Earlier this month, authorities closed Waimanola Bay Beach Park in Oahu, Hawaii after the carcass of a humpback whale washed ashore there. The carcass was removed on April 14, but there was concern about lingering elevated shark danger, as several hefty tiger sharks had been feasting on the huge corpse while it was still adrift:
Lieutenant David Loui of the Honolulu Ocean Safety Division had jet-skied out to the dead whale before it washed up, and had an up-close look at the scavenging sharks.
“One of the sharks, probably about 12 feet [3.7 metres], was actively coming up to the jet ski craft and almost making lunges toward it, and basically trying to scare us off,” Loui told Hawai’i Public Radio.
The carcasses of large whales provide a major food source for a dizzying host of scavengers and decomposers from the ocean surface down to the seafloor, where hagfish, molluscs, crustaceans, and loads of other bottom feeders celebrate the “whalefall.” It’s no surprise that sharks are often among the earliest attendees of these cetacean buffets, given their excellent sense of smell and those famously formidable mouthparts capable of tearing into freshly expired whale hide.
Tiger sharks boast some of the most formidable of those mouthparts, and combine them with dietary preferences that are about as far from “picky” as you can get. An in-depth review of shark scavenging on great whales (baleen whales and sperm whales) published in Global Ecology & Conservation in 2019 showed this widespread, blunt-headed carcharhinid (or requiem) shark to be among the most frequently recorded species at whale carcasses, along with the great white.
Indeed, white and tiger sharks have been seen more than once tucking in at the same time to whale-sized feasts. Perhaps unsurprisingly, given how much meat’s on hand to satisfy plenty of toothy mouths, antagonistic behaviour between the two species in such circumstances appears to be basically nil. Observers have noted some fairly low-key interactions between sharks of the same species while communal whale scavenging, often with a rough size-based hierarchy appearing to keep order, but overall the mood at these get-togethers, whether interspecific or intraspecific, seems to be pretty chill. (Pretty chill, we should qualify, depending on the whalemeat-to-shark ratio.)
The Global Ecology & Conservation report also described three new observations of whale scavenging in Australian waters, including a sperm whale fed on concurrently by both white and tiger sharks. From that and other published observations, the authors noted that white sharks typically employ head-shaking to tear off whale flesh, while tiger sharks more commonly use a slower “saw-biting” style often accompanied by body rolling.
Various scavenging events logged in the literature have turned up differing observations of where sharks tend to concentrate their munching on dead whales, but generally (and not exactly shockingly) they do seem to seek out more blubber-rich parts of the carcass.
Incidentally, great whites aren’t the only fellow apex predator tiger sharks have been seen joining in a good old-fashioned whale feed. In 2017, four tiger sharks and a saltwater crocodile were photographed attending to a dead, belly-up humpback about a kilometre off the Western Australian coast near Montgomery Reef. Here again, minimal direct interactions between the two well-armed predators were recorded, though at one point a shark seemed to direct a tail flick at the croc, and observers weren’t sure whether the reptile hauling out briefly on one of the whale’s flippers was it avoiding sharks or simply taking a breather. The tiger sharks took out great half-moon chunks of flesh, while the croc’s smaller, ripping tugs left less visible marks.
That well-gnawed 15-metre whale carcass later washed ashore and ended up drawing a whole battalion of scavenging crocs.
Expired Whales on Shark Menus
While observations of sharks scavenging whale carcasses aren’t all that common, researchers speculate dead whales may be an important, underestimated food source for the toothy fish. (And, the fossil record suggests, a longtime one.)
A 2013 paper out of a long-term study of white sharks and Cape fur seals in False Bay, South Africa documented several instances of great whites scavenging baleen whales there: southern right and Bryde’s whales, specifically. The authors speculated that the gradual disappearance of larger white sharks – those over four metres in length – from the seal rookeries at Seal Island, a seasonal hotspot for pinniped-hunting great whites, may reflect a shift in food preferences: Perhaps, they reason, sharks too big to effectively catch agile fur seals – or too big to rely on them as a nutrition source – spend more time patrolling the bay and beyond for dead or hampered whales. The rapid appearance of great whites north of four and five metres at the dead whales detected by the researchers, they suggested, further supports this idea.
