Great White Shark Versus Killer Whale, not the most recent popular straight to video B movie, but the topic of some recent research to cause some waves in the marine science world. It's conventional wisdom that the great white shark, Carcharodon carcharias, is the top predator roaming the oceans and their mere sight sparks fear in their prey and humans alike.
In 2017 the washed-up carcasses of five great whites appeared on the shores of South Africa’s Western Cape province. The animals ranged in size from 9ft to 16ft in length and all five individuals shared one odd similarity. There were holes puncturing the muscle wall between the pectoral fins with almost surgical precision. Weirder still all five were also missing their yummy calorie-dense livers.
Great white shark with it's liver missing
What in the ocean could be predating on these supposed apex predators with such strange eating habits? The characteristics of the bite marks, combined with confirmed sightings indicated orcas, Orcinus orca, were those responsible for this unique targeted predation.
A recent publication in Nature Scientific Reports by senior research scientist Salvador Jorgensen at the Monterey Bay Aquarium and his colleagues has shed some light on the relationship between these top ocean predators.
In 2009 Jorgensen and his team radio-tagged 17 sharks around Southeast Farallon Island in Greater Farallones National Marine Sanctuary off the coast of California. Through September and December, the sharks preyed upon on young elephant seals around the island, which is typical behavior. However, when a pod of orcas enters these waters even for just a couple of hours, the sharks immediately leave the area, and most do not return at all during that season. Jorgensen and his team looked back into historical data from 165 sharks from 2006 to 2013 to see if this situation was common or not. They also compared the telemetry data with whale, shark and seal surveys undertaken in the sanctuary over the last 27 years. They found a shared pattern over time.
“When confronted by orcas, white sharks will immediately vacate their preferred hunting ground and will not return for up to a year, even though the orcas are only passing through,” Jorgensen says in a press release.
In 1997, the first ever recorded interaction at Southeast Farallon was witnessed by fishermen where a pair of orcas killed a young great white and then ate its liver. In years where the orcas made an appearance near the island, which they did in 2009, 2011 and 2013, the number of elephant seals observed eaten by sharks dropped by 62 percent from the previous year. The presence of orcas creates some interesting dynamics, being a win for the seals, but causes a shift in great white shark predatory behaviour.
Interestingly, the great white sharks are displaying fear or risk aversion. How this could affect fitness in the long term? How fear affects the great white sanctuary population over time is yet to be delved into. The ability for the orca to create “fear” with wide-ranging impacts on the ecosystems could have really interesting implications and this relationship is one of the first to be documented in the vast oceans.
To understand how orcas could immobilize and kill a great white please see the following video
To read this fascinating full text publication please Click here
Jorgensen, S. J., Anderson, S., Ferretti, F., Tietz, J. R., Chapple, T., Kanive, P., ... & Block, B. A. (2019). Killer whales redistribute white shark foraging pressure on seals. Scientific Reports, 9(1), 6153.
