Humpback whales have been spotted ‘bubble-net feeding’ for the first time in Australia (and we have it on camera)


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Vanessa Pirotta, Macquarie UniversityIf you gaze at the ocean this winter, you might just be lucky enough to spot a whale migrating along Australia’s coastline. This is the start of whale season, when the gentle giants breed in the warm northern waters off Australia after feeding in Antarctica.

This north-south migration happens every year, but the whales can still surprise us. Thanks to a citizen scientist and his drone, humpback whales were seen feeding in a mass super group and “bubble-net feeding” off the New South Wales coast last year.

As my new research paper confirms, this a big deal for two reasons: it’s only the second time a super group of humpbacks has been observed in the southern hemisphere (a first for Australia) and the first time bubble-net feeding has been seen in Australia.

So what is bubble-net feeding, and why are these observations so important?

Blowing bubbles, catching krill

Bubble-net feeding is when whales deliberately blow bubbles from their noses to encircle their food — krill and fish — like a net, concentrating their prey into a tight ball. Then, the whale or group of whales swim together from beneath, rise to the surface opening their mouths, and gulp up their prey.

It remains a mystery as to why the whales feed in this way and how they learned to do it.

Drone footage of a super group of humpback whales, some of which are bubble-net feeding. Video: Brett Dixon.

2020 was a year full of unprecedented events, and the humpback whales certainly didn’t disappoint.

Humpback whales in this eastern Australian population are usually observed lunge feeding on their side, or feeding below the surface. Bubble-net feeding, on the other hand, is mostly documented in some Northern Hemisphere populations.




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But we know there are individual whales in the eastern Australian humpback population who bubble-net feed in Antarctic waters. This means the unique behaviour in Australian waters may have evolved independently, or through cultural transmission (learning new behaviours from different whales).

The drone footage and observations made in September from whale-watching boats was the first to document bubble-net feeding. To add to the excitement, citizen scientists also documented bubble-net feeding behaviour further south of Tasmania a month later.

Drone footage captures humpback whales feeding in large numbers off the New South Wales coast.
Brett Dixon

Using stills from the September drone footage, an estimated 33 humpback whales can be seen feeding at the same time. Unfortunately, it’s not known exactly what the whales were feeding on.

Until then, humpback whale congregations this large had never been observed in Australian waters.

In fact, the only other time a mass humpback feeding event has been seen in the Southern Hemisphere was off South Africa in 2011 (this now occurs regularly there). This was the first time the term “super group” was used to describe a group of 20 or more whales feeding this way.

Humpback whale rising up in the middle of a visible bubble-net to engulf its prey.
Jessica Millar/Sapphire Coastal Adventures

But why were they feeding in ‘breeding waters’ anyway?

The majority of the east Australian humpback whale population spends the summer months feeding in Antarctic waters. They then head north to warm breeding waters in the Great Barrier Reef during winter (June-August) to mate and give birth.




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They forego feeding for love — humpbacks can go for months without eating, relying instead on energy reserves in order to reproduce. Animals that do this are called capital breeders.

From August to November, humpbacks migrate southward back to Antarctica. Along the way, they sometimes take a “pit-stop” on parts of Australia’s east coast to feed.

It was originally thought this population never fed along the migratory route. However, we know they do now to possibly supplement their energy intake as they migrate.

Humpback whales migrate along the east coast of Australia annually for warmer breeding waters in the Great Barrier Reef.
Dr Vanessa Pirotta

So why are these observations important?

Whales play important an important role in the ecosystem of the ocean because they feed in one area and poo in another.

This action — known as the “whale pump” — moves nutrients around the ocean. Their poo feeds tiny organisms, such as plankton, which are eaten by krill, and then eaten by whales.

Seeing these super group feedings highlights changes in our marine environment we might not have otherwise been aware of.

Bubble net feeding in Antarctica.

One possible explanation for this behaviour could be favourable environmental conditions. A combination of ideal water temperatures and nutrients may have resulted in an abundance of food, which saw large numbers of humpback whales feeding in the same area.

Or perhaps it has something to do with the recovery of the east coast humpback whale population, which has been increasing in numbers since whaling ended in the 1960s.

Humpback whales engulfing their prey after bubble-net feeding cooperatively off the New South Wales coast.
Wayne Reynolds/Sapphire Coastal Adventures

Regardless, it’s important to understand how changes in the marine environment influence the extent humpback whales depend on feeding opportunities along their migratory route.

This will help to predict how whale populations respond to future changes in the ocean. This includes climate change, which will warm ocean temperatures and alter when and where the prey of humpback whales are found. As a result, humpback whales will also move to different locations.

One thing, at least, is abundantly clear: more eyes on land and sea through citizen science will provide a valuable opportunity to document such exciting future events. So keep your eyes peeled for whales this season, and be sure to tell a scientist if you see something unexpected.




