Baleen whale acoustic presence and behaviour at a Mid-Atlantic migratory habitat, the Azores Archipelago.

The identification of important areas during the annual life cycle of migratory animals, such as baleen whales, is vital for their conservation. In boreal springtime, fin and blue whales feed in the Azores on their way to northern latitudes while sei whales migrate through the archipelago with only occasional feeding. Little is known about their autumn or winter presence or their acoustic behaviour in temperate migratory habitats. This study used a 5-year acoustic data set collected by autonomous recorders in the Azores that were processed and analysed using an automated call detection and classification system. Fin and blue whales were acoustically present in the archipelago from autumn to spring with marked seasonal differences in the use of different call types. Diel patterns of calling activity were only found for fin whales with more calls during the day than night. Sei whales showed a bimodal distribution of acoustic presence in spring and autumn, corresponding to their expected migration patterns. Diel differences in sei whale calling varied with season and location. This work highlights the importance of the Azores as a migratory and wintering habitat for three species of baleen whales and provides novel information on their acoustic behaviour in a mid-Atlantic region.

A performance comparison of tonal detectors for low-frequency vocalizations of Antarctic blue whales.

Extraction of tonal signals embedded in background noise is a crucial step before classification and separation of low-frequency sounds of baleen whales. This work reports results of comparing five tonal detectors, namely the instantaneous frequency estimator, YIN estimator, harmonic product spectrum, cost-function-based detector, and ridge detector. Comparisons, based on a low-frequency adaptation of the Silbido scoring feature, employ five metrics, which quantify the effectiveness of these detectors to retrieve tonal signals that have a wide range of signal to noise ratios (SNRs) and the quality of the detection results. Ground-truth data were generated by embedding 20 synthetic Antarctic blue whale (Balaenoptera musculus intermedia) calls in randomly extracted 30-min noise segments from a 79 h-library recorded by an Ocean Bottom Seismometer in the Indian Ocean during 2012-2013. Monte-Carlo simulations were performed using 20 trials per SNR, ranging from 0 dB to 15 dB. Overall, the tonal detection results show the superiority of the cost-function-based and the ridge detectors, over the other detectors, for all SNR values. More particularly, for lower SNRs (⩽3 dB), these two methods outperformed the other three with high recall, low fragmentation, and high coverage scores. For SNRs ⩾7 dB, the five methods performed similarly.

Memory and resource tracking drive blue whale migrations.

In terrestrial systems, the green wave hypothesis posits that migrating animals can enhance foraging opportunities by tracking phenological variation in high-quality forage across space (i.e., "resource waves"). To track resource waves, animals may rely on proximate cues and/or memory of long-term average phenologies. Although there is growing evidence of resource tracking in terrestrial migrants, such drivers remain unevaluated in migratory marine megafauna. Here we present a test of the green wave hypothesis in a marine system. We compare 10 years of blue whale movement data with the timing of the spring phytoplankton bloom resulting in increased prey availability in the California Current Ecosystem, allowing us to investigate resource tracking both contemporaneously (response to proximate cues) and based on climatological conditions (memory) during migrations. Blue whales closely tracked the long-term average phenology of the spring bloom, but did not track contemporaneous green-up. In addition, blue whale foraging locations were characterized by low long-term habitat variability and high long-term productivity compared with contemporaneous measurements. Results indicate that memory of long-term average conditions may have a previously underappreciated role in driving migratory movements of long-lived species in marine systems, and suggest that these animals may struggle to respond to rapid deviations from historical mean environmental conditions. Results further highlight that an ecological theory of migration is conserved across marine and terrestrial systems. Understanding the drivers of animal migration is critical for assessing how environmental changes will affect highly mobile fauna at a global scale.

Anatomy and Functional Morphology of the Mysticete Rorqual Whale Larynx: Phonation Positions of the U-Fold.

