This study describes behavioral changes of wild cetaceans observed during controlled exposures of naval sonar. In 2006 through 2009, 14 experiments were conducted with killer (n = 4), longfinned pilot (n = 6), and sperm (n = 4) whales. A total of 14 6-7 kHz upsweep, 13 1-2 kHz upsweep, and five 1-2 kHz downsweep sonar exposures, as well as seven Silent vessel control exposure sessions and eight playbacks of killer whale sounds were conducted. Sonar signals were transmitted by a towable source that approached each tagged subject from a starting distance of 6 to 8 km with a ramp up of source levels (from 152 to 158 to a maximum of 198 to 214 dB re: 1 µPa m). This procedure resulted in a gradual escalation of the sonar received level at the whale, measured by towed hydrophones and by tags that record movement and sound (Dtags). Observers tracked the position of each tagged animal and recorded group-level surface behavior. Two expert panels independently scored the severity of diverse behavioral changes observed during each sonar and control exposure, using the 0 to 9 point severity scale of Southall et al. (2007), and then reached consensus with a third-party moderator. The most severe responses scored (i.e., most likely to affect vital rates) included a temporary separation of a calf from its group, cessation of feeding or resting, and avoidance movements that continued after the sonar stopped transmitting. Higher severity scores were more common during sonar exposure than during Silent control sessions. Scored responses started at lower sound pressure levels (SPLs) for killer whales and were more severe during sonar exposures to killer and sperm whales than to longfinned pilot whales. Exposure sessions with the higher source level of 1 to 2 kHz sonar had more changes and a trend for higher maximum severity than 6 to 7 kHz sessions, but the order of the sessions had no effect. This approach is helpful to standardize the description of behavioral changes that occurred during our experiments and to identify and describe the severity of potential responses of free-ranging cetaceans to sonar.

The largest animals are marine filter feeders, but the underlying mechanism of their large size remains unexplained. We measured feeding performance and prey quality to demonstrate how whale gigantism is driven by the interplay of prey abundance and harvesting mechanisms that increase prey capture rates and energy intake. The foraging efficiency of toothed whales that feed on single prey is constrained by the abundance of large prey, whereas filter-feeding baleen whales seasonally exploit vast swarms of small prey at high efficiencies. Given temporally and spatially aggregated prey, filter feeding provides an evolutionary pathway to extremes in body size that are not available to lineages that must feed on one prey at a time. Maximum size in filter feeders is likely constrained by prey availability across space and time.

In this study, we present for the first time a model for the social structure of Risso’s dolphins ( Grampus griseus Cuvier, 1812). Over the period 2004–2006, 1028 Risso’s dolphins were identified at Pico island, Azores. Individuals sighted on 10 or more occasions were included in the analysis of social structure (n = 183). High resighting rates indicate strong site fidelity for at least part of the population. We found that individuals form stable, long-term bonds organised in pairs or in clusters of 3–12 individuals. Social structure is stratified based on age and sex classes, with strong associations between adult males and between adult females. We suggest that clusters form the basic units of Risso’s dolphin society. Thirteen pods consisting solely of adults, likely males, and 3 pods consisting of mother–calf pairs were identified. Males are organised in stable, long-term associations of varying size that occur throughout the complete range of behavioural states observed. For females, associations can be of similar strength, but the time scale may vary depending on the presence of nursing calves. As subadults, associations also occur (pair formation), but are less stable than those observed for adults. We propose a new model for Risso’s dolphin societies known as a stratified social organisation, which differs from the fission–fusion and matrilineal society models.

