Great White Shark Threats — from Humans and Orcas

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ARE GREAT WHITE SHARKS ENDANGERED?

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The number of great white sharks worldwide is believed to have declined over the past half century. Their numbers dropped by 75 percent off the U.S. Atlantic coast in the 1980s and 90s. Commercial and long line fishing were blamed. Often they were accidentally caught by fishing vessels seeking tuna and other commercial fish. By one estimate the number of great white shark decline by 37 percent between the late 1970s and the late 2010s. But since the mid 2000s, great white sharks appeared to have a comeback along the U.S. Atlantic coast.

Scientists say there are still thousands of great white sharks off the coasts of Australia, Canada and the United States. On the east coast of the U.S. they appear to have made a comeback. The species seems to be most threatened off the coast of South Africa (See Below).

Erik Vance wrote in National Geographic: Are great whites thriving or dwindling? The world has about 4,000 tigers and 25,000 African lions. Using the lowest estimates, global great white numbers resemble the estimate for tigers, an endangered species. Using the highest estimate, the population is closer to that of the lions, which are classified as vulnerable. Several experts see them heading toward extinction; others see a positive trend. Some say rising seal populations are a sign that great whites are nearly gone, while others say more seals mean more sharks. Aaron MacNeil, an Australian statistician who crunches shark data, says the appearance of sharks around Cape Cod and the increased activity in the Southern Hemisphere suggest the latter. “I haven’t seen any evidence in the last decade that white sharks are declining,” says MacNeil. “Yes, there is a historical depletion of white sharks. But the story is not that they are going extinct. The story is that they are probably increasing very, very slowly.” [Source: Erik Vance, National Geographic, July 2016]

“There’s reason to be hopeful. Few if any fishermen target great whites today, yet a global pact, the Convention on International Trade in Endangered Species, gives white sharks its second strongest conservation rating because fishermen catch them unintentionally. With numbers so low, even accidental catches can play havoc with the species, which, as a top predator, has an ecologically important role in managing the oceans.

Websites and Resources: Shark Foundation shark.swiss ; International Shark Attack Files, Florida Museum of Natural History, University of Florida floridamuseum.ufl.edu/shark-attacks ; Animal Diversity Web (ADW) animaldiversity.org; National Oceanic and Atmospheric Administration (NOAA) noaa.gov; Fishbase fishbase.se ; Encyclopedia of Life eol.org ; Smithsonian Oceans Portal ocean.si.edu/ocean-life-ecosystems ; Woods Hole Oceanographic Institute whoi.edu ; Cousteau Society cousteau.org ; Monterey Bay Aquarium montereybayaquarium.org ; MarineBio marinebio.org/oceans/creatures

Why Great White Sharks Are Threatened

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But despite its fearsome reputation, its large size and low productivity (reproductive rates, growth rates, age at maturity, longevity, etc.) make the white shark vulnerable to declines from human impacts. Due to these natural vulnerabilities, the white shark is one of the most widely protected sharks.[Source: NOAA, National Geographic, July 15, 2021]

Great white sharks are apex predators. They are at the top of the food chain and face few predators themselves. Occasionally great white sharks are killed by killer whales and juveniles are attacked by other sharks Human-caused threats include habitat impacts, overfishing and : fishing bycatch. [Source: Animal Diversity Web (ADW)]

In the past great whites were deliberately caught, primarily for their jaws. In South Africa, one single fisherman caught 18 large great white sharks and sold the jaws for as much as $5,000 a piece on the American market. A complete great white shark jaw with all of its teeth could fetch $25,000 on the black market in the United States and a single tooth could bring $500.

According to Animal Diversity Web: Traded products that come from great white sharks include fins, jaws, teeth and meat, cartilage, and skin for leather. Liver oil is used in medicines, and the carcass can be used for fish-meal and fertilizer. The trade in shark fins is generally on the increase with records from the Food and Agriculture Organization (FAO) of the United Nations indicating that the international fin trade increased significantly between 1980 and 1990. The demand for shark fin escalated further during the 1990s, making it one of the most expensive fishery products. Jaws and teeth are the most valuable great white shark products in trade. [Source: Dana Chewning and Matt Hall, Animal Diversity Web (ADW)]

Protecting White Sharks

Great white sharks have been declared endangered and are protected in South Africa, Australia, the Maldives and Namibia and parts of the United States.

