Biology and Ecology
Feeding
Humpback whales in the Southern Hemisphere feed primarily on krill, small shrimp-like crustaceans that are highly abundant in the waters around Antarctica10. Populations in the Northern Hemisphere feed on a variety of prey, including many different species of small shoaling fishes, such as anchovies, herring, sand lance, and sardines1,11. Humpback whales use a range of feeding strategies, including lunge feeding and bubble netting, a process in which whales either singly or cooperatively blow a circle of bubbles from under water in order to create a wall or curtain of bubbles that traps small schooling fish and makes them easier to capture in a single lunging gulp through the centre of the bubble curtain12,13. Humpback whales need to feed intensively throughout the summer and autumn, as they generally fast during migration and on the breeding grounds and rely on fat reserves for energy during those months. However, there is mounting evidence that at least some individuals engage in opportunistic feeding during migration or at lower latitudes associated with breeding habitat.14-16 There is also evidence that at least some individuals from some populations forego migration altogether in some years and remain on feeding grounds throughout the winter months. Shifts in ocean productivity, probably a result of climate change, have almost certainly played a role in some of the recently observed changes or anomalies in migration patterns and feeding grounds14,17. The non-migratory population of humpback whales in the Arabian Sea, probably split from other humpback whale populations in the Indian Ocean roughly 70,000 years ago18 , process most likely facilitated by the seasonal upwelling of cold, nutrient rich waters, creating feeding opportunities in the same areas that are suitable for mating, calving, and nursing.
Reproduction
Humpback whales mate primarily on their breeding grounds in the tropics in the “wi nter months” (July-October in the Southern Hemisphere and December-March in the Northern Hemisphere). A pregnant female swims thousands of kilometers to nutrient-rich temperate or polar feeding grounds to gain sufficient strength and body mass for successful birth and lactation by feeding intensively for several months. Pregnant females usually arrive earlier than males, non-pregnant females and juveniles. Then she returns to the breeding ground to give birth after a gestation period of approximately 11.5 months3. Mothers and calves generally remain in shallow, sheltered waters19 where the calf nurses and gains the weight and strength required to migrate back to the feeding grounds. Males on the breeding ground engage in aggressive competitive behaviours to gain access to females20, and also produce long complex songs, with all males in the population singing roughly the same song, but slowly changing it over the course of a breeding season21.
Research, threats and conservation
Research
Much of what we know about humpback whales today has been learned through photo-identification studies, in which individual whales are photographed and recognized over time by the unique serrations and patterns on the trailing edges and undersides of their tail flukes. In well-studied populations, such as the feeding grounds in Alaska and the Gulf of Maine, some individual whales have been monitored for over 40 years22. Technologies like genetic sampling and satellite telemetry (the attachment of small devices that send the whales’ GPS position to satellite receivers) allow researchers to track whales’ movements and gain more insight into their (seasonal) migrations and fine-scale use of habitat on the breeding grounds and feeding grounds23. More information about research techniques used to study whales and dolphins can be found here.
Threats
Natural Predators: Humpback whales often bear rake-like scars on their bodies indicating that they survived an attack by killer whales. Some researchers have proposed that the threat of killer whale attacks, particularly on vulnerable calves, has an important influence on humpback whale behaviour and migration24-26. Large sharks are also potential predators of this species, especially of very young calves27.
Human-induced threats: Humpback whales may be at risk from a number of threats, including entanglement in fishing gear, ship strikes, habitat degradation, oil and gas development and climate change17. The significance of the impacts of these threats vary across populations. Those populations that are small or that have a restricted range, such as the endangered Arabian Sea population,7 are of particular concern.
Conservation status
Many populations of humpback whales were heavily hunted through the 1960’s, when Soviet whaling operations were still catching humpback whales in the Southern Oceans, the Pacific and the Arabian Sea despite an IWC agreement to stop hunting this species from 1963 onward28-30. The majority of humpback whale populations are recovering well – for example, the recent IWC assessment of Southern Hemisphere humpback whales estimated that overall numbers were at around 70% of the number of whales thought to be in the Southern Hemisphere before hunting began. Globally the species was moved from a status of Vulnerable to Least Concern by the IUCN Redlist of Threatened Species31. However, it is under Appendix 1 of the Convention on Migratory Species (CMS), and certain (sub)populations, such as that in the Arabian Sea, are considered endangered by, IUCN7, the United States Endangered Species Act (ESA)32, and the IWC33.
Humpback whales are still hunted in very small numbers under aboriginal subsistence whaling permits and conservative and sustainable quotas are set by the IWC in Greenland and St. Vincent and the Grenadines. There may also be some small-scale hunting of humpback whales around the island of Pagalu in the Gulf of Guinea, but no recent information is available.
Humpback whales and whale watching
Please see the IWC Whalewatching Handbook