REACTION OF FIN WHALES BALAENOPTERA PHYSALUS TO AN EARTHQUAKE

ABSTRACT

Whales living within seismically active regions are subject to intense disturbances from strong sounds produced by earthquakes that can kill or injure individuals. Nishimura & Clark (1993) relate the possible effects of underwater earthquake noise levels in marine mammals, adducing that T-phase source signal level (10- to 30- Hz range) can exceed 200 dB re: 1 μPa at 1 m, for a magnitude 4–5 earthquake, sounds audible to fin whales which produce low frequency sounds of 16–20/25–44 Hz over 0.5–1s, typically of 183 dB re: 1 μPa at 1 m. Here we present the response of a fin whale to a 5.5 Richter scale earthquake that took place on 22 February 2005, in the Gulf of California. The whale covered 13 km in 26 min (mean speed = 30.2 km/h). We deduce that the sound heard by this whale might have triggered the costly energy expenditure of high speed swimming as a seismic-escape response. These observations support the hypothesis of Richardson et al. (1995) that cetaceans may flee from loud sounds before they are injured, when exposed to noise in excess of 140 dB re: 1 μPa 1 m.     

Beaked whales respond to simulated and actual navy sonar

Beaked whales have mass stranded during some naval sonar exercises, but the cause is unknown. They are difficult to sight but can reliably be detected by listening for echolocation clicks produced during deep foraging dives. Listening for these clicks, we documented Blainville's beaked whales, Mesoplodon densirostris, in a naval underwater range where sonars are in regular use near Andros Island, Bahamas. An array of bottom-mounted hydrophones can detect beaked whales when they click anywhere within the range. We used two complementary methods to investigate behavioral responses of beaked whales to sonar: an opportunistic approach that monitored whale responses to multi-day naval exercises involving tactical mid-frequency sonars, and an experimental approach using playbacks of simulated sonar and control sounds to whales tagged with a device that records sound, movement, and orientation. Here we show that in both exposure conditions beaked whales stopped echolocating during deep foraging dives and moved away. During actual sonar exercises, beaked whales were primarily detected near the periphery of the range, on average 16 km away from the sonar transmissions. Once the exercise stopped, beaked whales gradually filled in the center of the range over 2-3 days. A satellite tagged whale moved outside the range during an exercise, returning over 2-3 days post-exercise. The experimental approach used tags to measure acoustic exposure and behavioral reactions of beaked whales to one controlled exposure each of simulated military sonar, killer whale calls, and band-limited noise. The beaked whales reacted to these three sound playbacks at sound pressure levels below 142 dB re 1 μPa by stopping echolocation followed by unusually long and slow ascents from their foraging dives. The combined results indicate similar disruption of foraging behavior and avoidance by beaked whales in the two different contexts, at exposures well below those used by regulators to define disturbance.     

IMPACTS OF COMMERCIAL WHALE WATCHING ON MALE SPERM WHALES AT KAIKOURA, NEW ZEALAND

Abstract Male sperm whales are the basis for a commercially important whale-watching industry at Kaikoura, New Zealand. We examined the influence of whale-watching boats and aircraft over three years using observations from an independent research boat and from shore. We employed an information-theoretic approach to determine which factors were necessary to explain variation in blow interval, time at surface, and time to first click. In almost all analyses, models required the inclusion of the presence of the research boat or whale-watching boats or airplanes. The only exception was the model explaining variation in blow intervals observed from shore, which required only season. We also analyzed spatial behavior at the surface. Resident whales changed direction significantly more in the presence of whale-watching boats compared to encounters with only the research boat present. No such difference was observed for encounters with aircraft. Our results thus indicate that sperm whales off Kaikoura respond to whale-watching activities, although these changes are small and most likely not of biological importance. However, resident whales responded less to these activities compared to transient whales, possibly indicating habituation and, more importantly, the need to monitor continued activities closely.     

