ICES Journal of Marine Science, 58: 719–724. 2001
doi:10.1006/jmsc.2000.1057, available online at http://www.idealibrary.com on
Abundance and distribution of ichthyolarvae from upper pelagic
waters of the northwestern Arabian Sea during different monsoon
periods, 1992–1994
Samina Kidwai and Shahid Amjad
Kidwai, S. and Amjad, S. 2001. Abundance and distribution of ichthyolarvae from
upper pelagic waters of the northwestern Arabian Sea during different monsoon
periods, 1992–1994. – ICES Journal of Marine Science, 58: 719-724.
Surface to subsurface ichthyolarval distribution and abundance in the northwestern
Arabian Sea is presented. Fish larvae were sorted from zooplankton samples from five
NASEER (North Arabian Sea Environment and Ecosystem Research) cruises carried
out during different monsoon periods between 1992 and 1994. No areas of exceptionally high fish larval concentration were identified. However, there was a weak
concentration of fish larvae at stations southeast of Karachi during three of the cruises,
though its actual location was not the same during each cruise, and there was a peak
in concentration of fish larvae off the west coast of Pakistan during May 1994.
Abundance of fish larvae is compared with zooplankton standing stock, temperature,
salinity, wind speed and dissolved oxygen using non-parametric tests. However, no
clear relationship between biotic and abiotic factors at surface to subsurface water
depths was found.
2001 International Council for the Exploration of the Sea
Key words: abundance, distribution, ichthyolarvae, non-parametric tests, northwest
Arabian Sea, oceanography.
Received 10 March 2000; accepted 6 December 2000.
S. Kidwai and S. Amjad: National Institute of Oceanography, ST 47, Block 1 Clifton,
Karachi 75600, Pakistan. Tel: +92 21 5960028; fax: +92 21 5860129; e-mail:
[email protected] & [email protected]
Introduction
The abundance and the distribution of fish larvae
have direct relevance to the fishery potential of an
area and have been studied extensively worldwide
(Manickasundaram et al., 1987; Siraimeetan and
Marichamy, 1988; Doyle and Ryan, 1989; Nilssen et al.,
1994; Beckley, 1995; Munk et al., 1995). In the northwestern Indian Ocean (in the waters off Pakistan and in
the Gulf of Aden), studies on fish larvae date back to the
early 1970s (Ali-Khan, 1976; Haq et al., 1973). However
more recent research has focused on samples collected in
the 1970s and by the RV ‘‘Meteor’’ 1986 (Roepke et al.,
1990, 1993; Roepke and Freitas, 1991, 1995; Ali-Khan
and Aftab, 1993).
Climate and oceanography are linked to fish
abundance and distribution (Laevastu and Hela, 1970).
Recent studies have investigated the relationship
between oceanographic parameters (biotic and abiotic)
and abundance of fish larvae (Nilssen et al., 1994;
1054–3139/01/030719+06 $35.00/0
Beckley, 1995; Munk et al., 1995; Zelck and Klein, 1995;
Lauth and Olson, 1996). For the Arabian Sea, AliKhan (1976) briefly discussed the possibility that phytoplankton production influences the abundance of
Sardinella sindensis larvae, and Roepke and Freitas
(1991, 1995) discussed how short-term hydrographic
fluctuations relate to the occurrence and distribution
of Indian oil sardine Sardinella longiceps in Omani
waters.
Fish larvae were one of the 12 most dominant groups
in zooplankton samples collected during NASEER
(North Arabian Sea Environment and Ecosystem
Research) cruises, (Amjad et al., 1995; Kidwai et al.,
1997; Kidwai and Amjad, 2000). The purpose of the
present study was to document the abundance and
distribution of fish larvae in the northwest Arabian Sea
and briefly to investigate the relationship between biotic
(abundance of fish larvae and zooplankton standing
stock) and abiotic (temperature, salinity, wind speed,
dissolved oxygen) parameters.
2001 International Council for the Exploration of the Sea
720
S. Kidwai and S. Amjad
26
PAKISTAN
IRAN
25
Ormara
Pasni
62
Gwadar
200
1000
2000
Karachi
60
15
3000
24
s
du
In
4
18
12
53
23
8
21
40
49
e
idg
00
20
yR
rra
00
u
OMAN
M
22
45
0
20 0
0
10
°N
57
24 300
0
42
00
10
27
30
37
21
33
20
59
60
61
62
63
64
65
66
67
68
°E
Figure 1. Positions of the stations occupied during five NASEER (North Arabian Sea Environment and Ecosystem Research)
cruises carried out between 1992 and 1994.
Table 1. Physical parameters during four of the NASEER cruises.
Cruise
Temperature
(Cs.d.)