South Africa was the first country to ban commercial hunting of great white sharks, in 1991, followed by Namibia, Australia, the United States, Malta and New Zealand. In 2004, The United Nations Convention on International Trade on Endangered Species (CITES) outlaws most international trade of great white jaws, teeth, fins and meat.

Great white shark are categorized as vulnerable on the International Union for Conservation of Nature (IUCN) Red List. They are listed by the Convention on International Trade in Endangered Species (CITES) in Appendix II, which lists species not necessarily threatened with extinction now but that may become so unless trade is closely controlled. According to the World Wildlife Fund (WWF), great white sharks are considered a vulnerable species, with a "high risk" of extinction in the wild.

As for fishing, the white shark is a prohibited species (no retention allowed) in all U.S. waters and fisheries. There are no commercial fisheries for white sharks, but they are occasionally caught as bycatch. White sharks are occasionally caught by recreational and commercial fishermen but must be released immediately. Other countries have similar regulations. [Source: NOAA]

Great White Shark Numbers in U.S. Waters Appear Okay

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The stock status for white shark populations in U.S. waters — off Alaska, New England, the Mid-Atlantic, Pacific Islands, Southeast and the West Coast — is unknown and no stock assessments have been completed. Research by NOAA Fisheries scientists indicates that abundance trends have been increasing in the northwest Atlantic since regulations protecting them were first implemented in the 1990s. In the northeastern Pacific white shark population appears to be increasing and is not at risk of becoming endangered in U.S. waters.[Source: NOAA]

The return of great white sharks to U.S. waters has been at least partly attributed With the passage of the Marine Mammal Protection Act in 1972. Seal and sea lion population increased rebuild along the U.S. West Coast. Since white sharks eat seals and sea lions their numbers increased too. Now we’re seeing seals returning to parts of the Northeast where they haven’t been for nearly a century. White sharks are making a comeback there. [Source: George Burgess, Director, Florida Program for Shark Research and Coordinator of Museum Operations, Florida Museum of Natural History, University of Florida, The Conversation, July 22, 2015]

There have been reports of a great white population "boom" in both New Zealand and California. Shark scientist and Marine Biologist Riley Elliott told 9news.com.au in 2021 a spate of great white shark sightings in New Zealand has lead to the Bowentown area on the North Island being deemed a "hotspot". Meanwhile two factors have caused numbers along the Californian coastline to skyrocket since 1994, according to Marine Biologist Chris Lowe. "Great whites became protected and the use of gill nets were banned," Dr Lowe told 9news.com.au. "Their biggest population growth has been since the 90s."[Source: Raffaella Ciccarelli, Tara Blancato, Nine News, February 17, 2022]

Great White Sharks Seen Less Often in South Africa

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The cool waters off Gansbaai, on South Africa western cape, were once regarded as the great white shark capital of the world. Now they are rarely seen there. And their decline has been rather abrupt. Sara Andreotti, a marine biologist at the University of Stellenbosch, told CBS News in 2016 you would see five to 20 great white sharks a day during peak season. Now you'd be lucky to see that many in an entire year. Their numbers are in steep decline, and sightings of the deadly predator off the country's have been dropping rapidly for the past five years. "It's sad also, the disappearance of such a large predator," Andreotti said. [ Debora Patta., Source: CBS News, June 5, 2021]

“Scientists like Andreotti and her colleagues believe long-line fishing is one of the main culprits. It legally targets smaller shark species exported to Australia for fish and chips. The problem, explains marine biologist Mary Rowlinson, is this is also the shark's food. "And so we are depleting their food resources. And if you deplete the food resources, it creates greater competition between individuals, which makes it more difficult for each individual white shark to survive," Rowlinson said.