“The ease of encountering and observing white sharks predating upon seals at seal rookeries worldwide likely creates a biased and misleading view of white shark foraging behavior,” they wrote. “Despite being efficient predators of Cape fur seals [...], we suggest that whale scavenging represents a critical and more frequent, but rarely observed, component of white shark ecology.”
The paper further speculated that whale-carcass bonanzas could offer an opportunity for white sharks to find mating partners, given how they can draw together so many large, mature individuals.
Great whites and tiger sharks commonly star in the whale-scavenging events actually witnessed by people, but certainly other shark species partake. The Global Ecology & Conservation review cited an observation from 2017 of tiger and bull sharks feeding together on a sperm-whale carcass in the Seychelles, with tawny nurse sharks circling below for scraps. Last month, sandbar sharks were among the dinner guests at a dead North Atlantic right whale off the South Carolina coast that also drew in great whites and tiger sharks. Oceanic whitetip sharks, once exceedingly common pelagic requiem sharks whose numbers have plunged in recent decades, were frequent scavengers at whale carcasses in the heyday of industrial whaling.
(The 1971 documentary Blue Water, White Death, which ended up capturing groundbreaking underwater footage of white sharks off Australia – and whose influence shows up not only in Jaws but in Wes Anderson’s The Life Aquatic With Steve Zissou – also features striking, cage-diving shots of oceanic whitetips, blue sharks, and dusky sharks swarming sperm whales killed by whalers off the Durban, South Africa coast.)
Deepwater sharks, meanwhile, beeline for whalefall. A few years back, the BBC crew filming for Blue Planet II captured a gang of bluntnose sevengill sharks ripping into a sperm-whale carcass (and getting kind of testy in the process) on the Atlantic seafloor.
Whale Hunters?
That a variety of sharks are enthusiastic scavengers of whale carcasses is well-established. But there’s increasing scientific recognition of sharks as occasional predators of decent-sized whales, as well. (And we’re not just talking that bygone shark-of-all-sharks, Megalodon.)
It’s long been known that large sharks will prey on smaller cetaceans, mainly those of the toothed-whale or odontocete family. A 2001 survey of shark interactions with dolphins named five shark species as “relatively frequent” predators of dolphins and porpoises – white, tiger, bull, sixgill, and sevengill sharks – and called oceanic whitetip and dusky sharks “occasional” ones. It noted several other suspected odontocete hunters, including Pacific sleepers, Greenland sharks and shortfin makos, plus a few other midsize requiem sharks.
The degree to which sharks may prey on baleen whales is less well-established, but it does happen here and there. White sharks have previously been known to take odontocetes as large as beaked whales, but research over the past several years suggests they may be threats to young and compromised baleen whales as well.
Maybe “suggests” is too weak a word: Last year turned up indisputable evidence that great whales sometimes fall to great whites. A paper released in Marine & Freshwater Research at the start of 2020 provided the first published record of successful predation by white sharks on a humpback whale. The event took place in 2017 in Mossel Bay, South Africa. Observers noticed a 7-metre-long humpback tangled in fishing rope, suffering from skin lesions and emaciation but otherwise vigorously spouting. A half-hour later, a white shark estimated at 3.5 to 4 metres approached the whale and began circling it.
Eventually the shark delivered a quick bite behind the whale’s left flipper, which let loose quite a bit of blood. The shark withdrew right away, and only bit the humpback again – this time on the underside of its tailstock – after some 40 minutes had passed. “By this time,” the authors of the paper wrote, “the whale had lost a large amount of blood and slowed its swimming patterns.”
The shark hung back again after this tail bite, and then a second, slightly bigger white shark appeared – the cue for the first shark to exit the scene. The second shark also bit the whale’s tailstock, which at this point was bleeding profusely. As the beleaguered humpback became more and more lethargic, the remaining shark kept circling, and eventually bit the upper side of the tailstock – a more aggressive attack, complete with head-shaking. The whale sank a few minutes later.
The paper noted that the tactics of the attacking sharks fit the “bite-and-spit” pattern defined for great-white predation on pinnipeds. This strategy sees the shark chomp its prey, then retreat and essentially allow it to bleed out, lessening the chance of injury to the predator.
