I’m in mid-water, surrounded by a vast undersea forest. I move to the edge of the kelp, wrap both hands around a thick stipe and hang like an amphibious monkey, staring out into the great blue-green abyss of False Bay. It’s winter, so the visibility is good, but I am on my own and I don’t feel safe outside the kelp. For most surfers and divers along South Africa’s most southerly coast, going into the water holds a certain edge, and visions of black fins and torpedo-shaped shadows dance menacingly at the fringes of one’s imagination. This is the kingdom of one of the largest populations of white sharks on the planet and even after 10 years of regular diving, for me primal terrors die hard. But somehow, on this particular dive, the ocean feels more benign. Perhaps it’s because my rational mind is in on a not-so-secret secret: there’s a new ruler in the bay and multiple rows of razor-sharp teeth don’t scare it.
For decades, this part of the coast has been an energy-rich haven for white sharks. In winter they feed on healthy populations of naive Cape fur seal pups and in summer they move inshore to feast on shoals of migrating yellowtail fish. Similar patterns have been observed 100 kilometres (62 miles) away at the ‘sharkdom’ of Gansbaai on the Overberg coast. For cage-diving operators, winter should be the season of plenty with good visibility, an abundance of white sharks and boatfuls of clients, but this season there was hardly a shark to be seen and one company was forced to close down.
What would cause the uncontested king of South Africa’s marine food chain to vanish from his well-established territory? To answer that we need to return to the scene of a series of grisly discoveries made by shark researchers along the Overberg coast.
The first clue that something was amiss for the white sharks at Gansbaai was the carcass of a 2.7-metre (9-foot) female that washed ashore on 9 February 2017. Researcher Alison Towner and a team from the Dyer Island Conservation Trust (DICT) found nothing conclusive. The animal was completely intact, with just a couple of scratches around its head, and there were no obvious signs of what might have killed it. Even more extraordinary was the fact that every other shark in the area left the bay and did not return for more than three weeks. South African officials refused to grant permission for a more in-depth necropsy and for the next three months the death of the small female and the departure of the others from their kingdom remained a mystery.
Then, at 8 am on 3 May 2017, Towner and the DICT team responded to a call about a large white shark that had washed up dead during high tide. When they reached the shore they were saddened by the sight of a massive female shark that had visited their research boat on multiple occasions and been named ‘Khaleesi’, after the Game of Thrones character. She was almost five metres (16 feet) long and weighed more than a ton – a very dominant female shark. Shark scientists travelled from around the country and the next day the shark was autopsied in front of the public. As external measurements were being taken, nothing seemed out of the ordinary with Khaleesi, but when they rolled her mammoth body onto its back, a huge gaping wound was revealed. They opened her stomach cavity and waited for her liver to slide out – but the liver wasn’t there.
No sooner had Towner arrived home that evening after the nine-hour necropsy when she received another call. She and her team rushed down to a different part of the coast, where they found the remains of a smaller, male white shark that had been documented at a cage-diving boat just four days earlier. ‘His torso was completely twisted. The head was there and the lower end of the abdomen towards the tail, but then there were huge gaping chunks out of both sides of his flanks. His liver, testes and heart were missing,’ explains Towner. Apart from the missing organs, the mutilated shark showed another clue: his pectoral fins were covered in rake marks and tooth impressions that looked very much as if they had been made by an orca. By 25 June, five white sharks had washed up dead and in all of them, apart from the animal discovered in February, the livers were missing.
These were not the first sharks with missing livers to be found by South African biologists. About 100 kilometres down the coast, in the south-western corner of False Bay, lies Castle Rock Reserve, a tiny kingdom that is ruled not by great whites, but rather by some of the most prehistoric fish in the sea: sevengill cowsharks. These animals grow up to three metres (10 feet) long and aggregate in large groups; up to 70 animals have been observed at this particular spot. Since 2014, local scuba divers have been sending in reports of dead sevengills that have come to the attention of Dr Alison Kock, a marine biologist now with South African National Parks who has been researching sharks in False Bay for almost a decade. She could tell very little from most of the images and videos received, as most of the carcasses were severely decayed, but one photograph showed a shark lying on the bottom with just a single injury between its pectoral fins. ‘It looked as if someone had sliced it open, and so clinically it seemed to have been done by human hands. Everybody assumed a fisherman had done it,’ recalls Kock.
Castle Rock is a protected area and Kock and her team were concerned about the possibility of humans killing sharks, so on 13 April 2016 they went to investigate. When they found the carcass it was very decomposed. On examination, they realised that both of the shark’s pectoral fins showed tooth impressions and its liver was missing. All its other organs were intact. Over the next few weeks more sevengills were discovered and all had lost their livers. The other sharks fled and Kock concluded that they were being predated on by orcas. ‘It looks like at least two orcas had to have worked together. We saw the bite marks on the pectoral fins and then the shark was torn open to the pectoral girdle. Based on that examination, it seems the orcas are biting on the pectorals, ripping the shark apart and then taking its liver out,’ she explains.
