Playing catch-up with all the interesting science stuff that went by while I was still chained to the election, and then attempting to recover from the election, we come to this Querencia post mentioning, in the course of describing the idea of “re-wilding” (which I’m in two minds about but follow quietly), the growing evidence that the general reliance of orcas- “killer whales”- on seals and other smaller prey (such as otters, on which they’re wreaking havoc) may not be all that natural to them, but rather a reaction to the decimation of their original primary prey- great whales.
The idea was hugely controversial when Estes and Springer published it, and remains controversial to a degree, but the evidence seems to be on their side- as populations of truly large whales slowly recover, more and more witnessed attacks of coordinated pods of orcas attacking one or more great whales- successfully, I might add- are recorded. If you’ve seen the fabulous documentary series Blue Planet, then you’ve probably seen the sobering footage they got of a pod of fifteen orcas taking six hours to kill a gray whale calf, of which they only ate the tongue and lower jaw. (They are, apparently, gourmands, a trait they share with another extremely intelligent and inventively nasty generalist predator I know.) This is perhaps among the least impressive of their witnessed accomplishments, which include successfully killing off an apparent entire group of sperm whales. Estes and Springer’s work is described in the rather wonderful book Where the Wild Things Were (among the ones I’m slowly making my way through right now), whose entire premise is the massive ripples in ecology caused by the disappearance of top predators and of the megafauna in general.
If we think of it, the idea that was apparently the orthodox among marine mammal biologists- that the great whales had not had any significant predators at all since the disappearance of Megalodon and then the rise of industrial whaling- is a slightly odd one. Sure, elephants are currently unmolested once they get out of vulnerable calfhood, but that wasn’t true until humans strolled along and extincted the hell out of most of the Pleistocene megafauna. (Of which Megalodon was a part, actually, but we probably had a lot less to do with that one.) Such massive sources of pure, concentrated, fatty and delicious energy are an incredible resource to go unexploited for so long, and as filter feeders, they are significantly less limited than elephants in their foraging and range capacity. Before whalers got around to making whales into Earth’s first pre-fossil fuel, great whale populations amounted to a seriously nontrivial amount of seafood whose only major defense was sheer size.
It makes a great deal of sense to me that orcas might have relied more on these traveling meat lockers than on such relatively light snack food as seals and sea otters; not only does it fit better with their size, but also with their anatomy and social lives. Orcas are, famously, social hunters that travel in groups; this is a strategy normally adopted by predators that are significantly smaller than their prey- the advantage of numbers and intelligence to take on a dangerously large and formidable animal. Lions use it to take out Cape Buffalo. Wolves use it to take out moose and sometimes even musk oxen, hyenas will sometimes try for hippo. In all cases, social predators at such a significant size disadvantage to their prize prey use the same strategy- they steadily rip pieces off it until shock and blood loss mount up enough for it to slow down and stop thrashing enough to be eaten. This is the famous “cruelty” of the orcas, wolves, and hyenas: only predators that can manageably lock down their prey well enough to deliver a lethal stroke without serious risk can afford such “mercy” as killing something before they start to eat it.
Animals that hunt that way see this reflected in their teeth and jaws- designed for slashing and tearing rather than gripping. The jaws of a modern cat, that delivers a killing bite, are short, strong, and grippy- a wolf’s jaws are longer and have better leverage for a long slash. (Hyena jaws are short, but this is for a different reason- they crush bones for marrow and need that strength.) And then there’s these teeth:
This skull is immediately recognizable as one of the Smilodon- “saber-toothed tiger”- skulls pulled out of the La Brea Tarpits. Knowing that Smilodon are believed to have hunted mammoths and others of the massive herbivorous megafauna, the popular imagination scales them up to fit, giving them the same general size relative to their prey as lions to zebras or wildebeest; for exhibit A, see this screencap from cinematic cheeseburger 10,000 B.C.:
In truth, though, even the very largest of the sabre-toothed cats, Smilodon populator, was only the size of a largish lion. It DID prey on the mammoth and the giant sloth and the other giants- but rather than using those huge sabers to stab prey to death, which would be a very quick way to snap its teeth off, it much more likely used them to slash out huge chunks of flesh, probably from the belly area if they could get at it… and allow them to bleed slowly to death in the same fashion as the wolves and the hyenas. Big slashing teeth are extremely well-suited to this tactic. And, yes- all three Smilodon species are believed to have lived and hunted in groups.
Except for the orcas (whose teeth have been compared to the Tyrannosaur’s, the largest carnivorous dinosaur and which may have used the same general strategy against its own huge herbivores), nothing I have written so far is terribly controversial. The sabretoothed strategy outlined is (so far as I know) currently the accepted one among those who study these cats, and all you need to do to see how a wolf kills a musk ox is to drive somewhere likely to be very cold and unpleasant and wait awhile. But when I read of the orcas, another species, whose habits are only very recently being researched in any depth, who also has slashing teeth and treats its largest known prey by slashing big chunks out of it and leaving it to bleed out, and who has recently been discovered to have some degree of a complex social life popped into my head:
Ever since the enaction of the Marine Mammal Protection Act, or as I like to think of it, the Seals-For-Meals shark protection act, the image of the great white shark- and the degree to which it’s studied by interested researchers- has been changing radically. Now that we’ve shed some of our mammalian chauvinism and stopped assuming that the “lower” phyla are something like behavioral automatons, we’ve discovered that many species of fish- unsurprisingly, the same sorts that fill roles associated in terrestrial ecosystems with high intelligence and complex behavior- are far more than swimming/eating/mating machines, and that many species of shark are particularly clever. White sharks, as it turns out, are social animals: they have a wide variety of recognized gestures for communication (and there are likely to be more, as we find those that are more subtle), they have a social order and pecking system, and, most surprisingly of all…. they travel from rich feeding ground to rich feeding ground in “clans” of associated individuals, although they don’t appear to hunt together.
