The indices of echo abundance in Table 1 are, as stated previously in this report, subject to errors and the figures both in Tables 1 and 2 should, therefore, be considered as preliminary and used with care. From the length distributions of the fish it is seen that sardinellas and horse mackerels less than 10 cm in length are almost completely lacking in the catches although considerable quantities of these small fish must have been present somewhere at least during one of the two survey periods. As a rule the observed fish lengths decreased towards the shore and the small juvenile fish may have a too nearshore distribution pattern to be recorded with the survey grid used. However, for reasons of safety the most shallow waters, shallower than 15 m, can only to a very limited extent be covered by "Dr. Fridtjof Nansen". The estimates of abundance in Table 2 can, therefore, roughly be considered as estimates of that portion of the pelagic fish stocks that exceed 10-12 cm in length. Hence they are underestimates for the total biomass of small pelagic fish. Yet, it should be borne in mind that the areas shallower than 15-20 m are rather limited in the larger part of the survey area and that the possible uncovered portion of the pelagic fish biomass, therefore, only will lead to a limited increase of total fish weight.
There seem to be three main areas were "commercial" concentrations of small pelagic fish are concentrated. These are: The northeast Somali coast (Sub-area 3), the Arabian coast between Ras al Kalb and Ras al Hadd (Sub-areas 6 and 7) and the shelf off southern Pakistan (Sub-area 10). In these three areas both the estimates of abundance and the catch rates (Table 3) were significantly higher than elsewhere in the survey area. Both off the north-east Somali coast and off south-western Oman large schools of oil sardinella, the largest exceeding 100 tonnes, were observed during the autumn survey, and in addition to the maximum catch rates in Table 3, several catches larger than 1 tonne/hour trawling were made. Bearing in mind that nearly all fishing operations during this first year of operation have been carried out for reasons of identification of echo records and no detailed searching for the best fishing grounds have been made, the observed catch rates seem promising.
During 1976 most of the research vessel time should, therefore, be spent within the areas pointed out above. The very high abundance of demersal fish together with the observation on mackerel in deep water off the Somali coast (5°-10°N) justify also further investigations. Effort should also be made to locate areas and seasons where and when the highest catch rates of mesopelagic fish can be obtained by the most suitable gear.
