European whalers had virtually exterminated the whales in European waters by about 1700. Whales occupied a point near the top of the food chain-so once they were gone, what other animals moved into the place they occupied? Or, did the animals that the whales ate just increase their numbers? The fact that whales from other oceans never moved in (to replace the vanished native species) also is interesting-why didn’t some alien whale species move in?
Are whales really the top of the food chain? The toothed whales eat fairly large prey, but the baleen whales feed by filtering tiny creatures out of the water.
I watched a cool whale documentary the other day. However IAMAWEBAM (i am not a whale expert by any means)
Whales are so diverse, that they really sit on several branching food chains, it could be said.
For instance you have the various baleen whales who eat plankton (plankton is any small crustacean that doesn’t locomote itself but is moved by the current, so the doco said). Whilst they eat a lot of plankton, it can probably still be diluted into the ocean size without whale consumption with no problems.
then there are toothed meat eaters - sperm whales etc, and also killer whales (who aren’t really whales I think it also said). So Sperm Whales prime meal is giant squid from the very deep. Perhaps this explains the high incidence of ship loss that occurred 1800 - 1960, as the giant squid numbers increased and starting stealing ships from the surface 
A really interesting flow on effect is that there are several species of deep ocean bottom dwelling animals that survive almost entirely on ‘whalefall’ - that is to say, whale carcasses that sink to the ocean floor post death.
However in the context of the ocean, and despite their voracious appetites, I very much doubt their reduced numbers had a significant impact on the local ecosystem. And given many whale numbers are now rebounding, perhaps not enough time in the evolutionary timescale has passed in the past 2-300 years for a major effect to be felt. The ocean is a big, big place with a biomass that significantly outweighs the dry land one.
There is a jellyfish explosion occurring in the oceans right now. It has a lot to do with the fact that humans have emptied the oceans of whales and other large predators.
Which whales eat jellyfish?
Causation might not be that direct. Completely made up but semi-plausible examples:
Once the nonexistent whales no longer eat the 90% of all krill that they used to, then jellyfish eat the krill. Those 10x fed jellyfish now reproduce like mad.
Or maybe whatever used to eat jellyfish now prefers to eat all the extra krill, reducing predation pressure on the jellyfish.
Or maybe the same big idea, but transmitted through a web of 15 interlocking species of plants, microorganisms, and middle-sized critters.
Bottom line: Biology is complex. Ecology is insanely complex. Looking for one-step cause-effect is rarely the right answer.
Niches don’t actually exist, absent the organisms that occupy them. And when organisms do adapt to fill niches they didn’t before, it’s a slow process, like almost everything in evolution. There hasn’t been nearly enough time since whaling started for that to happen, especially not with large, long-lived animals.
For context - I am a marine biologist, but I’ve been working in the Pacific for the last decade or so, and have little experience in European waters.
Had they? That’s only true of some species…
There’s an annual pilot whale hunt that has occurred in the Faroe Islands ever year continuously since 1709, and with some records going back to the 1580s. There are hundreds of thousands of pilot whales in European waters.
Finnmark, the northernmost portion of the Scandinavian peninsula, has been host to whaling throughout the 1800s and into the present day, mostly targeted on minke whales, so clearly minkes were not extirpated either.
It’s also clearly not true for the largest of the baleen whales - the blue whale…
What you are probably referring to are that some specific whale species were eliminated from European waters by 1700:
The Atlantic grey whale was extirpated from European waters well before 1700, and even from western Atlantic waters, the most recent known example died around 1675.
The other is the North Atlantic right whale, one of the most endangered species in the world due to whaling, with the European population believed to be less than 100 animals:
There are also less than 500 animals in the North American population.
I have to question the basic premise of the question - whale numbers were greatly reduced, but few whale species were extirpated from European waters, and certainly not by 1700. The main fault is that once whales became very difficult to catch, whalers could relatively easily move their operations to Arctic and Antarctic waters where whales were more easily found - which is indeed what happened in the modern whaling era from 1860 or so until the 21st century.
In theory, the reduction of whale numbers should also create an opportunity for competitors to move in, but the hunting pressure has only been for the last 40 years or so, and whales from adjacent areas (the western North Atlantic and Arctic) gained hunting pressure immediately even before whale numbers were reduced in Europe - i.e. there weren’t enough grey whales from the western North Atlantic to move into the eastern North Atlantic because by that time the eastern North Atlantic population was also moving to extinction.
It’s even further complicated because for the numbers of critters whales eat - in the case of blue whales, krill, and in the case of grey whales, amphipods (these are good whales to use since they tend towards the specialist end of whale feeding while most whales are more generalist and willing to eat a wide variety of food) - were not monitored in the days before whaling. In addition to LSLGuy’s good point about multiple branching strands in the food web, the birth of modern oceanography (the voyage of HMS Challenger, often considered the first oceanographic trip, didn’t happen until the mid-1870s) came too late to detect a difference in krill or amphipods between then and the 1700s.