KILLER WHALE PREDATION ON SPERM WHALES: OBSERVATIONS AND IMPLICATIONS

In October 1997 we observed a herd of approximately 35 killer whales ( Orcinus orca ) attack a pod of nine sperm whales ( Physeter macrocephalus ) 130 km off the coast of central California. During the four hours we watched, adult female killer whales, including some with calves, attacked in waves of four to five animals in what was apparently a "wound and withdraw" strategy. Adult male killer whales stood by until the very end when one charged in and quickly killed a seriously wounded sperm whale that had been separated from the group. The sperm whales appeared largely helpless: their main defensive behavior was the formation of a rosette ("marguerite"-heads together, tails out). When the killer whales were successful in pulling an individual out of the rosette, one or two sperm whales exposed themselves to increased attack by leaving the rosette, flanking the isolated individual, and leading it back into the formation. Despite these efforts, one sperm whale was killed and eaten and the rest were seriously, perhaps mortally, wounded. We also present details of two other encounters between sperm whales and killer whales that we observed. Although sperm whales, because of various behavioral and morphological adaptations, were previously thought to be immune to predation, our observations clearly establish their vulnerability to killer whales. We suggest that killer whale predation has potentially been an important, and underrated, selective factor in the evolution of sperm whale ecology, influencing perhaps the development of their complex social behavior and at-sea distribution patterns.     

Diversity in sound pressure levels and estimated active space of resident killer whale vocalizations

Signal source intensity and detection range, which integrates source intensity with propagation loss, background noise and receiver hearing abilities, are important characteristics of communication signals. Apparent source levels were calculated for 819 pulsed calls and 24 whistles produced by free-ranging resident killer whales by triangulating the angles-of-arrival of sounds on two beamforming arrays towed in series. Levels in the 1–20 kHz band ranged from 131 to 168 dB re 1 μPa at 1 m, with differences in the means of different sound classes (whistles: 140.2±4.1 dB; variable calls: 146.6±6.6 dB; stereotyped calls: 152.6±5.9 dB), and among stereotyped call types. Repertoire diversity carried through to estimates of active space, with “long-range” stereotyped calls all containing overlapping, independently-modulated high-frequency components (mean estimated active space of 10–16 km in sea state zero) and “short-range” sounds (5–9 km) included all stereotyped calls without a high-frequency component, whistles, and variable calls. Short-range sounds are reported to be more common during social and resting behaviors, while long-range stereotyped calls predominate in dispersed travel and foraging behaviors. These results suggest that variability in sound pressure levels may reflect diverse social and ecological functions of the acoustic repertoire of killer whales.     

Southern right whales show no behavioral response to low noise levels from a nearby unmanned aerial vehicle

Unmanned aerial vehicles (UAVs) are increasingly used for wildlife research and monitoring, but little information exists on their potential effect on marine mammals. We assessed the effects of a UAV on the behavior of southern right whales (Eubalaena australis) in Australia. Focal follows of ten right whale mother-calf pairs were conducted using a theodolite. Control data were recorded for 30 min, and then a DJI Inspire 1 Pro was flown above the whales for 10 min at 5 m altitude. Potential changes to horizontal behavior (swim speed and turning angle) and surfacing pattern (interbreath intervals) were investigated by comparing mother-calf behavior before and during UAV approaches. Changes in respiration rate were used to quantify energetic effects. We also explored acoustic cue perceptibility of the UAV at 5, 10, and 30 m altitude, by measuring the received UAV underwater noise level on whales equipped with acoustic tags (DTAGs). The received noise levels were 86.0 ± 3.9 dB re 1 μPa, while the measured ambient noise was 80.7 ± 7.3 dB re 1 μPa in the same frequency band (100–1,500 Hz). No behavioral response to the UAV was observed. This provides support for UAVs as a noninvasive tool to study baleen whale behavior and ecophysiology.     

TEMPORARY THRESHOLD SHIFTS AFTER NOISE EXPOSURE IN THE BOTTLENOSE DOLPHIN (TURSIOPS TRUNCATUS) MEASURED USING EVOKED AUDITORY POTENTIALS

The time course of recovery from temporary threshold shift (TTS) was measured in a bottlenose dolphin, Tursiops truncatus , using an evoked-potential procedure. The envelope-following response (EFR), which is a rhythmic train of auditory brainstem responses (ABR) to sinusoidally amplitude-modulated tones, was used as an indicator of the sound reception by the animal. Variation of the intensity of the stimulus allowed us to measure the animal's hearing via EFR thresholds. During each session, following an initial measure of threshold, the trained animal voluntary positioned itself within a hoop 1 m underwater while a 160 dB re 1 μPa noise of a 4–11 kHz bandwidth was presented for 30 min. After the noise exposure, thresholds were measured again at delays of 5, 10, 15, 25, 45, and 105 min. Measurements were made at test frequencies of 8, 11.2, 16, 22.5, and 32 kHz. The maximum TTS occurred 5 min after exposure and rapidly recovered with a rate of around 1.5 dB per doubling of time. TTS occurred at test frequencies from 8 to 16 kHz, with the maximum at 16 kHz. TTS was negligible at 22.5 kHz and absent at 32 kHz.     