Each year, a phytoplankton spring bloom starts just north of the North Atlantic Subtropical Gyre, and then expands northwards across the entire North Atlantic. Here, we investigate whether the timing of the spring migration of baleen whales is related to the timing of the phytoplankton spring bloom, using 4 yr of dedicated whale observations at the Azores in combination with satellite data on ocean chlorophyll concentration. Peak abundances of blue whale Balaenoptera musculus, fin whale B. physalus, humpback whale Megaptera novaeangliae and sei whale B. borealis were recorded in April-May. The timing of their presence tracked the onset of the spring bloom with mean time lags of 13, 15, 15 and 16 wk, respectively, and was more strongly related to the onset of the spring bloom than to the actual time of year. Baleen whales were actively feeding on northern krill Meganyctiphanes norvegica in the area, and some photo-identified individuals stayed in Azorean waters for at least 17 d. Baleen whales were not observed in this area in autumn, during their southward migration, consistent with low chlorophyll concentrations during summer and autumn. Our results support the hypothesis that baleen whales track the secondary production generated by the North Atlantic spring bloom, utilizing mid-latitude areas such as the Azores as foraging areas en route towards their summer feeding grounds.KEY WORDS: Baleen whales · Balaenopteridae · Phytoplankton spring bloom · Whale migration · Feeding area · Satellite remote sensing · North Atlantic Ocean · Azores Resale or republication not permitted without written consent of the publisherMar Ecol Prog Ser 440: [267][268][269][270][271][272][273][274][275][276][277][278][279] 2011 tune their migration to the timing of the North Atlantic spring bloom. Baleen whales need dense aggregations of krill or fish to enable efficient foraging (Whitehead & Carscadden 1985, Friedlaender et al. 2006, Goldbogen et al. 2011, and temporal synchrony with the presence of suitable prey is evident in these species. Most baleen whale species undertake extensive north-south migrations associated with feeding at mid-to high latitudes in summer and breeding in (sub)tropical regions during winter (Kellogg 1929, Norris 1967; but see Simon et al. 2010 for a counterexample). Seasonal presence of baleen whales at the summer feeding grounds coincides with increased food availability in these waters. Nevertheless, migratory patterns over the North Atlantic are still largely unknown for most species of baleen whales.The North Atlantic spring bloom could temporarily produce sufficient prey densities to induce foraging of baleen whales during their spring migration towards the high-latitude feeding grounds. This might particularly apply to areas where the phytoplankton spring bloom combines with physical factors to con- centrate prey. Physical conditions conducive to concentrating prey may include coastal zones, upwelling areas, fronts and seamounts. For example, offshore regions of high marine productivit...

Although northern bottlenose whales were the most heavily hunted beaked whale, we have little information about this species in its remote habitat of the North Atlantic Ocean. Underwater anthropogenic noise and disruption of their natural habitat may be major threats, given the sensitivity of other beaked whales to such noise disturbance. We attached dataloggers to 13 northern bottlenose whales and compared their natural sounds and movements to those of one individual exposed to escalating levels of 1–2 kHz upsweep naval sonar signals. At a received sound pressure level (SPL) of 98 dB re 1 μPa, the whale turned to approach the sound source, but at a received SPL of 107 dB re 1 μPa, the whale began moving in an unusually straight course and then made a near 180° turn away from the source, and performed the longest and deepest dive (94 min, 2339 m) recorded for this species. Animal movement parameters differed significantly from baseline for more than 7 h until the tag fell off 33–36 km away. No clicks were emitted during the response period, indicating cessation of normal echolocation-based foraging. A sharp decline in both acoustic and visual detections of conspecifics after exposure suggests other whales in the area responded similarly. Though more data are needed, our results indicate high sensitivity of this species to acoustic disturbance, with consequent risk from marine industrialization and naval activity.

