The units of acoustic reflection is 0.1 × 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 hair-tails in the south. The Cape horse mackerel Trachurus capensis dominated on the outer shelf, see below for estimate of ratios between the two species. The densest concentrations of horse mackerels are found near the shelf edge, but the distribution usually extended 5-10 nm off the shelf, its limits appearing to coincide with the tongue of warm water of the Angola current found here. 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 35 cm with a prominent mode in the low 20 cm's, see ANNEX I. An estimate of total biomass based on the acoustic integration data is 140 000 tonnes. The similar estimates for the same period of the year in 1985 and 1986 were 120 000 t and 110 000 t respectively. Using the species composition in the catches from the outer shelf gives 126 000 t of Cape - and 14 000 t of Cunene horse mackerel.
Pelagic type 1 species were only found close inshore in the Baia dos Tigres and up towards Tombua. A great number of dense schools were observed in the bay itself with very high integrator readings over this small area and with a few schools up along the coast. Sampling with midwater trawl gave a mixture of sardines Sardinops ocellata, Cunene horse mackerels and smaller amounts of flat sardinella and anchovy, but judging from the observed schooling behaviour it is thought that the sardine formed the main contributor to the biomass inside the bay. The sardines had a bimodal size composition with modes at 25 cm and 13 cm, see ANNEX I. The total biomass of this inshore aggregation of Pelagic 1 species is estimated at 90 000 tonnes, of which 50 000 t sardines and 40 000 t sardinellas and anchovies. The variance of these estimates will, however, be high compared with the estimate of the horse mackerel biomass. Most of the large size sardines had maturity stages 3-4, pre-spawning.
The distribution of demersal fish recorded in mid water is shown in Figure 4. This is thought mainly to show seabreams that lifts off the bottom and the densest recordings are from the outer shelf.
Tombua to Benguela
As shown in Figure 4 significant recordings of fish were only made between Tombua and Namibe. The fish distributions in this part seem to represent an extension of those on the shelffurther south, a demonstration of the inshore extention of this whole frontal regime northwards towards Namibe. The pelagic 2 group, horse mackerel had an estimated biomass of 17 000 t.
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. They are located further offshore in other parts of the Angolan coast and must represent an important part of the food chain for the slope regime.