SPERM WHALES TAGGED WITH TRANSPONDERS AND TRACKED UNDERWATER BY SONAR

Abstract: Two sperm whales tagged with acoustic transponder tags were tracked by sonar during a cruise from 16 to 30 October 1991 in the southeast Caribbean west of Dominica Island. The whales dove to depths of 400–600 m and more, including a dive to 1,185 m and one possibly to 2,000 m. They were tracked for periods of 3–14 h, over distances of 8.5–40 km. The tagged whales were found together four and eight days after tagging, and were tracked simultaneously for 13 h, over 31 km. Whale movements on different days at the surface averaged from 0.68 to 0.82 m/set, with dive descent rates from 0.82 to 1.13 m/set, ascent rates from 0.74 to 1.16 m/set, and horizontal movement during dives from 0.76 to 1.29 m/set. Dives lasted from 18 min to 1 h and 13 min, averaging 33 and 41 min on different days. Every track ended when tag signals became obscured at night by dense biological scatterers concentrated in offshore areas where the whales were diving. Both tagged whales appear to have been males of 15 and 11m, each dominant in different groups; but when together the larger whale was dominant, as evidenced by chases and agonistic vocalizations. The whales did not appear to react to the tags or to the sounds associated with tracking (30, 32, and 36 kHz).     

ASSESSING KILLER WHALE PREDATION ON STELLER SEA LIONS FROM FIELD OBSERVATIONS IN KENAI FJORDS, ALASKA

The behavioral and predatory patterns of Gulf of Alaska (GOA) transient killer whales ( Orcinus orca ) were studied between 2000 and 2005 using remote video and vessel-based observations near the Chiswell Island Steller sea lion ( Eumetopias jubatus ) rookery and in the broader Kenai Fjords (KF) region of the northern GOA. GOA transient killer whales were observed on 118 d over the 6-yr period; the median group size was two (range: 1–9). Nine predation events were observed from vessels and an additional sixteen were inferred from remote video studies; all involved Steller sea lions. Estimates from field observations suggest that fifty-nine sea lions were consumed over the summer seasons of 2002–2005; whereas estimates based on published caloric requirements of transient killer whales would suggest a loss of 103 sea lions over the same time period. GOA transients spent a large proportion (43%) of their time resting which may be a strategy for conserving energy. Predation on sea lion pups at the Chiswell Island rookery was greatest during years when a single killer whale was foraging alone and when a 1.5-yr-old calf was evidently being trained to handle prey. Predation on pups was low during years when killer whales were foraging in groups and were observed and presumed to be taking mostly juvenile sea lions. Our study suggests that GOA transients are having a minor effect on the recovery of Steller sea lions in the GOA.     

High Source Levels and Small Active Space of High-Pitched Song in Bowhead Whales (Balaena mysticetus)

The low-frequency, powerful vocalizations of blue and fin whales may potentially be detected by conspecifics across entire ocean basins. In contrast, humpback and bowhead whales produce equally powerful, but more complex broadband vocalizations composed of higher frequencies that suffer from higher attenuation. Here we evaluate the active space of high frequency song notes of bowhead whales (Balaena mysticetus) in Western Greenland using measurements of song source levels and ambient noise. Four independent, GPS-synchronized hydrophones were deployed through holes in the ice to localize vocalizing bowhead whales, estimate source levels and measure ambient noise. The song had a mean apparent source level of 185±2 dB rms re 1 µPa @ 1 m and a high mean centroid frequency of 444±48 Hz. Using measured ambient noise levels in the area and Arctic sound spreading models, the estimated active space of these song notes is between 40 and 130 km, an order of magnitude smaller than the estimated active space of low frequency blue and fin whale songs produced at similar source levels and for similar noise conditions. We propose that bowhead whales spatially compensate for their smaller communication range through mating aggregations that co-evolved with broadband song to form a complex and dynamic acoustically mediated sexual display.     

