It’s unquestionably one of our planet’s greatest conservation success stories – the comeback of the humpback whale (Megaptera novaeangliae) from the brink of extinction. And nowhere in the world is it so strongly evident as along the Western Australian coast.
The humpback is a species with a global distribution, but there are two geographically separate and genetically distinct populations – one in the Northern Hemisphere and one in the Southern Hemisphere. In winter, both migrate near coastlines towards calving grounds in warmer waters and return to polar feeding grounds each summer. And both were decimated by commercial whaling during the 20th century. In fact, by the mid-1960s, when whaling of humpbacks ended in WA waters, only a few hundred adults remained in the population that migrates annually along the state’s coast.
Today, WA’s humpback population could be well over 50,000, but no one is sure. The last accurate scientific estimate of the population was done by husband-and-wife whale researchers Curt and Micheline Jenner in 2008 using mainly aerial surveys, and was reported by them and others in the scientific literature two years later.
At that time – more than four decades after the cessation of whaling – the population that migrates along WA was reliably estimated by the Jenners to contain approximately 26,100 individuals and said to be increasing at an annual rate of about 11–12 per cent.
“So, the expectation is that they would have been increasing quite a lot since,” explains Professor Chandra Salgado Kent, an Edith Cowan University marine ecologist with expertise in bioacoustics.
“But we don’t know [exactly] how much, and we don’t know if they have reached their carrying capacity [the maximum population an environment can support].”
Whatever the real figure is now, there’s no question it has been a truly extraordinary outcome for such a long-lived species. Humpbacks have a potential lifespan of almost a century, with females capable, from the age of five to 10 years, of producing only a single calf every two to three years.
“We’re just waiting now to do the next round of aerial surveys,” Micheline says, explaining that should confirm the true extent of the comeback by WA’s humpbacks.
In the meantime, these whales have become so numerous off Australia’s west coast that the migratory route they take – up to 16,000km return – is known popularly as WA’s Humpback Highway, a term first coined by the Jenners in 1990. And that description certainly seems apt during the southward spring-summer migration; a constant stream of these marine mammals file past the coastline after breeding as they head for Antarctic feeding grounds.
“We now know humpbacks migrate from the Southern Ocean, where they feed and then travel up across that ocean and along the WA coastline all the way up to the Kimberley,” Chandra says. “As the population has grown, we increasingly have sightings further afield – we’re even getting sightings now off the Northern Territory, Indonesia and, recently, Christmas Island.”
Not all WA humpbacks travel the entire distance up to the Kimberley. But in the late 1990s the area was recognised as particularly significant for humpbacks when a winter-time nursery site for the species was identified by the Jenners at Camden Sound, about 300km north-east of Broome.
Their discovery ultimately led to the establishment of the Lalang-garram/Camden Sound Marine Park in 2012 to help preserve the crucial site. About a quarter of the park’s 7062sq.km total area protects a humpback nursery. And the humpbacks that arrive here each year are now recognised as the largest aggregation of the species seen anywhere in the world.
“But there’s evidence that humpback births are also occurring [further south], a lot of them off Exmouth as well,” Chandra says, adding that occasionally very young calves are now seen off the WA south coast, a long way from the Kimberley calving ground. “It seems that as the population is increasing, it needs to expand its calving areas.”
After giving birth in sheltered and safe waters, humpback mothers pause for a while, feeding and fattening their offspring, which are born with no blubber and need to build reserves of this crucial energy source for migration.
Humpback mothers then turn around, calves in tow, and head south to their Antarctic feeding grounds in the Southern Ocean – often attracting the attention of male escorts en route. A male hoping to mate can follow a female for up to two days, but usually only trails her for several hours.
“Females can come into postpartum oestrus within a month, so they can become pregnant within a month of giving birth,” Micheline explains. “Generally, they won’t – but the males will certainly give it a go!”
