Colombia
Figure 10 shows the distribution of fish along the shelf measured in units of the acoustic integration system. Densities are generally low with only few patches of somewhat higher values. The small aggregation 2°50'N consisted mainly of Pacific anchoveta Cetengraulis mysticetus somewhat mixed with Pacific bumper Chloroscombrus orqueta. The aggregations off Buenaventura were mainly by the Pacific bumper.
Of the Gulf of Cupica some hauls in the 200-300 bottom depth zone were carried out. The catches consisted mainly of nylon shrimp Heterocarpus and mantis shrimp Squilla.
Panama
Fish distribution by acoustic density intervals is shown in Figure 11. In the Gulf of Panama the highest densities are as previously mainly encountered in the shallow parts of the gulf. The central and outer parts were during the recent coverage virtually absent from acoustic registrations, in close resemblance with the situation during the first survey. The main reason for this pattern is the inflow of oxygen-deficient water masses to this part of the shelf, causing the fish to migrate out of the area. The scad Decapterus macrosoma were still present in the central and outer parts of the gulf, but in scattered to very scattered distribution only. In the shallow waters the densest patches observed consisted mainly of Pacific bumper, while less dense aggregations of threadfin herring, anchovy and again the bumper were found. The threadfin were mainly found in the western part, the anchovy in the eastern, while the bumper were spread all around the gulf in the shallow waters.
The recordings from the western part of Panama were as previously less abundant. A minor aggregation in Bahia Arenas consisted of bumper, anchovy and barracuda. A detailed acoustic survey were made over the Hanibal Bank, and gave registrations just above the threshold of the acoustic system only.
Costa Rica
Figure 12 demonstrates the fish distribution as observed by the acoustic system. In general the picture is similar to the distributions found in the previous surveys. In Golfo Dulce there is only scattered fish in the entrance and near the surface. Surface hauls in the gulf with pelagic trawl at night gave rich samples of juveniles from anchovies, hake, and hairtails. These were not recorded by the acoustic system. It might be that the surface waters in Golfo Dulce is a major nursery area for several species, and thus constitute an important link for fish living mostly outside the gulf.
In the outer parts of Gulf of Nicoya dense registrations were made, mostly from anchovies settling on the bottom during daylight hours. At dusk they would lift from the bottom forming small schools in intermediate waters, for soon to completely avoid detection by the acoustic system during darkness, as the fish were concentrating in the very surface waters.
The lighter aggregations located in the shallow waters of Bahia del Coronado is mainly made from yellowfin herring (Pliostostoma) and mojarra (Diapterus).
