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Low energy expenditure and resting behaviour of humpback whale mother-calf pairs highlights conservation importance of sheltered breeding areas.

ABSTRACT: Understanding the behaviour of humpback whale mother-calf pairs and the acoustic environment on their breeding grounds is fundamental to assessing the biological and ecological requirements needed to ensure a successful migration and survival of calves. Therefore, on a breeding/resting ground, Exmouth Gulf, Western Australia, we used animal-borne DTAGs to quantify the fine-scale behaviour and energetic expenditure of humpback whale mothers and calves, while sound recorders measured the acoustic environment. We show that: (i) lactating humpback whales keep their energy expenditure low by devoting a significant amount of time to rest, and their use of energy, inferred from respiration rates, is ~half than that of adults on their foraging grounds; (ii) lactating females mainly rest while stationary at shallow depths within reach of the hull of commercial ships, thus increasing the potential for ship strike collisions; (iii) the soundscape is dominated by biological sources; and (iv) even moderate increases of noise from vessels will decrease the communication range of humpback whales. Planned commercial infrastructure in Exmouth Gulf will cause a substantial increase in shipping traffic with the risk of ship strikes and acoustic disturbance potentially compromising energy reserves for the southern migration of humpback whales.

SUBMITTER: Bejder L

PROVIDER: S-EPMC6347592 | biostudies-literature | 2019 Jan

REPOSITORIES: biostudies-literature

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Low energy expenditure and resting behaviour of humpback whale mother-calf pairs highlights conservation importance of sheltered breeding areas.

Bejder L L Videsen S S Hermannsen L L Simon M M Hanf D D Madsen P T PT

Scientific reports 20190125 1

Understanding the behaviour of humpback whale mother-calf pairs and the acoustic environment on their breeding grounds is fundamental to assessing the biological and ecological requirements needed to ensure a successful migration and survival of calves. Therefore, on a breeding/resting ground, Exmouth Gulf, Western Australia, we used animal-borne DTAGs to quantify the fine-scale behaviour and energetic expenditure of humpback whale mothers and calves, while sound recorders measured the acoustic ...[more]

PMID: 30683890

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Project description:Getting maternal milk through nursing is vital for all newborn mammals. Despite its importance, nursing has been poorly documented in humpback whales (Megaptera novaeangliae). Nursing is difficult to observe underwater without disturbing the whales and is usually impossible to observe from a ship. We attempted to observe nursing from the calf's perspective by placing CATS cam tags on three humpback whale calves in the Sainte Marie channel, Madagascar, Indian Ocean, during the breeding seasons. CATS cam tags are animal-borne multi-sensor tags equipped with a video camera, a hydrophone, and several auxiliary sensors (including a 3-axis accelerometer, a 3-axis magnetometer, and a depth sensor). The use of multi-sensor tags minimized potential disturbance from human presence. A total of 10.52 h of video recordings were collected with the corresponding auxiliary data. Video recordings were manually analyzed and correlated with the auxiliary data, allowing us to extract different kinematic features including the depth rate, speed, Fluke Stroke Rate (FSR), Overall Body Dynamic Acceleration (ODBA), pitch, roll, and roll rate. We found that suckling events lasted 18.8 ± 8.8 s on average (N = 34) and were performed mostly during dives. Suckling events represented 1.7% of the total observation time. During suckling, the calves were visually estimated to be at a 30-45° pitch angle relative to the midline of their mother's body and were always observed rolling either to the right or to the left. In our auxiliary dataset, we confirmed that suckling behavior was primarily characterized by a high average absolute roll and additionally we also found that it was likely characterized by a high average FSR and a low average speed. Kinematic features were used for supervised machine learning in order to subsequently detect suckling behavior automatically. Our study is a proof of method on which future investigations can build upon. It opens new opportunities for further investigation of suckling behavior in humpback whales and the baleen whale species.

Project description:Why do humpback whales sing? This paper considers the hypothesis that humpback whales may use song for long range sonar. Given the vocal and social behavior of humpback whales, in several cases it is not apparent how they monitor the movements of distant whales or prey concentrations. Unless distant animals produce sounds, humpback whales are unlikely to be aware of their presence or actions. Some field observations are strongly suggestive of the use of song as sonar. Humpback whales sometimes stop singing and then rapidly approach distant whales in cases where sound production by those whales is not apparent, and singers sometimes alternately sing and swim while attempting to intercept another whale that is swimming evasively. In the evolutionary development of modern cetaceans, perceptual mechanisms have shifted from reliance on visual scanning to the active generation and monitoring of echoes. It is hypothesized that as the size and distance of relevant events increased, humpback whales developed adaptive specializations for long-distance echolocation. Differences between use of songs by humpback whales and use of sonar by other echolocating species are discussed, as are similarities between bat echolocation and singing by humpback whales. Singing humpback whales are known to emit sounds intense enough to generate echoes at long ranges, and to flexibly control the timing and qualities of produced sounds. The major problem for the hypothesis is the lack of recordings of echoes from other whales arriving at singers immediately before they initiate actions related to those whales. An earlier model of echoic processing by singing humpback whales is here revised to incorporate recent discoveries. According to the revised model, both direct echoes from targets and modulations in song-generated reverberation can provide singers with information that can help them make decisions about future actions related to mating, traveling, and foraging. The model identifies acoustic and structural features produced by singing humpback whales that may facilitate a singer's ability to interpret changes in echoic scenes and suggests that interactive signal coordination by singing whales may help them to avoid mutual interference. Specific, testable predictions of the model are presented.

Dataset Information

Low energy expenditure and resting behaviour of humpback whale mother-calf pairs highlights conservation importance of sheltered breeding areas.

Publications

Low energy expenditure and resting behaviour of humpback whale mother-calf pairs highlights conservation importance of sheltered breeding areas.

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