Journal of Ecoacoustics

(ISSN: 2516-1466) Open Access Journal
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JEA 2018, 2(2), 12; doi: 10.22261/JEA.R1156L

Investigating the utility of ecoacoustic metrics in marine soundscapes

1 Department of Marine Earth and Atmospheric Sciences, North Carolina State University, 2800 Faucette Dr., Raleigh, North Carolina 27695, USA
2 Center for Geospatial Analytics, North Carolina State University, 2800 Faucette Dr., Raleigh, North Carolina 27695, USA
3 Center for Marine Science and Technology, North Carolina State University, 303 College Circle, Morehead City, North Carolina 28557, USA
* Author to whom correspondence should be addressed.
Received: 15 May 2018 / Accepted: 13 Aug 2018 / Published: 14 Sep 2018
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Soundscape analysis is a potentially powerful tool in ecosystem monitoring. Ecoacoustic metrics, including the Acoustic Complexity Index (ACI) and Acoustic Entropy (H), were originally developed for terrestrial ecosystems and are now increasingly being applied to investigate the biodiversity, habitat complexity and health of marine systems, with mixed results. To elucidate the efficacy of applying these metrics to marine soundscapes, their sensitivity to variations in call rate and call type were evaluated using a combination of field data and synthetic recordings. In soundscapes dominated by impulsive broadband snapping shrimp sounds, ACI increased non-linearly with increased snapping rate (∼100–3500 snaps/min), with a percent range of variation (∼40–50%) that exceeds that reported in most studies. H, however, decreased only slightly (∼0.04 units) in response to these same snap rate changes. The response of these metrics to changes in the rate of broadband snapping was not strongly influenced by the spectral resolution of the analysis. For soundscapes dominated by harmonic fish calls, increased rates of calling (∼5–120 calls/min) led to decreased ACI (∼20–40% range of variation) when coarse spectral resolutions (Δf = 94 or 47 Hz) were used in the analysis, but ACI increased (∼20% range of variation) when a finer resolution (Δf = 23 Hz) was employed. Regardless of spectral resolution used in the analysis, H decreased (∼0.20 units) in response to increased rates of harmonic calling. These results show that ACI and H can be modulated strongly by variations in the activity of a single sound-producing species, with additional sensitivity to call type and the resolution of the analysis. Variations in ACI and H, therefore, cannot be assumed to track call diversity, and the utility of these metrics as ecological indicators in marine environments may be limited.
Keywords: acoustic indices; acoustic ecology; marine soundscapes; call rate; acoustic complexity index; acoustic entropy
This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).
Bohnenstiehl, D.R.; Lyon, R.P.; Caretti, O.N.; Ricci, S.W.; Eggleston, D.B. Investigating the utility of ecoacoustic metrics in marine soundscapes. JEA 2018, 2, 12.
Bohnenstiehl DR, Lyon RP, Caretti ON, Ricci SW, Eggleston DB. Investigating the utility of ecoacoustic metrics in marine soundscapes. Journal of Ecoacoustics. 2018; 2(2):12.
Bohnenstiehl, DelWayne R.; Lyon, R. Patrick; Caretti, Olivia N.; Ricci, Shannon W.; Eggleston, David B. 2018. "Investigating the utility of ecoacoustic metrics in marine soundscapes." JEA 2, no. 2: 12.
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