The Suriname shelf
The Guyana shelf
Venezuela and the Joint Fishing Area south of Trinidad
Figure 4 illustrates the distribution of all fish as observed with the acoustic integration system. This will mainly show 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 4 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.
Very high densities were found over the inner shelf, particularly off the Coppename river. The inner boundaries of the fish areas were usually located outside the 20m depth line. Identification by fishing with mid water and bottom trawls indicated that various species of anchovy formed the main part of this fish mixed with sardines and smaller carangids and with the various predators: Spanish mackerels, barracudas, sharks and demersal fish.
No high concentrations of fish were located over the mid and outer shelf. The dispersed fish here consisted mainly of horse mackerels with some sardinellas and the predators: snappers, Spanish mackerels and barracudas.
As seen in Figure 4 the high densities of recorded fish over the inner part of the Suriname shelf were only found to extend a short distance into the Guyana shelf where in general only low levels of densities were recorded. The few and restricted areas over the mid shelf with somewhat higher levels contained a mixture of anchovies, sardines and horse mackerels with predators: Spanish mackerels, barracudas and hairtails. A denser concentration was again found inshore in the north-west where the pelagic part of the catches consisted of anchovies, hairtails and some carangids. The offshore shelf towards the slope held only thinly scattered fish identified as horse mackerels, snappers and some sardinella.
A band of relatively high density of fish was found off the Orinoco Delta between approximately 20 and 40 m of depth. Samples showed a predominance of anchovies and sardines with hairtails, larger carangids and Spanish mackerel as predators together with the demersal fish. The outer shelf was incompletely covered, but few and scattered recordings were made here.
When relating fish distribution, Figure 4 with surface temperature, Figure 2 there is a tendency for the highest fish densities off Suriname and Guyana to be located in areas with cooler upwelled water. Off the Orinoco Delta the higher fish densities are in the extreme inshore waters affected by the river discharge.