Humpback Whales Blow Poloidal Vortex Bubble Rings

Humpback whales (Megaptera novaeangliae) have long been known to generate bubbles by physically striking the air–water interface or releasing air through the blowholes or mouth. Melville (1851) was the first to note this propensity by penning “humpbacks churned the water … making more gay foam and whitewater than any of them.” In the Norwegian Sea, a whaleship observed a humpback whale that “appeared to dive a short distance below the water's surface and then release air while swimming in a circle. The rising bubble rose to the surface like a thick wall of air bubbles, and these formed a net” (Ingebrigtsen 1929). The first formal studies of humpback whale bubble use commenced in the North Pacific in the late 1960s (Jurasz and Jurasz 1979) followed by a description in the North Atlantic (Hain et al. 1982). Subsequent research across many cetacean species has shown that they produce bubbles in various shapes, sizes, and complexities. A recent review on bubble production (with a focus on odontocetes) classifies this wide diversity of bubble structures into several categories: trails, bursts, clouds, and rings (Moreno and Macgregor 2019). Bubble production can occur in a variety of behavioral contexts. Male humpback whales use bubbles on the breeding grounds during agonistic displays where they compete for proximity to a female. These blowhole and mouth expulsions of air typically produce bursts or curtains (Baker and Herman 1984) that are thought to serve as “displays of ferocity” and to possibly disorient intruding whales (Baker and Herman 1984; Helweg et al. 1992). Mouth-released bubbles are generated after gulping air at the surface (Baker and Herman 1984) and possibly via a laryngeal–oral connection, which may allow for “oral exhalations” of fine-misted clouds (Reidenberg and Laitman 2007). Blowhole-bubble exhalation has also been observed between humpback mother and calf pairs when passively resting (Ejrnæs and Sprogis 2021). Male humpback whales have been observed releasing bubbles directed at the female genital-mammary area on the breeding grounds (Jones et al. 2022). On the feeding grounds, humpback whales use bubbles to herd, corral, and concentrate prey (Hain et al. 1982; Jurasz and Jurasz 1979; Wiley et al. 2011). Bubbles produce a strong acoustic, visual, and mechanical barrier that schooling prey are reluctant to cross (Sharpe and Dill 1997). These barrier structures may be simple, as in the case of bursts, which are created by a sudden, forceful release of many small bubbles (Baker and Herman 1984; Rountree et al. 2022). Plumes or columns often form a continuous airstream that can be produced as a vertical array when whales are stationary, or a horizontal array when the whale is moving. Arguably, the most complex bubble structure is the bubble net, whereby a whale or multiple whales swim in a closing spiral while releasing an air curtain (Figure 1a). Bubble net feeding is most often performed cooperatively. The sculpting of intricate spiral nets and other bubble structures utilizes the unique morphological adaptations of humpback whales for maneuverability, including flexible, spindle-shaped bodies, highly elongated flippers, outsized tails, and knobs on leading surfaces (Fish 1994; Fish and Battle 1995; Tomilin 1967; Wiley et al. 2011). The flippers and/or flukes may also be swiped at the surface to inject air below the air–water interface (Weinrich et al. 1992). This note focuses on bubble rings (Figure 1b), a unique and sparsely documented genre of bubble features produced by baleen whales, although well-described among odontocetes, including Atlantic bottlenose dolphins (Tursiops truncatus, McCowan et al. 2000), beluga whales (Delphinapterus leucas, Hill et al. 2011), and Orinoco dolphins (Inia geoffrensis, Gewalt 1989). Not to be confused with a bubble net (spiral-shaped fish trap; Figure 1a), a ring is a poloidally spinning, air-infused vortex. At Stellwagen Bank in the North Atlantic Ocean, Payne (1995) described them as “madly spinning doughnut-shaped clouds that look like giant smoke rings about three feet in diameter that rise rapidly to the surface.” Payne opines on their frequency, noting: “Only one particular whale has been known to engage in this activity, and even she seldom does it. However, once she gets going, the process becomes obvious and is done vigorously. For example, she may blow twenty bubble ‘smoke rings’ in a row during a bout lasting half an hour … we are still only guessing at how it works and what its real purpose is.” Payne's description represents the only published mention of bubble rings in the mysticetes. Bubble rings in mysticetes may be produced in similar contexts to those in odontocetes; however, the much larger bubble rings of mysticetes differ in their appearance from those produced by odontocetes as the former are filled with a multitude of smaller bubbles giving them a smoky opaque appearance, rather than being a single translucent