Figure 5 illustrates the distribution of all fish as observed with the acoustic integration system. This will mainlyshow the pelagic species, but some demersal fish which lifts off the bottom, especially at night will also be included. The units of acoustic reflection is 0.1 x 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 5 gives a fair picture of the main distributional features of the 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 Oriente.
High densities of pelagic fish were observed at night along the coast southeast of Isla Margarita, and on the shelf outside the Margarita Island. The main contributors to these recordings were adult Sardinella aurita and Etrumeus teres inside and outside the Island respectively. Schools were seen at surface in day hour and dense schools were recorded on the echo sounder at night. Two large samples were obtained with pelagic trawl, one from inside (St. No. 465) and one from outside (St. No. 475) the Margarita Island. It is assumed that these catches represent the schools of sardines whitsh were observed in surface layer during day. In the same areas juvenile sardines were caught together with carangids and scombrids in day hauls at bottom. The catches in these areas also included other pelagic fishes as barracudas, scombrids and carangids in addition to demersal fish. It is noted that the highest fish density is located in the cool upwelled water masses southeast of Isla Margarita, as can be seen by comparison with the temperature profile in Figure 3. Schools of anchovies were recorded inside and at the entrance of the Cariaco gulf. The present results thus confirm the findings during the previous coverage as reported in Preliminary Cruise Report I, Part 3.
Over most of the deeper pans of the shelf only scattered recordings were made indicating a general low level of fish density in mid water. The recordings usually consisted of traces of small schools or single fish not far off the bottom. Identification with bottom trawl showed that in addition to sardines they should be attributed to carangids, scombrids, barracudas and demersal fish lifting off the bottom.
Western part, from Cabo Codera to Penininsula de Guajira.
In the western part the registration of pelagic fish was more scattered then farther to the east with two small areas of concentration of schooling fish in the central part of the Gulf of Venezuela (Figure 6). On the basis of the bottom trawl samples these schools were identified as anchovies and sardines mainly. Sardines were also caught at bottom in the inner and western part of the gulf but not recorded in any significant abundance on the echo sounder. This may however be due to blanking by a very dense scattering layer of plantonic organism witch occured in that pan of the gulf.
