Abstract
Understanding movement of marine megafauna across the ocean is largely based on approaches and models based on analysis of tracks of single animals. While this has led to major progress, the possibility of concerted group dynamics has not been sufficiently examined, possibly due to challenges in exploring massive amounts of data required to this end. Here we report a sonification experiment, where the collective movement of northern elephant seals (Mirounga angustirostris) was explored by coding their group dynamics into sound. Specifically, we converted into sound data derived from a tagging program involving a total of 321 tagged animals tracked over a decade, between 20 February 2004 and 30 May 2014, consisting of an observation period of 90063 hours, composed of 1,027,839 individual positions. The data parameters used to provide the sound are position (longitude) and spread (degree of displacement taken for the active group). These data parameters are mapped to the sonic parameters of frequency (pitch) and amplitude (volume), respectively. Examination of the resulting sound revealed features of motion that translate into specific patterns in space. The serial departure of elephant seals to initiate their trips into waves is clearly reflected in the addition of tonalities, with coherent swimming of the animals conforming a wave reflected in the modulated fluctuations in volume, suggesting coordinated fluctuations in dispersion of the wave. Smooth changes in volume, coordinated with pitch variability, indicate that the animals spread out as they move further away from the colony, with one or a few animals exploring an ocean area away from that explored by the core wave. The shift in volume and pitch also signals at group coordination in initiating the return home. Coordinated initiation of the return to the colony is also clearly revealed by the sonification, as reflected in an increase in volume and pitch of the notes denoting the movement of each animal in a migration wave. This sonification reveals clear patterns of covariation in movement data, which drivers and triggers, whether intrinsic or environental, cannot be elucidated here but allow to formulate a number of non-trivial questions on the synchronized nature of group
Highlights
The development of tracking devices has allowed fundamental insights into how large marine animals use the vast ocean environment (Costa, 1993; Costa et al, 2012), providing fundamental ecological insights to ensure their conservation (e.g., Maxwell et al, 2013; Hussey et al, 2015; Hays et al, 2016)
The animals departed from the colony in waves associated with the end of a breeding or molting cycle, each wave by a set of animals constituted a sonification set
The 10 year data set of northern elephant seal movements included tracks extending from their California colonies across much NE Pacific Ocean (Figure 3), and was summarized in a 54 min audio file (Figure 4), thereby achieving a 1:90,000 compression of the duration of the data set
Summary
The development of tracking devices has allowed fundamental insights into how large marine animals use the vast ocean environment (Costa, 1993; Costa et al, 2012), providing fundamental ecological insights to ensure their conservation (e.g., Maxwell et al, 2013; Hussey et al, 2015; Hays et al, 2016). The sonification presented here focuses on the methodological implementation of the representation, as an additional tool, together with visualizations, provided here, to explore the collective movement of this species We use this as a heuristic tool to pose questions, acknowledging that the interpretation or possible mechanisms driving the observed patterns cannot be resolved and would require a more quantitative approach better suited for hypothesis testing. Terms such as coordinated, concerted or synchronized to refer to features of the data are used here in their phenomenological sense, without implying the existence of specific mechanisms leading to these features in collective movement
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