The units of acoustic reflection is 0.1 x m2/nm2 reflecting surface. An arbitrary scale has been used to illustrate different levels of concentration. The integrator values were allocated to the following groups on the basis of trawl sampling and characteristic behaviour:
Pelagic fish type 1, Clupeids and anchovies;Cunene to Tombua
Pelagic fish type 2, Carangids, scombrids, barracudas etc.;
Demersal fish in mid water.
Figure 3 illustrates the distribution of fish as observed with the acoustic integration system. The pelagic type 2 species are nearly exclusively horse mackerels with a little hairtails in some areas. The Cape horse mackerel Trachurus capensis dominated on the outer shelf south of 16°30' S, wheras the Cucune horse mackerel is found in the shallow waters of Baia dos Tigres and on the northern shelf. The densest concentrations of horse mackerels are found on the shelf edge, and the distribution usually extended only one mile or less off the shelf during daytime. The horse mackerels were observed to feed on Euphaucides. The size composition of the cape horse mackerel on the outer shelf ranged up to about 33 cm with a prominent mode in the low 20 cm's, wheras the fish caught on the inner shelf were juveniles ranging from 5 cm to 11 cm, see ANNEX I. The lenght distribution of the Cunene horse mackerel has modes at 8 cm, 15 cm, and 21 cm at the inner shelf, wheras the fish caught at the outer shelf ranged from 17 cm to 30 cm. An estimate of total biomass of horse mackerel based on the acoustic integration data is 138 000 tonnes. The similar estimates for the same period of the year in 1985 and 1986 were 100 000 t and 37 000 t respectively. The similar estimate of the servey in February this year was 140 000 tonnes.
Pelagic type 1 species were only found close inshore in the Baia dos Tigres and up towards Tombua. Sampling with the bottom trawl in midwater by the use of floats on the headline gave a mixture of the sardine Sardinops ocellata, Cunene horse mackerels and some few specimens of Sardinella maderensis. Judging from the observed schooling behaviour it is thought that the sardine formed the main contributor to the biomass inside the bay, but the sardinella may be underestimated by these samples due to possible differences in the catchability of the pelagic species. The total biomass of this inshore aggregation of Pelagic 1 species is estimated at 22 000 tonnes, compared to 90 000 t in the previous servey. The sardine ranged from 23 cm to 27 cm.
The distribution of demersal fish recorded in midwater is shown in Figure 3. This is thought mainly to show fish that lifts off the bottom, particularly during night time.
Tombua to Benguela
As shown in Figure 3, significant recordings of fish were made between Tombua and Namibe and in the bay of Cuio. The fish distributions in the first part seem to represent an extension of those on the shelf further south. The pelagic 2 group in the Tombua-Namibe area had an estimated biomass of 22 000 t, whereas the biomass of the pelagic 2 fish on the Namibe-Benguela shelf was estimated at 2 000 t.
Pelagic type 1 species were found in dense schools in the inner part of the bay of Cuio (Fig. 3). Sampling with midwater trawl gave a mixture of Sardinella aurita, Sardinella maderensis, horse mackerel and some anchovies. Judging from the schooling behaviour observed during the sampling, it is assumed that the sardinella forms the main part of the fish biomass recorded as pelagic 1 type fish in this area. This biomass is estimated at 20 000 t. The sardinella ranged from 23 cm to 43 cm.
As in previous surveys extensive and dense recording were made of mesopelagic fish, myctophids over the slope along this coast (not shown in fish distribution map). They are usually found in a layer at about 200 m depth during the day, but rise towards the surface at night.
