•
COL O NIAL O FFICE
F ISHER Y P U B LICATI O N S: Vol. 1, N o.4, 1953
A PRELIMINARY STUDY
OF THE PHYSICAL, CHEMICAL AND
BIOLOGICAL CHARACTERISTICS
OF SINGAPORE STRAITS
By
THAM AH KOW, B.SC. (Lond.)
Fishery Officer (Research)
Department of Fisheries, Federatioll of Malaya
and Singapore
•
PERPUSTAKAAN
NEGARAMALAYSI
A
•
817046 /
LONDON : HER MAJESTY'S STATIONE RY OFFICE
1953
•
- 7 SEP 1995
CONTENTS
1.
II.
III.
IV.
V.
.
Introduction
Page 1
Materials and Methods
2
Notes on certain aspects of the General Meteorology
of the Area
5
Hydrology
A. Tides and Currents
6
B. Temperature
9
C. Salinity
11
D. Phosphate
15
The Plankton
A. Seasonal Variation in Other Regjons
18
B. Seasonal Variation in the Plankton of Singapore
Straits
(i) Phytoplankton
(n) Pigment Content
(iii) Zooplankton
(iv) Volume of the Plankton
(v) The Plankton Calendar of Singapore Straits
19
19
22
24
29
30
C. Correlation between the Plankton of Singapore
Straits and certain Environmental Factors
34
D. Factors Influencing Plankton Production
36
E. Plankton Production
39
PERPUSTAKAAN
NEGARAMALAYSI
A
VI.
VII.
VIII.
The Nekton
42
Interrelationships
54
Some Possible Applications of Results to Fisheries
Development
57
S
59
Acknowledgments
60
References
60
Appendix
65
•
IV
SECTION I
INTRODUCTION
THE value of oceanograpillc investigations had long been recognized in Europe and elsewhere
and in the past many oceanographic expeditions were undertaken to study the physical,
chemical and biological conditions in the different oceans and some, the" Challenger,"
"Valdivia," "Siboga," "Dana" and" Snellius" to mention a few, came very near to
the Malay Peninsula, but somehow the comparatively shallow seas around the Malay
Peninsula never attracted their attention. All these expeditions collected valuable data
willch served to indicate what oceanographical and biological conditions might be expected
in different parts of the world. The very nature of these expeditions, which consisted of
extensive cruises of ocean-going sillps, however, precluded the intensive study of any
restricted area for any considerable period of time. In Europe and America the need for
intensive investigations was recognized many years ago. The International Council for
the Exploration of the Sea, amongst many other organizations, was formed and issued its
first report in 1902. Since then many intensive stud ies have been undertaken in Europe
and elsewhere. Intensive studies on the more important food fishes like the Hake (Hickling,
1927, 1930 and 1933), the Cod (ef Graham, 1948) and the Herring (ef Hodgson, 1934),
are examples and they have resulted in a clearer understanding of the many factors which
affect the stocks of these fishes.
In South and South-Ea t Asia, studies on the various aspects of the physical, chemical
and biological conditions in the sea were carried out by Sewell (1926, 1928, 1929a, 1929b
and 1932), Weel (1923), Delsman (1939), Chevey and Serene (1948), Rose (1926) amongst
others, but only in the case of Delsman were determinations of physical, chemical and
planktological conditions carried out concurrently. Delsman's observations, however,
covered only two months of the year, viz.: April and October, both months being the periods
of change-over from one monsoon to the other. Little is known of the seasonal variation
in the physical, chemical and biological conditions of Malayan seas.
In thi first study of the physical, chemical and biological characteristics of Malayan
seas, Singapore Straits has been chosen as the location because laboratory facilities are
readily available in Singapore. As Singapore Straits is the meeting point of three bodies
of water, viz. Malacca Straits, South China Sea and Java Sea, it may be expected to have
some of the characteristics, physical, chemical as well as biological, of these bodies of
water. It is a narrow stretch of water, not much more than ten miles wide, separating
Singapore and the southern tip of the Malay Peninsula on the one hand and the islands
of the Rillo Archipelago on the other. The average depth in the middle of the channel is
0
about 20 fathoms. It is a little more than 1 north of the equator.
