It’s the showdown that would make a hit Hollywood movie: monster squid vs monster shark. Both armed with their own weapons – the squid with serrated tentacles and the shark with its razor-sharp teeth – it would be a true nail biter to see who would be crowned victor before the credits rolled.
But this isn’t a movie… it’s real life.
Shark and cephalopod interactions aren’t new, having been documented in studies around the world due to cephalopods representing more than half of the diet in some shark species (e.g. blue sharks, scalloped hammerheads, and pelagic threshers). Just as humans enjoy the occasional octopus dish, these elasmobranchs seek out these animals for the proteins, carbohydrates, and fatty acids that make them so delicious. Great white sharks (Carcharodon carcharias) also like to dine on cephalopods, and they are considered an important component of their diet as large amounts have been found in their stomachs and the isotopic muscle values. However, there is little information about the encounters between white sharks and large squids in the eastern North Pacific Ocean, especially around Guadalupe Island.
Also known as Isla Guadalupe, this volcanic island located off the west coast of Baja California is an important feeding site for these big predators. Known for its clear visibility and thrilling shark encounters, both tourists and scientists flock to the remote location to get a glimpse of the largest predatory fish in the world. Found in cool, coastal waters worldwide, great whites grow to an average of 15 feet (4.6 meters) in length, although individuals measuring more than 20 ft (6 m) have been recorded.
Within the range of white sharks in the eastern North Pacific Ocean, there are areas where you also see a variety of large squid species such as the neon flying squid (Ommastrephes bartramii), purpleback squid (Sthenoteuthis oualaniensis), sharpear enope squid (Ancistrocheirus lesueurii), jumbo squid (Dosidicus gigas), and probably the giant squid (Architeuthis dux). Since white sharks and squid interaction studies are so rare, researchers are excited that a new study has provided evidence of these battles in Guadalupe Island, hoping to highlight the importance of squid as potential prey in subadult and adult stages of white sharks.
A total of fourteen white sharks were detected with unusual scars on their body between the years 2008 and 2019; the majority were subadults and had scarring mainly on the head and trunk. “The scars observed on the white sharks were double or single layers with multiple sucker marks around the shark’s head and in the trunk between the dorsal and pectoral fins,” write the authors in the study published in Nature. “Wounds near the shark’s mouth and trunk suggest a defensive response from squid to the white shark, although this could not be confirmed.”
The showdown probably happened in the squid’s home territory: the deep. And while that may be surprising, it is well-known that subadult and adult great white sharks can dive down to the deep waters nicknamed the “twilight zone,” just beyond the reach of sunlight. A layer of water that lies about 650 – 3,300 ft (200 to 1,000 m) below the ocean’s surface, the vertical movements of white sharks in deep waters have been identified as potential foraging behaviour in several places. For example, they reach an average depth of 1450 – 1634 ft (442-498 m) in the oceanic zone known as the Shared Offshore Foraging Area (SOFA) and can get deeper than 984 ft (300 m) in Guadalupe. As the researchers state: “Both SOFA and Guadalupe Island have been suggested as areas with a high diversity of potential prey, in which cetaceans, sharks, bony fish, and cephalopods seasonally occur.”
But who is responsible for the scars seen on the great whites? Well, that’s the tricky part. Without being able to see it in real time, the scientists could not confidently confirm the species. However, the marks from the analyzed sharks suggests it could have been the jumbo squid (D. gigas), the neon flying squid (O. bartramii), or the giant squid (A. dux) based on the estimated size of the scars and suckers.
The scientists hope that this new research highlights the importance of the twilight zone as a shared habitat for both of these predators, and that future ecosystem studies should consider both species for management and conservation purposes.