A group of killer whales are on the hunt. They work together to submerge and drown a whale calf. But then more whales appear.
The newly arrived humpbacks bellow a trumpet-like call, and wield their five-metre-long pectoral flippers like swords against the prowling killer whales.
The killer whales are driven away from the calf, and the humpbacks also move away. As they do, the killer whales turn back and descend on the calf once more. In response, the humpbacks swing around and return to the calf’s defence.
The humpbacks position themselves close to the calf, between it and the killer whales, potentially putting themselves in harm’s way.
This process continues and repeats for many hours, but it is not a calf of their own species, it is a grey whale calf.
This is not an isolated case. Robert Pitman, from the National Oceanic and Atmospheric Administration in the US, and his colleagues report more than 100 incidents where humpback whales have approached or actively intervened in killer whale hunting attempts.
Surprisingly, most of these have been predation attempts on other species, such as seals, other whales or even fish.
The question is: why would these humpback whales place themselves in danger by interposing themselves between one of their few predators – killer whales – and an individual of an entirely different species?
Altruistic behaviour is some of the most difficult to explain in evolutionary terms. In a biological context, altruism refers to cases where one individual’s behaviour provides a benefit to another individual at a cost to itself.
It doesn’t need to be as dramatic as throwing themselves on a grenade, but even placing themselves at a small disadvantage could jeopardise their chances of surviving and reproducing.
And if they don’t reproduce, then neither do the genes that encouraged the individual to be altruistic. This is why – all else being equal – you would expect altruistic genes to slowly disappear from a population over multiple generations.
But there are cases of altruistic behaviour in nature, particularly among closely related groups. One example is an individual meerkat who calls to alert its group to the presence of a predator, particularly as that call could make the predator more likely to notice the vigilant meerkat.
This kind of behaviour can evolve and remain stable in a population due to a process called kin selection. This is because the meerkat is closely related to the other members of its group, so it shares many genes with them. Even if it does end up sacrificing itself, if it helps its relatives survive, they may also be carrying the genes that encourage altruism.
Other cases of altruism in nature are supported by recriprocation: you scratch my back and I’ll scratch yours.
An example would be vampire bats that share blood meals. They do so on the assumption that their friend will return the favour at some later date.
However, for kin selection or reciprocal altruism to evolve, there needs to be a high level of social cohesion within the group.
For example, individuals need to be able to recognise who is a relative or a friend, and who is not. Presumably, you are less likely to put your neck on the line for a distant relative or for someone who is not likely to repay the favour.
So it might not be surprising that a humpback mother would vigorously defend her own calf from attacking killer whales. But why would a humpback approach and position itself between attacking killer whales and another whale’s calf?
As mentioned above, if an individual is prone to behave in a way that reduces their chance of surviving and reproducing, we would expect the genes that promote that behaviour to dwindle over generations and eventually vanish from the population. And even if an adult humpback puts itself at minimal risk by interfering with killer whales, minimal risk is more than zero risk by avoiding them altogether.
Pitman and his colleagues think there might be more social cohesion among humpbacks than we previously thought, and kin selection and/or reciprocal altruism could be playing a part.
Individual humpback whales return to the same region to breed. This means that there is a good possibility that humpbacks are related to their immediate neighbours. Pitman suggests this means it may be worth a humpback helping other humpbacks to protect their calves from killer whale attacks.
However, it is trickier to explain apparent altruism directed towards other species. Pitman and his colleagues explain that for the humpback whale, this intervention on behalf of other species is a “spillover” behaviour. They suggest it is an extension of the humpback whales’ “drive” to protect their own calves.
Humpbacks may have learned to respond to vocalisations of attacking killer whales, which trigger them to drive the killer whales away, regardless of the species being attacked.
If this tendency to drive away killer whales whenever they are attacking has helped humpbacks to protect their own calves, then the genes that promote it could be maintained in the population, even if other species benefit at times.
This interspecies altruistic behaviour may be “inadvertent” altruism – it can be altruism in the individual case but it is ultimately driven by self-interest.
When it comes to conservation, good news is pretty thin on the ground – and the ocean, for that matter. We have grown much more used to hearing about marine species that face extinction, decline or negative impacts than about those that are thriving. But if we are to avoid getting demoralised, conservation biology needs victories to celebrate.
