Orcas Are Terrorizing Sharks, And The Consequences Could Be Profound
Port and Starboard, as the orcas (Orcinus orca) are known, have been documented hunting white sharks (Carcharodon carcharias) off the coast of South Africa for years, handily eviscerating them to feast on their nutritious livers, potentially reducing shark numbers in the area.
The impact of a declining shark presence has been difficult to determine, but we may be closer to an answer. Over the last few decades, white sharks have disappeared entirely from False Bay near the Cape of Good Hope – and the cascading effects of the loss of a top predator have been remarkable.
"The loss of this iconic apex predator has led to an increase in sightings of Cape fur seals and sevengill sharks, which in turn has coincided with a decline in the species that they rely on for food," says marine ecologist Neil Hammerschlag, formerly of the University of Miami.
"These changes align with long established ecological theories that predict the removal of a top predator leads to cascading effects on the marine food web."
An ecosystem is a delicate balance maintained by the interaction of the organisms that inhabit it. Although the predators at the top are considered scary by some, removing them from the environment has significant consequences.
Suppression of natural predators in Pando forest in Utah, for example, has allowed deer and elk to run riot, feasting on the ancient aspen colony and slowly killing it.
For more than 20 years, scientists have been monitoring wildlife populations in False Bay. This meant that they were able to see, in real time, the decline and ultimate disappearance of white sharks from the ecosystem there, and the consequent changes in populations of other species in the food web.
From 2000, scientists conducted standardized surveys of white shark sightings at Seal Island, and until around 2015, the shark population was pretty stable. After 2015, however, sightings started to fall dramatically; by 2018, there were no sharks to be seen.
The reason for this hasn't been officially confirmed. It's worth noting, however, that white sharks started washing up along the southern coast of South Africa, without their livers, in 2015 – attacks that would later be traced to Port and Starboard.
Although the cause of the shark disappearance is yet to be confirmed, we know the effects. White sharks prey on Cape fur seals (Arctocephalus pusillus pusillus). With no sharks around to keep their numbers in check, seal populations boomed.
At the same time, sevengill sharks (Notorynchus cepedianus) started appearing – large-bodied sharks that are both prey and competitor to white sharks.
As the numbers of Cape fur seals and sevengill sharks rose, populations of the species they prey upon in turn dramatically declined – small fish for the seals, and small sharks for the sevengills.
We know, based on other animal population booms, that a sudden increase in food competition between members of the same species can have dire consequences, with individuals taking greater risks to access food, and the weaker individuals starving when they are unable to compete.
It may take some time for the ecosystem to recover balance; and, once it does so, it could be very different from the ecosystem it was before.
Such changes are pretty normal in the natural world – after all, the world we live in today looks very different from the world of, say, 11,000 years ago, at the end of the last glacial period, or the world 70 million years ago, before the dinosaurs were eradicated.
However, understanding what drives such changes in the Anthropocene can help us try to minimize our own impact, and protect vulnerable habitats and the animals that need them to survive.
Port and Starboard have been observed hunting white sharks around Gansbaai and Mossel Bay, both further along the southern coast of South Africa.
The pair has also been sighted hunting in False Bay, although white sharks are not among the prey observed in that specific area. Nevertheless, it's reasonable to infer that their ongoing mischief at least plays a role in the changes at False Bay.
However, we cannot rule out overfishing, pollution, and shark cull programs as contributing factors, either. This is information that is relevant to understanding the wider impact of our own activities.
"Future work at this site would benefit from understanding if and how community structure and function may have been altered and the extent to which they will continue to change through time," the researchers write in their paper.
"While impacts of apex predator declines are difficult to detect in the wild, especially in marine environments, they are likely more widespread than recognized given the pace and extent of apex predator declines globally."
The research has been published in Frontiers in Marine Science.
