Abstract
It remains an open question how well the increased bandwidth afforded by broadband echosounders can improve species discrimination in fisheries acoustics. Here, an objective statistical approach was used to determine if there is information available in dual channel broadband data (45-170 kHz) to allow discrimination between in situ echoes obtained from monospecific aggregations of three species (hake, Merluccius productus: anchovy, Engraulis mordax; and krill, Euphausiia pacifica) using a remotely operated vehicle. These data were used to explore the effects of processing choices on the ability to statistically classify the broadband spectra to species. This ability was affected by processing choices including the Fourier transform analysis window size, available bandwidth, and the method and scale of data averaging. The approach to normalizing the spectra and the position of individual targets in the beam, however, had little effect. Broadband volume backscatter and single target spectra were both used to successfully classify acoustic data from these species with ∼6% greater success using volume backscatter data. Broadband data were effectively classified to species while simulated multi-frequency narrowband data were categorized at rates near chance, supporting the presumption that greater bandwidth increases the information available for the characterization and classification of biological targets.
Highlights
Sensed data have played a significant role in revealing ecological processes at both large and small scales, and have provided critical data for the management of natural resources
Monterey Bay Aquarium Research Institute, 7700 Sandholdt Road, Moss Landing, California 95003, USA. It remains an open question how well the increased bandwidth afforded by broadband echosounders can improve species discrimination in fisheries acoustics
An objective statistical approach was used to determine if there is information available in dual channel broadband data (45–170 kHz) to allow discrimination between in situ echoes obtained from monospecific aggregations of three species using a remotely operated vehicle
Summary
Sensed data have played a significant role in revealing ecological processes at both large and small scales, and have provided critical data for the management of natural resources. One of the grand challenges in the remote sensing of biological systems is understanding the relationship between the measurements made and the organisms under study (Turner et al, 2003; Pettorelli et al, 2014). In fisheries and ocean ecosystem acoustics, the challenge is in the identification of the taxa creating the measured echoes (MacLennan and Holliday, 1996). How efficiently an individual animal scatters sound depends on its acoustic properties, for example, whether it has a gas inclusion, such as a swimbladder, or hard parts, such as a shell or bony skeleton. Scattering efficiency further varies strongly with acoustic frequency—different types of animals exhibit characteristic frequency responses that have been modelled and measured (see a recent synopsis in Benoit-Bird and Lawson, 2016)
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