Photo: Oleksandr Sushko//Unsplash
Shark cannibalism is something researchers have been aware of in the past but our overall understanding of the phenomenon has previously been limited to the largest adult versions of the apex predators eating relatively smaller animals, like infants. The discovery of a tracking tag in the Northeast Atlantic has shed light on something that had yet to be confirmed until now: large sharks hunt and prey on other large sharks.
The news comes from a study published on Monday, in which researchers at Arizona State University, Oregon State, and the Atlantic Shark Institute had to do some detective work when a satellite tag placed on an adult porbeagle shark returned some very odd data. The original research project was intended to understand the whereabouts, behaviors and, environmental preferences of porbeagles, whose populations are most prominent in colder waters of the North Atlantic and Southern Hemisphere. Tags placed on the sharks in 2020 were designed to break off after one year and then float to the surface of the water.
Once satellite data was retrieved from a specific tag, researchers could trace movement throughout the water column as well as across different locations, and more. One particular shark’s tag started returning data in 2021, just five months after researchers had tagged the adult female, which can grow up to almost 13 feet long and weigh 500 pounds. Not only that, researchers also recognized unusual data such as drastic temperature spikes and dips before the tag had risen to the surface.
At first, the researchers were curious about the pregnant porbeagle’s movement, which had tracked the animal through unusually warm water temps for its species ranging from 61.5 degrees Fahrenheit (16.4 degrees C) to 76 degrees Fahrenheit (24.7 degrees C). As mentioned, the findings encouraged the researchers to dig a little deeper into what seemed like peculiar behavior.
“A PSAT deployed on a pregnant porbeagle Lamna nasus in the Northwest Atlantic suggests the shark was predated upon in mesopelagic waters near Bermuda,” researchers wrote. “Predation was evident approximately 5 months after tagging based on depth and temperature data transmitted by the PSAT. Four days prior to PSAT pop-off, depth data indicated that the tag continued to descend and ascend in the water column while the temperature remained approximately 5°C above ambient levels, even at several hundred meters in depth, indicating ingestion. Given the location of predation and elevated temperature at depth recorded by the pregnant porbeagle’s tag, potential predators include endothermic shark species such as the white shark Carcharodon carcharias and shortfin mako Isurus oxyrhinchus. This is the first evidence of predation on a porbeagle globally and provides novel insight into inter-specific interactions for this large, threatened shark species.”
The new evidence may be confined to an isolated incident but it’s significant enough that more research is now expected to be directed at this exact phenomenon. And while the researchers don’t know who exactly was the culprit preying on their original pregnant porbeagle subject, at least one spokesperson involved in the project is putting their money on a large female great white based on its diving pattern.
