Skittish Males in High Latitudes: Complex Social and Acoustic Response of Adult Male Sperm Whales When Harassed by Orcas

Orcas (Orcinus orca) are an indisputable apex predator of the seas (Jefferson et al. 1991), predating on animals that are much larger and heavier than themselves, including the great whales (Ford and Reeves 2008; Pitman et al. 2014; Silber et al. 1990; Totterdell et al. 2022). Stomach content analysis from orcas in the 1970s revealed predation on sperm whales (Physeter macrocephalus, Yukhov et al. 1975), and the first published observation of a successful predatory event was in 1997 (Pitman et al. 2001). Previously, all reported aggressive interactions between orcas and sperm whales occurred in latitudes below 45 and involved groups of females, subadults, and young individuals (Gemmell et al. 2015; Nanayakkara et al. 2020; Sucunza et al. 2022), although in some cases adult males were also present (Arnbom et al. 1987; Pitman et al. 2001; Whitt et al. 2015). Females and juvenile sperm whales live in highly social groups in lower latitudes year-round, while sexually mature males migrate to higher latitudes, becoming, or at least appearing to be, increasingly solitary with age (Best 1979; Ohsumi 1966), occasionally returning to warmer waters to breed (Steiner et al. 2012). The descriptions of aggressive interactions between groups of orcas and sperm whales reveal that sperm whales will remain tightly clustered at the surface or possibly adopt a defensive formation: the Rosette or the Flotilla formation. In the Rosette formation, the animals form a circle with heads pointing to the center or outwards (calves are protected in the center), and in the Flotilla formation, sperm whales organize in rows and columns, positioning parallel to each other with heads pointing in the same direction (Arnbom et al. 1987; Nanayakkara et al. 2020; Pitman et al. 2001). Although the surface behavior of sperm whales has been well documented during these interactions, acoustic behaviors have not been investigated. Sperm whales produce short, broadband echolocation pulses, also described as clicks, which they use for navigation, foraging, and communication. The call types are described based on characteristics of the clicks themselves, as well as the variations in temporal patterning (some regular, others not so). Adult males in high latitudes are known to emit at least four types of sounds: usual clicks, creaks, clangs, and codas (Curé et al. 2013; Madsen et al. 2002; Oliveira et al. 2013; Teloni et al. 2008). Codas are primarily used for communication and social purposes, and therefore are not commonly produced by solitary males (Frantzis and Alexiadou 2008; Weilgart and Whitehead 1997). However, Curé et al. (2013) detected codas in tagged adult males in northern Norway exposed to sounds of marine mammal-eating orcas from the Northeast Pacific. Additionally, most whales in that study interrupted their dive and surfaced within a 100 m of conspecifics. This response was unexpected as sperm whale group formation off Andenes is uncommon, at least in summertime when the study was conducted (Lettevall et al. 2002; Morange et al. 2024), and orcas in the area feed mainly on fish and seals (Jourdain and Vongraven 2017; Jourdain et al. 2019, 2020; Similä et al. 1996). This response suggests that adult male sperm whales, which exhibit seasonal migration outside of Arctic waters, recognize orcas as a potential danger and might be able to distinguish that marine mammal-eating orcas are more of a threat than the other ecotypes. It is unknown how often aggressive interactions between orcas and sperm whales occur in higher latitudes; however, indirect evidence, such as rake marks, suggests it may be more common than observations indicate. For example, 65.3% of sperm whales caught by whalers south of 50° latitude between 1962 and 1974, including adult males, had orca rakes on their bodies. These rakes occurred more frequently on younger whales smaller than 13.5 m in length (Shevchenko 1975). Rake marks on sperm whales can occur on either the body or on appendages, such as the fluke or pectoral fins. Rake marks on the body, typically found on the left side of the male's head, are generally attributed to intraspecies interactions, while smaller rake marks on the fluke or fins are thought to result from a predation and/or harassment event from orcas or other large dolphins (Best 1979; O'Callaghan et al., 2024). In northern Norway, up to 70% of the photo-IDed individuals residing in that area had at one point in time scars presumably from orca rakes on their flukes (van Dongen 2022). Of course, animals documented in either whaler counts or by researchers' photo-ID catalogues are animals that have survived orca attacks. Here, we report four interactions between orcas and adult male sperm whales in northern Norway, occurring in 2008, 2009, 2011, and 2013. Three of the observations were made by researchers and crew from M/S Reine, a 30-m long whale-watching vessel operated by Whalesafari, in the Bleik Canyon, a submarine canyon located northwest off Andøya island, northern Norway (Figure 1). The interaction recorded in 2009 does not specify the vessel used in the notes; therefore, we cannot be certain which boat was employed. Due to the nature and priorities of whale-watching commercial enterprises, the exact