Many Mysticetes (baleen whales) are acoustically active marine mammals. This is epitomized by rorquals, and specifically male humpback whales (Megaptera novaeangliae) whose complex songs comprise a wide range of vocalizations. The sound production mechanism of odontocetes (toothed whales, including dolphins and porpoises) is well described, in contrast to that of mysticetes whose vocalization mechanism remains a subject of active scientific investigation. Anatomical observations and acoustic signal processing have led to divergent hypotheses under the framework of a production-based approach. We attempt to unify these hypotheses by broadening existing data with our new anatomical investigation, interpreted in light of known acoustical properties of mysticete vocalizations. We examined 15 specimens of four rorqual species: sei whale (Baleanoptera borealis), fin whale (Baleanoptera physalus), minke whale (Baleanoptera acutorostrata), and humpback whale (Megaptera novaeangliae). Based on these data and on previous literature, we propose a description of three functional positions (rest, breathing, and recirculation), unidirectional egressive airflow for sound production (from lungs to laryngeal sac), and new nomenclature for different parts of the U-fold (distal section, midsection, and corniculate flaps). Each of these sections has specific morphological and acoustical properties that support the concept of "mode variation" in baleen whale vocalizations. Anat Rec, 2018. © 2018 Wiley Periodicals, Inc. Anat Rec, 302:703-717, 2019. © 2018 Wiley Periodicals, Inc.

A Dynamic State Model of Migratory Behavior and Physiology to Assess the Consequences of Environmental Variation and Anthropogenic Disturbance on Marine Vertebrates.

Integrating behavior and physiology is critical to formulating new hypotheses on the evolution of animal life-history strategies. Migratory capital breeders acquire most of the energy they need to sustain migration, gestation, and lactation before parturition. Therefore, when predicting the impact of environmental variation on such species, a mechanistic understanding of the physiology of their migratory behavior is required. Using baleen whales as a model system, we developed a dynamic state variable model that captures the interplay among behavioral decisions, energy, reproductive needs, and the environment. We applied the framework to blue whales (Balaenoptera musculus) in the eastern North Pacific Ocean and explored the effects of environmental and anthropogenic perturbations on female reproductive success. We demonstrate the emergence of migration to track prey resources, enabling us to quantify the trade-offs among capital breeding, body condition, and metabolic expenses. We predict that periodic climatic oscillations affect reproductive success less than unprecedented environmental changes do. The effect of localized, acute anthropogenic impacts depended on whales' behavioral response to the disturbance; chronic, but weaker, disturbances had little effect on reproductive success. Because we link behavior and vital rates by modeling individuals' energetic budgets, we provide a general framework to investigate the ecology of migration and assess the population consequences of disturbance, while identifying critical knowledge gaps.

Context-dependent lateralized feeding strategies in blue whales.

Lateralized behaviors benefit individuals by increasing task efficiency in foraging and anti-predator behaviors [1-4]. The conventional lateralization paradigm suggests individuals are left or right lateralized, although the direction of this laterality can vary for different tasks (e.g. foraging or predator inspection/avoidance). By fitting tri-axial movement sensors to blue whales (Balaenoptera musculus), and by recording the direction and size of their rolls during lunge feeding events, we show how these animals differ from such a paradigm. The strength and direction of individuals' lateralization were related to where and how the whales were feeding in the water column. Smaller rolls (≤180°) predominantly occurred at depth (>70 m), with whales being more likely to rotate clockwise around their longest axis (right lateralized). Larger rolls (>180°), conversely, occurred more often at shallower depths (<70 m) and were more likely to be performed anti-clockwise (left lateralized). More acrobatic rolls are typically used to target small, less dense krill patches near the water's surface [5,6], and we posit that the specialization of lateralized feeding strategies may enhance foraging efficiency in environments with heterogeneous prey distributions.

Modelling the effects of environmental conditions on the acoustic occurrence and behaviour of Antarctic blue whales.

