Latest news with #Orcinusorca
Yahoo
31-03-2025
- Science
- Yahoo
Orcas Are Terrorizing Sharks, And The Consequences Could Be Profound
A pair of orcas terrorizing white sharks off the coast of South Africa may have captured the popular imagination, but their activities may be quite damaging, new research suggests. 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. Rock Used as a Doorstop For Decades Found to Be Worth Over $1 Million Antarctic Iceberg Breaks Away to Reveal a Never-Before-Seen Ecosystem Huge Trees Hiding in Plain Sight May Be a Species Totally New to Science
Yahoo
05-02-2025
- Science
- Yahoo
DNA Confirms Orcas Prey Upon One of Australia's Deadliest Marine Predators
It's not just the white sharks off the South African coast of Gansbaai that feel the deep, primal fear known only to prey. For years now, a single pair of orcas (Orcinus orca) has been recorded off the coast of Gansbaai, harrying and hunting the white sharks (Carcharodon carcharias) that make the area one of their homes, slurping out the sharks' nutrient-rich livers, leaving the rest of the carcasses to wash ashore. It now appears that the behavior is more widespread than we knew. In 2023, off the southeastern coast of Australia, half a world away from Gansbaai, the remains of a 4.7-meter (15.4-foot) white shark washed ashore, a gaping hole in its abdomen ringed by ragged tooth marks, and a marked absence of a liver. DNA sequencing has now confirmed that the culprit was none other than an orca. "There were four distinctive bite wounds, one of which was characteristic of liver extraction by killer whale, similar to what has been observed in South Africa," says biologist Isabella Reeves, of Flinders University in Australia. The researchers took swabs from the white shark's bite wounds and sequenced for any genetic material that the predator may have left behind. This confirmed the presence of orca DNA in the main bite, while three other wounds carried traces of DNA from scavenging broadnose sevengill sharks. As we are discovering, the predation by orcas on cartilaginous fish such as sharks and rays isn't uncommon. Orcas are highly adaptable and highly intelligent, and around the world, different groups of orcas have developed their own strategies for hunting and feeding. The strategy developed by the pair named Port and Starboard off the coast of South Africa is fascinating because it involves two such efficient species of marine predator, but a growing body of evidence suggests that it is not unique. Orcas in the Gulf of Mexico prey on whale sharks, for instance. And orcas off the coast of Australia have been recorded preying on multiple species of shark, including porbeagles, makos, blue sharks, tiger sharks, and ground sharks. But the discovery of the white shark carcass in 2023 was the first known instance of orca predation of the species in Australian waters. "These findings provide compelling evidence of killer whale predation on white sharks in Australian waters, with a strong indication of selective liver consumption," Reeves says. "This suggests that such predation events may be more widespread and prevalent across the globe than previously believed." Two days before the carcass washed ashore, near Portland in the Australian state of Victoria, two locally known orcas named Bent Tip and Ripple were seen hunting, and catching, large prey in nearby Bridgewater Bay. This may have been the hunt in question, although confirmation would be difficult to obtain. All we know for now is that the culprit was orcas – but that's quite mind-blowing. Orcas have their own habitats, hunting grounds, and specialties. Different groups in different locations don't intermingle, communicate, or breed with each other. It raises some interesting questions about how similar hunting behavior could have emerged in two very different locations. It's possible that orca predation of white sharks is just a more widespread, normal behavior than we knew about. If this is the case, we need to learn more about it and how it affects the rest of the ecosystem. The displacement of a top predator can have grave effects: in South Africa, for instance, reduced shark presence means a drop in shark predation on elephant seals, which could increase food competition for the seals later. If orcas in Australian waters have started preying on white sharks, that could have implications for populations of the animals sharks normally eat. "Evidence suggests that the white sharks being displaced or directly killed as a result of the killer whale predation in South Africa has led to cascading shifts in the wider marine ecosystem," says ecological geneticist Adam Miller of Flinders University. "We know that white sharks are key regulators of ecosystem structure and functions, so it's very important we preserve these top predators. Therefore, it is important that we keep a tab on these types of interactions in Australian waters where possible." The research has been published in Ecology & Evolution. 'Beyond Doubt': Proteins in Fossil From Actual Dinosaur, Claim Scientists 'Lost City' Deep Under The Ocean Is Unlike Anything We've Ever Seen Before on Earth Octopuses May Have The Oldest Sex Chromosomes in The Animal Kingdom