Fortnightly observations were started early in 1948 on the temperature, salinity and
phosphate content of sea water as well as the numbers, volume, total pigment content and
general composition of the plankton. Meteorological data of the area have been kindly
supplied by the Director, Meteorological Services, Malaya, Commander H. B. Moorhead,
with whose permission the data are included in this paper under the section " Meteorology
of the Area." At the same time records were kept of the daily catches of certain fixed traps
in Singapore Straits throughout the period of observation. All these observations were
initiated and continued for two full years with the object of elucidating the annual patterns
of the variation in the physical, chemical and biological conditions in Singapore Straits
and their inter-relation hips.
Tills study is considered important because it is the first time, as far as the writer is
aware, that quantitative planktological investigations including pigment content estimations
PERPUSTAKAAN
NEGARAMALAYSI
A
4
THE PHYSICAL, CH EMI CAL AND BIOLO GICAL
the deviations were 100 %in opposite directions, i.e. 2,060,000 cells in the case of the largest
catch and 12,500 cells in the case of the smallest (which was very unlikely), 12,500 would
be 0·6 % of 2,060,000. The difference between 2·4 %and 0·6 %was sufficiently small to be
disregarded. This was the line of argument of Hardy and Gunther (l. c.) in their study of
the plankton of South Georgia and appeared to the writer to apply equally well to this
investigation.
It was thought likely that the larger zooplankton organisms like the Salps and
Chretognaths, etc., being capable of swimming at higher speeds, might avoid being sucked
up through the hose of the pump by swimming away from the open end of the hose.
A surface tow was therefore made on sampling days with a net made of Indian muslinmouth 40 cm. in diameter and length 120 cm. The tow was always made between two
fixed points 2,700 metres apart during slack tide, in the afternoon in 1948 and in the early
hours of the morning in 1949, and was carried out at slow speed of the launch and completed in thirty minutes or very nearly so. If the filtration' of the net had been ideal, then
about 340 cubic metres of sea water would have been filtered in one haul.
In counting the numbers of organisms, the sample was diluted to 200 c.c. and an aliquot
part (about 20 c.c.) was taken after the usual mixing process used previously and poured
into a petri dish. After settling the organisms in ten fields taken at random were counted
under a low power binocular microscope. The numbers of different organisms per haul
were then .calculated using equation (1). The figures would then represent numbers per
half-hour haul.
Surface plankton samples collected in various months during 1935, in January 1936
and February 1947 were studied by the writer in 1947 in the Laboratories of the Department
of Zoology, University of Sydney, Australia, under the supervision of the late Professor
W. J. Dakin. As the samples were collected by surface tows for varying periods the results
could not be expressed quantitatively. The numbers of the various groups of organisms
were expressed as percentages of the total numbers of the whole sample.
At the same time as the pump hauls were made temperature readings of the sea water
were recorded and water samples for the determination of salinity and phosphate were
collected at a point 3 fathoms below the surface. The water samples were always tested
within ten hours after collection. For the determination of salinity Knudsen's procedure
as described by Mathews (1923) was followed. The standard sea water used was supplied
by the Conseil Permanent International pour I'Exploration de la Mer and the salinities
were calculated from Knudsen's Hydrographical Tables (1901). For the determination of
phosphate, Atkin's (1923) modification of Denige's method was followed, but only half
the customary amount of each of the reagents was used. Colour comparison was made
visually in daylight, using 60 cm. columns of liquid and the salt error, which was found to
be 1'2, was applied to all determinations.
In the study of the nekton it appeared desirable to get a picture of the variations in the
specific composition of the fish fauna in Singapore Straits as well as the variations in the
abundance of different species throughout the year. It was considered that a record of the
daily catches of a predominant method of fishing used in Singapore Straits, viz. a fish trap
known as the" kelong " in Malaya would give such a picture. The important features of
this method of fishing are (1) in Singapore Straits its fishing intensity is practically constant,
and (2) the fish in Singapore Straits are brought on to the long leads of these traps by the
tides and all fish lured into the traps are caught by means of fine-meshed lift nets. A full
description of this method of fishing has been given by LeMare and Tham (1947). Forms
were distributed to owners of three traps who were requested to record the quantities of
each type of fish caught each day. Forms were returned once a week and the quantities
were then tabulated in the laboratory.