ESTIMATED SOURCE LEVELS OF FIN WHALE (BALAENOPTERA PHYSALUS) VOCALIZATIONS: ADJUSTMENTS FOR SURFACE INTERFERENCE

We recorded a series of 34 fin whale vocalizations using four calibrated hydrophones in a towed array. The whale's location was determined using arrival-time differences of each call at the hydrophones. The recordings showed evidence of interference between signals propagating along direct and surface-reflected paths (the "Lloyd Mirror"). We made preliminary estimates of source level (SL) using a spherical spreading model of transmission loss. We then applied a conservative correction for the effect of interference by subtracting the maximum possible signal enhancement from the preliminary SL estimate. These adjusted spherical spreading estimates had a median of 171 dB re 1 μPa at 1 m, with a range of 159–184 dB. These are the first SL estimates that explicitly attempt to correct for possible interference effects. We also propose a method that simultaneously estimates SL and source depth by fitting a Lloyd Mirror transmission loss curve to the measured received level, known receiver depth, and source-to-receiver range. Attempts to apply this method to the present data set yielded inconsistent results, probably because of the small number of hydrophones available. With more hydrophones in the interference field, this new method should produce reliable estimates of SL and depth of vocalizing whales.     

SEASONAL AND DIURNAL TRENDS OF CHORUSING HUMPBACK WHALES WINTERING IN WATERS OFF WESTERN MAUI

A portable data logger controlled by a Tattletale 7 microcontroller was used to record humpback whale choruses during the 1998 humpback whale winter season in Hawaii. The data logger sampled the sounds for four minutes every half hour using a digitizing rate of 2 kHz, and the data were stored on a hard disk. The results between January and April showed a peak in the sound pressure level between mid-February and mid-March. This peak of approximately 120 dB re 1 μPa coincided with the peak in the number of whales sighted by aerial survey on 7 March 1998. The choruses had spectral peaks at 315 Hz and 630 Hz. Some of the sounds at 630 Hz were second harmonics of the 315 Hz peak and others were not. The data also indicated a diurnal pattern in the sound pressure level, with levels at night significantly louder than the daytime levels. The sound levels began to increase during sunset and remained relatively high until sunrise, when they progressively decreased to a minimum. The nighttime peak occurred within an hour before and after midnight, and the daytime minimum occurred between 1100 and 1500. That more humpback whales appear to sing at night may reflect a switch to sexual advertisement as the primary male mating strategy at this time. It may also indicate that daylight and vision play key roles in the formation of competitive groups. It is suggested that the relative number of humpback whales in a given locale may be estimated by monitoring changes in sound pressure levels.     

Behavioral responses of satellite tracked Blainville's beaked whales (Mesoplodon densirostris) to mid-frequency active sonar

The vulnerability of beaked whales (Family: Ziphiidae) to intense sound exposure has led to interest in their behavioral responses to mid-frequency active sonar (MFAS, 3–8 kHz). Here we present satellite-transmitting tag movement and dive behavior records from Blainville's beaked whales (Mesoplodon densirostris) tagged in advance of naval sonar exercises at the Atlantic Undersea Test and Evaluation Center (AUTEC) in the Bahamas. This represents one of the largest samples of beaked whales individually tracked during sonar operations (n = 7). The majority of individuals (five of seven) were displaced 28–68 km after the onset of sonar exposure and returned to the AUTEC range 2–4 days after exercises ended. Modeled sound pressure received levels were available during the tracking of four individuals and three of those individuals showed declines from initial maxima of 145–172 dB re 1 μPa to maxima of 70–150 dB re 1 μPa following displacements. Dive behavior data from tags showed a continuation of deep diving activity consistent with foraging during MFAS exposure periods, but also suggested reductions in time spent on deep dives during initial exposure periods. These data provide new insights into behavioral responses to MFAS and have important implications for modeling the population consequences of disturbance.     

