Social survival: Humpback whales (Megaptera novaeangliae) use social structure to partition ecological niches within proposed critical habitat.

Animal culture and social bonds are relevant to wildlife conservation because they influence patterns of geography, behavior, and strategies of survival. Numerous examples of socially-driven habitat partitioning and ecological-niche specialization can be found among vertebrates, including toothed whales. But such social-ecological dynamics, described here as 'social niche partitioning', are not known among baleen whales, whose societies-particularly on foraging grounds-are largely perceived as unstructured and incidental to matters of habitat use and conservation. However, through 16 years of behavioral observations and photo-identifications of humpback whales (Megaptera novaeangliae) feeding within a fjord system in the Canadian Pacific (primarily within Gitga'at First Nation waters), we have documented long-term pair bonds (up to 12 years) as well as a complex societal structure, which corresponds closely to persistent patterns in feeding strategy, long-term site fidelity (extended occupancy and annual rate of return up to 75%), specific geographic preferences within the fjord system, and other forms of habitat use. Randomization tests of network congruency and clustering algorithms were used to test for overlap in patterns of social structure and habitat use, which confirmed the occurrence of social niche partitioning on the feeding grounds of this baleen whale species. In addition, we document the extensive practice of group bubble net feeding in Pacific Canada. This coordinated feeding behavior was found to strongly mediate the social structure and habitat use within this humpback whale society. Additionally, during our 2004-2019 study, we observed a shift in social network structure in 2010-2012, which corresponded with environmental and demographic shifts including a sudden decline in the population's calving rate. Our findings indicate that the social lives of humpback whales, and perhaps baleen whales generally, are more complex than previously supposed and should be a primary consideration in the assessment of potential impacts to important habitat.

Social relationships and death-related behaviour in aquatic mammals: a systematic review.

Some aquatic mammals appear to care for their dead, whereas others abandon their live offspring when conditions are unfavourable. This incredible variety in behaviours suggests the importance of comparing and contrasting mechanisms driving death-related behaviours among these species. We reviewed 106 cases of aquatic mammals (81 cetaceans and 25 non-cetaceans) reacting to a death event, and extrapolated 'participant' (age class, sex, relationship and decomposition) and 'social' characteristics (escorting, calf dependence, alloparental care, herding and dispersal patterns) from published and unpublished literature. A multiple correspondence analysis (MCA) was performed to explore the relationships between these characteristics and death-related behaviours, with species clustered based on MCA scores. Results showed that both cetaceans and non-cetaceans react to death but in different ways. Non-cetaceans, characterized by a short maternal investment, were observed to protect the dead (defending it from external attacks), while cetaceans spent much longer with their offspring and display carrying (hauling, spinning, mouthing with the carcass and diving with it) and breathing-related (lifting and sinking the carcass) activities with the dead generally in association with other conspecifics. Our work emphasizes the need of increased documentation of death-related cases around the world to improve our understanding of aquatic mammals and their responses to death.This article is part of the theme issue 'Evolutionary thanatology: impacts of the dead on the living in humans and other animals'.

Learning to play: A review and theoretical investigation of the developmental mechanisms and functions of cetacean play.

Play is a behavioral phenomenon most commonly observed in the young of both solitary and social species. Documentation of play in cetaceans varies across species and settings. Cetacean play behavioral repertoires include a broad range of actions, such as the manipulation of diverse objects, blowing bubbles, chasing conspecifics, and swimming in spirals through the water. As is common in research on animal play, cetacean play has been grouped into categories by its form, including locomotor play, object play, and different variations of social play, such as affiliative games, play fighting, and socio-sexual play. Research has primarily focused on recording the topography of cetacean play and the demographics of the individuals engaging in play. However, these classifications are insufficient to address the possible developmental and societal functions of cetacean play behaviors, or the mechanisms with which play behaviors are spread between conspecifics and acquired by young members of cetacean populations. This article applies several developmental and social learning theories in order to organize current knowledge and guide future research.

Marine mammal audibility of selected shallow-water survey sources.

