" is the length at age t. The estimated growth curve of Hilsa toli is obtained applying Pauly's Integrated Method (1983) by fitting the growth curve by eye on the length frequency data (Fig. 3). The length at relative age (Table 1) obtained from the curve is used to estimate the growth parameters (Lc and K values) folIowing the Ford-Walford plot as, Lt+1
=
where
+ bLt Loo = a
a
1 - b and K
= -
and where Lt and Lt+
Logcb I
pertain to lengths separated
by a constant time interval.
FIG. 3: LENGTH FREQUENCY AND THE ESTIMATED GROWTH CURVE USING PAULY'S "INTEGRATED" METHOD (SAMPLE SIZE n = LWlj
FOR
Hi/sa
IO/i.
LENGTH-AT-AGE DATA ON THE SHAD (Hi/sa toli) AT LOWER BATANG LUPAR RIVER. (VALUES FOR RELATIVE AGE AND LENGTH (L) WERE DERIVED FROM GROWTH CURVE IN FIG. 3) Relative Age (months)
L(cm)
Rearrangement
for Ford- Walford Plot
1
7.2
L(
2
23.0
7.2
23.0
3
32.5
23.0
32.5
4
32.5
5
39.0 41.8
6
47.0
39.0 41.8
39.0 41.8
7
49.5
47.0
Lt
+ I
47.0 49.5
Using the data from Table 1 for Ford-Walford plot, the values of slope, "b", is -0.7 whereas the Lt + I intercept "a" is 17.6. Therefore, the value for L 00 is 58.7 cm and the value of K monthly is 0.357.
3.1
Fishing Methods, Gear and catch
The fish were caught by drift net (rantau). The net is of nylon material with a mesh size ranging from 2.5 to 3.5 inches. By a system of floats and sinkers, the net was made to drift 2 meters below the water surface. Fishing is carried out once or twice a day either during day or night time depending on the tidal pattern. During the fishing season, most fishermen fish once in the day and once at night. Two hours before the incoming tide, the nets were shot out and by the time the tide started coming upriver, the complete net (about 30-40 pieces) wpuld have been laid out. The extreme end of the net was tied to a float with a flag-marker and sinker, while the other end was tied to the boat. The nets and the boat would drift upriver with the in-coming tide. As the tide started to recede and the current started to flow downriver, the nets were hauled up. The fishing operation took about 3 hours on the average. The boats used were generally small (gross tonnage about 2) and normally powered by 5-10 h.p. pump engines and manned by one to two persons. The fish catch which comprised several groups of estuarine and brackish water species apart from lkan Terubok were sold directly to the local fishmonger. Normally the fisherman sell all the Ikan Terubok with eggs and retain a few tails of smaller fish. Ikan Terubok with full grown gonads is bought on the average $6.00/kilogram while those without eggs were bought at $3.00/kilogram. Immediately after landing the gonads were removed from the fish for salting process as salted eggs could fetch as much as $90.00/kilogram.
3.2
Fish Movement
During a normal fishing season, Hilsa toli was caught between Pulau Triso and Pulau Seduku area (Fig. 2). However during the "Bekawal" season, the fishermen caught the fish as far as Tanjong Bijat, that is, about 30 miles upriver. It is observed that wherever the fish was caught by the fishermen, the fish seemed to move upriver as far as Tanjong Bijat, probably to spawn. Most of the fish caught at Tanjong Bijat had ripe gonads. This suggests that the fish move upriver to spawn. 3.3
Fishing season of Hi/sa toti
Fig. 4 and Table 2 show the monthly catch pattern as obtained from the landing data of the fish dealer. The histogram shows the average catch. in weight (kg) per trip per fishermen. There was no catch in January and very little in February and March. The catch started to increase in April (1.7 kg/trip), and reached the first peak in June (2.9 kg/trip). The highest peak was in September (3.85 kg/trip). The catch started to decline in October and further decline in November. Fish with eggs were relatively abundant in July to October with a peak in September.
TABLE 2 TOTAL TRIP
Month
CATCH PER PER MONTH Tala! no. of [rip
MONTH.AND THE AVE~AGE CATCH PER OF Hilsa toti AT BAT ANG LUPAR RIVER Tota! Catch (kg) Fwith E
Average Catch/Trip (kg)
F without E
Fwith E
F without E
Tow! (kg/trip)
Jan. '85
14
Feb.
