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- Some aspects of the behaviour of pelagic species species off Angola and its implication on biomass estimationPublication . Velho, Filomena Vaz; Barros, Pedro Conte dePelagic fish off Angola constitute about 80% of the total fish landed and 75% of animal protein in the diet of the coastal population. In Angola, the primary means for estimating abundance of small pelagic fish is through acoustic surveys, a method that is sensitive to errors caused by effects of fish behaviour, particularly those that may reduce the acoustic detectability offish. This study describes the interannual variability of the fishery and stocks pelagic off Angola and their behaviour in relation to the abundance estimation. The dynamics of the two main pelagic species, Cunene horse mackerel and Sardinela spp off Angola differ. In recent years the biomass of Sardinela spp is at stable level, whereas the Cunene horse mackerel is at critical level. It was observe that a relatively straightforward analysis of conventional acoustic survey data collected at a single- frequency combined with ancillary spatio-temporal information can provide useful indications on the identification of single- and multi species aggregations of small pelagic fish. With regard to their behaviour, Cunene horse mackerel tend to concentrate in dense schools near the seabed, but at night they move into the pelagic zone, dispersing into widespread scattering layers. The present study found that under some conditions fish tend to avoid the vessel vertically, diving below 12 m depth as vessel was passing over the fish. In general, the results of this study should help improve Angola improve the knowledge of the behaviour of pelagic species off Angola and the quality of the abundance estimations produced.