Most attention about the acoustic effects of marine survey sound sources on marine mammals has focused on airgun arrays, with other common sources receiving less scrutiny. Sound levels above hearing threshold (sensation levels) were modeled for six marine mammal species and seven different survey sources in shallow water. The model indicated that odontocetes were most likely to hear sounds from mid-frequency sources (fishery, communication, and hydrographic systems), mysticetes from low-frequency sources (sub-bottom profiler and airguns), and pinnipeds from both mid- and low-frequency sources. High-frequency sources (side-scan and multibeam) generated the lowest estimated sensation levels for all marine mammal species groups.

Automatic detection and classification of odontocete whistles.

Methods for the fully automatic detection and species classification of odontocete whistles are described. The detector applies a number of noise cancellation techniques to a spectrogram of sound data and then searches for connected regions of data which rise above a pre-determined threshold. When tested on a dataset of recordings which had been carefully annotated by a human operator, the detector was able to detect (recall) 79.6% of human identified sounds that had a signal-to-noise ratio above 10 dB, with 88% of the detections being valid. A significant problem with automatic detectors is that they tend to partially detect whistles or break whistles into several parts. A classifier has been developed specifically to work with fragmented whistle detections. By accumulating statistics over many whistle fragments, correct classification rates of over 94% have been achieved for four species. The success rate is, however, heavily dependent on the number of species included in the classifier mix, with the mean correct classification rate dropping to 58.5% when 12 species were included.

The effects of acoustic misclassification on cetacean species abundance estimation.

To estimate the density or abundance of a cetacean species using acoustic detection data, it is necessary to correctly identify the species that are detected. Developing an automated species classifier with 100% correct classification rate for any species is likely to stay out of reach. It is therefore necessary to consider the effect of misidentified detections on the number of observed data and consequently on abundance or density estimation, and develop methods to cope with these misidentifications. If misclassification rates are known, it is possible to estimate the true numbers of detected calls without bias. However, misclassification and uncertainties in the level of misclassification increase the variance of the estimates. If the true numbers of calls from different species are similar, then a small amount of misclassification between species and a small amount of uncertainty around the classification probabilities does not have an overly detrimental effect on the overall variance. However, if there is a difference in the encounter rate between species calls and/or a large amount of uncertainty in misclassification rates, then the variance of the estimates becomes very large and this dramatically increases the variance of the final abundance estimate.

An automatic detection algorithm for extracting the representative frequency of cetacean tonal sounds.

Most studies on tonal sounds extract contour parameters from fundamental frequencies. The presence of harmonics and the frequency distribution of multiple tonal sounds have not been well researched. To investigate the occurrence and frequency modulation of cetacean tonal sounds, the procedure of detecting the instantaneous frequency bandwidth of tonal spectral peaks was integrated within the local-max detector to extract adopted frequencies. The adopted frequencies, considered the representative frequencies of tonal sounds, are used to find the presence of harmonics and overlapping tonal sounds. The utility and detection performance are demonstrated on acoustic recordings of five species from two databases. The recordings of humpback dolphins showed a 75% detection rate with a 5% false detection rate, and recordings from the MobySound archive showed an 85% detection rate with a 5% false detection rate. These detections were achieved in signal-to-noise ratios of -12 to 21 dB. The parameters that measured the distribution of adopted frequency, as well as the prominence of harmonics and overlaps, indicate that the modulation of tonal sounds varied among different species and behaviors. This algorithm can be applied to studies on cetacean communication signals and long-term passive acoustic monitoring.

Methodology and results of calibration of tonal click detectors for small odontocetes (C-PODs).