The necropsy was not the only clue that pointed to killer whales. About four months earlier, Kock and her team had been diving at Castle Rock to collect some data from a receiver. As they returned to the boat, someone shouted ‘Whale!’ Bryde’s and southern right whales are common in the bay, but this was a different kind – and there were two of them. ‘We had two killer whales that must have been swimming around us in the kelp forest without us knowing. They were right on the boat and they both had floppy dorsal fins,’ exclaims Kock.
Orcas have always been seen off the coast of southern Africa, but prior to 2009 they had never been recorded inside False Bay. Dave Hurwitz is an avid naturalist based in Simon’s Town. For the past 20 years he has run a whale-watching company from the local marina and he was one of the first people to see orcas here. ‘It was almost surreal,’ he says. ‘I had read a lot about them and seen some of the reports about them off our coast. The first time I saw them was only briefly and that was right inside the harbour here. We were coming along and suddenly there were two killer whales right in front of the boat. I thought I was dreaming. They swam up and around the boat a couple of times and then went off. I had goose bumps for the rest of the day. That was the first time I registered that there is a possibility of seeing killer whales in the bay here.’ Since then Hurwitz has collected records of more than 160 sightings in and around False Bay and witnessed incredible scenes of killer whales hunting large pods of dolphins that swim in during summer. But scientists know that orcas are fussy eaters and mammal hunters are highly unlikely to attack sharks.
Then, in 2015, Hurwitz saw two floppy-finned orcas swimming alone half a mile from Seal Island, the fabled home of breaching white sharks. ‘I named them “Port” and “Starboard”. The fin of one of them flops over to the left and the fin of the other to the right, so I named them so that it would be easy to re-identify them,’ he explains.
Two years later, Port and Starboard have become the prime suspects in the case of the ‘eliverated’ sharks. Recorded sightings of the pair correlate exactly with the discovery of the shark carcasses at Gansbaai, starting with the small female that washed up in February. Researchers suspect she beached herself while being chased by the orcas. Because of their distinctive fins, Port and Starboard are easy to recognise and have been seen at numerous points along the southern tip of Africa, from Walvis Bay in Namibia to Langebaan on South Africa’s West Coast and to Gansbaai in the east – a total distance of more than 1,400 kilometres (870 miles).
Although the recovery of shark carcasses without livers is a world first, incidents of orcas predating on sharks have been reported in California, Australia, New Zealand and Canada, and for some time experts have suspected that South Africa could also be home to shark-eating orcas. Dr John Ford has been studying orca populations in British Columbia since the late 1970s. Several years ago he was asked to review a paper by Dr Peter Best, South Africa’s top cetacean researcher at the time. ‘The report mentioned one or two stranded animals that showed profound wear of their teeth. In the manuscript he commented that this must be a sign of old age,’ Ford remembers. ‘I wrote back immediately and said, ”Don’t jump to that conclusion because we have a whole population on the West Coast of Canada (from California to Alaska) that have profound tooth wear of the same kind and for many years we hypothesised that it was due to something they were eating,”’ he continues.
After almost four decades of research, British Columbian researchers have uncovered a vast body of knowledge about Canada’s resident and transient killer whales, but it was only in the late 1980s that they first observed a group of orcas that they called ‘offshores’. ‘They often travel in really big groups of 100 or more, but sometimes they also occur as a pair and sometimes they are on their own. We didn’t even know this popu-lation existed for the first 20 years of our field work on this coast,’ explains Ford.
Apart from a subtle difference in fin shape and being slightly smaller, offshores appear to be identical to other types of orca. In the orca kingdom, it is culture rather than morphology that separates. The killer whales are divided into three groups, or ‘ecotypes’, and although their ranges can overlap, they are very xenophobic. Resident killer whales, which we know the most about, are highly vocal, tend to live in stable matrilineal family groups in inshore waters and feed on salmon. Mammal-eating transient killer whales are silent and have a more dynamic social structure. The offshores are also highly vocal, presumably because they target a prey that is not sensitive to sound. Ultimately, it was not the whales’ voices that alerted Ford to their dietary choice, but their teeth. ‘Both the transients and the residents have perfectly healthy teeth, but pretty much all the offshores have teeth that have worn flat to the gums,’ he says. ‘We reasoned that it was because of the abrasive qualities of the sharks’ dermal denticles. Offshores don’t have very useful teeth for piercing, but their flat teeth would still be fine for grasping, especially onto an animal with a very rough skin.’
Ford and his colleagues speculated about this for 20 years and then, once in 2008 and again in 2009, they witnessed events that confirmed their suspicions. They were running surveys in very deep water (200–350 metres, or 650–1,150 feet) when they came across a titanic deepwater battle between two great predators. The first incident involved five offshore orcas, the second a group of about 100. The animals were diving in unison for up to 10 minutes at a time. The researchers could see from their behaviour that they were feeding, but they had no way of telling what was going on at that incredible depth. Then, as the orcas surfaced, large pieces of soft, oily tissue floated to the surface with them. The researchers watched as the animals picked up the chunks and shared them with one another just beneath the surface – a cultural practice that helps to maintain harmony within orca pods. Ford and his team collected some of the floating tissue and tests later revealed that it was the liver of Pacific sleeper sharks and that orcas had killed at least 11 sharks during the first event and seven during the second.