So here’s one: the remarkable recovery of humpback whales that breed in Australian waters. Our review of the available data, published today in Marine Policy, suggests that humpback whale populations in Australian waters have recovered to the extent that we should consider downlisting them from the official list of threatened species.
The humpback whale should be a cause for optimism and hope. It’s an important counterbalance to the seemingly relentless communication of marine conservation problems with little in the way of good news. We hope this kind of optimism will convince politicians and the public that conservation problems can indeed be solved, and to stay dedicated to making that happen.
Australia has one of the highest rates of species extinction in the world. But despite this, the past decade has seen rare examples of animals that are rebounding and thriving.
Humpback whales are one such example. They are listed as “vulnerable” on Australia’s official list of threatened species, under the Environment Protection and Biodiversity Conservation (EPBC) Act.
But our review, led by Michelle Bejder of BMT Oceanica and based on the best available scientific data, suggests that humpback whales no longer need to be on the EPBC Act’s Threatened Species list. Both the east and west Australia populations of humpback whales have recovered substantially from the damage done in the commercial whaling era (roughly from 1912 to 1972).
As of 2012, Australia’s east coast humpback population was at 63% of the pre-whaling-era level. The west coast population had bounced back to 90%. Australian humpback whale populations are increasing at remarkable rates: 9% a year for the west coast population and 10% a year for the east coast – the fastest documented increases worldwide.
A recent global assessment of humpback whales suggested that nine populations from around the world (including the east and west Australian populations) are no longer at risk of extinction. This is to be expected when exploitation through commercial whaling is replaced with conservation legislation (both in Australia and worldwide). Though we don’t quite fully understand the biological forces driving this extraordinary population increase, it’s fair to say that the removal of the dominant negative human pressure has been a huge factor.
We believe that conservation biologists have a responsibility to protect species that are in peril by providing a sound, scientific basis for effective management. It therefore follows that we also have a responsibility to present information on recovering populations. The listing of threatened species under the EPBC Act is a dynamic process that is periodically assessed to determine the most appropriate management actions – so if species no longer needs to be on the list we should say so.
The future challenge will be to protect a marine environment that contains growing humpback whale populations and to develop alternative approaches to ecological sustainability. The history of environmental protection is based on saving depleted species, with very little guidance on how to manage recovering and recovered ones.
If humpback whales are downlisted from the threatened species list, the EPBC Act would still protect them from significant impacts because migratory species are deemed under the Act to be nationally significant. Beyond Australia, the International Whaling Commission manages the global moratorium on commercial whaling, which is essential for the humpback whales’ recovery to continue.
Management efforts must now balance the need to ensure humpback whale growth and recovery within a marine environment that is also expanding with industrial and exploration activities. There will be increases in interactions with ocean users, including acoustic disturbance from noise, collisions with vessels, entanglements in fishing gear, habitat destruction from coastal development, and interactions with the whale-watching industry. It will be vital to gain public support to help maintain the growth and recovery of Australian humpback whales and prevent future population declines.
The recovered humpback whale population could bring a positive shift in scientific research throughout Australia. If Australian humpback whales are removed from the list of threatened species, one of the most beneficial consequences could be the reprioritisation of research and funding to support other species that are at a greater risk.
Hopefully, other animal species such as the threatened blue whale, the understudied Australian snubfin and Australian humpback dolphins might get the same chance of scientific scrutiny that has been afforded to humpback whales.
For the first time in more than a generation, Australia’s iconic humpback whales have become a symbol of both hope and optimism for marine conservation, providing a unique opportunity to celebrate successful scientific and management actions that protect marine species. Optimism in conservation biology (which even has its own social media hashtag, #OceanOptimism) is essential to encourage politicians and the public to solve conservation problems.
Around the world, many marine mammal populations remain in peril, and conservation biologists should not detract from these cases. But we should still highlight the successes, as they provide hope that ongoing conservation actions can prevail. Ultimately, inspirational examples such as humpback whales can motivate people to use ocean resources wisely and to take sustainable and effective actions to safeguard marine wildlife for the future.
Lars Bejder is Professor, Cetacean Research Unit, Murdoch University at Murdoch University.
Ari Friedlaender is Associate Professor, Marine Mammal Institute at Oregon State University.
David Johnston is Assistant Professor, Marine Conservation Ecology at Duke University.
Joshua Smith is Postdoctoral Researcher at Murdoch University.