Females with calves will often resist the advances of males and fiercely defend their calves during any interactions. “There’s no long-term association between the males and females,” Micheline says. “The females have 10 to 11 months of gestation, and then they care for that calf for one further year. So, a female will invest two years into the life of her calf. But for the males it may only be hours – males just want to mate with as many females as they can across the season.”
It’s also now known that humpback mums take time during their southerly migration to pause at safe rest spots to feed and spell their calves. “Nursing females look for quiet spots where there is a lack of stimuli, so the calves aren’t revved up by males chasing females or each other,” Curt says.
There are many small, protected nooks and crannies along the Pilbara Coast where humpback mothers can rest with their calves while heading south. Exmouth Gulf, the gateway to Ningaloo Reef, and Shark Bay, more than 400km further south, are both renowned as resting spots for mothers and calves on their southerly migration.
The Jenners also believe Exmouth Gulf may be another important calving ground for the species. Curt explains that wintertime conditions in Exmouth Gulf are perfect in terms of temperature and protection for humpback mothers. So now, with expansion of the population post-whaling, it makes sense the area would be emerging as a significant calving area for the species.
“We think also that males go in there to find prospective females [for mating] as well,” Micheline adds.
Further south, the Geraldton coast and Abrolhos Islands also provide important rest areas for humpback mothers and calves, as do the waters between Perth and Rottnest Island. From there the next well-known resting location is Geographe Bay, more than 200km south of Perth. From around Cape Naturaliste they begin heading off into the Southern Ocean and then probably don’t stop until they reach Antarctica.
“The mums generally don’t eat [during] either all or most of the migration,” Chandra says. “Although we do have more and more evidence – a lot of it anecdotal – that there is some opportunistic foraging that occasionally happens. But it’s not the norm.”
And so, humpbacks feed almost exclusively in the Southern Ocean, mostly on small fish and tiny crustaceans known as krill. Whales filter this prey from the water using baleen plates in their mouths, which act as a sieve. These plates are made of keratin, the same protein found in human hair and nails, as well as in rhinoceros horns.
Survival skills
The phenomenal recovery of the humpback isn’t simply a consequence of the cessation of whaling, and not all species formerly targeted by commercial whaling have recovered as quickly or to such an extent.
“Humpbacks have done really well because they’re good at finding and exploiting small patches of prey in Antarctic waters,” says Curtin University Professor Robert McCauley, a marine scientist who has studied Australia’s west-coast whales for more than four decades.
Robert says their feeding success is largely due to their huge pectoral fins. Like the arms of bipedal terrestrial mammals, these stretch out from either side of the upper body and in adult humpbacks can reach lengths of more than 5m each. This is longer than in any other whale species and, in fact, longer than the appendages of any other animal, on land or at sea.
These huge pectoral fins make humpbacks particularly manoeuvrable in their ocean home, which helps them target prey. In contrast, many of their relatives – such as blue, fin and minke whales – have a more torpedo-shaped body with relatively stubby pectoral fins.
“Those whales have to target a patch of prey then come in at speed, open their mouths, then slow right up, take a gulp and accelerate back again,” Robert says.
“But the humpbacks, having those big pectoral fins, sit there and manoeuvre around to hoover everything up by just opening and closing their mouths continuously.”
Humpbacks are also often seen in Antarctic waters working cooperatively when feeding. In these instances, a lead animal is flanked by one or two others that catch krill coming out of its mouth as it feeds.
In addition to the cessation of whaling and a unique physiology, there’s another factor that has helped humpbacks bounce back so convincingly. It seems likely that a fair bit of the population’s cultural memory managed to survive the whaling years, and that has served WA’s humpbacks well.
“These whales tend to come back to the same areas, and we think there were small groups of humpbacks that didn’t get completely hunted out,” Robert says. “So, there was memory in the population, and they went back to those areas [they knew] so they could meet up and mate, and do all the things they need to do to breed.”
Other whale species
Although the recovery of the humpback has been a huge success story and it’s no longer considered endangered in this part of the world, it hasn’t been a similar story for other species hunted by commercial whalers in Australian waters. Notably, blue and southern right whales remain listed as endangered.