Sleeper sharks can grow to more than four metres (13 feet) long and are found at depths of up to 2,000 metres (6,560 feet). Their flesh is toxic, but this does not appear to be the case with their livers and somehow the orcas know that. ‘Of course, shark livers are wonderfully rich and killer whales love lipids. They are really driven by high lipid content – lots of oil or fat – and that is why they selectively remove the tongue and the skin as well as the blubber of large whales that they kill because these parts have the highest energetic punch. Some sharks can be up to 30% liver and of that liver, up to 80% can be lipids,’ explains Ford. So far, the research suggests that more than 93% of the offshores’ diet is shark and includes blue sharks, sleeper sharks and spiny dogfishes. Ford has also discovered that wear on the teeth starts very early in the animals’ lives, but does not appear to affect their general lifespan.
But why would the top predators in the ocean be so picky about their prey and does it serve them to have such limited diets? ‘I think it’s basically because by being specialists, they can actually out-compete generalists. If they get really good at a particular foraging tactic, and there is sufficient prey abundance over time, they can become sort of culturally specialised on that particular food resource,’ explains Ford. ‘It’s not necessarily a good thing, because as we have seen over the past few decades, when Chinook salmon abundance fails, the mortality rate in resident orca populations shoots right up and the numbers decline. Once they attain these cultural blinkers that have them focusing on a particular prey, they don’t seem to be able to switch quickly to an alternative.’
This might provide a clue as to what is happening in South Africa. In all likelihood, the shark-eating orcas have always existed in offshore waters and Port and Starboard are probably part of a larger pod that we have not seen yet. But what has motivated them to start hunting great whites? Ford can only speculate, but it appears that the floppy-finned animals are colonising new territory. They may have discovered the abundant source of shark liver by chance, but given the general decline in pelagic shark numbers, this new behaviour could also be driven by a need for new resources.
After the grisly spate of killings, the great whites were not seen again in Gansbaai for almost three months, despite the tantalising smell of a deceased sperm whale. In the meantime, shark researchers further east reported record numbers of sightings. Alison Kock is not surprised that the sharks fled after the death of their kin, but what fascinates her is why they were gone for so long. ‘I think there are a lot of really interesting theories, but you can imagine that when two orcas start predating on such a small aggregation, all the other sharks will hear and see the commotion, which could cause an immediate flight response. And if dead sharks are sinking to the bottom and being left there to decompose, the chemicals released by the decaying shark could also create a deterrent,’ she speculates. The animals have since trickled back and cage-diving operations have resumed, but it is impossible to predict how long peace will reign in the sharkdom of Gansbaai – or when the orcas might return. As Dave Hurwitz says, ‘They don’t follow a set path like other whales or cetaceans. They are such good predators because they are so unpredictable.’
The question is, given that white sharks are already vulnerable, what will this mean for the sharkdoms of the Cape? And will there be consequences for the local ecosystem? ‘Top predators are vital in that they shape the entire ecosystem from the top down. If you have an imbalance at the top, then the next trophic level is going to become too numerous,’ says Alison Towner. ‘We already have too many Cape fur seals on Geyser Rock. That affects us at Dyer Island because they start to predate on our penguins and the penguin colony is incredibly threatened. In fact, the species itself is under major threat. It cascades right down to the bottom. So we don’t really know what the effect will be, but we have to assume that there will be one of some sort or another,’ she continues.
A new study funded by the Save Our Seas Foundation will use sophisticated population models to combine data collected from all of South Africa’s white shark aggregation sites over the past two decades (including previously unpublished data) to assess how trends have shifted during that time. Currently, we do not have an accurate number for South Africa’s white shark population. Between 2007 and 2013, Towner observed about 1,000 individual sharks at Gansbaai and over a similar time period, Kock estimated that there were just over 700 in False Bay. Her sightings data show a steady decline in great white sightings from 2005 to now. While Port and Starboard are almost certainly responsible for the sudden disappearance of sharks at Gansbaai, the reason behind the overall decline in great whites is harder to pinpoint and for Kock that is the greater mystery. ‘We work in a dynamic environment. Sometimes it might be orcas. Sometimes it might be extreme water temperatures. These animals are adapted to move to where conditions are favourable. They can leave an area and move somewhere that is better for a short while and then they might come back. It’s really hard to say what is going to happen because these interactions are so complex. We just don’t know enough and that is the bottom line,’ she concludes.
A few months later I am swimming through a cave in the kelp forest when I hear what sounds like a conversation between two underwater sirens. I fly up to the surface to breathe and the sound disappears. I descend again and hover in the cave. The submarine chamber seems to amplify the noise. I hold my breath, suspended in awe. There are many whale species in False Bay and I don’t know enough about them to identify their voices, but I try to feel out into the ocean around me and picture what the sound is coming from. My mind stretches across the bay to Seal Island and I think of the sharks and wonder what they are picking up on and whether it fills them with fear.