Acoustical database dedicated to fish stock assessment being optimized to generate seafloor information and integrate biological, environmental and geomorphological studies

Abstract

The Fisheries Technology and Hydroacoustics Laboratory (TECPESQ-Institute of Oceanography, University of Rio Grande-IO-FURG-Brazil) has traditionally dedicated its working group to fish stock assessments using hydroacoustics. This technique allows the remote detection of organisms throughout the transmission of acoustic energy and the evaluation of the echoes. In order to attend different projects, we have prospected the Brazilian coast on board the R.V. AtlanticoSul, along more than 47,000 nautical miles. Acoustic data have been collected with scientific echo sounders SIMRAD EK 500 or SIMRAD EK 60. Complementary data have also been obtained, sampling organisms in the water column and bottom, as well as gathering environmental data. The large acoustic database was, at a certain moment, in contrast with the shortage of bathymetric and geomorphological data available, to be incorporated in the biological and environmental studies. This situation forced the group to start filtering and validating bathymetric and Bottom Surface Backscattering Strength (BSBS) data, collected along all cruises but not used previously and considered as secondary information. In 2004, part of the BSBS data base were analyzed and correlated to substrate composition and particle size which allowed to refine and detail the overall characteristics of the of the Southeast and South sectors of the Brazilian continental shelf and shelf break. In the same year, acoustic seafloor data were used to map three pockmarks, at a depth of 700 m, in the Santos Basin. In 2005, bathymetric data from seven surveys were integrated with satellite altimetry to generate three-dimensional maps of the Brazilian continental margin, which allowed a more detailed analysis of geological features, such as the Cone and the Plato do Rio Grande, Plato de Sao Paulo and the Vitoria Trindade Chain. In 2007, distinct seabed features were identified and entered in a GIS after the analysis of data collected in the Brazilian continental margin. In 2009, data from four cruises on the southern most part of the continental shelf were used to map the Albardao paleochannel, a vestige of ancient drainage of the La Plata River. BSBS values inside of this channel were significantly lower than from the external surrounding area, indicative of the presence of muddy sediments. In 2011, BSBS data were entered in a 3D GIS and integrated to bathymetric, environmental and sedimentological data, which allowed the identification of areas with acoustic features typical of phosphorite deposits, a mineral of great strategic and economical importance. Recently, in 2013, a map of the bottom reflectivity of the Pelotas Basin was finished, generated from 1,507,823 BSBS values, which allowed the identification of four important sea bottom features. The TECPESQ acoustic database increases at every research cruise. The ship is now fitted with new transducers, increasing the number of frequencies which will lead to more detailed studies of the characteristics of the reflective surface of the seabed of the Brazilian coast. This summary presents the feasibility of integrating and optimizing the use of vessels equipped with acoustic sensors, working for different projects, to build large databases, useful to generate integrated knowledge of the marine environment.