Videos and images shared online have helped scientists unlock a series of mysteries about the complex but often brutal relationship between two giants of the ocean.
While Facebook and Instagram are often vilified for having a negative effect on society, content shared on these platforms has provided a scientific breakthrough. New Zealand (Aotearoa) researchers spent two years meticulously analysing footage frame-by-frame to better understand why orcas are targeting sunfish, the world’s largest bony fish.
They witnessed orcas selecting them for their high water content, sucking them dry like popsicles. Equally interesting were the complex manoeuvres lumbering sunfish are using to escape. This behaviour has been reported all over the world wherever the two species touch paths.
It’s believed this is the first time data from social media sites has been harvested to make a discovery about a new aspect of an apex predator’s feeding behaviour.
Sunfish perform amazing tricks to escape orcas
The team included cetacean expert Dr Ingrid Visser, sunfish scientist Dr Marianne Nyegaard and reacher London Fletcher, who worked together to create three papers focusing on both predator and prey. “There’s never been anything like this done before,” Dr Visser told Yahoo News Australia.
The evasion behaviours used by the sunfish are believed to be an innate behaviour, rather than something learned. Some videos showed the fish breaching water, spinning and even swimming upside-down despite their massive weight and clumsy body shape.
Gory details of how orcas kill sunfish
Orcas groups are distinct enough for some scientists to consider them different subspecies. While some populations specialise in hunting fish, others target marine mammals, and surprisingly it was predominantly the latter group attacking sunfish.
If it wasn’t so gruesome it would be quite beautiful.Dr Ingrid Visser
Working to understand why, researchers focused on which individuals within the group were attacking sunfish and found a “high prevalence” of adult and juvenile pairs.
Because attacking sunfish has a low risk of injury, in some cases mothers were likely using them to teach their young to hunt, but the way in which the complex method orcas were using to slowly kill their prey indicated a separate motivation.
“The orca were ripping the sunfish’s pectoral fin joint open and then extracting the intestines out. The sunfish is still alive, and here’s the orca swimming around like a ribbon ballerina in the Olympics. If it wasn’t so gruesome it would be quite beautiful,” Dr Visser said.
Looking through 100 published papers, the team were unable to find evidence of orcas targeting intestines in 50 other prey species, instead there were multiple references of them being discarded.
After eating sunfish intestines, orcas would kill and systematically dismember the sunfish until they were left with what Dr Visser describes as a stripped vessel resembling an “envelope or a taco”.
Why mothers and calves are targeting sunfish
What came next she describes as “freaking weird”, as many videos showed orcas sticking their faces inside the sunfish bodies.
Researchers were interested to understand what makes sunfish biologically different to other species and focused on their body cavity and intestines being high in water.
They refocused on the significance of mother and juvenile pairs and found relatively high numbers of mothers and calves and pregnant orcas.
It’s believed orcas get up to 90 per cent of their water from food. Pregnant and lactating orcas require increased hydration, so anything they can do to increase their water intake will help. Dr Visser believes they are targeting sunfish like humans would a watermelon or popsicle. “They're eating them, and then metabolising them into a drink,” she said.
As well as documenting how sunfish and orcas interact, the team also made a discovery about species that are hunted. Orcas were previously known to attack 170 different prey species, but the study revealed two extra species of sunfish that had previously not been known to be part of their dining repertoire, the giant sunfish and the sharptail sunfish.
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