Then there is the problem of fishermen inadvertently catching sharks. "You put down a big net, and you're trying to catch hake, but instead, you catch the sharks and calamari and ray. So it's kind of collateral damage," Andreotti said. Some researchers blame the disappearance of the great whites on another predator: killer orcas whales. They say they've chased the shark population away. But Andreotti doesn't buy it. Orcas and great white sharks have lived within close proximity in the area before with no problems. "My bigger fear is that while we are arguing whether they moved or whether they're being killed off, we lose the few that are still left," she said.

Over 100 miles away in False Bay, another hotspot, the shark population has also declined dramatically. Seferino Gelderbloem has been a shark spotter for twelve years. His job has been to keep watch for great whites, sounding a warning when they swim dangerously close to surfers. But that siren has been silent for a long time now. "It does concern me because, I mean, they are on top of the food chain, so they keep the seals intact. So they feed on the sick and injured, so they just keep it balanced," Gelderbloem said.

Without the sharks circling the bay, there has been a proliferation of seals. More seals mean more fish are being eaten, affecting the delicate ecosystem of the ocean — an ocean we depend on for oxygen. "If you don't have those top predators there, keeping everything in balance and in check, unfortunately, our oceans will eventually die. So protecting the oceans is protecting ourselves," Rowlinson said.

South Africa's Great White Sharks Could Die Out — Study

A study released in July 2016 said South Africa’s great white sharks could die out due to human interference, ocean pollution and a limited gene pool. Reuters reported: “There are 350-520 great white sharks left off the South African coast, 50 percent fewer than previously thought, according to a six year study carried out mainly in Gansbaai, a shark hotspot 160 kilometers from Cape Town. "South Africa’s white sharks faced a rapid decline in the last generation and their numbers might already be too low to ensure their survival,” said Andreotti, research leader..[Source: Wendell Roelf, Reuters, July 20, 2016]

“Thousands of tourists travel to South Africa's Western Cape each year to catch a glimpse of the ocean's top predator from underwater cages, but human interaction has made the largest contribution to declining local shark numbers. Shark nets used to protect swimmers and surfers killed more than 1,000 great whites off the Durban coast in the 30 years up to 2008, while trophy hunting and pollution also killed off large numbers of the sharks.

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“South African great white sharks also have the lowest genetic diversity of all white shark populations globally, making breeding more problematic and the likelihood of illness higher, the study, which included documenting individual sharks by their dorsal fins, showed. There are only 333 great whites capable of breeding in South African waters, below the 500 usually needed to prevent "inbreeding depression", the study found. "We are already in a situation where our number of breeders is below the minimum level required for a population to survive," Andreotti told reporters.

“South Africa helped pioneer great white shark conservation and in 1991 became the first in the world to declare the predator a protected species, with other countries including the U.S. and Australia following suit.“Losing great white sharks, which have no natural predators, would have a knock-on effect on ocean ecology. Common prey, such as the Cape fur seal, could flourish in their absence and reduce fish numbers.

Orcas Blamed for the Decline of South African Great White Sharks

Orca attacks have likely been one reason — if not the main reason — why great white sharks are seen less frequently in waters around Cape Town, South Africa that before, according to a government report. Library of Congress reported: While the disappearance of great whites had been blamed on illegal hunting and overfishing, the report found that the sharks vanished around the same time two killer whales arrived in the area in 2015. Shark spotters initially reported declines in shark sightings in the area in 2017 when the remains of shark carcasses washed up on beaches. [Source: Sophia Ankel, Business Insider, November 22, 2020]

“Between 2010 and 2016, shark spotters recorded around 205 great white sharks living along the coastal sites of False Bay and Gansbaai, which lie off the eastern shore of Cape Town. However, in 2019 and 2020 only one shark sighting has been confirmed. The report stated the sharks vanished around the same time two killer whales arrived in the area in 2015. The disappearance of great whites had previously been blamed on illegal hunting, climate change, and overfishing

According to the researchers, they "found some evidence for a causative link between the appearances of a pod of orcas that had specialized on preying on white sharks." Two male killer whales, Port and Starboard — named for their collapsed dorsal fins that bend right on one and left on the other — are believed to the main culprits preying on the sharks, often eating only their livers.