The data, based on fortnightly samples, are averaged into monthly figures for the
purpose of showing the month to month variations. These data are also used for the
PERPUSTAKAAN
NEGARAMALAYSI
A
5
CHARACTERISTICS OF SINGAPORE STRAITS
statistical analysis. These monthly figures therefore constitute time series and it is possible
that in each of these time series the value of the variable at one period of time may influence
its value in a succeeding period. In such cases the use of partial correlation as an analytical
tool would not be valid. However, there should be no objection to the use of partial correlation as a preliminary measure. If the partial correlation coefficients are significant on the
usual tests, then the independence of the terms of the series correlated should be investigated. According to Bartlett (1935) the complete independence of observations in one series
is sufficient for a test to be valid. Walker (1950) even goes further by saying that complete
independence is not necessary. In this paper the "Mean-square Successive-difference"
0·01 being
method given by Ferber (1949) is used for testing for serial correlation, P
taken as the level of significance. If the terms of one of the two series were found to be
non-serially correlated then the partial correlation coefficient would be considered valid. If
both series were found to be serially correlated then the method of Fisher (1948) for series
correlation would be applied to remove the effect of time.
SECTION III
N OT ES O N C E R T AI N AS PE CT S O F T HE
G E N E RA L ME T E OROLOGY O F THE AREA
THE climate of Singapore, like that of other areas in South-East Asia, is characterized by
two monsoons. In Singapore the two monsoons are: (1) south-west monsoon from May
to September, and (2) north-east monsoon from November to March the following year,
with two periods of about eight weeks each between the two monsoons during which weather
conditions are changeable. During the north-east monsoon the prevailing wind is north
and north-east, whilst during the south-west monsoon the prevailing wind is south, southeast and south-west. Details of the monthly totals of the average hourly wind speeds as
observed by the Malayan Meteorological Services for the years 1948 and 1949 are given in
Table 1. These figures are reproduced here to give a picture of the wind force during the
different months of the year.
PERPUSTAKAAN
NEGARAMALAYSI
A
TABLE 1. Total monthly wind speed at Kallang, Singapore
(Extracted from the records of the Meteorological Department, Malaya)
Metres per second
Month
January • •
February ..
March • •
April
• •
May
• •
June
• •
July
• •
August • •
September
October ..
November
December
•
• •
•
• •
• •
• •
•
• •
•
•
•
• •
•
• •
• •
• •
• •
• •
• •
• •
•
•
•
• •
•
•
• •
• •
• •
• •
• •
• •
• •
•
•
• •
• •
• •
• •
• •
• •
• •
•
•
1948
1949
1,554
657
760
626
659
1,174
1,065
1,226
1,029
854
973
1,346
2,106
1,469
1,427
1,070
1,027
1,315
1,540
1,418
1,381
1,327
1,038
1,018
•
The rainfall for Singapore Island is more or less evenly spread over the different months
of the year. From the average figures for the different months during the period 1931-40
6
THE PHYSICAL, CHEMICAL A D BIOLOGICAL
the range is from 4·82 inches per month to 9·25 inches per month. On the whole the northeast monsoon brings more rain than the south-west monsoon. For the year 1948 rainfall
was. abnormally high, especially in January, causing widespread flooding in the Malay
Pernnsula. During 1949, however, the early part of the year was rather less wet than usual.
The rainfall data for Singapore are given in Table 2.
TABLE 2.
Rainfall of Singapore in inches per month
(Extracted from the records of the Meteorological Department, Malaya)
•
Month
January ..
February
March • •
April • •
May
• •
June
• •
July
• •
August ..
September
October ..