location is only known for two events (2008 and 2011), though all encounters occurred within 69.34°–69.47° N and 15.58°–15.86° E in the Bleik Canyon. There are currently no whale-watching regulations in the area; however, over the years, Whalesafari has developed its own protocol to reduce the impact, based on personal observations (see de la Cruz-Modino and Cosentino 2022). The M/S Reine has two custom hull-mounted directional hydrophones, sampling rate at 44.1 kHz (Nielsen and Møhl 2006), that allow the crew to listen for cetaceans and, based on differences in loudness between the hydrophones, get close to where the animals are before they surface. However, the audio stream from the hydrophones is not always recorded. Therefore, we focus our descriptive reporting on the 2011 encounter, which includes photographs, video footage, voice-recorded accounts, and underwater acoustic recordings. The others are based exclusively on photographs (2009), on voice-recorded accounts (2013), or on video footage (2008). Each harassment event was defined as orcas interrupting the behavior of the sperm whales. Where present, videos and photographs were used to describe the behavior of both species in as much detail as possible, to estimate the minimum number of individuals present, and for photo-identification attempts. Images of the flukes and bodies were matched against the Whalesafari photo-ID catalogue, which contains over 900 sperm whales photographed in the Bleik Canyon and surrounding waters from 1987 to 2021 (Whalesafari, unpublished data). Flukes were also inspected for orca rakes, as smaller rake marks located on an appendage are broadly assumed to originate from orcas in higher latitudes in studies analyzing orca interactions with large whales (Mehta et al. 2007; Weller 2002; Weller et al. 2018). Smaller rake marks contained three lines, roughly 2.5–5.1 cm apart, whereas rake marks likely originating from sperm whales are 12–16 cm (Best 1979; George et al. 1994; Mehta et al. 2007). Spacing between the rake marks was estimated by experienced observers based on the ratio between the average body length (14.35 m, Jørgensen 2000; Similä et al. 2022) and fluke width (26%, Nishiwaki et al. 1963), which is 3.7 m. Where present, the resulting two-channel wav files were manually audited for marine mammal vocalizations using Audacity version 3.0 (Audacity Team 2023), and further signal processing analysis (as described below) was completed using custom code in Matlab version 2020b (Mathworks, MA, USA). For the 2011 encounter, acoustic data was audited before (10 min), during (36 min), and after the event (10 min). The event begins at 0 h 58 min and ends at 1 h 20 min and 45 s in the acoustic file (Whalesafari 2025). The start sample (in both channels, if possible) was annotated for each sound detection (sperm whales or orcas). The amplitude was estimated as the root-mean-squared (rms) amplitude of individual signals (dB re: 1 μPa) on a window of a fixed length of 230 samples (60 samples before and 170 after the start, 3.85 ms). Species were determined based on the characteristics of the signal. In northern Norway, orcas produce a wide array of vocalizations, including whistles, burst pulses, and echolocation clicks that could be detected with the equipment used in this study (van Parijs et al. 2004). The presence of these multiple signal types is distinct from sperm whales, which only produce click types with a central frequency typically between 5 and 25 kHz (Madsen et al. 2002). Different sperm whale click types were identified based on spectral characteristics and repetition rates. Sperm whale clicks have a useful side effect: the signal contains the echoes from inside the head of the emitting animal, which can be used to estimate the size of the clicking whale. For codas and clangs, the inter-pulse interval (IPI, the time difference between the first and second, and the second and third peaks or reverberations within the click) was calculated using cross-correlation against themselves. To calculate the IPI, the window length was set to 2100 samples, starting 100 samples before the start of the click. With the IPI (in ms), the approximate length of the clicking animal (Figure S1) was estimated following Growcott et al. (2011): Length = 5.736 + (1.258*IPI). This information assisted analysts in keeping track of the number of animals present during post processing. July 23, 2011—M/S Reine left its home port of Andenes harbor at 15:00 (CEST) and began acoustic recordings at 15:57 after approaching the edge of the Bleik Canyon, where sperm whale clicks triangulated several km into the canyon could already be heard (Whalesafari, pers. comm.). As soon as the recordings began, usual clicks from more than one sperm whale were recorded (Whalesafari 2025). A descriptive summary of all sperm whale vocalizations recorded during this encounter is outlined in Table 1. Usual clicks (M/F) Regular repetition rates and ICI between 0.5 and 2 s. Usual clicks are used for echolocation (to inspect the environment and find prey). Goold and Jones 1995 Clangs or slow clicks (M) Weilgart and Whitehead 1988; Møhl et al. 2000; Madsen et al. 2002; Growcott et al. 2011; Oliveira et al. 2013 Codas (M/F) Watkins and Schevill 1977; Curé et al. 2013; Hersh et al. 2022; Weilgart and Whitehead 1997 “brief rapid trills of clicks, constituting