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Miami Herald
2 days ago
- Miami Herald
Corals keep cooking in climate-heated seas. These crossbreeds may keep hope alive
The first-in-the-world experiment began not with a splash, but with a gasp from a respirator. Neoprene-clad scientists sank to the shallow bottom of Flamingo Reef off Key Biscayne, clutching black milk cartons filled with precious cargo. Inside were a few dozen contraptions that looked like fancy desk toys — round pucks of concrete shielded by a spinning piece of metal resembling the ribs of an umbrella. Underneath the rotating spines were four thumbnail-sized chunks of coral. Two were the usual suspects for South Florida, hunks of elkhorn coral, and two were newcomers, a crossbreed of Florida elkhorns with their Honduran siblings. These 'Flonduran' corals are the first ever corals with parents from different countries to be planted in the wild, according to the University of Miami and Florida's Fish and Wildlife Conservation Commission, which approved the experiment. It's a revolutionary new strategy to save corals as human-caused climate change cranks up the temperature of oceans worldwide. The shallow, turquoise waters of the Caribbean have been hit particularly hard. A 2023 marine heat wave was devastating to the Florida reef tract and many neighboring island nations. Only about 1 in 5 staghorn corals on five major Keys reefs survived the event, the National Oceanic and Atmospheric Administration found. This pilot project, to share corals throughout the Caribbean and potentially breed new, more resilient varieties that have a chance of surviving the next heat wave, could be a step toward a world where more — but not all — corals survive. And while the scientific tide appears to have turned on the idea of breaking up corals into smaller pieces, growing them rapidly and planting them on reefs, new research suggests that genetically selecting for stronger coral might still give scientists a chance at restoring some reefs. 'We don't have to plant every single coral on the reef. We just have to plant the next generation. That is the goal of restoration, making these systems self-sustaining,' said Andrew Baker, lead scientist on the experiment and a professor at the University of Miami's Rosenstiel School of Marine, Atmospheric, and Earth Science. 'We're scattering the seeds. We have to wait for the oaks to grow up.' Baker and his team suited up earlier this month and slipped under the waters of Biscayne Bay to deliver these baby corals to their new home. Twenty feet under, they'll be neighbors with other coral experiments from UM, as well as a forest of colorful soft corals and sponges. They'll live here for at least a year, with regular checkups from an army of researchers, before they'll get yanked back to the surface for a round of stress tests. The big question for these tiny animals: Can they take the heat? From Tela Bay to Biscayne Bay Climate change is warming the whole planet, but the ocean is absorbing most of that heat. That's bad news for creatures that are sensitive to temperature changes, like corals. When waters get too toasty, corals spit out the algae that live within their skeletons, the stuff they rely on for food and protection from the sun's rays. Scientists call the ghostly white coral — starving and sunburning — bleached. If a coral stays bleached for too long, it dies. The oceans are always warming unevenly, with some hot spots turning into coral graveyards and others remaining resilient. That's where Baker and his team got the idea to find the sturdiest survivors and interbreed them with their Florida siblings. Over the last few years, Baker tried to scoop up corals from Mexico, Belize, the Cayman Islands, the Bahamas and even Cuba, where a massive amount of wild corals perished in 2023 when waters reached 95 degrees. He finally found success in Honduras, where waters are 2 degrees warmer than Florida and soupy with pollution from nearby coastal cities. And yet, Baker said, the corals in Tela Bay were 'remarkably resilient.' After a year and a half of permitting delays, Baker and his team managed to successfully airlift a handful of those resilient corals back to Florida. It was a 14-hour journey from sea to lab aquarium, featuring a small plane, a crate of seawater and plenty of bubble wrap. Once safely in the Sunshine State, the Florida Aquarium interbred the Honduras parents with a stock of Florida elkhorns, creating an army of 'Flonduran' children. Scientists call this assisted gene flow. In a commentary published Thursday in the journal Science, a team of leading coral scientists argued it may be the best way to save at least some corals. A reckoning in 2023 In Florida, elkhorn corals in particular are struggling to survive. Only 23 distinct genetic species, out of 153 cataloged before 2023, remain in the wild. The few remaining wild species have all but stopped reproducing in the Keys, scientists say. Some research suggests that, if temperatures continue to rise at the current pace, they could be locally extinct in a decade or two. 'The question is, how do we rescue those corals? They could withstand decades of additional heat stress in other places in the Caribbean,' Baker said. 