Well, if you mean niches as the arbitrary human construct to explain the continuum of ways that organisms gain nutrients and energy, then yes.
But if you take niches as inherent strategies that can be exploited to gain nutrients and energy, then they exist even when unoccupied. Magically wave a wand and get rid of the remaining blue whales in the Bay of Biscay and Irish waters without affecting the krill population, and an unoccupied niche remains (that will probably be filled by existing whales whose food preferences overlap with the blue whale, like fin whales.
There is no such thing as “The Food Chain”.
Food chains are linear connections and there are billions of them. None of these billions of chains can be said to be THE food chain. Put several chains together and you can make a food web (formerly called a food cycle). If you imagine ALL the chains put together into one huge complicated web that only an omniscient being could comprehend simultaneously, then I suppose that gigantic structure could be called THE food web. Food web - Wikipedia
We use the metaphors of chains and webs to imply whether the connections are linear or complex. In a simple linear chain, you could imagine that losing a single link could be catastrophic. But that’s generally not true of complex webs. You can lose several links and have the overall structure continue just fine.
Depending on one’s value of “just fine” - in general, humans are responsive to properties not of the entire food web, but of the quantity of certain components of the food web.
A good example is the northwestern Atlantic cod fishery - where human intervention changed the character of the food web through dramatic fishing pressure and also possibly ocean warming. It’s entirely possible that the northwestern Atlantic has reached a new relatively stable state with low numbers of cod… http://www.sciencemag.org/content/308/5728/1621
The food web is doing ‘just fine,’ but the humans who derived their livelihood from it are not.
Would you say that the niche of “gargantuan creature that swallows whales whole” exists and is just waiting to be filled? What about the niche of “autotroph that derives its energy from the temperature difference between the ocean surface and floor”? Or how about “fungus that derives its energy from gamma rays produced by radioactive material”?
Oh, wait, that last one actually does exist. But it it didn’t, or if we didn’t know about it, would we describe that as a “vacant niche”, or just as “no niche at all”?
This is simply wrong, according to the at least some of the standard ecological understandings of what a niche is.
Those are empty niches. At least, there exists a niche for organisms that prey on great whales. Currently that niche is filled by orcas; previously it seems to have been filled by the giant shark Megalodon. It may not be thermodynamically possible for the niche of whale predator to be filled by a giant creature that swallows them whole, given the population density of large whales.
Perhaps it would be more accurate to say that the number of potential niches is so mind-bogglingly huge that it’s pointless to even consider the ones that aren’t actually filled.
I’m not sure about ecological replacement of whales in the North Atlantic, but in Antarctic waters there seems to have been an influence of whales on penguin numbers. From the 1930s to the 1970s Antarctic penguins seem to have increased greatly, perhaps due to the reduction of whale numbers by whaling. More recently, as whales have recovered, penguins have been declining (a trend perhaps increased by global warming).
Theoretically, perhaps, but there are plenty of conventional niches that can be usefully discussed. For example, extirpation of large predators in much of the eastern US has left that niche empty in this region (except to the extent that humans choose to fill it), allowing for a huge increase in deer and other wildlife. Now coyotes, partly hybridized with wolves, are rapidly expanding to fill that vacant niche.
It should be pointed out that organisms have both potential (the total niche space they are physiologically able to exist in) and realized (the niche space they actually occupy) niches. They may be excluded from certain parts of their potential niche space by competitors. Extirpation of predators or competitors may allow them to expand into areas they previously didn’t occur in. Historically, coyotes, which prefer grasslands and prairies, were excluded from eastern forests by wolves, which prefer wooded country. Now that wolves are absent they can expand their realized niche.
The recent increase in jellyfish is thought to be due to overfishing of small pelagic fish like sardines.
This is part of the phenomenon of “fishing down the food web” that appears to be occurring in some areas. As we remove larger fish, we gradually end up taking smaller and smaller organisms at lower trophic levels. However, whether this is occurring at the global levelhas been disputed.
OK, some niches are easier to expand into than others. I don’t think the whale niche is one of them, though.
Reading that article is fascinating. Thanks for the link.
The mainstream thought seems to be that absent whales for the last few decades, the penguins have been feasting on the krill and their population has boomed as a result. As the whales’ population now recovers and the whales get more krill, the penguins are being starved out. There’s lots more to the story of course (much less to actual reality) but that’s one large bullet point from it.
So now we have tiny little aquatic surface-dwelling arthropods weighing just a gram or three being fought over by deep diving gigantic cetaceans weighing many tonnes and flightless but swim-capable land birds weighing 10s of kilos at most. The food web has interconnects all across different scales and modes of existence. Fun stuff to think about.
And people, right?