perhaps between 10 and 50 clicks. Characteristically the trills begin with very rapid clicks of uniform repetition rate and subsequently trail off with reducing click rate.” Chirrups may have occurred at the end of the encounter (Figures 3 and S2). Unknown (M) Early in the encounter, a series of click bouts were recorded. These had between four and 17 clicks and durations between less than a second to 3.5 s. (Figures 3 and S2). At 16:55, when usual clicks were still detected from distant (i.e., quieter) sperm whales, at least three orcas were seen near a minke whale (Balaenoptera acutorostrata) from the vessel (Figure 2). Usual clicks from distant sperm whales continued for another minute, alternated by orca sounds (clicks and burst pulses), then one clang, followed by approximately 40 s of silence. The silence was broken by orca sounds and a series of sperm whale clangs. A series of click bouts with mostly regular inter-click intervals (ICI) was recorded. Based on the waveform, at least three of these were emitted by sperm whales (Figure S2). The difference in amplitude between the ICIs within bouts indicates that they were likely emitted by more than one animal. No sperm whale sounds were detected for approximately 3 min between 16:58 and 17:01. During this period, the orcas had left the minke whale and approached, at a relatively fast pace, an adult male sperm whale that could be seen from the vessel resting at the surface. Upon arrival, the orcas started circling around the sperm whale. This moment (17:01) coincides with the sperm whale emitting four clangs, judged by the amplitude of the signal recorded on the vessel, followed by lobtailing and a 2-min dive without showing its fluke, a behavior known as a shallow dive (Gordon et al. 1992; 2). the sperm whale was only orca sounds were recorded the first male sperm whale a second male was seen fast approaching the A series of clicks were a with regular ICI ms). 5 min of one more was recorded. this the second animal its head of the the and the of the head while the underwater (i.e., Curé et al. The sperm whales within 10 m of each other for a more orca sounds and one emitted by a sperm whale were recorded At the sperm whale to the of the vessel its and into the sperm whale on its This the left sperm whale to its and shallow The sperm whale on the to the and the this only were identified in the two sperm whale both below m and a third animal with a length of approximately m was detected (Figure not Clangs recorded this event were emitted by all three males, the three distinct size and were emitted at detected or 3 s and with in At a third animal was seen approaching at high positioning parallel to the sperm in and with their heads to the the second male the three male sperm whales began on and started approaching M/S Reine, showing of including and at the and Orcas during this were detected in our recordings. For the the sperm whales continued to behaviors and emit clangs. At all males the by all three animals (Figure when other sounds emitted by the sperm whales were clangs, one of clicks with a and bouts of sperm whale clicks at repetition rates and durations below 1 s (Figure The are clicks with repetition rates from 45 to 10 clicks second that The sounds emitted at the end of the acoustic response of the sperm whales emitted at least 170 clangs, codas = and 20 click which could not be (Figure Table 1). At the three males surfaced while the orcas although still The sperm whales positioning parallel to each in the same direction and a with one animal more than the other in this formation for min after which they shallow and the surface. The males were heard emitting usual clicks at regular intervals from the end of the an including et al. 2001). Due to the behavior of the sperm whales at the surface and the that they without showing their it was not to the males involved in the However, one male photographed in the Bleik Canyon on July 23, 2011 at approximately 45 min after the event had orca and rakes on the of the fluke (Figure This was the first and the time this male was photographed in the at least the of this July are no descriptions of this are photographs of the interaction (Figure from which it was to some The individual sperm whale had been in the study area before the of the It was on the and of the encounter with no of orca rakes on its It was then photographed at with orcas in the the start of the interaction (Figure At the start of the encounter, the orcas are documented very close to the male sperm its fluke to at a (Figure The sperm whale then a a with body at the surface (Figure During this were at least three orcas in the near one adult male and two smaller either males or females, based on the ratio of the fins and were other sperm whales or orcas in the it is not from the the the smaller orcas are seen circling around the sperm their heads of the while the sperm whale was near the surface (Figure In the sperm whale direction multiple while fluke on the the (Figure At the sperm whale its fluke, a The time it was not in photographs, it was at the surface before at the event is based on photographs it is a group of orcas was photographed after The and of the photographs of the orcas were not for July of this event is based only on recordings made by observers on M/S The vessel left Andenes harbor at and the