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

www.nature.com/scientificreports OPEN Received: 27 June 2018 Accepted: 29 November 2018 Published: xx xx xxxx Low energy expenditure and resting behaviour of humpback whale mother-calf pairs highlights conservation importance of sheltered breeding areas L. Bejder 1,2,3 , S. Videsen4, L. Hermannsen4, M. Simon5, D. Hanf1 & P. T. Madsen4,6 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. Individual and population fitness is partly predicated on a balance between energy intake and expenditure, energy transfer to offspring, and predation mitigation1. Wildlife can be categorized as income or capital breeders based on their life history strategies for energy intake and expenditure, and for allocation of resources into their long-term reproduction and survival2,3. Income breeders replenish their energy reserves concurrently with reproduction, whereas capital breeders finance the energy cost of reproduction through stored energy reserves3. Most mysticetes (baleen whales) are capital breeders that typically breed in low-productive lower latitudes and feed in highly-productive higher latitudes. 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 pressures4. For baleen whales, these trade-offs have evolved into extreme migrations between spatially and temporally decoupled breeding and foraging areas5. Humpback whales (Megaptera novaeanglea) carry out some of the longest migrations on earth. For example, the southern hemisphere humpback whale Breeding Stock D migrates annually approximately 8,500 km from their breeding grounds in north-west of Western Australia (WA) to their feeding grounds in the Antarctic Management Area IV6,7. In the 1960s, this stock was decimated to critically low numbers (<300 individuals) during the modern whaling era8. Since the moratorium of commercial whaling in 1982, the stock has recovered significantly, with estimated annual population increases of 8–12% between 1 Cetacean Research Unit, School of Veterinary and Life Sciences, Murdoch University, Murdoch, WA, Australia. Marine Mammal Research Program, Hawaii Institute of Marine Biology, University of Hawaii at Manoa, Kaneohe, Hawaii, United States. 3Centre for Sustainable Aquatic Ecosystems, Harry Butler Institute, Murdoch University, Murdoch, WA, Australia. 4Zoophysiology, Department of Bioscience, Faculty of Science and Technology, Aarhus University, Aarhus, Denmark. 5Greenland Climate Research Centre, Greenland Institute of Natural Resources, Nuuk, Greenland. 6Aarhus Institute of Advanced Studies, Høegh-Guldbergs Gade 6B, 8000, Aarhus, Denmark. Correspondence and requests for materials should be addressed to L.B. (email: ) 2 Scientific Reports | (2019) 9:771 | https://doi.org/10.1038/s41598-018-36870-7 1 www.nature.com/scientificreports/ Figure 1. Study sites. (A) Exmouth Gulf, Western Australia: a known humpback whale breeding/resting area. (B) Godthaabsfjord and Disko Bay, Greenland part of the West Greenland humpback whale feeding ground. The location of whale tagging events and acoustics logger deployments in Exmouth Gulf (Stations 1–4) are depicted. 2008 and 20129,10. In 2008, estimates of the population size ranged between 19,200–33,850 individuals9–11. The population recovery is hailed as a conservation success, and provides an example of management interventions that result in a positive outcome, creating hope and contributing to ‘ocean optimism’12. It has been suggested that available undisturbed breeding/resting habitat along the WA coastline may partly explain the high population growth rate measured in WA’s Stock D13, but little data exist to qualify this critical notion. Exmouth Gulf (Fig. 1) and environs on the WA coastline serves as a resting and breeding area likely needed for Stock D humpback whale mothers to nurse their calves to enable them to gain adequate energy reserves before their annual southern migration6,7,14. Specifically, Exmouth Gulf provides calm waters and protection from predators and from open oceanographic conditions during the prevailing south-easterly winds between August and November – coinciding with the peak number of whales in the Gulf during the southern migration6,13. However, Exmouth also serves as an important onshore location to support and accommodate the hydrocarbon extraction industry, which exploit large-scale deposits located to the north of the Gulf (i.e., the north-west shelf). 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 industry15. 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. Noise levels in marine environments worldwide have increased considerably in the past decades as a result of increased anthropogenic marine activities16,17. Noise pollution, largely produced by the shipping industry, is considered a major contributor to habitat degradation in the marine environment18,19. Detailed insights into the behaviour of humpback whale mothers and calves and the acoustic environment on breeding/resting grounds are important to better understand their biological and ecological requirements; and to inform management in a region slated for human activities that have potential adverse effect (...truncated)