Static acoustic monitoring (SAM) is one major technology for observing small cetacean species. Automatic click loggers deployed for long time periods (>2 months) with a single hydrophone are a standard solution. Acoustic properties, like detection thresholds of these instruments, are essential for interpretation of results, but have nevertheless received little attention. A methodology for calibrating tonal click detectors in small tanks consisting of the determination of the horizontal directivity pattern and detection thresholds including a transfer function is presented. Two approaches were tested to determine detection thresholds by (a) determining the 50% detection threshold and (b) fitting a linear regression model to the recorded relative amplitudes. The tests were carried out on C-PODs (Cetacean PODs, tonal click detectors), the most commonly used instrument for SAM in Europe. Directivity and threshold were tested between 60 and 150 kHz. Directivity showed a maximum variation of 8.5 dB in the horizontal plane. Sensitivity is highest between 80 and 130 kHz and linear (± 3 dB) in this frequency range for most of the instruments tested. C-PODs have a detection threshold (calculated with the linear model) of 114.5 ± 1.2 (standard deviation) dB re 1 µPa peak-peak at 130 kHz.

Range estimation of cetaceans with compact volumetric arrays.

Passive acoustic monitoring is the method of choice to detect whales and dolphins that are acoustically active and to monitor their underwater behavior. The NATO Science and Technology Organization Centre for Maritime Research and Experimentation has recently implemented a compact passive acoustic monitor (CPAM), consisting of three arrays of two hydrophones each that are combined in a fixed three-dimensional arrangement and that may be towed at depths of more than 100 m. With its volumetric configuration, the CPAM is capable of estimating the three-dimensional direction vector of arriving sounds and under certain conditions on relative geometry between the whale and hydrophone array, the CPAM may also estimate the range to echolocating animals. Basic ranging methods assume constant sound speed and apply straightforward geometry to obtain depth and distance to the sound source. Alternatively, ray-tracing based methods may be employed to integrate the information provided by real sound speed profiles. Both ranging methods combine measurements of sound arrival angles and surface reflection delays and are easily implemented in real-time applications, whereby one could promote the ray-tracing approach as the preferred method because it may integrate real sound speed profiles.

Gain control in the sonar of odontocetes.

The sonar of odontocetes processes echo-signals within a wide range of echo levels. The level of echoes varies widely by tens of decibels depending on the level of the emitted sonar pulse, the target strength, the distance to the target, and the sound absorption by the water media. The auditory system of odontocetes must be capable of effective perception, analysis, and discrimination of echo-signals within all this variability. The sonar of odontocetes has several mechanisms to compensate for the echo-level variation (gain control). To date, several mechanisms of the biosonar gain control have been revealed in odontocetes: (1) adjustment of emitted sonar pulse levels (the longer the distance to the target, the higher the level of the emitted pulse), (2) short-term variation of hearing sensitivity based on forward masking of the echo by the preceding self-heard emitted pulse and subsequent release from the masking, and (3) active long-term control of hearing sensitivity. Recent investigations with the use of the auditory evoked-potential technique have demonstrated that these mechanisms effectively minimize the variation of the response to the echo when either the emitted sonar pulse level, or the target distance, or both vary within a wide range. A short review of these data is presented herein.

Marine mammal training: the history of training animals for medical behaviors and keys to their success.

The training of both domestic and exotic species for participation in medical behaviors is a helpful tool in the care and management of individual animals. The practice of training individual animals to help in their own health care is difficult to trace back to its origins. The use of these techniques on large exotic mammals became commonplace only as recently as the late 1990s and early 2000s. However, the practice seems to have been perfected and made popular with marine mammal species, starting in the 1970s. The development of better training techniques for a variety of medical behaviors is a foundational key worth examining and has been proven to be applicable across species.

Turismo de observação de cetáceos como ferramenta no estudo do comportamento de baleias Jubarte (Megaptera novaeangliae) / Whale-watching as a tool to study humpback whales (Megaptera novaeangliae) behavior

O comportamento das baleias jubarte foi observado para detectar diferenças nas probabilidades de ocorrência de determinadas categorias comportamentais observadas a partir de cruzeiros de pesquisa e de turismo. Foram analisados dados de 256 grupos observados durante os cruzeiros de pesquisa e 122 grupos em cruzeiros de turismo, nas temporadas de 2001 a 2003, no litoral norte da Bahia. A análise de rede bayesiana forneceu maiores probabilidades de ocorrência para as categorias do tipo deslocamento, socialização e agressivo, enquanto a análise comparativa não forneceu diferenças expressivas entre as duas categorias de cruzeiro. De acordo com as probabilidades de ocorrência da conduta repouso para grupos com filhote e devido a uma possível interrupção do ato de amamentação causada pelas embarcações, sugere-se uma distância mais conservativa e um menor tempo de permanência com esses grupos.