Fight or flight: antipredator strategies of baleen whales

• 1 The significance of killer whale Orcinus orca predation on baleen whales (Mysticeti) has been a topic of considerable discussion and debate in recent years. Discourse has been constrained by poor understanding of predator‐prey dynamics, including the relative vulnerability of different mysticete species and age classes to killer whales and how these prey animals avoid predation. Here we provide an overview and analysis of predatory interactions between killer whales and mysticetes, with an emphasis on patterns of antipredator responses.
• 2 Responses of baleen whales to predatory advances and attacks by killer whales appear to fall into two distinct categories, which we term the fight and flight strategies. The fight strategy consists of active physical defence, including self‐defence by single individuals, defence of calves by their mothers and coordinated defence by groups of whales. It is documented for five mysticetes: southern right whale Eubalaena australis, North Atlantic right whale Eubalaena glacialis, bowhead whale Balaena mysticetus, humpback whale Megaptera novaeangliae and grey whale Eschrichtius robustus. The flight strategy consists of rapid (20–40 km/h) directional swimming away from killer whales and, if overtaken and attacked, individuals do little to defend themselves. This strategy is documented for six species in the genus Balaenoptera.
• 3 Many aspects of the life history, behaviour and morphology of mysticetes are consistent with their antipredator strategy, and we propose that evolution of these traits has been shaped by selection for reduced predation. Fight species tend to have robust body shapes and are slow but relatively manoeuvrable swimmers. They often calve or migrate in coastal areas where proximity to shallow water provides refuge and an advantage in defence. Most fight species have either callosities (rough and hardened patches of skin) or encrustations of barnacles on their bodies, which may serve (either primarily or secondarily) as weapons or armour for defence. Flight species have streamlined body shapes for high‐speed swimming and they can sustain speeds necessary to outrun pursuing killer whales (>15–20 km/h). These species tend to favour pelagic habitats and calving grounds where prolonged escape sprints from killer whales are possible.
• 4 The rarity of observed successful attacks by killer whales on baleen whales, especially adults, may be an indication of the effectiveness of these antipredator strategies. Baleen whales likely offer low profitability to killer whales, relative to some other marine mammal prey. High‐speed pursuit of flight species has a high energetic cost and a low probability of success while attacks on fight species can involve prolonged handling times and a risk of serious injury.

     

KILLER WHALES, ORCINUS ORCA, IN THE SOUTHEASTERN BERING SEA: RECENT SIGHTINGS andPREDATION ON OTHER MARINE MAMMALS

An unusual number of killer whales appeared in inshore waters of the southeastern Bering Sea in summer 1989 and 1990. Multiple sightings occurred in Bristol and Kuskokwim bays where killer whales had been seen only rarely in previous years. Three animals became stranded on mud flats in Kuskokwim Bay but were able to free themselves on a high tide. Killer whales were observed interacting with salmon, harbor seals, Steller sea lions, walruses, and beluga whales. Detailed observations were made of killer whales attacking belugas in the Naknek River. Local conditions and behavioral adaptations may reduce the susceptibility of belugas to killer whale predation. Continued killer whale activity in this area would be unlikely to affect fish resources, but might have some influence on beluga whales.     

Effects of Boat Engine Noise on the Auditory Sensitivity of the Fathead Minnow, Pimephales promelas

Fishes are constantly exposed to various sources of noise in their underwater acoustic environment. Many of these sounds are from anthropogenic sources, especially engines of boats. Noise generated from a small boat with a 55 horsepower outboard motor was played back to fathead minnows, Pimephales promelas, for 2 h at 142 dB (re: 1 Pa), and auditory thresholds were measured using the auditory brainstem response (ABR) technique. The results demonstrate that boat engine noise significantly elevate a fish's auditory threshold at 1 kHz (7.8 dB), 1.5 kHz (13.5 dB), and 2.0 kHz (10.5 dB), the most sensitive hearing range of this species. Such a short duration of noise exposure leads to significant changes in hearing capability, and implies that man-made noise generated from boat engines can have far reaching environmental impacts on fishes.     