November
December
• •
• •
•
• •
• •
• •
• •
• •
• •
• •
• •
•
• •
• •
• •
•
• •
• •
• •
• •
• •
• •
• •
•
•
•
•
•
•
•
•
•
•
•
• •
• •
• •
• •
• •
• •
•
• •
• •
•
A verage for
52 years
Average
1931-40
1948
1949
9·88
6·62
7·40
7·64
6·65
6·85
6'77
7·95
6·77
8·07
9·92
10·55
9·25
4 ·82
7·36
6·57
8·40
7·52
5·89
6·52
7·23
7·03
9·08
8·88
24·03
8·38
14·26
10·08
9·92
6·71
10·92
3·29
5·18
4·11
13·52
12·83
5·95
5·84
4·47
9·22
7-86
6·85
5·01
2·95
8·09
10·22
11·73
12·18
As Singapore Straits is so near to the equator, there is no great variation in the number
of hours of sunshine per day throughout the year. No figures are available for sunshine
during 1948 and the first half of 1949. Table 3 gives the average nllmber of hours of sunshine
per day for the different months of the year as observed during the period 1931--40.
TABLE 3. Average number of hours sunshine per day for the period 1931-40
(Extracted from the records of the Meteorological Department, Malaya)
Average number of hours
of sunshine per day
Month
January
February
March
April • •
May • •
June • •
July • •
August
September
October
November
December
• •
• •
• •
•
•
• •
• •
• •
•
•
• •
• •
• •
•
•
• •
• •
• •
•
•
5·17
6·95
6·09
5'67
6·14
6·36
6.72
6'18
5·70
5·70
4·77
4'70
PERPUSTAKAAN
NEGARAMALAYSI
A
• •
•
•
• •
• •
• •
• •
• •
•
• •
• •
••
• •
• •
• •
• •
•
• •
• •
•
•
• •
• •
• •
•
•
• •
• •
• •
• •
•
• •
• •
• •
• •
•
•
•
•
SECTION IV
HYDROLOGY
Sub-section A. Tides and Currents (see Map)
IN general during the twenty-four hours of the day the tides in Singapore consist of one high
and one low water, succeeded by a second high and low water of lower range. During
neap tides the difference between the heights of this inferior high and low water is sometimes
7
CHARACTERISTICS OF SINGAPORE STRAITS
I. Pangko r
2. Aro. Is.
3. One Fathom B.nk
~ . Sing. pore Is.
•
5. Singapore Straits
6. Kanmon Is.
7.
8.
9.
10.
II.
D
DurJan Straits
Keli.n
Banka Straits
Singkep
Bintang
Malay
Peninsula
South
I
China
•
()
().
OJ"
2
Sea
•
•
•
••
•
•
Borneo
•
o
\\ Lingga
C Archipelago
8.
.,'.~R
er~
'""--...:% Jtr
•
Banko
PERPUSTAKAAN
NEGARAMALAYSI
A
Sumatra
9
C'
'--~
""0
o ~o
~ -"....r
~ Bil/iton
I.
'\i.
Indian
Ocean
Java
•
Java
Sea
10
.
THE PHYSICAL, CHEMICAL AND BIOLOG[CAL
South China Sea flowing south-west past Nhatrang during tills period enters Singapore
Straits.
In the case of the Java Sea, Weel (I.e.) found a range of 4·6° C. (30·5° C.- 25·9° C.) during
the four months of the year 1917 (i.e. February, May, August and November). The mean
temperature for each of these four months was 27·65° C., 28·5° C., 27·7° C. and 28·8° C.
respectively, indicating illgher temperatures in May and November and lower temperatures
in February and August. Excepting for November, tills is true for Singapore Straits.
Returning to the temperature pattern of Singapore Straits, with the onset of the northeast monsoon cooler water from the South Chlna Sea passes into Singapore Straits. Tills
is caused by the pressure of the south-westerly currents in the vicinity of the eastern entrance
to Singapore Straits. At the same time the rainy season begins and solar radiation is at
a minimum (ef Tables 2 and 3). During the first half of the north-east monsoon wind
speeds are also illgh. All these factors tend to lower the water temperature in Singapore
Straits, so that with the onset of the north-east monsoon the water temperature drops
to a minimum in January. After January the temperature begins to rise to a maximum
in April or May. This is not surprising, since in February rainfall is usually low and solar
radiation increases. Wind speeds also begin to drop in February to a minimum in April
or May. A rising temperature is therefore consistent with these facts.
The change from the north-east monsoon to the south-west monsoon, lasting about
eight weeks, takes place during the period April-June, and weather conditions are then more
or less uncertain. The seas are calm and wind speeds are comparatively low. These conditions are conducive to the maintenance of high temperature. With the onset of the
south-west monsoon in June, the temperature drops again to a minimum in July or August.
