Abstract
We have used a lately established workflow to quantify rhythms of three fish sound types recorded in different areas of the Mediterranean Sea. So far, the temporal structure of fish sound sequences has only been described qualitatively. Here, we propose a standardized approach to quantify them, opening the path for assessment and comparison of an often underestimated but potentially critical aspect of fish sounds. Our approach is based on the analysis of inter-onset-intervals (IOIs), the intervals between the start of one sound element and the next. We calculate exact beats of a sequence using Fourier analysis and IOI analysis. Furthermore, we report on important parameters describing the variability in timing within a given sound sequence. Datasets were chosen to depict different possible rhythmic properties: Sciaena umbra sounds have a simple isochronous—metronome-like—rhythm. The /Kwa/ sound type emitted by Scorpaena spp. has a more complex rhythm, still presenting an underlying isochronous pattern. Calls of Ophidion rochei males present no rhythm, but a random temporal succession of sounds. This approach holds great potential for shedding light on important aspects of fish bioacoustics. Applications span from the characterization of specific behaviours to the potential discrimination of yet not distinguishable species.
Highlights
Rhythms can be found everywhere in the world, from human speech to music and animals’ communication [1,2]
We aim to provide an overview of the performances and interpretation of this methodology when applied to different fish sounds recorded at sea
The rhythms of animals’ acoustic signals, produced internally or by tool-use, were so far quantified in birds [13,39], sea mammals [2,7,40], bats [2,12], primates [41] and, to some extent, in insects [42], but they were never quantitively measured in fish
Summary
Rhythms (i.e. non-random, ordered and recurrent alternation of different elements in a sequence of sounds and silence) can be found everywhere in the world, from human speech to music and animals’ communication [1,2]. They can be an inherent royalsocietypublishing.org/journal/rsos R. Rhythms can code for individual or context-related information They are for example used to discriminate between familiar and unfamiliar opponents in northern elephant seals [7]. The listeners are less likely to miss the element of an acoustic signal sequence This is only true if the respective species are capable of perceiving the rhythmic pattern. Important terminology with regards to rhythm, used in this study, is explained in table 1, and the terms that are explained there are written in bold on the first appearance in the text
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