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The Conversation


Vanessa Pirotta, Wildlife scientist, Macquarie University

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Humpback whales may have bounced back from near-extinction, but it’s too soon to declare them safe


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Olaf Meynecke, Griffith UniversityThe resurgence in humpback whale populations over the past five decades is hailed as one of the great success stories of global conservation. And right now, the federal Department of Agriculture, Water and the Environment is considering removing the species from Australia’s threatened list.

But humpback whales face new and emerging threats, including climate change. Surveying whales is notoriously hard, and the government has not announced monitoring plans to ensure humpback populations remain strong after delisting. We need a plan to keep them safe.

Australia’s whale season is about to begin. Each year between May and November, the mammals migrate north along Australia’s coastline from their feeding grounds in Antarctica to warmer waters. There, they breed before returning south.

So now’s a good time to take a closer look at the status of this iconic, charismatic species.

A pod of humpback whales lunge feeding.
The resurgence of humpback whales is one of conservation’s greatest success stories.
Shutterstock

A host of threats

Humpback whales live in every ocean in the world, and have one of the longest migrations of any mammal.

Humpback whale numbers dwindled as a result of commercial whaling, which in Australia began in the late 18th Century. Whaling and the export of whale products was Australia’s first primary industry. Between 1949 and 1962 Australia’s whalers killed about 8,300 humpback whales off the east coast, until only a few hundred were left.

The International Whaling Commission banned humpback whaling in the Southern Hemisphere in 1963. By then, humpback populations had fallen to about 5% of pre-whaling numbers. In the years since, some whaling continued, but has now largely ceased.

Today humpback whales face new threats. These include:

  • underwater noise which interferes with whale communication
  • pollution
  • vehicle collisions
  • getting caught in fishing gear
  • over-harvesting prey such as krill
  • marine debris
  • habitat degradation
  • climate change.

In particular, the effects of climate change – such as warming waters, shifting currents and ocean acidification – may affect the availability of prey that humpback whales need to survive.

Combined, these worsening threats could disrupt humpback whales’ recent resurgence. Indeed, under one scenario, scientists predict the increase Australia’s humpback numbers could stall — or worse, start declining – in the next five to ten years.




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A humpback whale calf caught in a fishing net.
A humpback whale calf caught in a fishing net.
SeaPix, Author provided

The humpback whales’ plight

According to the federal government’s delisting assessment, humpback whales’ strong recovery suggests current threats are not a risk to the population. But this assessment has shortcomings.

It states humpback whales on Australia’s east and west coast have reached, or are exceeding, the original population size – increasing by 10-11% a year over the past decade or longer.

But this information is based on models using data collected prior 2010 for Australia’s west coast, and prior to 2015 for the east coast. This data isn’t readily available to the public and does not include recent population trends.

The predicted population growth from these models doesn’t account for current and future impacts from major threats, including climate change. This is despite recent research and observations suggesting changes in the humpback population.

For example, 2019 research showed potential shifts in calving locations, with newborn humpback whales now frequently spotted outside Australian tropical waters. This — along with the early arrival of migrating humpback whales in Australia in the past years — may be a first sign of changes in breeding and migration habits.

It’s also important to compare humpback whale populations in Australia with those elsewhere, such as in the North Pacific. There, calving rates are declining, and whale abundance and distribution is showing marked shifts. The risk of entanglements with fishing gear is also rising.




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How climate change is reducing numbers of humpback whale calves in the north-west Atlantic


A whale tail with a fishing line caught in it
Whales can get caught in fishing gear.
Todd Burrows, Author provided

The problem with counting whales

The pre-whaling population size of humpback whales on the east and west coast of Australia is thought to be between 40,000 and 60,000. But information is limited and the actual number may have been much higher

Today, the estimated numbers from population models are similar: roughly 28,000 on the east cost and up to 30,000 on the west coast. But counting humpback whales accurately is very difficult. For example, on the east coast of Australia humpback whales frequently move between populations and during a census may not be attributed to their original population.

What’s more, conditions prior to whaling are not comparable with today’s conditions. Krill is a major food source for whales, and widespread whaling in the Southern Hemisphere caused krill numbers to increase. Research from 2019 suggests humpback whales’ fast recovery after whaling ceased may have been due to widely available krill.

But krill numbers have declined or their availability has shortened in recent years due to threats such as climate change and industrial fishing.




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Humpback whales have been spotted in a Kakadu river. So in a fight with a crocodile, who would win?


Aerial view of humpback under icy water .
Every year humpback whales migrate from Antarctica where they feed, to breed in Australia.
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Proceed with caution

Humpback whales off Australia’s coast will continue to have some protection under the Environment Protection and Biodiversity Conservation Act, even if they’re taken off the threatened species list.

Generally, all marine mammals are protected in Australian waters. But getting delisted means fewer resources devoted to their protection.

Forecasting the complex interactions of today’s threats, in order to predict tomorrow’s humpback whale populations, is challenging. A cautionary approach should therefore be taken.

In 2016, the US delisted some humpback whale populations. But before doing so, it established a ten-year monitoring plan to track population changes, threats and species abundance.

