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Naval sonar can disrupt beaked whale diving behaviour, in some cases leading to lethal strandings. Diving disruption likely involves a physiological response, which remains poorly understood. Beaked whales may exceed their aerobic dive limit during long-duration deep-foraging dives and later in those dives, during ascent, initiate a unique strong gait (B-strokes), hypothesized to recruit anaerobic fast-twitch fibres. We compared the use of B-strokes during exposed and unexposed dives in four species of beaked whales. Contrasting the highly context-specific use of B-strokes during ascents from deep-dives in baseline conditions, during sonar exposure, B-strokes were used during descent and ascent phases of both deep and shallow dives. B-stroke onset occurred during all sonar exposure periods with levels above 100 dB re 1 µPa that lasted more than three minutes. The use of B-strokes during descent indicates these animals start using an oxygen-saving strategy earlier in exposed (16 ± 13 min) vs. unexposed dives (33 ± 14 min). This change in swimming gait when exposed to an external threat likely evolved to enable flexible escape responses from predators. However, if prolonged, such responses could lead to physiological changes that contribute to gas bubble formation and growth that could lead to animals stranding.

Harris et al outline a two-decade-long research effort funded by US and European Navies to understand how marine mammals respond behaviorally to navy sonar. They discuss the extensive data collected across various species and contexts, including both controlled exposure experiments and observational studies. In 2024, a comprehensive synthesis of this Behavioral Response Study (BRS) data will be conducted. This effort aims to catalog existing datasets, the research questions addressed, and the analytical methods used. The goal is to create a valuable resource for guiding future research, particularly in developing sonar dose-response functions for environmental compliance. The synthesis will also assess whether existing data can be repurposed to answer new questions by combining information across studies and platforms. Additionally, it will identify gaps in current analytical methods, helping shape future research priorities and better meet navy needs related to marine mammal protection and sonar use

Lipid-store body condition influences how animals balance the risk of starvation against other perceived threats, such as predation. Animals in poor condition may be expected to prioritise immediate foraging needs over protection of future assets; tolerating greater risks to obtain foraging benefits. However, in some species where condition influences escape or defensive abilities, an opposite response pattern can emerge. Similar trade-offs are expected to drive response to anthropogenic noise. We used DTags to quantify tissue density (a proxy for body condition) and record behaviour in 29 free-ranging sperm whales and tested for an association between body condition and behaviour during undisturbed baseline periods and sonar exposures. Less dense individuals (in better body condition) were more likely to employ a deep-diving foraging strategy during baseline and showed smaller reductions in foraging performance during sonar exposures compared with denser individuals. At a sound exposure level of 160 dB re 1 µPa2s and after controlling for other covariates, GAMM modelling predicted a reduction in probability of buzz initiation (a proxy for prey capture attempts) of 20-41% relative to baseline for animals with a body density of 1031 kg/m2 For those with a body density of less than approximately 1029.75 kg/m2, the models predicted no significant decrease. These results are consistent with state-behaviour feedback predicted to exacerbate disturbance impacts from repeated or multiple stressors, with potential to inform predictions of their population consequences.

Understanding the drivers and consequences of individual-level response to anthropogenic activities is important for preventing population-level impacts of human disturbance on wildlife. However, considerable uncertainty remains in models attempting to predict behavioural and physiological responses and their fitness consequences. We address this by incorporating mechanistic knowledge of response drivers into individual-level effects models. We synthesize multi-disciplinary literature to identify both proximate (e.g., ecological, behavioural) and ultimate (evolutionary) drivers of response and derive a new modelling framework. The \"Functional dose-detection-response\" (FDDR) framework consists of three key components: the probability of detection, the probability of response given detection, and potential effects. These components are mediated by the environment and individual status, and incorporate both exogenous and endogenous drivers of sensory processing. We apply the framework in case studies of marine mammal responses to noise, for which the first stage of the model, exposure and probability of detection, 1s relatively well understood. Through mechanistic simulations, we show how assumptions about response drivers lead to different probability, type, and fitness consequences of response. We also identify knowledge gaps for improved understanding of physiological responses, individual health, and life history outcomes. We conclude by discussing how the FDDR framework can inform the development of models and studies of the population consequences of disturbance.

Time allocation to different activities and habitats enables individuals to modulate their perceived 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.

The Atlantic Behavioral Response Study is a multi-disciplinary collaboration with the U.S. Navy to quantify mid-frequency (1-10 kHz) active sonar (MFAS) effects for marine mammals. We will present baseline behavior and MFAS response results for goose-beaked whales (Ziphius cavirostris). Our study site is a biologically rich area where Navy coordination is possible and MFAS occurs but at lower rates than sonar ranges where many BRS' have occurred. We use multi-scale tagging approaches with strategically programmed satellite-transmitting tags yielding weeks of coarser position and diving data and shorter, fine-scale movement and acoustic tags. Controlled exposure experiments (CEEs) provide exposure-response results for different sound sources, including: no noise controls (n = 20), experimental pulsed active sonar (PAS; n = 53), naval vessel PAS (n = 34) and continuous active sonar (CAS). Responses are evaluated relative to key variables (received level [RL], behavioral state, and horizontal range) and specifically assess spatial avoidance, changes in diving and foraging behavior, and social response. Response results for PAS CEEs will be given; CAS studies are ongoing. We observed subtle behavioral changes in control CEEs at similar, low rates as the lowest (< 100 dB) MFAS RLs but a clear escalation of avoidance and diving responses with increasing RL for 100-140 dB exposures. Results amplify earlier indications of Ziphius sensitivity to MFAS by substantially expanding sample sizes and temporal scales, but suggest differences in aspects of response from studies on ranges.