Humpback whales behavior was observed to determine the existence of differences between observations occurring from research vessels vs. whale-watching vessels. A total of 256 groups were observed from research vessels and 122 groups from whale-watching vessels during the breeding seasons from 2001 through 2003 in the northern coast of the state of Bahia, Brazil. A Bayesian network analysis yielded greatest probabilities of occurrence of the behavioral conducts traveling, socialization and aggressive. Significant behavioral differences between cruise types were not obtained through comparative analysis. Given the probability of occurrence of resting conducts in calf pods and the possibility of the interruption of suckling caused by vessels, it is suggested that a more conservative distance and shorter visits be adopted by whale-watching groups.

Turismo de observação de cetáceos como ferramenta no estudo do comportamento de baleias Jubarte (Megaptera novaeangliae) / Whale-watching as a tool to study humpback whales (Megaptera novaeangliae) behavior

O comportamento das baleias jubarte foi observado para detectar diferenças nas probabilidades de ocorrência de determinadas categorias comportamentais observadas a partir de cruzeiros de pesquisa e de turismo. Foram analisados dados de 256 grupos observados durante os cruzeiros de pesquisa e 122 grupos em cruzeiros de turismo, nas temporadas de 2001 a 2003, no litoral norte da Bahia. A análise de rede bayesiana forneceu maiores probabilidades de ocorrência para as categorias do tipo deslocamento, socialização e agressivo, enquanto a análise comparativa não forneceu diferenças expressivas entre as duas categorias de cruzeiro. De acordo com as probabilidades de ocorrência da conduta repouso para grupos com filhote e devido a uma possível interrupção do ato de amamentação causada pelas embarcações, sugere-se uma distância mais conservativa e um menor tempo de permanência com esses grupos(AU)

Humpback whales behavior was observed to determine the existence of differences between observations occurring from research vessels vs. whale-watching vessels. A total of 256 groups were observed from research vessels and 122 groups from whale-watching vessels during the breeding seasons from 2001 through 2003 in the northern coast of the state of Bahia, Brazil. A Bayesian network analysis yielded greatest probabilities of occurrence of the behavioral conducts traveling, socialization and aggressive. Significant behavioral differences between cruise types were not obtained through comparative analysis. Given the probability of occurrence of resting conducts in calf pods and the possibility of the interruption of suckling caused by vessels, it is suggested that a more conservative distance and shorter visits be adopted by whale-watching groups(AU)

The face that sank the Essex: potential function of the spermaceti organ in aggression.

'Forehead to forehead I meet thee, this third time, Moby Dick!' [Ahab (Melville, 1851)] Herman Melville's fictional portrayal of the sinking of the Pequod was inspired by instances in which large sperm whales sank whaling ships by ramming the ships with their heads. Observations of aggression in species of the four major clades of cetacean and the artiodactyl outgroup suggest that head-butting during male-male aggression is a basal behavior for cetaceans. We hypothesize that the ability of sperm whales to destroy stout wooden ships, 3-5 times their body mass, is a product of specialization for male-male aggression. Specifically, we suggest that the greatly enlarged and derived melon of sperm whales, the spermaceti organ, evolved as a battering ram to injure an opponent. To address this hypothesis, we examined the correlation between relative melon size and the level of sexual dimorphism in body size among cetaceans. We also modeled impacts between two equal-sized sperm whales to determine whether it is physically possible for the spermaceti organ to function as an effective battering ram. We found (i) that the evolution of relative melon size in cetaceans is positively correlated with the evolution of sexual dimorphism in body size and (ii) that the spermaceti organ of a charging sperm whale has enough momentum to seriously injure an opponent. These observations are consistent with the hypothesis that the spermaceti organ has evolved to be a weapon used in male-male aggression.