Friday, January 31, 2025

Genomic evidence confirms white shark liver is on Australian killer whales' menu

Flinders University

For the first time, DNA evidence has confirmed killer whales in Australia hunted a white shark for its liver.

Based on DNA analysis from the bite wounds on the carcass of a large white shark washed ashore near Portland in Victoria in 2023, the Flinders University-led study identified that killer whales were responsible for consuming the mid-section containing the nutritionally rich liver.

Around the world, killer whales (Orcinus orca) have been observed preying on various shark species including white sharks (Carcharodon carcharias) – as previously documented in California and South Africa.

The discovery of a 4.7 metre white shark missing its liver on a beach in southeastern Australia offered a rare opportunity to analyse distinctive bite wounds and unravel the predator’s identity.

“The liver, digestive and reproductive organs were missing, and 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 lead author Isabella Reeves, a PhD candidate with Flinders University’s Southern Shark Ecology Group and the West Australian Cetacean Research Centre (CETREC).

“Swabs were taken from bite wounds on the white shark and sequenced for remnant genetic material from the shark’s predator. We were able to confirm the presence of killer whale DNA in the primary bite area, while the other three wounds revealed DNA from scavenging broadnose sevengill sharks.

“These findings provide compelling evidence of killer whale predation on white sharks in Australian waters, with a strong indication of selective liver consumption. This suggests that such predation events may be more widespread and prevalent across the globe than previously believed.”

The study, published in Ecology and Evolution, used wildlife forensic techniques to confirm killer whales were responsible for excising and consuming the liver from the white shark. Civilian bystanders had witnessed several killer whales, including locally known individuals called ‘Bent Tip’ and ‘Ripple, catching a large prey in Bridgewater Bay two days before the white shark carcass washed ashore.

The beached large white shark carcass was collected by state government fisheries officers for investigation.

Killer whales in Australia have occasionally recorded preying on various shark species, including blue shark (Prionace glauca), porbeagle (Lamna nasus), shortfin mako (Isurus oxyrinchus), ground sharks (most likely school shark, Galeorhinus galeus), and tiger shark (Galeocerdo cuvier). But white shark liver consumption had yet to be observed in Australia – despite numerous reports of such behaviour in California and by notorious duo ‘Port’ and ‘Starboard’ in South Africa.

Several interactions between killer whales and white sharks have been reported in Australia, including at least one suspected kill at the Neptune Islands Group Marine Park in South Australia in February 2015. On that occasion, an oil slick indicative of a successful predation was observed following the interaction, although no carcass was recovered to confirm the kill.

Rhodes University (South Africa) marine biologist, Dr Alison Towner, an author in the study, says similar killer whale predation on white sharks have led to disruptions in local shark populations in both South Africa and California. “However direct observations of these interactions remain rare and their frequency is poorly understood,” she says.

Senior author, Flinders adjunct Associate Professor Adam Miller, says: "We don’t know how frequently these events occurred in Australian waters and therefore how significant these findings are," says Associate Professor Miller, who is also a senior ecologist with Cesar Australia.

"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.

"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.”

Another author, Flinders University Research Fellow Dr Lauren Meyer, adds, “This study also provides DNA evidence that scavenging is facilitated by killer whales’ tissue selection, whereby the liver and internal organs are consumed, but much of the carcass remains as a nutrient source benefiting local ecosystems.”

The ‘Nature Notes’ article ‘Genetic Evidence of Killer Whale Predation on White Sharks in Australia’ (2025) by Isabella MM Reeves, Andrew R Weeks, Alison V Towner, Rachael Impey, Jessica J Fish, Zach SR Clark, Paul A Butcher, Lauren Meyer, David M Donnelly, Charlie Huveneers, Nicky Hudson and Adam D Miller has been published in Ecology and Evolution (Wiley) First published: 27 January 2025 https://doi.org/10.1002/ece3.70786

The study was supported by experts from Victoria’s EnviroDNA, The University of Melbourne, Rhodes University in South Africa, the South African International Maritime Institute, Deakin University’s EcoGenetics Lab, the NSW Department of Primary Industries National Marine Science Centre, Killer Whales Australia and Dolphin Research Institute in Victoria and the Gunditj Mirring Traditional Owners Aboriginal Corporation, Victoria.

