Hydrography
Figures 2-5 show the distribution of temperature, salinity, density and oxygen content in the four hydrographic sections carried out. These sections were identical to those carried out during September 1983. The temperature in the surface layer is about 6°C lower than in September 1983
Due to reduced freshwater outflow during this cruise, the salinity of the surface layer is higher close to the coast on this cruise. The well-mixed and homogeneous upper layer reach to about 150 m compared to about 25 m in September 1983. As a result of this, the oxygen rich waters are reaching much deeper than in September 1983, e.g. the 4 ml/l isoline at this cruise was usually observed at depths of more than 100 m.
Demersal fish
The distribution of echo abundance from bottom fish is shown in Figure 6. The recordings were usually scattered.
The catches along the Makran coast were dominated by rays and catfish (Arius sp.). The seabream (Argyrops spinifer), grunters (Pomadasys hasta (= P. kaaki), Pomadasys stridens) and sharks also made significant contributions to the catches.
In Sonmiani Bay the catfish (Arius sp.) dominated the catches. Significant contributions came from the threadfin bream (Nemipterus japonicus) and the false trevally (Lactarius lactarius).
Along the Sind coast the catches of bottom fish were nearly exclusively made up by the threadfin breams (Nemipterus metopias and N. japonicus) with the first as the most important.
Pelagic fish
The recordings of pelagic fish along the Makran coast were scattered (Figure 7). Around Astola Island some good recordings of the scad (Decapterus russelli) and the anchovy (Thryssa sp.) were made.
Also along the Sind coast the recordings of pelagic fish were generally low with a few exceptions. South of Karachi some dense concentrations of the anchovy (Stolephorus sp.) were observed. At the southernmost coast some good recordings of sardinella (Sardinella sindensis) were made. The two other areas of some more dense recordings were made up by ponyfish (Leiognathus sp.).
Mesopelagic fish
As on the previous cruises recordings of mesopelagic fish were made off the continental shelf (Figure 8). It was found at 150-200 m depth during daytime and migrated to the surface layer during night. The recordings were made up almost exclusively by the lanternfish (Myctophidae).
During night time, when the mesopelagic fish were in the surface layer, it was mixed with the plankton. During night it was therefore difficult to separate the integrator readings into contribution from each of these groups.
Plankton
As on the previous cruise the planktonic scatterers made up the major part of the integrated echo abundance over the shelf area. The main contribution seems to come from jellyfish and krill. However, the echo abundance attributed to plankton was considerable less on this cruise than in September 1983. In some shallow areas along the western Makran coast, the jellyfish was the major catch and might reduce the efficiency of the fishing operations.
Karachi, 2 February 1984.
Roald Sætre
Fig. 2. Hydrographic section I: Ras Jiwani - South, 21 Jan 1984.
Fig. 3. Hydrographic section II: Astola Island - South, 23-24 Jan 1984.
Fig. 4. Hydrographic section III: Sonmiani Bay - Southwest, 26 Jan 1984.
Fig. 5. Hydrographic section IV: Indus River - Southwest, 29-30 Jan 1984.
Fig. 6. Distribution of demersal fish (integrated echo intensities).
Fig. 7. Distribution of pelagic fish (integrated echo intensities).
Fig. 8. Distribution of mesopelagic fish (integrated echo intensities).