ring-shaped bubble. Among dolphins, their translucent bubble rings are well-studied and have been linked to play in captivity as well as to foraging and social aggression in the wild (Herzing 1996, 2000; Hill et al. 2011; Marten et al. 1996; McCowan et al. 2000; Moreno and Macgregor 2019; Pace 2000; Paulos et al. 2010; Pryor 1990; Pryor and Kang 1980; Rountree et al. 2022). Here we report on 12 ring-production episodes involving 39 bubble rings produced by 11 individual humpback whales. The aim of this research is to describe contexts in which humpback whales produce bubble rings and provide insights into their potential functions. We examine evidence for Payne's (1995) hypothesis that bubble rings are associated with foraging as defined by being produced in the presence of prey and feeding activity (vertical lunges, open mouths, extended ventral pleats). Next, we examine the hypothesis that rings are associated with social aggression, as proposed for wild spotted and bottlenose dolphins (Herzing 1996, 2000; Pryor 1990; Pryor and Kang 1980). We use Baker and Herman's (1984) and Pitman et al.'s (2017) definition of aggressive behavior in humpback whales, which includes high levels of arousal, wheezed blows, trumpet blows, slashing of the tail and flippers, and charges directed toward antagonists (e.g., male rivals, killer whales [Orcinus orca]). We also examine whether rings are linked to inquisitive behavior in which whales approach boats and swimmers (Mangott et al. 2011; Swartz 2018). Finally, using drone observations collected by several private investigators, we searched for ring production in the absence of boats and close human presence. Bubble ring events were collected by naturalists, citizen scientists, and researchers with whom we conducted interviews and analyzed their video footage (seven episodes) or photos (five episodes). We gathered bubble ring events through social media and reports from colleagues. We solicited reports through a cetacean-focused Facebook group (Cetal Fauna) and presentations at three scientific conferences (World Marine Mammal Conference [2019], 24th Biennial Conference on the Biology of Marine Mammals [2022], and Humpback Whale World Congress [2023]). These observations were opportunistic, while observers were on the water for a variety of reasons (see “Mission” in Table 2), and were obtained from one private vessel, two research vessels, three commercial whale-watch vessels, two commercial and one private whale-swim vessels, and two light airplanes. All vessels were motorized. Whenever possible, a still photo or screen capture was obtained of the ventral side of the flukes for comparison with regional fluke photo-identification catalogs. Successful matches were used to help establish each animal's identity, age, sex, and history of human interactions to determine if there were repeated sightings of the same individual or general demographic patterns to ring production. For events in the North Atlantic Ocean, we compared photographs with the North Atlantic Humpback Whale Catalog (NAHWC), Allied Whale (Bar Harbor, Maine), and the Gulf of Maine Humpback Whale Catalog (Center for Coastal Studies [CCS], Provincetown, Massachusetts). For North and South Pacific cases, we consulted Happywhale.com. Using the growth curves of Stevick (1999) we categorized individuals of known age into one of three classes (yearling: 1 year; subadult: 4–6 years; adult: 6 or more years). We also documented the type of vessel (whale-watch, research, or private), presence of occupants (or swimmers), and their general demeanor (loud/boisterous or quiet/passive). Video and photos of bubble ring episodes were obtained from various perspectives, including from underwater cameras (held by swimmers or dipped from vessels), filmed above the surface at water level from boats, or obtained from the air (fixed-wing aircraft) (for details see Supporting Information S2). We use several interchangeable and equivalent descriptors to characterize ring creation, including “produce,” “release,” “blow,” and “generate.” Estimates of ring diameter were obtained when the ring surfaced adjacent to objects of reference, such as a whale or vessel. We also documented the distance and orientation of the ring blower to the closest object in the water (boats, swimmers, or other whales). We then used behavioral categorizations based on definitions in the literature for humpback whales to help determine the context for bubble ring production (Table 1). To assess if rings were produced in the absence of humans, we contacted three investigators using semiremote sampling techniques. All unoccupied aerial vehicle (UAV; i.e., drone) flights were conducted at a distance from nearby vessels on breeding grounds (Hawaii), feeding grounds (Antarctica, Alaska), and migratory routes (Bermuda). M. Van Aswegen (personal communication, July 2022)1 did not observe any bubble structures resembling rings during a five-year study of humpback whales in Hawaii and Southeast