Tills minimum occurred in August in 1948 and in July in 1949. It is significant that the
wind speed maximum for this period also occurred in August in 1948 and in July in 1949.
As the wind speeds drop after these maxima the temperature rises again until the period
of change from the south-west monsoon to the north-east monsoon, i.e. about eight weeks
from September to November. Static conditions prevail once again. After this, with the
onset of the north-east monsoon, the temperature drops again to the minimum in January.
It will be noticed from Fig. I that the temperatures during 1949 were in general lower
than the corresponding ones in 1948. It will also be clear from Table 1 that in 1949 the total
wind speeds were almost always higher than those for 1948. This suggests that the higher
wind speeds of 1949 were responsible, to some extent at least, for the lower temperatures
of the sea water in the same year. The similarity between the temperature pattern of
Singapore Straits and those of Nhatrang and the Java Sea indicates that the movement of
water masses, from the South China Sea during the north-east monsoon and from the Java
Sea during the south-west monsoon, sets the basic temperature pattern for Singapore
Straits. The effect of (1) decreased solar radiation due to rainy weather during DecemberJanuary and (2) high wind speeds during the periods (a) December-January and (b) JuneAugust are then superimposed on this basic pattern to give the observed pattern for Singapore
Straits.
It is clear from the graphs in Fig. I that the maxima of May-June and September in
1948 shifted in 1949 to April-May and August respectively and that there was an extra peak
in October in 1949. It will be seen later that tills irregularity appeared also in other environmental factors studied in this investigation.
PERPUSTAKAAN
NEGARAMALAYSI
A
Partial cor. eoeff.
t
r 4' 3
0·513
r4'3 ( 2' 5)
0·6294
3·62
r 4' 2
0·2862
r 4' 2 ( 3' 5)
0·3283
1·55
r 4' 5
0·1931
r4' 5 ( 2'3 )
0·3385
1·61
The" t " and " P " values are for the partial correlation coefficients.
I
1
I
!
!
I
I
I
•
!
j
(
I
~
D
i
,
•
I
~
j
,
u
I
T
I
U
The total and partial correlation coefficients are as follows:Total cor. eoeff.
I
I
P
0·0 1--{)·()() 1
0'1--{)'2
0·1- 0·2
I
•
n
a
\1
U
~
•
11
CHARACTERISTICS OF SINGAPORE STRAITS
,
On testing the series for rainfall, windforce~ temperature and salinity for serial correlation
the results are as follows:p
Series
S2
r:?
K
greater than ·01
Rainfall X 2 ••
.,
25·7706
20·3753
1·2696
less
,, ·01
WindforceX 3 ..
.•
117,874
113,774
1·0360
Temperature Xl
. . 0·4439
0·8516
0·5212
" ·01
"
Salinity Xs . .
. . 0·7701
0 ·7908
0·974
" ·01
"
When P 0'01, K 1'1606; P 0·99, K 3·0133 (N 24)
S2 = mean value of sum of the squares of differences between each pair of two successive
observations.
=
n
e
•
1
s
,
I
I
I
I
r
r
I
•
•
I
variance of sample data.
K
=
S2
-';2 '
a
When the value of K is less than 1·1606 then it may be presumed that positive serial correlation exists and when it is greater than 3 ·0133 then negative serial correlation exists. If it
is intermediate between the two values then it is presumed that serial correlation in the
series has not been certainly proved, i.e. the terms may be presumed to be independent.
On this basis, the series for rainfall may be presumed to have no serial correlation, but serial
correlation is certainly present in the series for windforce, temperature and salinity. Of the
three partial correlation coefficients only that between rainfall and temperature is valid and
the other two are not valid.
The method of series correlation of Fisher (l.c.) is then applied to these two relationships.
The basic annual temperature curve of the water entering Singapore Straits may be expected,
from a study of the annual temperature patterns at Nhatrang in French Indo-China and
in the Java Sea to have two peaks (one during April-May and the other during OctoberNovember) and two troughs (one during December-January and the other during JulyAugust). Temperature will then be a function of time of the 4th degree. By eliminating
this function of time by the method of Fisher (l.c.) from the data of 1948 the results are:Correlation between
Temperature X4 and Windspeed X3
Temperature and Salinity Xs
• •
Series cor. coeff.