Blue whales (Balaenoptera musculus) have a global distribution, but Southern and Northern Hemisphere populations are separate. Two blue whale subspecies are found off WA: the Indo-Australian pygmy and the Antarctic blue whale. The term ‘pygmy’ is a bit of a misnomer because it’s still a massive mammal – adults grow to almost 25m in length and a weight of about 100 tonnes. Compared to its non-pygmy cousin, however, it’s certainly smaller. The Antarctic blue, on the other hand, is truly massive – bigger, in fact, than any other species that has ever lived on earth, including any dinosaur. It grows to almost 35m in length and a weight of about 200 tonnes.
Apart from the size difference, both these blue whale subspecies look very similar, especially when they’re glimpsed only fleetingly in the water. But researchers have identified differences in their songs, suggesting that the blue whales found in WA waters are mostly pygmy blues.
Indeed, all whale species have different calls or songs, so it’s easy to identify if they’re present in any particular body of water even if they can’t be seen. Whale songs can also be specific to populations from different regions, much like accents in humans.
The Antarctic blue whale populations that migrate through and stop in WA waters were also decimated by commercial whaling. However, unlike humpbacks, Antarctic blue whales haven’t bounced back nearly as well post-whaling. Antarctic blue whales are occasionally found in deeper waters off WA compared to humpbacks. Population estimates are uncertain but are of the order of 5000 or more animals worldwide, compared to approximately 350,000 pre-whaling.
In contrast, pygmy blue whales are regularly seen along the southern Australian, and particularly WA, coastline. “They travel as far north as the Banda Sea [almost 900km north-west of Darwin] in Indonesia, and between Indonesia and Timor-Leste,” Chandra says.
“We believe that’s an important calving area, but we’re not sure. Then they go back to the Southern Ocean as well to forage. But blue whales are a bit different [to humpbacks] in that they do feed opportunistically en route. And in some locations, that happens every single year while on migration.”
These stopping points are turning out to be so consistent that it’s thought blue whales may have regular feeding locations off the WA coast.
“One is on the other side of Rottnest, in the Perth Canyon. So, they come and might spend a few days to a few weeks foraging – depends on how much food is there – before moving on,” Chandra says.
“We think there’s probably another [foraging site] off Exmouth. We also think there’s perhaps some foraging that occurs off Scott Reef [near the edge of Australia’s continental shelf some 270km off the Kimberley coast]. And we have anecdotal evidence that they’re foraging off Timor-Leste.”
Blue whales are also known to regularly forage off the south-east Australian coast between Kangaroo Island and western Tasmania, an area known as the Bonney Upwelling, which is a notoriously rich and highly productive ocean site.
Robert describes some of the big whale species, such as the Antarctic blue, as “socially lost” post-whaling. By that, he means the population had a long-term loss of cultural knowledge at a population level due to whaling removing the larger experienced adults, and that may explain why they aren’t coming back nearly as strongly as the humpback.
“They don’t know where they are, what they’re going to do, how they find someone else [mates]…so it’s taking them a much longer time to recover,” Robert says.
Curt adds that the species was also illegally taken by “rogue Russian whalers” in the Southern Ocean, and then along the WA coast all the way up to Exmouth as late as the 1970s. “They’ve been hammered in terms of whaling for much longer – perhaps two decades more than the humpbacks have…so they haven’t recovered anywhere near as well,” he says.
The other large marine mammal often sighted off WA is the southern right whale (Eubalaena australis). Its name is quite literal and reflects a grim history – it was considered by whalers to be the ‘right’ whale to hunt. What made it so attractive to whalers is that it swims slower than other species and tends to float after death due to the high concentration of oil and baleen in its body, which made it relatively easy to harvest and handle for commercial processing.
While humpbacks and blue whales feed in Antarctic waters, southern rights feed primarily in subantarctic waters.