Alaska (involving over 3490 UAV flights, totaling > 1090 flight hours, with approximately 300 h in Alaska and 700 h in Hawaii). Similarly, in Antarctica, A. Friedlaender (personal communication, September 2022)2 made no detection of bubble rings from 100 to 200 UAV flights (20–30 flight hours). In Bermuda, A. Stevenson (personal communication, March 2024)3 also made no detection of bubble rings during 1200+ UAV flights during an eight-year study of humpback whale behavior. All drone flights were conducted at a distance from nearby vessels. A summary of each episode is provided in Table 2 and Figure 2. Details of these episodes can be found in the Supporting Information, including video, when captured (Supporting Information S2–S11). Stellwagen Bank, MA, USA N. Atlantic D. Knaub S. Pittman Maui, HI, USA N. Pacific F. Nicklin J. Darling J. Sturgis Makalawena, Kona, HI, USA N. Pacific Cape Cod Bay, MA, USA N. Atlantic Silver Bank, DR N. Atlantic Stellwagen Bank, MA, USA N. Atlantic Lahaina, Maui, HI, USA N. Pacific Lahaina, Maui, HI, USA N. Pacific Lahaina, Maui, HI, USA N. Pacific Makalawena, Kona, HI, USA N. Pacific Silver Bank, DR N. Atlantic Mo'orea, French Polynesia, S. Pacific In two instances (Episodes 1 and 3) we were able to determine the age of ring blowers as a result of repeated observations in fluke databases (Table 2). In a third instance (Episode 10), we felt confident enough to classify the animal as a yearling because of the individual's smaller size and gray fluke coloration. The individual observed to blow rings in Episode 1 had a known birthday obtained from CCS and was determined to be a subadult. The individual observed to blow bubble rings from Episode 3 had a series of sightings in the Happywhale database such that it is clear the individual has a minimum age of 6 and was determined to be an adult. No direct measurements were made of bubble ring diameters. However, one whale surfaced within or adjacent to several bubble rings (Episode 1). His dorsal hump and/or body girth were visible, providing estimations of ring diameter of 2–3 m for three rings (M. Van Aswegen, personal communication,4 October 2023, see Supporting Information S12 for calculations). Another ring surfaced next to a skiff, enabling its diameter to be estimated at 2–2.5 m (Episode 11). All events that permitted direct visual observation revealed that during ring release, whales were motionless or slowly idling forward with blowholes held upright and the body mostly in the horizontal position. All rings were observed to rise vertically with their elliptical plane parallel to the surface. This was visually confirmed for all bubble ring events occurring in the relatively clear waters of the breeding grounds (Episodes 2, 3, 5, 7, 8, 9, 10, 11, 12). On three occasions (Episodes 8, 9, 11), frame-by-frame video inspection revealed that bubble rings emanated from a single right nostril (Episode 8; Supporting Information S13). Most rings appeared radially symmetrical in their incipient stage (as opposed to bilobed), further suggesting a creation from a single aperture. Two out of twelve documented episodes (Episodes 4 and 6) were associated with foraging, as the rings were produced during active feeding (open mouths, expanded ventral pleats, surface lunging) within a bubble net (Figure 2d,f). Prey items could not be observed from the fixed-wing aircraft that opportunistically observed the bubble net feeding episodes (i.e., foraging context); however, the general configuration of the net the whales were et al. 1982). In case were whales observed to within an individual ring or of the ring the whales appeared to water adjacent to the rising of a barrier as opposed to prey being or confused within or by the poloidally spinning of the ring to the vertical rising rings are suggesting a more barrier of the other episodes were associated with feeding were prey (Jurasz and Jurasz 1979) within no other other were observed in proximity while the rings were being of the twelve episodes of ring production episodes were collected a or human swimmers, while episodes had more than one whale these for and aggression, there was no evidence of toward or aggression toward boats or swimmers in any of the ring (Supporting Information tail and tail trumpet blows, lunges, charges toward antagonists and bubble or clouds (Baker and Herman 1984; and of and (Baker and Herman et al. Sprogis et al. such as swimming or dive were not in any of the ring humpback whales observed bubble rings appeared and during their ring (see Table as well as during their various inquisitive tail than of ring blowers the two episodes during the or All bubble structures appeared and as opposed to bubble clouds and curtains associated with aggression (Baker and Herman 1984; Supporting Information In the of the inquisitive episodes 7, 8, 9, the ring blower was suggesting that the was not whale (Table 2). In all inquisitive the closest object to the blower the of ring was a or not whale (Table of ring blowers