Rest assured that, at any given point in time, somewhere a shark is eating something. That (admittedly pretty inane) statement has held true, in fact, for hundreds of millions of years. These days, though, the old shark-eating-something event sometimes ends up caught on video and sets the Internet alight: a new twist in an ancient routine.

There’s been a fair bit of that sort of thing going down in the past month or two, so we thought we’d present what you might consider a Sharks-Eating-Things News Bulletin Roundup. Enjoy!

It’s a Shark-Eat-Shark World Out There

Photographer/videographer Marissa Wil was flying her drone off the South Florida coast on August 14 when she keyed into some impressive splashing, which she initially suspected might be a pod of hunting dolphins. A tall sickle-shaped dorsal fin revealed the true cause: “As the whitewater faded,” she told the BBC, “I saw it was a great hammerhead.”

The great hammerhead – biggest of the hammerhead sharks, thought to reach lengths of six metres (20 feet) or more – has a real taste for its fellow cartilaginous fish. Rays, including stingrays, are popular main courses, but any number of smaller sharks are on the menu as well. This particular South Florida great hammerhead, which Wil reckoned at some 3.5 to 4.2 metres (11.5 to 13.8 feet), was “bringing the hammer down,” if you will, on an unfortunate reef shark.

Wil’s drone footage (which she posted to Instagram) beautifully captures the zig-zaggy and explosive hunting method great hammerheads commonly employ in shallow inshore waters: The bigger shark pursues its quarry with tight turns and surges of straight-line speed. In a violent conclusion to the main pursuit, the great hammerhead eventually tears the reef shark’s tail off.

“After the hammerhead ripped the tail from the reef shark, the head sank into some rocks,” Wil told Outdoor Life. “The hammerhead circled for about 10 minutes, then ate the remaining portion of the reef shark before leaving the area.”

A 2016 study on great-hammerhead predatory behaviour in shallow tidal flats identified a number of techniques with which the species takes advantage of the limited water depth to catch and consume rays and other sharks. These include the “pin-and-pivot” move, in which the hammerhead secures prey against the seafloor using its cephalofoil (aka its “hammer”), and “grasp-turning,” where a hammerhead with prey in its jaws twists and spirals tightly, perhaps using the force of swirling water to maintain its bite and aid swallowing.

Such vigorous hunting in warm tidal shallows that are often comparatively low in dissolved oxygen may exact quite the energetic and metabolic toll on large sharks. In one instance the study considered, a roughly 3.65-metre (12-foot) great hammerhead that had successfully caught a 0.9-metre (three-foot) nurse shark – executing 22 tight “grasp-turns” in the process – positioned itself facing the current, still gripping its prize, and used gentle tail-beats to remain basically stationary for some 15 minutes. Given that orientation maximises oxygen uptake through the shark’s gills, the researchers proposed it may represent a specific “post-predation energetic recovery behaviour.”

Mammal-Munching Makos

Over the last weekend of August, meanwhile, passengers aboard a Hyannis Whale Watcher Cruises boat off Cape Cod, Massachusetts saw more than just whales: They were also rare witness to a mako shark bloodily dispatching a grey seal, a good-sized pinniped found year-round in New England waters.

Grey (or “horsehead”) seals are linchpin fare for the dramatically recovering population of great white sharks – the bigger, bulkier cousin of shortfin and longfin makos – off the northeastern US coast, where observations of great-white attacks on seals have become rather commonplace in recent years (Exhibits A, B, and C). Marine mammals – from seals and sea lions to toothed whales and even the occasional young or ailing baleen whale – are indeed a dietary mainstay for adult white sharks in many populations.

By contrast, makos, famously zippy and possessing long, almost fang-like teeth, primarily target large bony fish such as tuna, mackerel, and billfish (which, to be clear, also land on the great white’s dinner plate). But large makos have also been documented preying on marine mammals occasionally, including dolphins (whose speediness the shark matches).

Last year, a whale-watching boat in Central California’s Monterey Bay observed a 3- to 3.6-metre (10- to 12-foot) shortfin mako feeding on the carcass of a sea lion. And in 2013, a 3.7-metre (12.2-foot), 600-kilogram (1,323-pound) female shortfin mako caught by rod and reel off Southern California was found to have recently gulped down a four-year-old California sea lion, and stable-isotope analysis of the shark’s tissues suggested marine mammals had constituted a not-insignificant part of its diet.

