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

Authors

Bejder, L. ; Videsen, S. ; Hermannsen, L.; Simon, M. ; Hanf, D. ; Madsen, P. T.

Year

2019

Journal

Scientific Reports

Volume

9

Issue

1

Pages

771

ISBN

2045-2322

Keywords

australia, breeding area, Breeding grounds, disturbance, DTAG, humpback whale, Megaptera novaeangliae, nursing, respiration, resting area, satellite telemetry, ship strike, ship strikes, shipping, Threat assessment, Underwater acoustics, vessel traffic, whale watching

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.

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