a or to one body or other whales were they as the ring blower a or (Episodes 2, 3, 11, 12). On two occasions (Episodes 3 and the blower in an including a (Episode ring was produced a (Episode 2), while was a (Episode In one a ring a after its at the surface (Episode 11). All ring blowers in the of a or and appeared in their (Episodes 2, 10, 12). whales had a history of inquisitive or behavior whereby a whale close to a vessel that the vessel also often in during these events such as et al. where whales their vertically out of the water or the surface in proximity to boats (Episodes 3, 7, 8, such as wheezed or trumpet blows, which may or were not ring blowers were in pairs behavior (Episodes 3 and 11), while was in object play with ring (Episode and In only one episode was the ring blower and not in other of foraging, or being inquisitive (Episode see Table 2). In this two whales were m below the surface and were slowly by several swimmers on the after which one of the two whales produced a bubble ring (Figure We found that humpback whales use rings in contexts including feeding bubble during inquisitive and while passively Most episodes evidence of inquisitive behavior with a of other of feeding or there was evidence of feeding during bubble ring this may be by the of collected sightings occurring on breeding grounds where feeding is there was no evidence of or aggression in any of the bubble production in humpback whales is most observed in on the breeding grounds whereby one to the of a female. observations of in humpback whales of from toward that on the breeding grounds personal communication, or when such as killer whales and Pitman et al. research is to study bubble ring production and what bubble rings are is not for inquisitive humpback whales and gray whales to release air while with boats (Jones is not whales inquisitive with et al. 2011; Supporting Information to bubble ring production. are several of baleen whales in which individuals approach and with however, in these contexts has and gray whales were first in in the 1960s where they of and even Swartz 2018). In Bay, humpback whales often inquisitive or behavior toward vessels et al. gray whales are known to release bubbles and the of these Swartz 2018). et al. that swimming and behavior humpback may be when in the presence of associated play as behavior in The during the of inquisitive ring episodes play as described by et al. and or on the with or no forward the water and within m of the surface. above the surface may tail tail and half or body many of which were also observed during inquisitive bubble production behavior by in Episode 1 with described by McCowan et al. To assess to what bubble ring production with human we contacted three investigators using semiremote sampling for humpback whales. all three there was no of bubble ring production in humpback whales observed during UAV these are they that bubble ring production may be to when human observers or boats are However, the to which the presence of human observers humpback whale bubble ring production other events have were not as as a of behavior in study events may have long to be in may if they to the surface (Episodes 5, 7, 11, or are by or Bubbles are as in many cetacean species (Jones et al. Moreno and Macgregor 2019). studies it is more to for use during interactions (Herzing For example, to the of human et al. 2022). Similarly, the a a to with et al. In (Episodes 7, 8, 9, 11), whales may be to the and of which may a between However, other episodes (Episodes 2, 3, 5, 10, were by smaller vessels in research or whale (or human suggesting other by ring blowers that to be of bubble production in a of not to study of ring in dolphins has provided into and et al. dolphins, which generate bubble rings using a variety of (Moreno and Macgregor we found that the blowhole was the of ring production in the humpback the blowhole is well as the of production for bubble nets in other studies (Hain et al. 1982; Wiley et al. 2011). than the whale and its a or there was no evidence that a bubble ring release was no no to the any or of the This from dolphins, often the body and the to ring release et al. 2000; Moreno and Macgregor 2019). In humpback whales, the blowholes are by of the et al. and are when the et al. 2019). play that be to the rapidly of the play via and et al. bubble ring mechanical of bubble rings using a bubble ring in the of studies could be for further of this studies could the at which humpback whales can their bubble rings in to human Bubble rings were often with other bubble structures These structures further as they occur a and behavioral for a review see Moreno and Macgregor 2019). structures may also be produced as at a bubble are from in air release and have a of features rather than the with which we personal communication, the for their creation, in the help the and of bubble We whale and researchers to for and report on ring production. 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