..
0·7862
+ 0·2273
• •
t
3·1804
0·5811
P
·02-·01
·6- ,5
PERPUSTAKAAN
NEGARAMALAYSI
A
The series correlation between windspeed and temperature is clearly significant. In addition
to a time-parallel element there is also a cause-effect element operating between these
variates in Singapore Straits. It may be concluded therefore that the temperature pattern
of Singapore Straits is the result of the superimposition of the effects of rainfall and windforce on a basic pattern which is set by the movement of water masses from the surrounding
seas. The apparent relationship between temperature and salinity is only a time-parallel one.
Sub-section C. Salinity (see Map)
The salinity values for the fortnightly samples have been averaged for each month and
these average monthly readings are plotted as graphs in Fig. II. In 194'8 the salinity for
Singapore Straits rose from a minimum value of 29'97%0 in January to 31·27%0 in February
and a maximum of 31·38%0 in March. This maximum was maintained in April, after which
it began to drop to another minimllm of 28-47%0 in August. From then onwards it rose
again to another maximum of 31·87%0 in November, after which it dropped again. In
1949 more or less the same sequence was observed in the fluctuations of salinity excepting
that (1) the first drop in salinity was in April instead of Mayas in 1948, (2) the rise in
salinity started in July instead of August as in 1948, and (3) in place of a clear-cut maximum
12
THE PHYS I CAL, CHEMICAL AN D BIO LOGI CA L
as in November 1948 there were two reduced maxi ma, one
other in November 1949. This shifting of the 1949 pattern
extra peak towards the end of the year were also observed
(ef previous sub-section). The range in salinity in 1948 was
3·29%0'
in September 1949 and the
by a month earlier and the
in the case of temperatures
5·54%0 and that in 1949 was
FIG. II
SALINITY
r-.
I \
I
_ _x- - ,,<;:-x,
J(- -
I
"-
I
\
I
"
,
\
'~
I
I
\
\
\
I
\
I
I
I
\
I
\
I
\
•
\
I
I
\
\
I
I
I
I
\
I
I
... _ _ _ _ _ _ A
I
1948
I
I
I
1949
,
I
.
29-
,
J<
/
\
\
/
'y '
28,
•
J
I
F
I
M
I
I
I
I
I
I
I
I
I
A
M
J
J
A
5
0
N
D
The salinity pattern for Singapore Straits therefore appears to consist of two maxima,
one during March-April and the other during November, and two minima, one during
December-January and the other July-August. The same sort of pattern was found in
1935 by the writer (ef Birtwistle 1936). As regards the salinity pattern of the adjacent
seas, Berlage (l.e.) , after a study of Wee!'s (l.e.) data, came to the conclusion that along
the north coast of Java in the region of the sea fisheries there were two maxima and two
minima. For the western part of the Java Sea the minima were expected in February and
July and the maxima in May and September. In French Indo-China, Chevey and Serene
(l.e.) found in 1941-42, for the Bay of Nhatrang, a maximum in July and a minimum in
November.
In Indo-China there is a salinity minimum in November; in Malaya there is one in
December-January; in the western part of the north coast region of Java there is one in
February. This sequence is significant since it is quite clear, from the figures given by
Stewart (1930), that the north-east monsoon rains along the east coast of Malaya set in
progressively later as one proceeds south. Since the same monsoon sweeps through the
whole region from French Indo-China to the Java Sea, it is very probable that the northeast monsoon rains set in progressively later as one proceeds south from French Indo-China
and that the effect of this phenomenon is reflected in the salinity patterns of the coastal
regions in the respective areas. For Singapore, at least, there is no doubt that the salinity
minimum in December-January is due in part to the heavy local rainfall during that period.
As the drift of the water in the South China Sea is south-west durin g this season, the effect
of rainfall on the salinity of the coastal water is expected to be more and more evident as
one proceeds south along the east coast of Malaya. The coastal stream that runs south
along the east coast of Malaya during this period will be progressively less saline on acco unt
PERPUSTAKAAN
NEGARAMALAYSI
A