N1
N3
N4
N5
24.10
25.40
28.91
25.95
(0.50)
(0.32)
(0.28)
(0.20)
Salinity
(s.d.)
36.58
36.50
36.65
36.31
(0.14)
(0.26)
(0.09)
(0.33)
Materials and methods
Fish larvae were sorted from zooplankton samples collected during five NASEER cruises conducted during
1992, 1993 and 1994. The five cruises (N1–N5) were
carried out in January 1992 (winter/northeast monsoon),
August 1992 (summer/southwest monsoon), March 1993
and May 1994 (spring/pre-southwest monsoon) and
December 1994 (winter/northeast monsoon), respectively. The cruise track followed a 1500 nautical mile
path (Figure 1) between 20–26N and 59–68E. In all,
there were 18 biological stations, five of which were 24 h
repeat stations.
The physical parameters on cruises N1, N3, N4, and
N5 were recorded by means of a Sea-Bird 911Plus CTD
system (Table 1). During cruise N2, the CTD was
damaged during deployment, so the data had to be
Wind speed
(m s 1 s.d.)
9.27
6.61
6.08
5.26
(4.74)
(2.3)
(2.41)
(2.31)
Dissolved oxygen
(ml l 1 s.d.)
4.39
3.83
3.33
3.25
(0.22)
(0.44)
(0.34)
(0.62)
recorded from other sources, but the data so collected
did not lend themselves to the rigorous analysis subjected to the data from the other cruises. A Bongo net
(diameter 60 cm, mesh size 335 µm during N1, N2, and
N3, and 150 µm during N4 and N5) was used to sample
zooplankton. The volume of water passing through the
nets was recorded by means of a digital flowmeter.
Sampling depth was surface to subsurface (0–5 m) and
the nets were towed horizontally for 10 minutes along a
circular path at a speed of 2–3 knots. Samples were
washed and stored in 10% buffered formalin and
brought back to the laboratory ashore for quantitative
and qualitative analysis (Amjad et al., 1995). Fish larvae
were sorted from the entire sample and stored in 4%
buffered formalin solution.
In order to provide an overview of the whole study
area, fish larval distribution patterns were derived using
Distribution and abundance of ichthyolarvae in the NW Arabian Sea
26
26
J
12
23
22
6
62
63
64
°E
65
66
67
20
59
68
26
60
30
25
62
63
64
°E
65
66
0
75 600 450
450
67
68
°N
0
0
22
30
30
21
0
60
23
0
9
60 0
21
150
0
150
0
23
M2
0
15
24
22
30
300
24
°N
61
26
M
25
20
59
4
8
4
4
61
8
21
12
60
23
22
18
6
20
59
°N
°N
24
6
6
4
4
24
A
25
8
25
21
721
61
62
63
64
°E
65
66
67
68
20
59
0
60
61
62
63
64
°E
65
66
67
68
26
D
0
25
20
0
°N
24
23
20
20
22
0
21
20
59
60
61
62
63
64
°E
65
66
67
68
Figure 2. Ichthyolarval abundance (numbers 100 m 3) during five NASEER cruises – J: January 1992 (northeast monsoon),
A: August 1992 (southwest monsoon), M: March 1993 (pre-southwest monsoon), M2: May 1994 (pre-southwest monsoon),
D: December 1994 (northeast monsoon). Dots indicate the position of the stations on the cruise track. The coordinates of the
Figure are 20–26N and 59–68E.
SURFER (6.0 WINDOWS). The data were arcsinetransformed for non-parametric analysis (Canonical
Correlation Analysis and Discriminant Analysis) using
a SAS program. Abundance of fish larvae during
each of the cruises was compared and its relationship
with various biological and physical factors investigated.
Results
The distribution of fish larvae was patchy; no areas of
very high concentration being identified during the study
(Figure 2). There was also no significant difference in
abundance between the distributions of fish larvae during different monsoon periods. During January 1992,
March 1993, and December 1994, small concentrations
of fish larvae were found southeast of Karachi, and the
most larvae recorded per m3 was during the presouthwest monsoon period of May 1994, off the west
coast of Pakistan (Figure 2).
The results of earlier studies on analyses of data from
the same cruises have reported that the distribution of
zooplankton standing stock (biomass) was uneven and
722
S. Kidwai and S. Amjad
that the movement of these high-density patches corresponded to patterns of wind reversal (Kidwai and
Amjad, 2000).
The abundance of fish larvae (m 3) was not normally
distributed and was arcsine-transformed for statistical
analysis. The results of the non-parametric tests on the
biological and physical data of cruises N1, N3, N4, and
N5 revealed no distinct relationship between fish larval
abundance and zooplankton standing stock (ml m 3),
or between the biotic (fish larval abundance, zooplankton standing stock) and abiotic (temperature, salinity,
wind speed, dissolved oxygen) parameters for any of the
four monsoon periods observed.