AFP reported.“Shark spotters initially reported declines in shark sightings in the area in 2017 when they found the remains of five sharks killed by orcas in the Gansbaai area. Another shark killed similarly was found washed up on a beach this year and there could be many more, according to Alison Kock, a marine biologist and one of the authors of the report. “Each and every time that this happened, there was an immediate drop and gap in white sharks sighting," Kock said during the report presentation.

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“A US-based study published in the journal Scientific Reports last year found that the mere presence of orcas in the water led to a noticeable absence of great white sharks. The study's authors suggested that eating great whites' highly caloric livers could give orcas an energy boost. “It's a bit ironic — when we think about white sharks, it's hard to imagine they are risk-averse," Salvador Jorgensen, a shark expert at the Monterey Bay Aquarium told Business Insider at the time. “But this study shows that even for these massive predators, knowing when to pull out and flee is an important part of their repertoire."

“A great white shark can grow to 20 feet or longer. The orca is slightly bigger but weighs much more. Male orcas weigh 7 to 10 tons. The biggest great white sharks weigh about 2.5 tons.

Liver-Eating, Shark-Killing Orcas of South Africa

In March 2023, AFP reported: Marine biologists were alerted to the find by beach walkers who stumbled upon the grim sight in Gansbaai, a small fishing port 150 kilometres (93 miles) south east of Cape Town. "The dead sharks are torn open at the pelvic girdle, they have Orca teeth marks known as rake marks on their pectoral fins and their liver is missing," said Alison Towner, 37, a shark scientist with the Dyer Island Conservation Trust.[Source: Julie Bourdin, AFP, March 4, 2023]

All evidence points to "Port" and "Starboard", an infamous pair of killer whales spotted off Gansbaai only three days earlier. Recognisable by their twisted dorsal fins, the animals are well known to locals, who have developed a penchant for sharks. "We found in total 20 sharks," said Ralph Watson, 33, a marine biologist with local conservation and diving group Marine Dynamics. Victims included 19 broad nosed seven-gill and one spotted gully sharks, he added.

Towner said the slaughter was noticeable as it was the first time that Port and Starboard had hunted those species in the area and "so many of them washed out after one visit." Yet, it wasn't the orcas' most daring hunt. Experts credited the duo with having caused white sharks to disappear from some of the waters near Cape Town. Orcas, the ocean's apex predator, usually hunt dolphins in these parts and have been known to prey on smaller shark species. But evidence of attacks on great whites was previously limited.

Port and Starboard were first spotted near Cape Town in 2015. "They probably came from somewhere else. West Africa, east Africa, the Southern Ocean, we don't know," said 45-year-old Simon Elwen, who heads Sea Search, a scientific collective. Unlike other killer whales, the pair likes to hunt near the coast — something that has made their peculiar fins a common sight in the region. "Within southern Africa, Port and Starboard have been seen from as far west as Namibia to as far east as Port Elizabeth," said Elwen.

The marine mammals' killing technique is "surgical", added Watson, explaining the pair targets sharks' liver, "a very nutritious organ, full of oils." "They tear open the pectoral girdle chest area... then the liver flops out," said Watson. Such behaviour is not hard-wired, but learned — one of the arguments for suggesting that whales have 'culture'. In the clip, the other four orcas shown were not known to have attacked white sharks before."This is now an additional threat to shark populations on coastal South Africa," said Towner.

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Elwen said it was "fascinating, and frustrating" to see "a rare, endangered animal killing another endangered species". Still, the overall danger Port and Starboard posed to South Africa's shark population remained very limited. Hundreds of thousands of sharks are fished out of the sea every year, said Watson. "Two killer whales are not going to wipe out a species," Elwen said.

Evidence of Orca Attacks on Great White Sharks off South Africa

An article in African Journal of Marine Science focuses on two killer whales Port and Starboard killing great white shark. "Initially, following an orca attack in Gansbaai, individual great white sharks did not appear for weeks or months," the article's lead author, Alison Towner, told SWNS. "It mirrors what we see used by wild dogs in the Serengeti in Tanzania in response to increased lion presence," she added. "The more the orcas frequent these sites, the longer the great white sharks stay away." [Source: People, July 1, 2022]

According to the article's findings, between 2017 and 2022, eight great white sharks have washed up dead on South African shores with identifiable orca bite marks. Seven of those sharks had their livers removed by the whales during the attack, and some of them had their hearts removed too. All of the dead sharks found had distinctive wounds traced to the same pair of killer whales.