Images & captions: https://drive.google.com/drive/folders/14dzGYj5_lzHyD2jh0ADnA_AcnuKaNGtm?usp=drive_link

Acknowledgements: Researchers acknowledge the Traditional Owners of the land on which this research was conducted, the Gunditjmara and Wurundjeri peoples. Thanks to Cameron McCallum and John Melis from the Victorian Fisheries Authority and the Gunditj Mirring Traditional Owner Aboriginal Corporation. The carcass is now held by Museums Victoria.

Infographic of Reeves et al. 2025 study based on using DNA to identify that killer whales killed white shark carcass for liver.

Credit

Emma Luck

Journal

Ecology and Evolution

DOI

10.1002/ece3.70786

Method of Research

Data/statistical analysis

Subject of Research

Animals

Article Title

Genetic Evidence of Killer Whale Predation on White Sharks in Australia

Article Publication Date

27-Jan-2025

Burn grasslands to maintain them: What is good for biodiversity?

Kobe University

250131-Ushimaru-Burning-Burning — image:
It has been unclear which soils are better candidates for being managed by prescribed burning in terms of allowing a high diversity of endangered plants or plant species in general. To settle this question, a Kobe University team led by master’s student ASADA Airi from the group of ecologist USHIMARI Atushi turned to Mount Fuji, where grasslands covering different soil types are kept by prescribed burning once a year in April.
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Credit: ASADA Airi

As grasslands get abandoned, controlled burning is discussed as a labor-saving method of keeping forests at bay. A Kobe University research team found that this method results in higher biodiversity and a higher prevalence of endangered plant species in some grasslands compared to others, depending on what soils they grow on.

Humans have been keeping grasslands since millennia by grazing, mowing and controlled burning, all of these are means to keep forests from overgrowing the grasslands. Grazing and mowing are, however, labor intensive and as rural areas become increasingly depopulated, grasslands have been disappearing worldwide. One consequence of this is the loss of the habitat of plant and insect species, also many endangered ones, that depend on grasslands. To maintain grasslands nevertheless, “prescribed” burning, which is what land managers call controlled burning, is being discussed as a labor-efficient option. But not all grasslands are equal. The Kobe University ecologist USHIMARU Atushi says, “Many studies have focused on examining the effects of different management measures on plant diversity, but few researchers have paid attention to those of soil differences.” Therefore, it has remained unclear which soils are better candidates for being managed by prescribed burning in terms of allowing a high diversity of endangered plants or plant species in general.

To settle this question, Ushimaru’s team led by master’s student ASADA Airi turned to Mount Fuji. There, on a training site of the Japan Self-Defense Forces, grasslands covering different soil types are kept by prescribed burning once a year in April. “We noticed that there were some areas, especially on young lava flows, where endangered species were concentrated,” Ushimaru explains the choice of the research site, allowing them to study which soil factors influence species abundance. On site, they set up 100 one-square-meter plots across the grasslands on four different soil types and in each identified all plants as well as measured a range of physical and chemical factors.

Their results, now published in the journal Plants, People, Planet, show that grasslands on young lava flows exhibit higher total species richness, native species richness and prevalence of red-listed plant species than grasslands on both young and old scoria bedrock. They also found that the soils were different in their acidity, depth and coverage by rocks and stones, which allowed them to infer that these factors are important to the persistence of rare plants.

Previous studies showed that acidic soils make it difficult for plants to take up nutrients and shallow soils favor slow-growing plants. Asada thus argues that, as prescribed burning resets plants growth on the grasslands, these conditions suppress the growth of otherwise fast-growing and thus dominant species and so give those that are usually outcompeted and that are therefore rare a better chance of gaining a foothold.

Ushimaru sums up, “Our study was able to identify environments where grasslands managed by burning alone can harbor a significant variety of endangered species.” The team concludes their paper saying, “Identifying environments where high plant diversity can be maintained through prescribed burning not only elucidates the survival conditions of grassland plants in Japan but also proves essential for the conservation and restoration of grassland environments and grassland species in the future.”

In their paper published in Plants, People, Planet, ASADA Airi and her team report that grasslands on young lava flows (pictured) exhibit higher total species richness, native species richness and prevalence of red-listed plant species than grasslands on both young and old scoria bedrock.