Anti-predator strategies are often defined as ‘flight’ or ‘fight’, based upon prey anatomical adaptations for size, morphology and weapons, as well as observed behaviours in the presence of predators. The humpback whale Megaptera novaeangliae is considered a ‘fight’ specialist based upon anatomy and observations of grouping behaviour and active defence when attacked by killer whales. However, the early stage of humpback whale anti-predator strategy, when the prey detects the presence of a distant potential predator that may not have perceived it, has never been described. Our aim was to experimentally examine this initial stage of anti-predator responses. Humpbacks are likely to hear well at the frequencies of killer whale vocalisations, thus the perception of killer whale sounds could trigger anti-predator responses. To address this hypothesis, we played mammal-eating killer whale sounds to 8 solitary or paired humpback whales in North Atlantic feeding grounds and monitored their behavioural responses. We found that predator sound playbacks induced a cessation of feeding, a change in the diving pattern and a clear directional and rapid horizontal avoidance away from the speaker. Interestingly, in mother-calf pairs with young calves, the directional horizontal avoidance was atypically alternated by 90 degree turns, which may serve as a mechanism to better track the pre dator or a stealth tactic when more vulnerable animals are present. These results provide experimental evidence that humpback whales can exhibit a strong horizontal avoidance as an initial stage of anti-predator defence, indicating that anti-predator responses may be more graded and mixed than previously recognized.

Statistical habitat modelling is often flagged as a cost-effective decision tool for species management. However, data that can produce predictions with the desired precision are difficult to collect, especially for species with spatially extensive and dynamic distributions. Data from platforms of opportunity could be used to complement or help design dedicated surveys, but robust inference from such data is challenging. Furthermore, regression models using static covariates may not be sufficient for animals whose habitat preferences change dynamically with season, environmental conditions or foraging strategy. More flexible models introduce difficulties in selecting parsimonious models. We implemented a robust model-averaging framework to dynamically predict harbour porpoisePhocoena phocoenaoccurrence in a strongly tidal and topographically complex site in southwest Wales using data from a temporally intensive platform of opportunity. Spatial and temporal environmental variables were allowed to interact in a generalized additive model (GAM). We used information criteria to examine an extensive set of 3003 models and average predictions from the best 33. In the best model, 3 main effects and 2 tensorproduct interactions explained 46% of the deviance. Model-averaged predictions indicated that harbour porpoises avoided or selected steeper slopes depending on the tidal flow conditions; when the tide started to ebb, occurrence was predicted to increase 3-fold at steeper slopes.

As human activities impact virtually every animal habitat on the planet, identifying species at-risk from disturbance is a priority. Cetaceans are an example taxon where responsiveness to anthropogenic noise can be severe but highly species and context specific, with source–receiver characteristics such as hearing sensitivity only partially explaining this variability. Here, we predicted that ecoevolutionary factors that increase species responsiveness to predation risk also increase responsiveness to anthropogenic noise. We found that reductions in intense-foraging time during exposure to 1- to 4-kHz naval sonar and predatory killer whale sounds were highly correlated (r = 0.92) across four cetacean species. Northern bottlenose whales ceased foraging completely during killer whale and sonar exposures, followed by humpback, long-finned pilot, and sperm whales, which reduced intense foraging by 48 to 97%. Individual responses to sonar were partly predicted by species-level responses to killer whale playbacks, implying a similar level of perceived risk. The correlation cannot be solely explained by hearing sensitivity, indicating that species- and context-specific antipredator adaptations also shape cetacean responses to human-made noise. Species that are more responsive to predator presence are predicted to be more disturbance sensitive, implying a looming double whammy for Arctic cetaceans facing increased anthropogenic and predator activity with reduced ice cover.

Impact assessments for sonar operations typically use received sound levels to predict behavioural disturbance in marine mammals. However, there are indications that cetaceans may learn to associate exposures from distant sound sources with lower perceived risk. To investigate the roles of source distance and received level in an area without frequent sonar activity, we conducted multi-scale controlled exposure experiments ( n = 3) with 12 northern bottlenose whales near Jan Mayen, Norway. Animals were tagged with high-resolution archival tags ( n = 1 per experiment) or medium-resolution satellite tags ( n = 9 in total) and subsequently exposed to sonar. We also deployed bottom-moored recorders to acoustically monitor for whales in the exposed area. Tagged whales initiated avoidance of the sound source over a wide range of distances (0.8–28 km), with responses characteristic of beaked whales. Both onset and intensity of response were better predicted by received sound pressure level (SPL) than by source distance. Avoidance threshold SPLs estimated for each whale ranged from 117–126 dB re 1 µPa, comparable to those of other tagged beaked whales. In this pristine underwater acoustic environment, we found no indication that the source distances tested in our experiments modulated the behavioural effects of sonar, as has been suggested for locations where whales are frequently exposed to sonar.