The incredible shrinking fish
The 1957 sci-fi movie The Incredible Shrinking Man suggests that humans can have a pretty startling impact on the world.
As a result of exposure to a cloud of pesticide and something else probably involving "radiation", our hero Scott Carey begins to shrink until he's just a few inches high and is seriously threatened by the family cat (OK, the film's title didn't win any awards for lateral thinking but the special effects were pretty good for the 1950s).
Sci-fi directors usually care more about the fi than the sci, and as with many other films in the genre the precise causes of the incredible shrinking aren't detailed too carefully, nor whether all the factors are entirely of human origin.
Out in the natural world, the picture is clearer. Some animals and plants are shrinking. Human activities are responsible, and we know the reason why.
The first time I came across the phenomenon of the incredible shrinking fish was in Australia a few years ago, when I met researchers who'd noted that the world's biggest fish, the whale shark, is getting smaller - and at a startling rate, with the average length falling from 7m to 5m in a decade.
The most likely explanation is that fishermen are pulling the biggest whale sharks they can find out of the ocean, either because they're the easiest to spot or because they're the most lucrative catches.
Individuals that are naturally smaller are more likely to survive and reproduce - and so over time sets of genes producing fish of smaller size become more common in the population.
Over time, the fish shrink.
Different groups of researchers have studied the shrinking phenomenon in lots of other fish - cod, flounder, salmon, pilchard - and, to a lesser extent, in land animals and even plants. Now a group of US and Canadian researchers has pulled all of this data together for a paper in this week's Proceedings of the National Academy of Sciences (PNAS).
Chris Darimont and his colleagues assembled a list of studies tracking changes in 29 different species which are hunted or fished or plucked for human consumption.
Some studies had looked at the overall size of the animals (or plants), while others followed changes in the size of various body parts.
The height at flowering of the Himalayan snow lotus (used in traditional medicine) has fallen, the weight of Norwegian caribou has reduced, the horns of bighorn sheep are not as long as they used to be, the volcano keyhole limpet is shrinking.
And commercial fish species after commercial fish species is also getting smaller.
Some researchers had also found that the average age at which species reproduce has changed. On the eastern coast of Canada, for example, cod now reproduce a year earlier than they did two decades ago. Fishing has removed so many of the bigger, later-reproducing fish that the genetic mix has again changed; and this has implications for the long-term health of the stock, as bigger female fish carry more eggs.
The overall picture is startling - across these 29 species traits such as body length are changing about three times faster than in species unnaffected by human hunting.
I called up Chris Darimont (who, holding posts at the Universities of Victoria and California, must be a busy chap) for a chat about what this might mean.
Does it give us a comprehensive view of how human hunting is changing animals and plants? No, because by no means all the species involved have been studied.
Would the organisms grow longer again if hunting stopped? We don't know.
What can we do about it? Is it just a question of reducing the amount of hunting we do?
Here, things get intriguing. Chris pointed out that human hunting generally targets the biggest, whereas in nature predators generally target the young, the old and the sick. The "genetic winnowing" is very different.
So in fisheries, for example, regulators (and sometimes fishermen) often set mesh sizes delberately designed to let the younger and smaller fish escape.
Could this be entirely the wrong thing to do from an evolutionary perspective? Here I thought back to a radio feature my ex-colleague Tim Hirsch made years ago on the collapse of the Grand Banks cod fishery.
An old-timer who'd lived through the collapse told Tim in his distinctive Newfoundland brogue that fishermen had targeted the old fish, "the mother fish which had been out there spawning over the years", knowing that it was the wrong thing to do. They'd done it anyway because it was the most profitable approach (and also probably because it was what convention dictated).
Economics would almost always push hunters, fishers and gatherers to take the largest of a kind, Chris suggested. It would be challenging too to think of technology that could target the sick, the old and the young as nature does.
The obvious technological shift would be to go back to pre-industrial catching methods, which do not appear to have had the same shrinking impact, as Chris Darimont's colleague Stephanie Carlson found a few years ago when analysing the bones of fish caught in prehistoric hunts and preserved in middens.
Old-fashioned hunters could not target the biggest and strongest in the way we can today. The technology didn't allow it, and presumably getting close-up and personal with a vigorous rampaging caribou in the prime of health could have led to the demise of the hunter rather than the hunted.
Turning the technological clock back is unlikely to be an attractive option. So unless fine minds can come up with another way of doing it, which also adds up economically, it looks as though we will have to live with the fact that our hunting is re-shaping species at an unnatural rate.
It turns out that we don't need clouds of pesticides or mysterious "radiation" experiences to make living things shrink. The modern way of consuming nature is quite powerful enough.
