262
S. M. HAG, ]. ALI KHAN, and S. CHUGTAI:
absent or poorly represented from the shelf. The highest number 164 per m 2 was recorded
for station 64/18 at the head of the Swatch.
The euphausids were found in large numbers in areas where oceanic influence predominated. A comparison shows the largest numbers in the slope water regions during
October and March 1968. A somewhat higher number in the southern shelf during
November is presumably associated with penetration of oceanic water into this region.
They were completely absent during March from the west coast but were present in small
numbers on the southern shelf. The cladocerans, on the other hand, were found to be
restricted to the shelf. A comparison between various sectors indicates the largest concentration on the shelf during March 1968 and fair abundance in the area north and
south of the Swatch. They were completely absent in the Swatch area itself.
Among micro-crustaceans, the ostracods at times formed the significant fraction of the
plankton in both the shelf and slope water sectors. Their highest concentrations were
restricted to small areas as in October and March in the slope water regions. They
formed a significant fraction of the plankton in the sector north of the Swatch, particularly
close to the continental margin. The highest number (28,730 per m 2 ) was recorded from
station 64/3. Surprisingly, they declined to almost rare occurrence in the southern sector.
The doliolids were common in all sectors. They were most abundant in March in the
shelf area of the southern region. In all other sectors they were less. As compared to
this, the salps were highly restricted in distribution and an occasional dense swarm
accounted for a high biomass value. They were generally confined to the shelf in vicinity
of the continental margin. The highest concentration of salps (27,000 per m 2 ) was
found in the sector south of the Swatch which contributed the bulk of the biomass
(405 ml m- 2 ). In March 1967 the largest number of 6613 per m 2 was found at station
67/13, contributing the bulk of the biomass (Fig. 6; Stn 67/13).
At times the siphonophores formed a significant part of the plankton, the number
being largest during March and October in the western region. In March they were the
dominating feature of the plankton biomass in the shelf and most of the eastern sector.
The appendicularians were abundant in both the slope and shelf sectors in association
with rich zooplankton. The largest number was found in the western sector in March
1967 but they were very rare in other parts of the shelf and the eastern sector. A similar
trend was seen in March 1968. In November they were most abundant north of the
Swatch, rare in the Swatch and south of the Swatch. The chaetognaths were the most
widely distributed group, the largest numbers being associated with areas rich in zooplankton in October and March 1968. They were present in large numbers in the shelf
during November. In March 1967 they were less variable in all the sectors.
Composition and Abundance of Copepods
Of all the major groups found, the copepods formed the bulk of the zooplankton
stock. As the principal source of energy in the building of higher trophic levels, their
numerical abundance at different stations in different periods provides a better measure
of productive areas than other groups. The species have been studied and their quantitative
abundance determined. In this paper the copepods are divided into 2 groups: the epiplanktonic species which are largely confined to the surface area on the shelf and slope
water, and the mesopelagic species living in subsurface oceanic waters. The criteria for
categorization of species into one or the other group were based on the work in this
S. M. HAG, ]. ALI KHAN, and S. CHUGTAI:
absent or poorly represented from the shelf. The highest number 164 per m 2 was recorded
for station 64/18 at the head of the Swatch.
The euphausids were found in large numbers in areas where oceanic influence predominated. A comparison shows the largest numbers in the slope water regions during
October and March 1968. A somewhat higher number in the southern shelf during
November is presumably associated with penetration of oceanic water into this region.
They were completely absent during March from the west coast but were present in small
numbers on the southern shelf. The cladocerans, on the other hand, were found to be
restricted to the shelf. A comparison between various sectors indicates the largest concentration on the shelf during March 1968 and fair abundance in the area north and
south of the Swatch. They were completely absent in the Swatch area itself.
Among micro-crustaceans, the ostracods at times formed the significant fraction of the
plankton in both the shelf and slope water sectors. Their highest concentrations were
restricted to small areas as in October and March in the slope water regions. They
formed a significant fraction of the plankton in the sector north of the Swatch, particularly
close to the continental margin. The highest number (28,730 per m 2 ) was recorded from
station 64/3. Surprisingly, they declined to almost rare occurrence in the southern sector.
The doliolids were common in all sectors. They were most abundant in March in the
shelf area of the southern region. In all other sectors they were less. As compared to
this, the salps were highly restricted in distribution and an occasional dense swarm
accounted for a high biomass value. They were generally confined to the shelf in vicinity
of the continental margin. The highest concentration of salps (27,000 per m 2 ) was
found in the sector south of the Swatch which contributed the bulk of the biomass
(405 ml m- 2 ). In March 1967 the largest number of 6613 per m 2 was found at station
67/13, contributing the bulk of the biomass (Fig. 6; Stn 67/13).
At times the siphonophores formed a significant part of the plankton, the number
being largest during March and October in the western region. In March they were the
dominating feature of the plankton biomass in the shelf and most of the eastern sector.
The appendicularians were abundant in both the slope and shelf sectors in association
with rich zooplankton. The largest number was found in the western sector in March
1967 but they were very rare in other parts of the shelf and the eastern sector. A similar
trend was seen in March 1968. In November they were most abundant north of the
Swatch, rare in the Swatch and south of the Swatch. The chaetognaths were the most
widely distributed group, the largest numbers being associated with areas rich in zooplankton in October and March 1968. They were present in large numbers in the shelf
during November. In March 1967 they were less variable in all the sectors.
Composition and Abundance of Copepods
Of all the major groups found, the copepods formed the bulk of the zooplankton
stock. As the principal source of energy in the building of higher trophic levels, their
numerical abundance at different stations in different periods provides a better measure
of productive areas than other groups. The species have been studied and their quantitative
abundance determined. In this paper the copepods are divided into 2 groups: the epiplanktonic species which are largely confined to the surface area on the shelf and slope
water, and the mesopelagic species living in subsurface oceanic waters. The criteria for
categorization of species into one or the other group were based on the work in this