8.3.7 Humpback whales

Individuals in the eastern Australian subpopulation of humpback whales typically migrate from feeding areas in the Southern Ocean along the east coast of Australia to breed in the Region. Prior to exploitation, the eastern subpopulation comprised an estimated 26,000 whales 2134 but whaling had reduced the subpopulation to 200 to 500 whales in 1962.2135 The population was estimated to consist of more than 24,000 whales in 2015, comparable to estimates of the pre-whaling population, and it continues to grow at a rapid rate.504 The recovery of humpback whales has been assisted by having little competition for food with other whale species whose populations were also historically depleted. 

Humpback whales have recovered to pre-whaling levels

A humpback whale sticking its head out of the water to take a breath of air. There are mountains in the background and some clouds amid a blue sky.
Humpback whale taking a breath off the coast of Lucinda. © Connie Rowe 2023

The influence of climate variability on humpbacks in the Southern Hemisphere is under-studied.501 However, some breeding habitats are predicted to become unsuitably warm by the end of this century.2136 Climate-related changes to prey supply may also result in calving occurring further south.2137 Generally, baleen whale populations are predicted to decline by the year 2100 because of increasing inter-specific competition 2138  and because ocean acidification, warming and sea ice dynamics are reducing habitat for krill development.2139

Declines in reproductive success have been associated with environmental conditions generating insufficient prey to support the energy demands for pregnancy and lactation in some Northern Hemisphere humpback whale populations.2140 Timing of migrations has also shifted in response to earlier ice break and increases in sea surface temperature.2141 The resilience of humpback whales to ongoing climate change depends on behavioural adaptability in terms of diet and movements. 

Local-scale threats to humpback whales include the risk of vessel strike, which is increasing as more vessels and whales share the water of the Marine Park.506 Humpback whales’ abundance in coastal waters makes them prone to injury or mortality from entanglement in fishing equipment, shark nets and marine debris. Underwater vessel noise can cause behavioural disturbance in humpback whales: simulated loud boat noise has been shown to increase swim speeds and respiration rates in individual animals.2142 Habitat degradation, including from coastal development, may become a greater issue as humpback whale and human populations grow. 

Management

Since whaling was banned, other management initiatives have included establishing best-practice guidelines for whale watching, researching gear modification, spatial closures and using whale alarms to reduce entanglement.2138 As the population increases and climate changes, ongoing monitoring will be required to assess the future risk to humpback whales from marine activities, coastal development and changes to prey communities.

Humpback whales are a matter of national environmental significance under the EPBC Act because they are protected as Cetaceans and are a listed migratory species under the Bonn Convention. In 2021, the humpback whale was removed from the vulnerable list under the Nature Conservation (Animals) Regulation 2020 (Qld) and is now considered least concern. The Operational Policy on Whale and Dolphin Conservation in the Great Barrier Reef Marine Park complements measures outlined in Queensland’s Nature Conservation (Whale and Dolphin) Conservation Plan 1997 to further address the risks to whales.

Evidence for recovery or decline 

After decades of whaling reduced the population to possibly as few as 200 individuals by the early 1960s, the eastern Australia humpback whale population has since recovered to its pre-whaling levels. The population size was estimated to be approximately 24,000 whales in 2015,504 and the growth rate was estimated growth rate to be 10 to 11 per cent per year (close to the maximum plausible rate of increase of 11.8 per cent).2143 The population may have increased to a projected 40,000 animals and is predicted to reach carrying capacity by 2026.504 Humpback whales exhibit the strongest recovery of all whale species and, as a result, were removed from Australia’s threatened species list in 2022.505

  • 501. Meynecke, J., De Bie, J., Barraqueta, J.M., Seyboth, E., Dey, S.P., et al. 2021, The role of environmental drivers in humpback whale distribution, movement and behavior: A review, Frontiers in Marine Science 8: 720774.
  • 504. Noad, M.J., Kniest, E. and Dunlop, R.A. 2019, Boom to bust? Implications for the continued rapid growth of the eastern Australian humpback whale population despite recovery, Population Ecology 61(2): 198-209.
  • 505. Threatened Species Scientific Committee 2022, Listing advice – Megaptera novaeangliae – humpback whale, Department of Agriculture, Water and Environment, Canberra.
  • 506. Smith, J.N., Kelly, N., Childerhouse, S., Redfern, J.V., Moore, T.J., et al. 2020, Quantifying ship strike risk to breeding whales in a multiple-use marine park: the Great Barrier Reef, Frontiers in Marine Science 7: 67.
  • 2134. International Whaling Commission 2015, Annex H: Report of the sub-committee on other southern hemisphere whale stocks, Journal of Cetacean Research and Management 16: 214-232.
  • 2135. Chittleborough, R.G. 1965, Dynamics of two populations of the humpback whale, Megaptera novaeangliae (Borowski), Australian Journal of Marine and Freshwater Research 16(1): 33-128.
  • 2136. Derville, S., Torres, L.G., Albertson, R., Andrews, O., Baker, C.S., et al. 2019, Whales in warming water: Assessing breeding habitat diversity and adaptability in Oceania's changing climate, Global Change Biology 25(4): 1466-1481.
  • 2137. Torre-Williams, L., Martinez, E., Meynecke, J.O., Reinke, J. and Stockin, K.A. 2019, Presence of newborn humpback whale (Megaptera novaeangliae) calves in Gold Coast Bay, Australia, Marine and Freshwater Behaviour and Physiology 52(5): 199-216.
  • 2138. Tulloch, V.J., Plagányi, ÉE., Brown, C., Richardson, A.J. and Matear, R. 2019, Future recovery of baleen whales is imperiled by climate change, Global Change Biology 25(4): 1263-1281.
  • 2139. Cavanagh, R.D., Melbourne-Thomas, J., Grant, S.M., Barnes, D.K.A., Hughes, K.A., et al. 2021, Future Risk for Southern Ocean Ecosystem Services Under Climate Change, Frontiers in Marine Science 7.
  • 2140. Kershaw, J.L., Ramp, C.A., Sears, R., Plourde, S., Brosset, P., et al. 2021, Declining reproductive success in the Gulf of St. Lawrence’s humpback whales (Megaptera novaeangliae) reflects ecosystem shifts on their feeding grounds, Global Change Biology 27(5): 1027-1041.
  • 2141. Ramp, C., Delarue, J., Palsbøll, P.J., Sears, R. and Hammond, P.S. 2015, Adapting to a Warmer Ocean—Seasonal Shift of Baleen Whale Movements over Three Decades, PloS One 10(3): e0121374.
  • 2142. Sprogis, K.R., Videsen, S. and Madsen, P.T. 2020, Vessel noise levels drive behavioural responses of humpback whales with implications for whale-watching, eLife 9: e56760.
  • 2143. Zerbini, A.N., Clapham, P.J. and Wade, P.R. 2010, Assessing plausible rates of population growth in humpback whales from life-history data, Marine Biology 157(6): 1225-1236.