There are two subpopulations of the species – west and east coast – that migrate in Australian waters. The west coast population includes animals from SA waters west of Ceduna more than 500km west of Adelaide. The east coast animals occur east of Ceduna, and there are historical records of the species in the waters off all the eastern states.
The western population is far better understood and more intensively researched. An annual census of the west coast population indicates its numbers have been increasing, albeit slowly, post-whaling, which ceased in Australian waters for the southern right in the mid-1930s after the species was granted protection. The earliest documented signs of recovery in the population came in the 1980s, although the comeback has been frustratingly slow.
According to the latest National Recovery Plan for the species, published last year, the western population contains about 3200 animals and is growing at a rate of about 5.5 per cent. The eastern population contained just a few hundred animals post-whaling and has shown no signs of growth.
Southern rights used to be seen along the southern Australian coast in large numbers before commercial whaling and estimates of total numbers for the species were as high as 200,000. The most recent estimate for the combined Southern Hemisphere population is no more than 16,000 – less than 10 per cent of their pre-whaling abundance.
“But small groups survived, and they would go back to their natal beaches, the ones that the females were used to,” Robert says. “Those spots are showing recovery, and now we’re beginning to see a spillover effect. The Head of the Great Australian Bight is a good example, because now it gets to the point where it fills up [with southern rights]. So, then they start turning up in adjacent bays, and we’re seeing those now increase as well.”
The Head of the Bight is perhaps the best-known calving location for southern rights in SA waters, while Point Ann is the best-known off south-west WA.
“We’re seeing increasing numbers come up towards Perth and as far as Hillarys [Boat Harbour, about 20km north of Perth], although it’s only a few,” Chandra says. “And Geographe Bay is increasingly now being used as a calving area and by males looking for opportunities to mate.”
But Flinders Bay, just south of Augusta on the south-western coast of WA, is the area that’s been used more consistently for calving in this part of the species’ distribution.
“And along the southern coast of Western Australia there are other key aggregation locations,” Chandra says. These include Cheynes Beach east of Albany, the waters off Fitzgerald River National Park, and a calving area at Israelite Bay east of Esperance.
Recently, however, Chandra says there has been a “worrisome” and inexplicable slowing down of the species’ recovery. That undoubtedly relates to a concerning and so far unexplained recent feature of reproduction in WA’s southern rights: a shift in the calving rate. Southern rights normally calve every three years. “But now we’re seeing the females calve at three to five years,” Chandra says. “And we don’t know why.”
An uncertain future
Ongoing threats post-commercial whaling are huge for all species. Climate change is a big one, particularly because warming ocean waters can impact and reduce their prey. Coastal wind farms and other large constructions along whale migration routes are another emerging threat and source of potential conflict, although these are like a giant experiment in progress where we don’t know what will happen.
Entanglement in fishing apparatus is also a problem because it can lead to infections and physically restrict the animals’ movements and behaviours. Ship strikes are a potential issue for all whales, but for blue whales they’re particularly problematic because they can be slow to respond to a large ship’s presence.
“They either respond at the last minute or not at all,” Chandra says. “And there are a range of underwater noise impacts that can cause hearing impairment or [that can] stress or mask communications between whales.”
As the populations of these large whales grow, so does their interaction with humans, particularly in areas where human populations are also increasing. This too has led to heightened concerns about potential impacts.
Researchers are working hard to educate people to enjoy these huge marine creatures while also keeping their distance as their populations come back from the brink of extinction. It’s particularly critical in calving and resting areas for mothers and calves, where the mothers are trying to fatten and strengthen calves for the rigours of their Southern Ocean journey ahead of them.
Unnecessary stimulation does not help them; it’s recommended that boats stay at least 300m away from the front and back of a whale, and 100m from its sides. At least one study has shown a significant decrease in suckling rates of calves in response to loud underwater noises and boats that come too close.
“So, while it’s heartening to see the recovery story for humpbacks, there are other pressures that are increasing,” Chandra says. “And we certainly have our work cut out for us to ensure that we see the other species come back.”