'If we leave them where they are, they will potentially die off in the next big bleaching event.' Florida approved the outplanting of the new crossbred coral, but it denied an opportunity to outplant another hybrid coral — Florida corals mixed with corals from Curaçao — a few years back. Those offspring are still stored at a research aquarium in Florida. That's because the Honduras corals are genetic siblings to Florida corals, while Curaçao corals are further removed, like cousins once or twice removed. Corals from other locations, like Hawaii, are essentially strangers, scientists say. That leaves an increasingly shrinking pot of corals for Florida to choose from, if this is a strategy the state continues to pursue. While some may look at this strategy of swapping corals around a small region as the whole ocean cooks more like rearranging the deck chairs on the Titanic, Baker said he prefers to see it as buying time. 'We need to buy time for as many species to thrive while we as a society figure out whatever the solution is going to be to climate change,' he said. 'It's an inconvenient truth that while this method can be used to help corals in some parts of the region, it's not a solution for all.' The science backs him up. An increasing amount of research has soured on the once very popular idea of rescuing dying reefs by choosing fast-growing species, breaking them up into tiny fragments and planting those regrown pieces on reefs. 'Coral restoration has been a very hot and sexy topic for years. Because of the growing recognition in the coral reef science community that restoring coral is difficult, the research is losing a little bit of momentum,' said Giovanni Strona, a researcher at the European Commission who has studied tropical reefs since 2008. In a paper published in April, Strona and his team argued that restoration only works under narrow circumstances. Replanting a huge number of genetic copies of one type of coral is like building an entire city with only one-bedroom apartments. It's not enough to attract the diverse, healthy ecosystem needed to survive disease, predators or climate change. 'You need to create a reef that's as diverse as the original one. Of course, having something is better than having nothing,' Strona said. It's also simply not happening fast enough. He compared replanting new corals to reforestation projects happening all around the world; they're not keeping up with the global loss of forests — at all. In total, he found, only a few square meters of reef around the world have been restored in recent years. 'It's not about restoring even three soccer fields. We're really talking about very tiny islands,' he said. However, the newest wave of coral research suggests that genetically selecting for stronger, better corals — including interbreeding via assisted gene flow — could still be a visible solution to keep some reefs in selected areas viable. A paper published last year found that lab-reared corals survived the 2023 Caribbean marine heat wave better than nursery-grown or native corals. But in some places, it may already be too late. 'Elkhorn and staghorn corals in some of the region's warmest areas, off the south coast of Cuba, were exposed to unprecedented heat stress during the 2023 bleaching event and have experienced major losses. It is not clear whether these reefs can recover through immigration of even more thermally tolerant genets from elsewhere because these reefs are among the warmest in the region,' the authors wrote in the Science commentary.
Washington Post
20-07-2025
- Washington Post
Here's what shark experts do to stay safe in the ocean
Discovery Channel's 'Shark Week' begins Sunday for the 37th year. And Steven Spielberg's movie 'Jaws' celebrated its 50th anniversary in June. Despite the fanfare and some highly publicized reports of shark bites, researchers are quick to point out the apex fish are not the bloodthirsty predators they're made out to be. Instances of sharks biting humans are extremely rare. You're more likely to die falling into a hole at the beach, in a riptide or in an alligator attack than from a shark bite, according to data from the Florida Museum of Natural History's International Shark Attack File. Last year, the museum recorded 47 unprovoked bites worldwide. 'They're not these monster killers that just come flying in whenever there's bait,' said Neil Hammerschlag, a shark researcher based in Nova Scotia, Canada, who charters cage-diving expeditions to bring tourists up close to blue, mako and great white sharks. 'They're very cautious.' Hammerschlag, who's been studying sharks for 24 years, said some are more curious about the color of the boat or the sound of the engine than the 20 pounds of sushi-grade tuna he brings on each trip as bait. Chris Lowe, the director of the Shark Lab at California State University in Long Beach, said he has 'hundreds, if not thousands of hours footage' of sharks near the shore in California. And, most of the time, they're there to relax, he said. For three years, researchers in Lowe's lab surveyed 26 beaches from Santa Barbara to San Diego with drones and saw sharks swim right under surfers without changing course. 'It's like they are ignoring us,' he said. 'We're just flotsam, not food or foe.' The Washington Post asked Hammerschlag and Lowe what they do and the advice they give beachgoers who want to avoid a shark encounter. Lowe said when he's out in the water he spends some time looking behind himself and others, 'like checking my mirrors when I'm driving.' Sharks are stealthy and try to approach other animals from behind. Don't treat the ocean like Disneyland, Lowe said. You're in a wild place where you can't eliminate all risks. His advice: Be vigilant. It will reduce your likelihood of a shark swimming up too closely to investigate you. And, do your homework about the body of water you're swimming in. 