hydrophones were on at however, for therefore no recordings were after on the hydrophones, a group of four to orcas were 1 km from the vessel, by northern over as the orcas were below the surface. At a sperm whale surfaced close to the The researchers on the animal as In the following minute, at least one orca against the sperm its The 25 m from the vessel, while was a vessel from another 50 m Although the exact location for this event is the vessel was 10 from the Andenes in approximately m At the sperm whale was by multiple presumably including one or The sperm whale was the keeping the same and at began clicking at 1 click second, to usual clicks with of during one of which sounds of orcas were for the s of the dive before at at the and at was a regular of the Bleik Canyon, first photographed in July and subsequently seen between and from Images from these that had orca rakes on fluke, that this was not the first time was by orcas (Figure this was seen with orca rakes on fluke was not after 2013. were a sperm whale and the event was on video (Figure though the exact time of is The video with a sperm whale resting on the parallel to the vessel into or 10 The animal was identified as also known as can be by the on an orca the surface at side into Therefore, fluke to the body and a with fluke time into then body left to form a with the fluke on the surface into the same or another orca a or was seen near and fluke on the surface into body, and from the At this the had into The orcas were not seen in the then fluke to surface after which it the surface for 20 and resting the video ends s The sperm has been in the Bleik Canyon from to with over individual by Whalesafari Based on photographs, orca rakes at least four over the These are the first of aggressive interactions between orcas and sperm whales in high latitudes, where only adult male sperm whales are Although are some groups of orcas off northern Norway that feed on both fish and smaller marine 2015; Jourdain et al. is no of successful predatory events on sperm whales. the other the presence of orca rakes in individuals in the area (van Dongen 2022) suggests that these interactions are more common than observations indicate. is that the orcas are the sperm whales to individuals for In our however, the sperm whales the harassment relatively to the fluke in the form of we cannot the of orcas predating on male sperm whales in these waters, are multiple of including In orcas around the made for et al. 2022). dolphins both or the of harbor and for either or at least et al. et al. in orcas has been to be to or et al. 2022; et al. Additionally, the predation and that sperm whale adult males, larger and therefore able to against an can migrate to high latitudes where orcas are more and whereas and juvenile sperm whales in lower latitudes to reduce the of formation by males in high latitudes may to further against harassment by orcas et al. The of the orcas was in all though the of the orca groups Although and surface behavior were not it is that the sperm whales not in to the In 2011, soon after orcas were detected all sperm whales within detection The silence was broken with a clang, which has been to a in male sperm whales (Madsen et al. 2002). observations this as the emitted animals and were then produced by all animals the The males also emitted a response to when male sperm whales were exposed to Northeast orca sounds in northern Norway (Curé et al. recorded to be codas and click bouts with repetition rates that could not be to the of our to call types described in The and parallel positioning the sperm whales is of the in lower latitudes and may a The and during the 2011 in to the lobtailing the orcas during the and 2009 were with behaviors of a group of mostly sperm whales by orcas in the (Arnbom et al. a or a at the could also be as a defensive or of as it is a response to predation in multiple species of fish and However, as sperm whales are more than and are not this behavior may have a In in response to as during the event in 2008, might or orcas et al. though it is this behavior is used The study is the first typically solitary adult male sperm whales of and likely in a and response to the presence of orcas in a the 2011 adult males in three known click including codas which are not of males in higher latitudes outside of (Curé et al. 2013; and Alexiadou 2008; Weilgart and Whitehead 1997). Sperm whales in 2011 also produced two types of click with ICIs not and therefore have As this is an further of the male sperm whale acoustic behavior is from other However, it is that the response to orcas likely on for example, are more than one animal and the orcas are Three of the four events we described involved sperm whales that solitary the though it is that other sperm whales were in the during the In accounts of male sperm whales orcas (Jefferson et al. Whalesafari, pers. which may of It has also been that sperm whales might be able to between sounds of orca only the vocalizations of orcas as a potential threat (Curé et al. is to these data and and data and data and The to Whalesafari the data used in this for the video footage from 2008, Jourdain for the photographs from 2009 and of the orcas and for from to This was with from the Whalesafari The no of The is not for the content or of information by the than be to the for the