The long-range echo scene of the sperm whale biosonar

Abstract

Sperm whales use their gigantic nose to produce the most powerful sounds in the animal kingdom, presumably to echolocate deep-sea prey at long ranges and possibly to debilitate prey. To test these hypotheses, we deployed sound recording tags (DTAG-4) on the tip of the nose of three sperm whales. One of these recordings yielded over 6000 echo streams from organisms detected up to 144 m ahead of the whale, supporting a long-range prey detection function of the sperm whale biosonar. The whale navigated this complex acoustic scene by maintaining a stable, long-range acoustic gaze suggesting continual resource evaluation. Less than 10% of the echoic organisms recorded by the tag were targeted for capture and only 18% of the buzzes were emitted within the 50 m depth interval of maximum organism encounter rate, demonstrating echo-guided prey selection. Buzzes were initiated more than 20 m from the prey, showing that sperm whales do not debilitate their prey with sound, but trade echo levels for reduced forward masking and rapid updates on prey location in keeping with the lower manoeuvrability of these large predators. We conclude that the powerful biosonar of sperm whales enables long-range echolocation and selection of prey, but not acoustic debilitation.

Echolocation click parameters and biosonar behaviour of the dwarf sperm whale (Kogia sima)

“…This buzzing click rate is comparable to those reported in porpoises (Wisniewska et al, 2012;DeRuiter et al, 2009) and dolphins (Wisniewska et al, 2014;Ladegaard et al, 2015;Martin et al, 2018). The pattern of buzzing initiated at a range of around 1-2 body lengths from a prey item appears consistent across a broad range of sizes of toothed whales, from large sperm whales (Fais et al, 2016;Tønnesen et al, 2020) and Blainville's beaked whales (Johnson et al, 2008) to porpoises (Wisniewska et al, 2012), and appears to be in agreement with the buzzing Kogia sima presented here. These 'hand-off distances'from an approach phase to a buzzing interception phaseseem, along with maximum clicks rates, to be scaled with the whale's size and manoeuvrability .…”

“…Conversely, the deep-diving sperm whale (Physeter macrocephalus), which can reach a length of up to 18 m, employs a long-range echolocation system (of the order of hundreds of metres) via clicks with very high source levels (up to 240 dB re. 1 µPa pp at 1 m), high directionality (directionality index of >27 dB), low absorption with peak frequencies at 15-20 kHz, and ICIs between 0.4 and 1 s (Møhl et al, 2000(Møhl et al, , 2003Madsen et al, 2002Tønnesen et al, 2020).…”

Behaviour and vocalizations of two sperm whales (Physeter macrocephalus) entangled in illegal driftnets in the Mediterranean Sea

“…Particularly, in this study, the term ‘single clicks’ is used to indicate those sounds which resembled regular echolocation clicks (“usual clicks”) associated primarily with an echolocation-based foraging [ 79 ] but with some substantial differences. Firstly, click analysis shows a high average ICI (2.86 and 4.91s for first and second whales, respectively), consequently average click rates were very low (0.4 and 0.2 sec -1 for first and second whales, respectively) in comparison with typical echolocation clicks used by whales in search of food [ 51 , 79 ]. Jaquet et al [ 38 ] described “surface clicks” as “vocalizations had a long inter-click interval (5 to 7 s on average, also called ‘slow clicks’) and sounded very metallic” (“clangs” according to Gordon [ 80 ]).…”

“…However, for the second whale, the clicks emitted at the surface, did not fit perfectly with the description of “surface clicks” [ 38 ]. Commonly, “usual clicks” are usually produced in prolonged bouts interspersed with buzzes [ 79 ], which is true for the first whale (it constantly emitted clicks with slight fluctuations of the inter-click interval in accordance with the activity level, Table 1 ), but it is not clear for the second whale, which emitted just a 12-click train at a very slow rate between a long creak sequence and coda sequence, both triggered during high activity situations. Previous studies have shown that the click rate can be subjected to variations related to activity, group size, and physical condition [ 38 , 44 , 46 ].…”

“…Creaks are a wide kind of vocalizations that include two main categories: long and shortlasting creaks [34,45]. The first type is mainly associated with deep dives echolocation, especially in prey detection and targeting [34,38,45,79,80,[82][83][84][85]; while the second type includes "coda-creaks", "chirrups" or "rapid-click" [47,80] and is emitted in a social context for scanning other whales while lying at the surface [34]. In this study, creaks were recorded for both whales and shared similar acoustics parameters, of which some were consistent with previous literature.…”