KILLER WHALE ATTACKS ON MINKE WHALES: PREY CAPTURE AND ANTIPREDATOR TACTICS

We describe nine incidents of predation or attempted predation of minke whales ( Balaenoptera acutorostrata ) by mammal-hunting "transient" killer whales ( Orcinus orca ) in coastal waters of British Columbia, Washington, and southeastern Alaska. Pursuits of minke whales were characterized by prolonged chases on a straight heading at velocities of 15–30 km/h. In four of the nine cases the adultsized minke whale gradually outdistanced the killer whales, which abandoned the high-speed pursuit after 0.5–1 h. In one case the minke beached itself and died. Four attacks were successful. In one instance a subadult minke was killed in open water following a chase. In two cases the fleeing minke entered a confined bay and was killed by the killer whales. One adult minke was taken after apparently attempting to seek cover beside a large sailboat. Minke whales made no attempt to physically defend themselves and were killed by repeated ramming or by asphyxiation. Although killer whales are capable of sprinting speeds greater than those of minke whales, it appears that adult minkes can maintain higher sustained speeds and evade capture if sufficient space for an extended escape trajectory is available. Successful predation of minke whales in coastal waters is rare compared to pinnipeds and small cetaceans, the main prey of transient killer whales.     

Killer whale (Orcinus orca) predation in a multi-prey system

Predation can regulate prey numbers but predator behaviour in multiple-prey systems can complicate understanding of control mechanisms. We investigate killer whale (Orcinus orca) predation in an ocean system where multiple marine mammal prey coexist. Using stochastic models with Monte-Carlo simulations, we test the most likely outcome of predator selection and compare scenarios where killer whales: (1) focus predation on larger prey which presumably offer more energy per effort, (2) generalize by feeding on prey as encountered during searches, or (3) follow a mixed foraging strategy based on a combination of encounter rate and prey size selection. We test alternative relationships within the Hudson Bay geographic region, where evidence suggests killer whales seasonally concentrate feeding activities on the large-bodied bowhead whale (Balaena mysticetus). However, model results indicate that killer whales do not show strong prey specialization and instead alternatively feed on narwhal (Monodon monoceros) and beluga (Delphinapterus leucas) whales early and late in the ice-free season. Evidence does support the conjecture that during the peak of the open water season, killer whale predation can differ regionally and feeding techniques can focus on bowhead whale prey. The mixed foraging strategy used by killer whales includes seasonal predator specialization and has management and conservation significance since killer whale predation may not be constrained by a regulatory functional response.     

Gray whales hear and respond to signals from a 21–25 kHz active sonar

Shore-based theodolite tracking of eastern gray whale (Eschrichtius robustus) movements was conducted to test for potential whale responses to a high-frequency sonar system. Southbound migrating whales were observed from two California shore observation stations as the whales swam past the source vessel that was moored in their migration path. The sonar transducer was deployed from the vessel during all observations, broadcasting 21–25 kHz sweeps for half of each day, the other half remaining silent. The order of control and experimental periods was randomized. No readily apparent response to sonar transmissions was observed in the field or in the visual data. Statistical analysis of tracking data indicates that, compared to control data, gray whales deflected inshore at ranges of 1–2 km from the vessel during sonar transmissions at a received sound pressure level of approximately 148 dB re 1 μPa² (134 dB re 1 μPa²s). These data suggest that the functional hearing sensitivity of gray whales extends to at least 21 kHz.     

CATCHES OF HUMPBACK AND OTHER WHALES FROM SHORE STATIONS AT MOSS LANDING AND TRINIDAD, CALIFORNIA, 1919–1926

Logbook data from California shore whaling stations at Moss Landing (1919–1922 and 1924) and Trinidad (1920 and 1922–1926) are analyzed. The logs for the two stations record the taking of 2,111 whales, including 1,871 humpbacks, 177 fin whales, 26 sei whales, 3 blue whales, 12 sperm whales, 7 gray whales, 1 right whale, 1 Baird's beaked whale, and 13 whales of unspecified type (probably humpbacks). Most whales were taken from spring to autumn, but catches were made in all months of some years. The sex ratios of humpback, fin, and sei whales (the three species with sufficient sample sizes to test) did not differ from parity. Primary prey, determined from stomach contents, included sardines and euphausiids for both humpback and fin whales, and 'plankton' (probably euphausiids) for sei whales. The prevalence of pregnancy was 0.46 among mature female humpbacks and 0.43 among mature female fin whales, although these values are reported with caution. Information on length distribution for all species is summarized. Analysis of the catch data for this and other areas supports the current view that humpback whales along the west coast of the continental United States comprise a single feeding stock and also suggests that the present population is well below pre-exploitation levels.