Harvested to perilously low numbers by commercial whaling during the past century, the large scale response of Antarctic blue whales Balaenoptera musculus intermedia to environmental variability is poorly understood. This study uses acoustic data collected from 586 sonobuoys deployed in the austral summers of 1997 through 2009, south of 38°S, coupled with visual observations of blue whales during the IWC SOWER line-transect surveys. The characteristic Z-call and D-call of Antarctic blue whales were detected using an automated detection template and visual verification method. Using a random forest model, we showed the environmental preferences pattern, spatial occurrence and acoustic behaviour of Antarctic blue whales. Distance to the southern boundary of the Antarctic Circumpolar Current (SBACC), latitude and distance from the nearest Antarctic shores were the main geographic predictors of blue whale call occurrence. Satellite-derived sea surface height, sea surface temperature, and productivity (chlorophyll-a) were the most important environmental predictors of blue whale call occurrence. Call rates of D-calls were strongly predicted by the location of the SBACC, latitude and visually detected number of whales in an area while call rates of Z-call were predicted by the SBACC, latitude and longitude. Satellite-derived sea surface height, wind stress, wind direction, water depth, sea surface temperatures, chlorophyll-a and wind speed were important environmental predictors of blue whale call rates in the Southern Ocean. Blue whale call occurrence and call rates varied significantly in response to inter-annual and long term variability of those environmental predictors. Our results identify the response of Antarctic blue whales to inter-annual variability in environmental conditions and highlighted potential suitable habitats for this population. Such emerging knowledge about the acoustic behaviour, environmental and habitat preferences of Antarctic blue whales is important in improving the management and conservation of this highly depleted species.

Acoustically invisible feeding blue whales in Northern Icelandic waters.

Fixed passive acoustic monitoring can be used for long-term recording of vocalizing cetaceans. Both presence monitoring and animal density estimation requires the call rates and sound source levels of vocalizations produced by single animals. In this study, blue whale calls were recorded using acoustic bio-logging systems in Skjálfandi Bay off Húsavík, Northeast Iceland, in June 2012. An accelerometer was attached to individual whales to monitor diving behavior. During 21 h recording two individuals, 8 h 45 min and 13 h 2 min, respectively, 105 and 104 lunge feeding events and four calls were recorded. All recorded calls were down-sweep calls ranging from 105 to 48 Hz. The sound duration was 1-2 s. The source level was estimated to be between 158 and 169 dB re 1µPa rms, assuming spherical sound propagation from the possible sound source location to the tag. The observed sound production rates and source levels of individual blue whales during feeding were extremely small compared with those observed previously in breeding grounds. The feeding whales were nearly acoustically invisible. The function of calls during feeding remains unknown.

Non-song vocalizations of pygmy blue whales in Geographe Bay, Western Australia.

Non-song vocalizations of migrating pygmy blue whales (Balaenoptera musculus brevicauda) in Western Australia are described. Simultaneous land-based visual observations and underwater acoustic recordings detected 27 groups in Geographe Bay, WA over 2011 to 2012. Six different vocalizations were recorded that were not repeated in a pattern or in association with song, and thus were identified as non-song vocalizations. Five of these were not previously described for this population. Their acoustic characteristics and context are presented. Given that 56% of groups vocalized, 86% of which produced non-song vocalizations and 14% song units, the inclusion of non-song vocalizations in passive-acoustic monitoring is proposed.

Acoustic detection and long-term monitoring of pygmy blue whales over the continental slope in southwest Australia.

A 9-yr dataset of continuous sea noise recording made at the Cape Leeuwin station of the Comprehensive Nuclear-Test-Ban Treaty hydroacoustic network in 2002-2010 was processed to detect calls from pygmy blue whales and to analyze diurnal, seasonal, and interannual variations in their vocal activity. Because the conventional spectrogram correlation method for recognizing whale calls in sea noise resulted in a too high false detection rate, alternative algorithms were tested and the most robust one applied to the multi-year dataset. The detection method was based on multivariate classification using two spectrogram features of transients in sea noise and Fisher's linear discriminant, which provided a misclassification rate of approximately 1% for missed and false detections at moderate sensitivity settings. An analysis of the detection results revealed a consistent seasonal pattern in the whale presence and considerable interannual changes with a steady increase in the number of calls detected in 2002-2006. An apparent diurnal pattern of whales' vocal activity was also observed. The acoustic detection range for pygmy blue whales was estimated to vary from about 50 km to nearly 200 km from the Cape Leeuwin station, depending on the ambient noise level, source level, and azimuth to a vocalizing whale.