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4. Fish distribution

Figure 3 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 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 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.

Several areas of high density were located over the inner and mid shelf areas. Densities were, however, not as high as those found here in Survey I, but there is now a tendency for the fish to be distributed further away from the shore and over larger areas. A shift in species distributions seems also to have occurred with various sardines forming the main part of the biomass, while anchovies dominated in Survey I. Various Carangids were found mixed with the sardines and anchovies as well as predators such as Spanish mackerels, barracudas, sharks and demersal fish.

Guyana.

As seen in Figure 3 notable aggregations of pelagic fish were only found over the easternmost half of the Guyanese shelf, a situation which is largely similar to that found in Survey I. There is as in Surinam an impression of a shift in species composition from anchovies to Clupeids. Recordings (not included in Figure 3) indicate the presence of an abundance of fish larvae and postlarvae over considerable parts of the shelf.

Venezuela off the Orinoco Delta.

Fish aggregations were only recorded in a narrow belt inshore in the depth range 20 - 30 m. Most of these were identified as anchovies with some sardines. Fish larvae were abundant in this zone. Very little fish was recorded over the mid - and outer shelf off the Orinoco delta.


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