Pelagic species identification using multifrequency acoustic in the Northern Humboldt Current System off Peru

The Peruvian Marine Research Institute — IMARPE, has been conducting scientific hydroacoustic survey since 1983 in order to estimate the biomass of the main pelagic resources for fishing management. The multifrequency analysis used for species identification was recommended in 2000 by the International Council for the Exploration of the Sea (ICES). From 2014 IMARPE began to use multifrequency acoustic (18, 38, 70, 120 and 200 kHz). The calibrated data was collected during the hydroacoustic assessment cruise of pelagic resources conducted in spring 2016. Multifrequency analyzes were performed with Echoview 5.2, which allowed the identification of pelagic species with similar acoustics properties with the use of different frequencies. The results showed that the anchovy juvenile (Engraulis ringens) (< 12 cm of total length) presented a greater resonance in the frequency of 18 kHz compared to the adult counterpart. Pacific chub mackerel (Scomber japonicus) and south jack mackerel (Trachurus murphyi) have similar curves, however, jack mackerel has higher energy values. Coastal species such as samasa (Anchoa nasus) and catfish (Galeichthys peruvianus) present an energy differentiation at the 18 and 70 kHz frequencies. The carrot squat lobsters (Pleuroncodes monodon) show an upward increase in energy from the frequency of 18 kHz, unlike the other species. For mesopelagic species, such as lightflsh (Vinciguerria lucetia), showed a similar tendency curve to the juvenile anchovy with slightly higher values. These analyses will continue to be carried out in order to increase the accuracy of the identification of pelagic resources, especially in the records detected during daytime hours.