<b>Biological scatterers detected along the Exclusive Economic Zone of northeast Brazilian coast, a classification o echo-records into functional echo-types</b>

Abstract

One hydroacoustics cruise was carried out along the shelf, shelf-break and oceanic adjacent waters along the northeastern Brazilian coast and the oceanic banks of Ceará, Rocas Atoll, and Fernando de Noronha and São Pedro and São Paulo archipelagos. A total of 1.653 nautical miles were assessed in order to investigate the distribution and abundance of small pelagic fishes. Hydroacoustics data were collected with a Scientific Echo-sounder EK 500, operating at 38 kHz. The acoustic records were stored as digital echograms from where morphological information about the scatterers aggregated into acoustic layers could be obtained. Also, acoustic density proportional to biological density were collected as well as biological samples using a mid water trawl net. Data were processed in order to identify patterns of echo-records which resulted in the classification of five functional echo-types represented by different species assemblies: 1) Neritic; 2) Oceanic layer; 3) Myctophidae; 4) Oceanic layer with Myctophidae; and 5) Shelf Break Plume. Sound Scattering Layers (SSLs) were the typical biologic aggregation structures registered in the area, as much superficially as in deep strata of water column. Nycthemeral migrations related to the SSL were frequently observed, being of great ecotrophic importance for the area.