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

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

doi:10.1038/s41598-018-36870-7

L. Bejder, S. Videsen + Show 4 more

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https://doi.org/10.1038/s41598-018-36870-7

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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.

Highlights

Individual and population fitness is partly predicated on a balance between energy intake and expenditure, energy transfer to offspring, and predation mitigation[1]
The behaviour of whales on their breeding/resting ground was inferred based on DTAG accelerometers, Minimum Specific Acceleration (MSA; sensu[20]; Methods Section)
This study used DTAGs to quantify the fine scale behaviour and energetic expenditure of humpback whale mothers and calves, and passive acoustic monitoring to quantify the acoustic environment on a whale breeding/resting ground planned for human development

Summary

Introduction

Individual and population fitness is partly predicated on a balance between energy intake and expenditure, energy transfer to offspring, and predation mitigation[1]. While geographic and temporal scales of animal migrations vary considerably, all are functional adaptations to spatio-temporal fluctuations in resource availability (e.g., prey, mates and optimal habitat for successful reproduction) and predation pressures[4] For baleen whales, these trade-offs have evolved into extreme migrations between spatially and temporally decoupled breeding and foraging areas[5]. Current development plans in the Gulf include a multi-purpose deep water wharf, cruise ship tourism, export of limestone and agriculture products, and to expand the capabilities of the defence industry[15] Such expansions will see a substantial increase in marine traffic and a concomitant increase in anthropogenic noise within humpback whale breeding/resting habitat, with the potential for increased risk of ship strikes and acoustic disturbance to resting and nursing mother and calf whales. Largely produced by the shipping industry, is considered a major contributor to habitat degradation in the marine environment[18,19]

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