'Who are you going to be sharing the ocean with? Is it sharks? Is it stingrays?' Lowe said. 'When we go in the ocean, we are entering someone else's home.' Sharks may confuse a human foot for a fish, or a surfboard for a seal, when visibility is poor, such as in lowlight conditions. Sharks use their mouth and teeth to inspect what's in front of them like we use our hands, Hammerschlag said. 'Most shark bites of people are not predatory,' he said. 'When sharks have bitten people, it seems that they're investigatory or mistaken identity.' The light glimmering off jewelry can look like a fish scale to a shark, Hammerschlag said. He adds reflective stickers to the cage he uses on diving expeditions to try to catch a shark's attention. A fish caught on a line could get the attention of a shark. 'Those vibrations are like ringing the dinner bell for a shark,' Hammerschlag said. However, it can help to swim near other people, Lowe said, since groups of people might be more intimidating than solo swimmers. If you see fish jumping out of water or birds diving for a meal, there could be a 'bait ball' of fish nearby, and that's a feeding opportunity for sharks, Hammerschlag said. There's a myth that a pod of dolphins can ward off sharks. But, he said, the opposite may be the case. 'If there's a big bait ball of fish that dolphins are feeding on, the sharks could be feeing on that, as well,' Hammerschlag said. If you see a shark in the water, don't panic and swim away, Hammerschlag said. If you do, the shark might see you as prey. And, 'you're not going to outswim a shark,' he said. Instead, orient your body so you're always facing the shark and maintain eye contact, Hammerschlag said. Sharks can't sneak up on you if there's no element of surprise. 'You're showing the shark that you see it, and you're responding to it,' he said. 'And that is not a situation that a hunting shark wants to be in.' If you're scuba diving, you can also sit on the ocean floor; sharks tend to approach potential prey from below, Hammerschlag said.
CBS News
17-07-2025
- CBS News
Increased shark sightings may scare swimmers, but scientists say that's good news for conservation
Great white shark sightings off the coast of Maine triggered warnings Wednesday for people to stay out of the water. Those sightings are not new in South Florida, but they do get a lot of attention. That's why CBS News Miami went out on the water to learn why we see sharks so often and what it means for our ecosystem. A shark reeled in miles off the coast of Fort Lauderdale in May and just weeks later, a little girl was bitten off the Gulf Coast. Shark stories are everywhere. "The thing we like to say is that if you're in the water and it's salty, there's probably a shark nearby," said Catherine MacDonald, the director of the University of Miami's Shark Research and Conservation program. For MacDonald and her team, that's exactly what they are hoping for. This nurse shark was one of many they caught on their trip. "We take a few small tissue samples, blood samples and measurements that we use to study the health of sharks here," she said. Here in Biscayne Bay, it's a perfect place for researchers to monitor shark populations over the long term. In 2024 alone, UM's Shark Research and Conservation program reeled in and tagged over 550 sharks. The bay is perfect for these species to have and raise their young, but it's changing. "Because the estuary is warming 6.9 times faster than the ocean, there is reason to be concerned that, between human impact and warming, we may see this habitat become less good for them as time goes on," MacDonald. For Delaney Reynolds, preserving this habitat is a calling and has been a longtime goal of hers. "I went on my first shark tagging trip with the University of Miami in high school, and I knew the second I stepped on the boat that this was something I wanted to do," she said. Reynolds has been doing that for years now as a PhD student at UM. She is seeing how the changing water is affecting the sharks. From that first tagging trip to now this, Reynolds — now the teacher for current high school students — may be the future for these summer scholars taking part in their first shark tagging trip. "You get an adrenaline feeling when they come on board, you get those lines in and it's exciting," said UM summer scholar Sam Lambert. High school students come to South Florida from across the country to explore firsthand with the research team. "We don't have an ocean in Chicago — we have a lake," said Camila Johnson, another summer scholar. "I wanted to explore the exotic wildlife [and] learn more." Excitement was felt four times when three nurse sharks and a black tip shark were reeled in and tagged. "Every time we see a shark, it's not the summer scholars that are excited but my team as well," MacDonald said. So no matter what the species, the students and researchers like what they see today. Researchers told CBS News Miami that the number of sharks here is mostly stable, or even increasing slightly, which is good news for South Florida's environment. "Sharks being present in the ecosystem is a good sign for how well it is functioning and sharks being absent means there are more problems with the system itself, or it has become so damaged that sharks have moved," MacDonald said. A good sign so far, but something these current and potential future scientists will continue to monitor.