In the recent case of the Cape Cod mako attacking the grey seal, the incident also demonstrated the impacts unethical human activity can have on such natural phenomena: The Hyannis Whale Watcher Cruises post on the sighting noted, “Unfortunately, we also watched as a recreational boater approached the scene which scared the shark away.” 

Seal-Hunting Dusky Shark

Along with orcas, sharks are the most all-around important (non-human) predators of marine mammals in the World Ocean. When the totality of sharkdom is considered, however, it’s really only a relative handful of species that carry out that predation. Among the leading mammal-eaters are great whites (of course) and tiger sharks (notable hunters of Hawaiian monk seals, dolphins, and dugongs, even the odd whale calf) as well as bull sharks, various sleeper sharks, sixgill sharks, and broadnose sevengills (which have been seen pack-hunting South African fur seals).

Makos, as we’ve established, are among the other large sharks that may occasionally target dolphins, porpoises, and pinnipeds. This past July, a couple of beachgoers on the New England island of Nantucket documented what’s likely an even more occasional mammal-hunter in action.

Sandy Fink was filming seals off Great Point, the barrier beach forming Nantucket’s northernmost peninsula, while her boyfriend fished when she noticed something dramatic. “[...] I was like, ‘Is that blood?’ Wait! That is a shark, and he is eating the seal,” Fink told the Nantucket Current.

 

Greg Skomal, a Massachusetts Division of Marine Fisheries senior fisheries biologist and expert on New England white sharks, identified the seal predator in this case not as the “usual” great white, but as a dusky shark.

Dusky sharks, also known as black whalers, are among the larger members of the so-called requiem-shark family (Family Carcharinidae), sometimes reaching 4.2 metres (13.8 feet). But their main eats are bony fish, smaller sharks, rays, skates, and squid. Aside from scavenged carrion, marine mammals are probably a much rarer food source.

(A good-sized dusky shark trying for a seal is one thing, but more once-in-a-blue-moon predation attempts by this species have been recorded: In 2014, some 10 to 20 dusky sharks attacked a humpback calf in South Africa’s Pondoland Marine Protected Area. The calf eventually stopped surfacing, and observers concluded it likely drowned due to exhaustion and stress.)

The dusky shark is comparable in length, though not necessarily in bulk, to the bull shark, a requiem shark posing a much more significant threat to marine mammals. As an academic review of shark-dolphin interactions noted, bull sharks will sometimes attack prey bigger than themselves and start targeting larger animals while still on the smallish side. Research from South Africa’s KwaZulu-Natal coast suggests bull sharks there begin hunting Indo-Pacific bottlenose dolphins at a smaller size as compared to three other local dolphin-eating shark species: great whites, tigers, and duskies.

While bull-shark predation on marine mammals may be widespread, it’s not often observed firsthand. Early last year, though, a bull shark was filmed attacking a dolphin off Sydney, Australia’s Shelly Beach, an event which interrupted a surf carnival there. The mortally wounded dolphin ended up washing ashore and dying.

News From the Shark-Scavenging Beat

Sharks aren’t just top-level marine predators: They’re also grade-A scavengers, performing an essential cleanup role on our ocean planet.

And they’ve been fulfilling those duties for an awfully long time. A new paper published in the Journal of Vertebrate Paleontology proposes that, back in Miocene-time Venezuela some 11.6 to 23 million years ago, a “caimanine crocodilian of small to medium body size” preyed on a prehistoric sea cow, whose fossil skeleton suggests possible dispatching by a hallmark crocodilian “death roll.” An embedded tooth and various toothmarks, meanwhile, show that the sea cow’s carcass later served as a readymade feast for tiger sharks. (Incidentally, tiger sharks and crocodiles have been documented co-scavenging in modern times.)

And a scavenging shark certainly doesn’t turn up its nose at sharkmeat. On August 21, the cruise and charter operator Captain John Boats posted video from off Cape Cod showing a number of blue sharks feeding on an expired basking shark, second-biggest fish in the sea.