99
1.94
51.43
0.020
0.5\9
0.539
Mar.
172
18.20
60.69
0.106
0.353
0.459
349.71
0.453
1.300
1.753
Apr.
269
\21.83
May
406
245.60
567.99
0.605
1.399
2.0()()
June
363
360.50
714.28
0.993
1.96X
2.961
Jul.
352
541.40
212.96
1.538
0.605
2.143
351
530.50
430.84
1.5\1
1.22X
2.739
1.426
H4X
Aug. Sept.
263
637.20
375.08
2.422
Oct.
210
377.85
218.08
1.799
1.039
2.X3X
Nov.
46
24.63
21.00
0.535
0.457
0.992
Dec. Jan. 'X6
4
Feb.
50
5.26
8.95
0.105
0.179
0.2X4
Mar.
12
1.20
1.57
0.1
0.131
0.231
•• F E -
Fish Egg
ITD -
Fish with eggs
o - Fish without eggs
3.4
IJan. Feb. Mar. Apr. May June
Jul. Aug.
(1985)
MONTHS
Sep. Oct. Nov. Dec.
Jan.
Feb.
Mar.
(1986))
Length Frequency of the Catch
There were five length groups (Fig. 5). About 89 percent of the largest group caught was between was 33 cm with size ranging from
of the fish as shown by five peaks of the histogram fish caught were within the 22-44 cm length, while the 38-40 cm length. The mean length caught for the year 16 cm to 59 cm.
There is a tendency for the increase in size of fish caught from June onwards, as shown by the increase in mean length. (Table 3). TABLE 3 MONTHL Y MEAN Months Mean size .. Sample number
SIZE OF Hilsa tali
Mar.
May
June
July
Aug.
Sept.
Oct.
36.3
37.9
28.9
31.8
32.5
35.2
35.5
3
20
292
98
153
617
171
2M
0
150 135
120 105
Ii
90
Ii
>.
u
s::
~ ==' 0"
II
75
I
~ e.t..•..
I I
I
60
I
i
Ii ,I
I
45
"
30
"
15 0 4
8
12
16
20
24
28
32
36
40
44
48
Length (cm)
3.5
Length-weight Relationship
The equation
for length-weight
for Hi/sa toti is as follows:
(a) Male and female combined
3.312 log L - 2.474 Correlation
coefficient
=
(b) Male Log W = 3.122 log L - 2.224 Correlation n = 54
coefficient
= 0.954
(c) Female Log W n = 77
coefficient
=
Log W n = 55
=
=
3.328 log L - 2.500, Correlation
0.954
0.959
52
56
60
3.6 Estimated Growth Curve Using the "integrated" Lt
=
58.7 [1 - e -
method, 11.357 (t - to
the growth curve was found to be as follows:
J]
3.7 Reproductive Biology 3.7.1
Sex Ratio
From laboratory observations, invariably, "flat stomach" fish turn out to be males on examination of the gonads. Applying this observation to the field, the sex ratio was derived (Table 4). Generally, for all the months (except August), there were more male to female fish. The average ratio is one female to every two males.
Months F:M Sample (n) no.
* F M
3.7.2
March
June
July
Aug.
Sept.
Oct.
1:1.3
1:3.9
1:2.0
1:1
1:2.5
1:1.3
14
275
211
6
21
161
Female Male
Length at First Maturity
The percentage occurrence of mature fish for each group was used to determine length at first maturity (Table 5). The length at which 50% of the fishes are mature was considered as the minimum length at first maturity (Kagwade, 1968). From Fig. 6a, the length at first maturity was estimated at 28 cm. From the plot of GSI values versus standard length, the length at first maturity was estimated at 30.5 cm (Fig.6b).
3.7.3.
Spawning Season
Table 6 shows the monthly percentage occurrence of female Hi/sa tali for different stages of maturity. Mature fish seemed to be present from March onwards. By June the gonads were already developed and gravid stage by August. Spawning started in September to October and decline towards November.
100 u.l U
Z
80
:J
60
0
50
0
40
u.l ~ ~
U U
u.l