Then, in July of last year, another humpback was taken out by a white shark farther east off the South African coast, near Port Elizabeth. Captured by drone footage, the roughly 4-metre-long shark – a female known as “Helen” to researchers who’d tagged her – attacked a 10-metre-long whale, which was also rope-entangled, over more than an hour, first lodging a bloodletting bite to the tail. After about a half-hour, Helen targeted the weakened humpback’s head, and appeared to force the whale underwater sufficiently to drown it.
Helen’s behaviour dispatching the humpback raised the possibility of an experienced whale-hunter. “The shark was very strategic about it, there was no hesitation, it was as if she knew exactly how to go about it,” Ryan Johnson of the Blue Wilderness Shark Research Unit, who filmed the attack, told The Times.
In July 2013, meanwhile, an intriguing sighting off Western Australia suggested white sharks may, like local orcas, sometimes try for the calves of migrating humpbacks. Divers filming a humpback mother, her calf, and one of the adult “escort” whales that commonly accompany such cow-calf pairs witnessed a 4- to 5-metre great white cruise toward them.
“The escort began spyhopping when the shark approached from directly behind the whales,” a 2014 paper in Marine Mammal Science that described the incident noted. “The mother humpback, apparently recognizing the danger, lifted the calf out of the water on her head. A few minutes later the calf breached several times. The escort remained behind the mother/calf pair, and began slapping its flukes vigorously when the shark approached, while the mother moved away from the calf. The shark disappeared and all three whales joined up again shortly afterward.”
The vigorous response of the escort whale to the white shark jibes with similar active defence of calves against orcas, suggesting these Western Australian humpbacks recognise both killer whales and great whites as potential threats to their young.
Among living sharks, it’s hard to imagine one better equipped for occasional snacking on living baleen whales than the great white. But medium- to large-sized requiem sharks have also been seen attacking injured and sick whales.
One such incident also came from South Africa: a July 2014 observation off Port Johns near the mouth of the Mzimvubu River, when some 10 to 20 dusky sharks were seen harrying a humpback calf reckoned at less than two weeks old and apparently abandoned. This was during the great annual sardine run along the South African coast that draws in significant numbers of duskies, and which overlaps with the migration and calving time of humpbacks headed for wintering grounds off Mozambique.
The sharks – all of which were about two to three metres long – repeatedly bit the whale calf’s flanks, particularly its left side, and particularly when the humpback dove down. But some deeper bites were also lodged near the calf’s head. The distressed calf – whose only real defensive response appeared to be fleeing from the trailing, relentless sharks – eventually stopped surfacing and was presumed “drowned due to exhaustion and stress.”
In 2006, an estimated 25 tiger sharks participated in a fatal attack on an “ailing” humpback whale, thought to be about a year old, off the Big Island of Hawaii. Shark attacks have been recorded on young humpbacks in Hawaiian waters before, including a juvenile stranded on a reef in 1995 and a calf attacked and presumed killed the next year by multiple tiger sharks despite the efforts of its mother and an escort. Also in 1996, large tiger sharks were seen circling an entangled adult humpback that was ultimately freed by rescuers.
Among the more dramatic cases of shark predation on baleen whales comes from 2002, when bull sharks apparently delivered the coup de grace to a 17.4-metre blue whale stranded for several weeks in Prony Bay, New Caledonia. That rorqual ended up attracting a bevy of tiger sharks, providing an opportunity for scientists to document hierarchical behaviour among the heavy-jawed scavengers: Dominance seemed to be established based on “size and level of aggression.”
It’s worth closing on the requisite note about circle-of-life predation. Challenging as it may be to watch sharks capitalise on an injured or poorly whale, we might suspect that death by a hundred sharkbites might (might) be a preferable way for a leviathan to meet its maker than a slower-burn demise. And it’s likely that the shredding of a freshly dead whale by razor-toothed sharks helps spread the love among scavengers less well-equipped for slice-and-dice enjoyment of such gargantuan bounty.
Top header image: Barry Skinstad
Predator vs Prey
Predator vs Prey
Predator vs Prey
