Figure 4 illustrates the distribution of all fish as observed with the acoustic integration system. This will mainly show the pelagic species. The units of acoustic reflection is 0.1 × m2/nm2 reflecting surface. This unit is not directly proportional to fish density since small sized fish gives a higher acoustic reflection per unit weight than bigger fish, but in gross terms Figure 3 gives a fair picture of the main distributional features of the small pelagic fish in the area. An arbitrary scale has been used to illustrate different levels of concentration. The acoustic data will later be used for biomass estimates.
The Suriname shelf.
The distributional picture is the same as observed in the previous surveys with high densities inshore and especially between the Surinam - and Corentyn River mouths. A progression of generally lower densities was observed through surveys I, II and III in February, May and August respectively, but this time patches of high densities were again found as in January and the observed changes may have been a seasonal effect. The types of echo sounder recordings and the samples with bottom- and mid water trawls showed that by far the main part of this inshore biomass consisted of juveniles of various forms of small pelagic fish, sardinella, thread -, scaled - and dogtooth herrings, pellona, various scads and anchovies. The high density areas were distinctly patchy. The much lower densities recorded offshore consisted as previously of adult sardinella and various small Carangids. Pelagic predators such as Spanish mackerels, barracudas, sharks and jack mackerels occurred in most of the catches both in mid water and at the bottom especially inshore and thus formed part of the biomass.
Guyana.
As seen in Figure 3 notable aggregations of pelagic fish were found inshore over the easternmost part of the Guyanese shelf as an extention of that off the Surinam coast. Another more restricted area of high densities was found at abt. 15 - 30 m depth to the west of the Essequibo river. Trawl sampling showed that as in Suriname these areas of aggregation contained predominantly juvenile fish but mixed with predators such as Spanish mackerels and barracudas.
Venezuela off the Orinoco Delta.
As in all of the three previous surveys fish aggregations in this area were only recorded in a narrow belt inshore in the depth range 20 - 30 m. Trawl catches showed anchovies with some Clupeids, Carangids etc. Very little fish was recorded over the mid - and outer shelf off the Orinoco delta.