Discussion
The patterns of distribution of fish larvae offshore in the
northwestern Arabian Sea was neither notable nor consistent, but closer to the coast there were relatively more
fish larvae (Figure 2). Studies from other areas and on
specific species have reported similar distributions
(Lauth and Olson, 1996). During the present study, a
weak concentration was recorded during January 1992,
March 1993, and December 1994 southeast of Karachi.
The east coast of Pakistan has extensive mangrove cover
that would provide excellent spawning habitat and nurseries for fish species (Snedaker, 1984), so there may be
some connection between the two. Other research in the
area has shown that the waters south of Karachi contain
an abundance of small pelagic species such as sardine
Sardinella longiceps and round herring (Haq et al., 1973;
Sharp, 1995). Survey cruises of the Norwegian RV ‘‘Dr
Fridtjof Nansen’’ during 1977 found the area south of
Karachi to be rich in fish eggs, larvae, and juveniles
(Anon., 1977, 1986). Elliott and Savidge (1990) and
Roepke and Freitas (1995) report that the weak southerly directed current may be responsible for transporting
shelf species offshore. Roepke and Freitas (1995) suggest
that the extensive horizontal variability in abundance
and distribution of sardine larvae could be influenced by
wind-induced lateral transport of water.
Variability of fish stocks in the North Sea, off Japan,
and off Peru have been linked to the availability of food
to the early life stages (Robinson, 1994; Williams, 1984).
Although the results of the present study did not
demonstrate a relationship between food availability
and abundance of fish larvae, earlier studies have
reported small schooling pelagic species in large
numbers off the south coast of Pakistan (Sharp, 1995).
Sharp showed that just over half of the annual fish
harvest there is Sardinella longiceps (Indian oil sardine),
a first-level consumer that normally feeds on phytoplankton. Although the fish larvae collected during this
work have not yet been subject to rigorous taxonomic
scrutiny, several families (Clupeidae, Myctophidae,
Lutjanidae, Apogonidae, and others) were found during
an initial search. Fish larvae of some of those families
also feed on zooplankton or a mixture of phyto- and
zooplankton (Williams, 1984), so the lack of a relationship between zooplankton standing stock and distribution patterns of fish larvae is rather surprising. Detailed
taxonomic investigation of the samples is clearly
essential if information on fish feeding preference and
behaviour is required.
Temperatures off the coast of Oman during a southwest monsoon tend to be low (Owens et al., 1993),
suggesting upwelling and possibly also a corresponding
increase in biological productivity (Smith, 1982, 1984).
Although coastal stations off Oman were not sampled
during cruises N4 (pre-southwest monsoon) and N5
(northeast monsoon), the results of the other cruises do
indicate a slight increase in the numbers of fish larvae
there when the temperature declines (Figure 2).
Upwelling per se is not as pronounced along the west
coast of Pakistan, but there is upsloping of cool, anoxic
water, originating in the upper oxygen minimum zones
of the continental shelf during the southwest monsoon
period (June–November/December; Banse, 1984;
unpublished NASEER data). The water temperatures
cool by several degrees and this, coupled with a low
oxygen concentration, affects the distribution of
demersal fish and shellfish, which tend to move to
shallower waters upshelf. Williams (1984) and Sharp
(1995) observed large aggregations of fish and enhanced
abundance during winter. During the present study, the
greatest number of fish larvae in a single cruise was
taken in this area (west coast of Pakistan), but during
the May 1994 cruise, which marked the onset of the
summer southwest monsoon. The wind circulation
pattern then moves towards the coast, and surface
currents are landwards and clockwise (Banse, 1984;
Slater and Kroopnick, 1984).
Areas of low oxygen tend to shift on a daily basis
(Williams, 1984), so whether this movement follows a
pattern needs to be investigated. To predict the exact
location of fish on the basis of the oxygen minimum
waters is beyond the scope of the present study.
Acknowledgements
The study was part of Pakistan-US ONR (Office of
Naval Research) programme for cooperation in
oceanography, funded by Grant No. N00014-86-G0230. The authors acknowledge the efforts of all participating NIO scientists and the crews of the NASEER
cruises. Thanks are due to Mohsin Tabrez of the
NODC, NIO-Pakistan, for assistance with SURFER, to
Dr Nasseer Idrisi of the Rosenstiel School of Marine
and Atmospheric Science, University of Miami, USA,
for help with the statistical analysis, to Ronnie Snyder of
the Aquatic Science Division, Agriculture and Food
Distribution and abundance of ichthyolarvae in the NW Arabian Sea
Science Centre, Belfast, UK, for constructive suggestions on how to improve an early draft of the manuscript, and to two referees for advice on finalizing the
manuscript.
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