EVALUACIÓN HIDROACÚSTICA DEL MACHUELO (OPISTHONEMA OGLINUM) Y LA SARDINA (SARDINELLA AURITA), EN LA ZONA NORTE DEL CARIBE COLOMBIANO, DURANTE JULIO-AGOSTO Y DICIEMBRE DE 1997

Abstract

The objective of the present work was to assess the biomass of Atlantic thread herring (Opisthonema oglinum) and the Spanish sardine (Sardinella aurita) in the north area of the Colombian Caribbean sea by means of two acoustic surveys (one in July-August and other in December, 1997). 'llie scientific echosounder used for bodi surveys was the SIMRAD EK500. Emphasis was made on Atlantic thread herring and Spanish sardine because these small pelagic fish have been the most abundant in previous studies in this area. Systematic sampling using parallel transects perpendicular to the coast was carried out. The transect spacing used was 12 nautical miles. The Elementary Sampling Distance Unit (ESDU) was set in lnm. In order to know about the species composition and size frequency distribution fishing trawls were carried out. For this objective, a pelagic fishing trawl was used. For fish Target Strength (TS), the equation TS = 20 log L — 71.9 for physostome fish suggested by Foote was used. The results showed that Atlantic diread herring reached the highest biomass during December survey, 14 183 ton, CV = 0.02, and July-August 12 954 ton, CV = 0.30. The distribution of Adantic diread herring apparently is influenced by the season. 'Fhis species goes to especially where the temperature is higher. In the July-August survey a higher distribution was observed between the area of Santa Marta and Riohacha, while in the December survey die highest distribution corresponded to La Guajira. The Spanish sardine did not show differences in the geographical distribution depending on the season, and apparently it was related to colder and high salinity waters, besides it did not represent any importance due to the low values obtained. This two species in both surveys were always distributed inside the continental shelf.