Researchers believe the orcas have killed more than the eight great whites found washed up on shore and that other killer whales are capable of similar attacks. Towner, a Ph.D. student at Rhodes University in Makhanda, South Africa, said that this research "is particularly important" because it determines "how large marine predators respond to risk."

She added that the research can also help scientists understand the "dynamics of coexistence" between "other predator communities." Towner's recently published study used long-term sightings and tagging data to show that the two orcas have scared great whites away from South Africa's Gansbaai coast, which the sharks dominated for years. Located 60 miles east of Cape Town, Gansbaai was known for great white sightings. Towner, a senior biologist at the Dyer Island Conservation Trust off the southern tip of Africa, lives in Gansbaai and has witnessed firsthand how the two shark-hunting orcas have driven great whites out of the area and changed the sea's ecosystem. "It's triggered the emergence of a new mesopredator to the area, the bronze whaler shark, which is known to be eaten by the great white shark," she explained. "Balance is crucial in marine ecosystems. For example, with no great white sharks restricting Cape fur seal behavior, the seals can predate on critically endangered African penguins or compete for the small pelagic fish they eat," Towner added.

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Video of Orcas in South Africa Attacking a Great White Shark

In May 2022, Starboard, one of the orcas described above, and another four orcas were captured on video chasing and killing a great white off Mossel Bay, a southern port town in South Africa. The unusual behavior had never been witnessed in detail before. It suggested the practice of orcas killing sharks for their livers was spreading and that orcas have capacity to teach the hunting technique to each other. [Source: Julie Bourdin, AFP, March 4, 2023]

In paper in the Ecological Society of America’s journal Ecology scientists analyzed the video of a group of orcas hunting a great white shark at Hartenbos Beach, South Africa, a statement from the Ecological Society of America said. Authors of the paper believe the footage suggests this behavior of killing great white sharks is spreading among orcas, highly intelligent and social marine mammals that hunt in groups. Previous studies found orcas spread new behaviors over time through cultural transmission. [Source: Camille Fine, USA TODAY, October 7, 2022]

Only two killer whales have been linked to hunting great white sharks in South Africa, but attacks have never been seen in action. In the video, five whales circle the shark and eat it. Researchers assume the same group was witnessed by another pilot just before the event attacking two sharks in the same area. Starboard can be seen eating the shark's liver in the video.

The study provides new insight into how sharks are defending themselves against orcas. “This behavior has never been witnessed in detail before, and certainly never from the air,” said lead author Alison Towner, a senior shark scientist at Marine Dynamics Academy in Gansbaai, South Africa.

The presence of killer whales caused sharks to use evasion strategies commonly seen in seals and turtles and attack caused all but one great white shark in the area to flee for a period of time, according to survey data before and after the attack. Researchers first observed the flight response to killer whales in 2015 and 2017 in False Bay, South Africa. “The sharks ultimately abandoned former key habitats, which has had significant knock-on effects for both the ecosystem and shark-related tourism,” said Dr. Alison Kock, South African National Parks shark expert and marine biologist.

“It may be that great white sharks are rebounding across the world: following the bigger seal and sea lion populations, re-establishing themselves in their old hunting grounds, reclaiming the coasts they nearly lost.

“Then again, it may be that great whites today are hanging over the abyss of extinction, clutching the edge by the skin of their jagged teeth. Will we look past our fear and reach out a hand to this creature? Can we take pity on the pitiless eyes of a monster?

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Image Sources: Wikimedia Commons; YouTube, Animal Diversity Web, NOAA

Text Sources: Animal Diversity Web (ADW) animaldiversity.org; National Oceanic and Atmospheric Administration (NOAA) noaa.gov; Wikipedia, National Geographic, Live Science, BBC, Smithsonian, New York Times, Washington Post, Los Angeles Times, The New Yorker, Reuters, Associated Press, Lonely Planet Guides and various books and other publications.

Last Updated March 2023

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