I'm Richard Black, environment correspondent for the BBC News website. This is my take on what's happening to our shared environment as the human population grows and our use of nature's resources increases.
© MMIX~RS~q~RS~~RS~z~RS~49~RS~)
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I'm sure I have read an article which also explains, how the whole predator / prey role is being turned upside down.
Big fish hunts smaller fish, which tries to hunt the big fishes fry. Big fish is hunted by man, but smaller fish is not hunted by man. Smaller fish becomes dominant because the big fish fry are eaten before they grow. Whole ecosystem cocked up.
I will try to find the link, but this is another example of man over explotation of the seas.
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Actually, here in Mozambique we have worked on developing a sport hunting model that was originally conceived by Craig Packer in Tanzania: it goes something like this: sport hunters are only allowed to "remove" male lions that are over 6 years old (by which time they have successfully bred and their first litter of cubs is weaned) - i.e., they have been "replaced" in the population. One can tell six-year old (and older) male lions from younger lions by the colour of their noses and teeth wear. If hunters shoot younger lions, their quota (and profit) is penalised. And it seems to be working: the hunters are complying, the lion population should be recovering. And money from the hunting is going towards management of the national reserve in which this hunting is taking place.
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Cuckootoo
I read about this recently apropos the cod on the Grand Banks - once the larger fish had been caught, their main prey (caplin, capelin, depending where you come from) are apparently eating young cod before they reach maturity, and so preventing the cod population from recovering.
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It's interesting to see evolution in action, but I don't necessarily see the link to environmentalism and preservation. As part of the ecosystem, we naturally have an impact on the evolution of plants and animals around us. The impact isn't always destructive and the point of evolution is to reshape organisms.
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To xyz273:
I'm interested in your understanding of evolution. As I understand it, size is a function of the 'kind'. Big and little cod are still cod and always will be.
The ability of a species to exit in both large and small capacities is a positive attribute to survival as conditions change. Look what happened to the dinosaur and the sea creators many times larger than our current whales. They could not adapt and therefore died out. Being able to exit in a smaller form is positively beneficial to long term survival.
On the wider issue I agree that predators take out the weak and old. However, the piece that is generally missed is that the species themselves keep their own big boys in check. The human equivalents of the warlords and emperors make sure of that.
I may be totally screwed up on this so feel free to pitch in.
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Richard:
That is one incredible 'shrinking' fish that you were reporting about.....
~Dennis Junior~
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In many species size is related to age. Was the study able to correct the data to reflect this impact? Human activity that takes the older animals/fish may affect the average size of the population without affecting the genetics of the species. Just because A and B occur does not necessarily mean they are related.
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That raises an interesting issue regarding the protection of for instance mangroves, as nursery areas of fish. Some species of fish enjoy the protection of such an area when young, and migrate to open water when large enough. If the nurseries would be protected, but the open seas are a free-for-all, we are having the opposite effect to natural predatory pressure on the young.
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CuckooToo and hrp1000, I mentioned the cod/capelin issue in a previous post but I wasn't able to trace the source material on a quick web search. I'll try to locate it later and post a reference.
stuart_moz, you've touched on an interesting one there with a top predator such as a lion. My guess would be that the same issue might arise - naturally the young and the old would have a higher natural mortality than the healthy middle-aged specimens that your sport hunters might be most keen on. So perhaps in time this sport hunting model might similarly have an effect on the population. But it probably also depends on how many are taken - one of Chris Darimont's points about fisheries was that sometimes the take can be really high, 50% of the stock, which is far higher than the natural loss in these species. What do you reckon?
Washburns, some of the studies in this analysis measured age at maturity as a separate variable. But I'm not sure any looked at the average age of the population - it's not always that easy to measure, in fact.
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As an avid scuba diver, I have some concern about intensive spear fishing because of the selective component. Many spearfishers will argue that they are not as wasteful as net or line fisheries which is true. However, spearfishers are selective and selective for large, reproductively mature and healthy fish. As you explained above, the effect of this selection is to pressure evolution from the wrong end of the bell curve.
We have had further discussion about this topic on our blog http://scuble.com/blog/?p=24#respond
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In a recent BBC series 'Oceans', I was horrified to hear about the human-caused demise of the hammer-head shark in one of our oceans, and its replacement at the top of the food-chain by the humboldt squid. Could we have foreseen that event? Of course we could. If we had put sensible amounts of money into research and disregarded corporate viewpoints, or corporately funded viewpoints we would no doubt have a much better respect for our world and more importantly a future that included humankind. Governments have spent trillions on defence on the basis that they might just be attacked. Shame they didn't spend it on defence from themselves.
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#9
See Richard, I do read your articles ;)
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