If Australia proceeds with the delisting, it should follow the US’ lead. Humpback whales should remain listed for another five years so a monitoring plan can be developed. Federal and state governments must invest resources into this process, and react swiftly if changes are detected.

A number of whale researchers and organisations concerned about the humpback whale delisting, including the author, prepared a detailed response to the proposal here.The Conversation

Olaf Meynecke, Research Fellow in Marine Science, Griffith University

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Humpback whales have been spotted in a Kakadu river. So in a fight with a crocodile, who would win?



Northern Territory Government

Vanessa Pirotta, Macquarie University

In recent months, three humpback whales were spotted in the East Alligator River in the Northern Territory’s Kakadu National Park. Contrary to its name, the river is full of not alligators but crocodiles. And its shallow waters are no place for a whale the size of a bus.

It was the first time humpback whales had been recorded in the river, and the story made international headlines. In recent days, one whale was spotted near the mouth of the river and scientists are watching it closely.

The whales’ strange detour threw up many questions. How did they end up in the river? What would they eat? Would they get stuck on the muddy river bank?

And of course, there was one big question I was repeatedly asked: in an encounter between a crocodile and a humpback whale, which animal would win?

A crocodile partially submerged in a river
The whales swam into a crocodile-infested river.
Dean Lewins/AAP

Scientists double-take

The humpback whales were first spotted in September this year by marine ecologist Jason Fowler and fellow scientists, during a fishing trip. Fowler told the ABC:

I noticed a big spout, a big blow on the horizon and I thought that’s a big dolphin … We were madly arguing with each other about what we were actually seeing. After four hours of raging debate we agreed we were looking at humpback whales in a river.

The whales had swum about 20 kilometres upstream. Fowler photographed the humpback whales’ dorsal fins as evidence, and reported the unusual sighting to authorities and scientists.

Thankfully, two whales returned to sea on their own, leaving just one in need of help. There was concern it might become stranded in the shallow, murky tidal waters. If this happened, it might be attacked by crocodiles – more on this in a minute.




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Experts considered a variety of tactics to encourage the whale back out to sea. These included physical barriers such as nets or boats, and playing the sounds of killer whales – known predators of humpback whales.

But none of these these options was needed. After 17 days, the last whale swam back to sea on its own.

The whale that spent two weeks in the river has recently returned and been spotted swimming around the mouth of the river. It appears to have lost weight – most likely the result of migration. It is now being monitored nearby in Van Diemen Gulf.

Questions are now being raised about the health of the animal, and why it has not headed south for Antarctic feedings waters.

A humpback whale that spent two weeks in the East Alligator River has recently been spotted nearby.
Dr Carol Palmer

So why were whales in the river?

The whales are part of Australia’s west coast humpback whale population, which each year travels from cold feeding waters off Antarctica to warm waters in the Kimberley to breed.

There are various theories as to why they swam into the East Alligator River. Humpback whales are extremely curious, and may have entered the river to explore the area.

Alternatively, they may have made a navigation error – also the possible reason behind September’s mass stranding of pilot whales in Tasmania.

And the big question – what about the crocs?

Long-term, a humpback whale’s chances of surviving in the East Alligator River are slim. The lower salinity level may cause them skin problems, and they may become stranded in the shallow waters – unable to move off the muddy bank. Here the animal might die from overheating, or its organs may be crushed by the weight of its body. Or, of course, the whale may be attacked by crocodiles.

In this case, my bet would be on the whale – if it was in relatively good condition and could swim well. Humpback whales are incredible powerful creatures. One flick of their large tail would often be enough to send a crocodile away.




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If a croc bit a whale, their teeth would likely penetrate the whale’s skin and thick blubber. But it would take a lot more to do serious harm. Whale skin has been shown to heal after traumatic events, including the case of a humpback whale cut by a boat propeller in Sydney 20 years ago. Dubbed Bladerunner, it survived but still bears deep scars.

Humpback whales are very large and powerful. One flick of their tail could send a crocodile away.
Dr Vanessa Pirotta

What next?

The whale sighting continues to fascinate experts. Scientists are hoping to take poo samples from the whale in Van Diemen Gulf, and could also collect whale snot to learn more about its health. However, the best case scenario would be to see the whale swim willingly to offshore waters.

This unusual tale will no doubt go down in Australian whale history. If nothing else, it reminds us of the vulnerability – and resilience – of these marine giants.


The author would like to thank Northern Territory Government whale expert Dr Carol Palmer for her assistance with this article.The Conversation

Vanessa Pirotta, Wildlife scientist, Macquarie University

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Whale of a problem: why do humpback whales protect other species from attack?


Tracey Rogers, UNSW Australia

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.

You can see the drama unfold as the humpbacks fend off the killer whales.

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?

You scratch my back…

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?

Killer whales are a dangerous predator but they pose little threat to an adult humpback whale.

Spillover

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.

The Conversation

Tracey Rogers, Associate Professor Evolution & Ecology, UNSW Australia

This article was originally published on The Conversation. Read the original article.