If you read the article, you’ll note how deeply dependent white sharks are on fatty foods to maintain their size, their pseudo-”warm-bloodedness”, and their (for fish) voracious metabolisms. They do mention whales- in that they mention that whale blubber could be such a valuable meal for a white shark that one found carcass could sustain the shark for as much as a month and a half with no meals in between. Whale carcasses in general represent one of the biggest “jackpots” for all trophic levels in the ocean- a whale comes down with a fatal case of the sniffles, and everything from great whites to lobsters and hagfish eat like kings for weeks or more.
If you’ve seen Discovery’s documentary Air Jaws- a retarded sensationalist title for what was actually a well-produced and interesting program (with Discovery’s required pauses for irrelevant information or experiments they predict will look cool)- you’ve seen the footage of the large groups of white sharks feeding on a whale carcass. The carcass itself is from a beached whale, and was towed out to hot restaurant spot Seal Island on a more or less “this could be cool, let’s see what happens” basis. The most interesting thing they found was something never before observed in whites- mating behavior. You can see a clip here- but turn down your speakers first, I don’t know if I was just lucky, but there’s an INCREDIBLY annoying banner ad up there. After a good gorge on the whale, the sharks are apparently experiencing not only a serious down-dialing of aggression, but, uh, the Great White Hardon for the males. What makes this so very interesting is that white sharks mating has never, ever been observed.
The way the narrator sells it- as a “white shark orgy occasion”, I believe the phrasing was- is a bit absurd. The evidence they have there isn’t quite enough to suggest that this is the context for white shark mating, especially given that a species structuring its mating strategy around found whale carcasses is rather an absurd one. However, the idea that successsful whale hunts could be- or possibly, had been- a major mating occasion is a lot more plausible, at least in terms of being a hypothetical good mating strategy. It makes getting both sexes together easy, it provides the mother a massive guaranteed meal that will fuel her for months to feed the pups (white sharks are viviparous- think pregnancy without the placenta), and if there’s really a significant aggression-reduction effect, that could be a large advantage for the female; one distressingly common feature of shark mating is a lot of biting of the female by the males.
I haven’t exactly provided compelling proof so much as a lot of suggestion, but here’s a few more things for you to chew on before you dismiss the idea that white sharks, like orcas, may be social predators evolved to take on high-value prey much larger than themselves. First, if white sharks are traveling together in clans, why have the social group at all, if they hunt separately? It makes keeping a potential mate on hand a little easier, but we’ve never observed that they do mate within their own clan, and other large predators that hunt separately have other ways to get around that. You could propose that the complex social behavior the sharks exhibit makes sorting out kills easier in cases like the whale carcass, but in that case, why not have a much simpler social system, and why the traveling clans at all?
The pattern I’m proposing- we only see white sharks hunting individually (but associating anyway) now because of the damage done to whale populations- isn’t a new one. Coyotes are one generalist predatory species that changes its social order both on the number of dominant predators in the area and available prey; while they are relatively solitary in most places (under very heavy hunting pressure and pressure from other predators), when they aren’t heavily harassed and don’t have competition from wolves and bears… they form packs and take deer and even elk. We’ve only begun to observe this in places like Yellowstone before the wolf re-introduction, and the East coast after the coyotes colonized it (where, unlike Westerners, they don’t have a cultural tradition of zealously pursuiing the coyotes as “varmints”)- the strategy requires a special set of circumstances to emerge.
With the orcas, we have the convincing evidence that the more the orcas and the whales bounce back, the more observations we have of this actually happening, and even then the complaint is that there’s not enough observations to warrant making the conclusion that this is not remotely unusual or unnatural behavior for them. As Estes and Springer have pointed out, this is a LOT of observations for what amounts to a jackpot kill for the orcas and given that the ocean is not exactly humans’ natural environment- in order to make the observation, the orcas must perform their equivalent of a big-occasion hunt, and there has to be a boat with observers on it there to see it. And orcas are mammals- they are truly warm-blooded animals, wrapped in vast fatty (expensive) layers, and their appetites are absolutely enormous.
White sharks are fish, with fast metabolisms only relative to other fish- remember, sixty-five pounds of blubber is enough food for more than a month for one of them. More than that, they don’t have six-foot dorsal fins making them easy to track through the water (you’ll only see their fins from the surface if they’re mid-kill), and people don’t follow them around specifically hoping to get a glimpse of them. We had barely bothered to observe them at all until the last twenty years or so- and this is when they’re in deep trouble from being a favorite target of sport fishermen, being finned for shark’s fin soup, being caught and killed in anti-shark nets, and having their available pool of prey- which may also have been sharply reduced, as the orcas’ was- absolutely massacred.
If the ecological landscape has such profound effects on the hunting behaviors of coyotes- and for that matter on wolves, which kill rabbits during lean times- why not the white shark? How would we know what we had missed, when we only thought to look after we’d torn the place to bits?