Figure 4 illustrates the distribution of all fish as observed with the acoustic integration system. The unit of fish abundance is 0.1 m2 per nm2 acoustic reflection. With further analysis these observations can be converted to biomass by weight. Fish that occur down to about 0.5m from the bottom will be observable with this system. The distribution chart shows three categories of fish concentration: 1 - 9 units = scattered fish; 10-49 units = slightly gathered fish; > 50 units = concentrated fish.
Nicaragua
The fish distribution on this shelf can conveniently be described by reference to an inshore and an offshore community. The inshore community is found along the coast out to a depth of about 50 m and consists of small pelagics, mainly scads, thread herring and anchovies, Spanish mackerel, barracudas. sharks and various bottom fish, predominantly snappers. The offshore community is found near the edge of the shelf, over the slope and further off over the deep ocean. An important component in the food chain of this community is the mesopelagic fish, small (3 - 4 cm) mainly lanternfish with a regular diurnal migration between 250 - 300 m during the day and the surface layer during the night. High concentrations of mesopelagics were recorded over roost of the slope and further off during the survey (not included in the fish distribution chart). They are known to form the food for squid and tunas and they are no doubt an important food source for the various types of fish found on and over the slope such as silver smelt, cutlassfish, threadfin bass and others. Langostino and deep water shrimps form another important component of this offshore community. The fish and the crustacea found in these deep waters are adjusted to the ambient conditions here, temperatures of 12-15°C and an oxygen level of less than 1 ml/l.
The acoustic observations of the inshore community (Figure 4) show only scattered or slightly gathered formations of fish. Jack mackerels, spanish mackerel and demersal fish especially snappers dominated with some thread herring and anchovy in the north. One should note that the extreme inshore grounds fished by the small artisanal boats are not covered by this survey.
The more significant concentrations offshore consisted of often dense schools of cutlassfish and of looser schools and layers of silver smelt and threadfin bass close to the bottom at 160 - 200 m of depth. Poor weather conditions for acoustic survey may have caused underestimates of this offshore fish especially in the north.
Golfo de Fonseca
Fish was found over all of the parts of this shallow gulf that could be surveyed by the vessel, but not in concentrations of any significance. But in the approaches to the Gulf along the shores of both the Nicaraguan and el Salvador side small pelagic fish was found in some concentrations. The main part of the fish observed in the shallow part was jacks, spanish mackerel, thread herrings, anchovies and various bottom fish with an occasional domination of barracudas in the catches.
El Salvador.
Also when describing El Salvadors resources one can conveniently refer to an inshore- and an offshore component. Inshore several areas of fairly good concentrations were found, see Figure 4. These consisted of small pelagic fish, carangids, thread herrings and anchovies and their predators, sierra, baracudas and sharks. The distribution of deep water fish offshore is mainly limited to an area in the outer part of Golfo de Fonseca.