Abstract. Time allocation to different activities and habitats enables individuals to modulate their per-ceived risks and access to resources and can reveal important trade-offs between fitness-enhancing activities (e.g., feeding vs. social behavior). Species with long reproductive cycles and high parental investment, such as marine mammals, rely on such behavioral plasticity to cope with rapid environmental change, including anthropogenic stressors. We quantified activity budgets of free-ranging long-finned pilot whales in order to assess individual time trade-offs between foraging and other behaviors in different individual and ecological contexts, and during experimental sound exposures. The experiments included 1-2 and 6-7 kHz naval sonar exposures (a potential anthropogenic stressor), playback of killer whale (a potential predator/competitor) vocalizations, and negative controls. We combined multiple time series data from digital acoustic recording tags (DTAG) as well as group-level social behavior data from visual observations of tagged whales at the surface. The data were classified into near-surface behaviors and dive types (using a hidden Markov model for dive transitions) and aggregated into time budgets. On average, individuals (N = 19) spent most of their time (69%) resting and transiting near surface, 21% in shallow dives (depth <40 m), and only 10% of their time in deep foraging dives, of which 65% reached a depth 10 m from the sea bottom. Individuals in the largest of three body size classes or accompanied by calves tended to spend more time foraging than others. Simultaneous tagging of pairs of individuals showed that up to 50% of the activity budget was synchronized between conspecifics with decreased synchrony during foraging periods. Individuals spent less time foraging when forming larger non-vocal aggregations of individuals in late afternoons, and more time foraging when in the mid-range of water depths (300-400 m) available in the study area (50-700 m). Individuals reduced foraging time by 83% (29-96%) during their first exposure to sonar, but not during killer whale sound playbacks. A relative increase in foraging during repeat sonar exposures indicated habituation or change in response tactic. We discuss the possible adaptive value of these trade-offs in time allocation to reduce individual conflict while maintaining benefits of group living.

fear of predation can induce profound changes in the behaviour and physiology of prey species even if predator encounters are infrequent. for echolocating toothed whales, the use of sound to forage exposes them to detection by eavesdropping predators, but while some species exploit social defences or produce cryptic acoustic signals, deep-diving beaked whales, well known for mass-strandings induced by navy sonar, seem enigmatically defenceless against their main predator, killer whales. Here we test the hypothesis that the stereotyped group diving and vocal behaviour of beaked whales has benefits for abatement of predation risk and thus could have been driven by fear of predation over evolutionary time. Biologging data from 14 Blainville's and 12 Cuvier's beaked whales show that group members have an extreme synchronicity, overlapping vocal foraging time by 98% despite hunting individually, thereby reducing group temporal availability for acoustic detection by killer whales to <25%. Groups also perform a coordinated silent ascent in an unpredictable direction, covering a mean of 1 km horizontal distance from their last vocal position. This tactic sacrifices 35% of foraging time but reduces by an order of magnitude the risk of interception by killer whales. these predator abatement behaviours have likely served beaked whales over millions of years, but may become maladaptive by playing a role in mass strandings induced by man-made predator-like sonar sounds. Deep-diving marine mammals are expected to maximise time spent foraging in deep prey layers to offset the energetic and physiological costs of diving 1. But Cuvier's and Blainville's beaked whales (Ziphius cavirostris and Mesoplodon densirostris, respectively) employ a diving behaviour unlike that of other deep-diving toothed whales: they restrict echolocation to the deepest part of long and deep foraging dives that are typically followed by extended series of shallower and silent non-foraging dives that result in less than 20% of time devoted to biosonar-mediated foraging 2-5. Further, these species ascend slowly and silently from deep dives at a low pitch angle 2. This unusual and costly diving style has been interpreted as serving to mitigate decompression sickness or to accommodate lactate build up from foraging dives that may exceed the aerobic dive limit 6 , but, see 7. However, satisfactory physiological mechanisms to support these interpretations have yet to be found. When other toothed whales dive to similar depths, they do not display such a diving behaviour: both pilot whales that are similar in size to these beaked whales and the larger sperm whales ascend nearly vertically from their deep foraging dives 8,9 and often emit calls during the ascent to mediate reunion with non-diving group members 10-13. Because the highly stereotyped group diving and vocal behaviour of beaked whales is difficult to explain by foraging niche or physiology 2 an alternate proposition is that it serves to abate predation risk 2,4,14. Fear of predation can induce profound...

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