Is Your Salmon Small Because of Hungry Cavemen?

Stone Age hunters didn’t need to tell fish tales—the fish they caught really were whoppers, according to a new study.

Remains of prehistoric fish dinners from caves in northern Spain suggest that Atlantic salmon (Salmo salar) and brown trout (Salmo trutta) have shrunk significantly in size over the past 20,000 years—from a combined average of up to 5 pounds (2.2 kilograms) to about a pound (0.4 kilogram).

A fisherman releases an Atlantic salmon into Norway’s Orkla River in September 2008. Photograph by Wild Wonders of Europe/Lundgren/National Geographic

What’s more, it’s because of our ancient ancestors’ fishing skills that rivers in the region today are populated with much smaller fish, according to a team of scientists from the University of Oviedo in Spain. (See “Hot Stew in the Ice Age? Evidence Shows Neanderthals Boiled Food.”)

That’s because the scientists suspect that the Stone Age fishers deliberately targeted larger specimens.

“Bigger fish will be more valuable as food,” said archaeologist Pablo Turrero, who led the study. “They would only have caught the small fish if they absolutely had to because there was nothing else.”

Over time, prehistoric hunters’ preference for catching big ones caused salmon and trout to downsize, because proportionally more small fish survived to breed and pass on their genes.

A trend for shrinking sizes starts to show up in the cave fish fossils about 10,000 years ago, “but size selection had been going on all the time,” said Turrero.

Big Fish, Little Fish

Published October 22 in the journal Royal Society Open Science, the study compared the backbones of about 30 Atlantic salmon and brown trout specimens unearthed at ten prehistoric sites in the northern province of Asturias (map) with those of their living descendants. (See “Salmon Farming Gets Leaner and Greener.”)

These calculations revealed the ancient fish averaged 6 to 10 inches (16 to 26 centimeters) longer than those types of salmon and trout in the same rivers today.

Turrero said this equates to a typical weight of 2.9 to 5 pounds (1.3 to 2.2 kilograms), whereas the modern-day Asturias angler can expect an average catch that weighs less than a pound (0.4 kilogram).

The fossils also indicate that the modern humans who replaced the Neanderthals some 40,000 years ago were serious about fishing “pretty much as soon as they started settling in the region,” according to Turrero.

Fish meal leftovers found in the caves aren’t as abundant as those of prey animals such as deer, “but you always get them,” Turrero added.

Prehistoric Fish Fry

Often burnt, the fish fossils show that hunters “would catch the fish in the nearest stream, then bring them to the cave to cook by the fire,” he said.

Past excavations at the fishbone sites have found evidence for these fires, as well as the human remains of these prehistoric salmon-eaters. (See “Cooking Gave Humans Edge Over Apes?“)

Though no fishing gear remains have been identified to date, such artifacts have been found at similarly aged sites elsewhere in Europe.

The ancient salmon hunters may have used hooks made from mollusk shells, traps made of branches, spears, or even their bare hands, Turrero added.

The importance of salmon and trout to these cavemen can also be seen in two Asturias caves that boast extremely rare Ice Age examples of ancient fish paintings, Turrero noted.

Human Influence

In addition to human preference, climate change and other factors also likely played a role in shrinking fish size over time, the study authors said.

Karin Limburg, a fish expert at the State University of New York’s College of Environmental Science and Forestry, agreed.

However, “given that humans have been in that region for a very, very long time, and salmon running into rivers would have been a great source of protein,” the new finding is “not so surprising,” Limburg said. (See “Eating Crocodile Helped Boost Early Human Brains?”)

 “What strikes me about the study is that it shows, yet again, size declines in a fish that is exploited by humans,” she added. “The more we look, the more we see this has occurred.”
James Owen is a journalist and author based in Stockholm, Sweden. After cutting his teeth on the news and features desks of several UK newspapers, he struck out as a freelance writer, specializing in life sciences and natural history. His fish biography 'Trout' (Reaktion Books) was published in 2012.
  • Fran Parker

    I am sure that cavemen went for larger fish because they were easier to catch,took less time to fill the menu and they best be a good spear thrower.

  • Daggar

    I’m mising something, perhaps. Between 8 and 10,000 years ago, this planet was as warm as it had ever been in a 100,000 year cycle. What then, was the effect on these fish? I like the story but I think there is much more to it than prehistoric fishing habbits. The bears may also agree? 😀

  • Charles Salekin

    This makes perfect sense to me. When I was a kid in the 1950’s stream fishing, the law did not allow keeping undersized fish. As a result all the larger, older and breeding sized fish were targeted. Small, juvenile fish caught were discarded, likely to their death anyway. Today these same streams hold few, if any fish at all.

  • Mars Chan

    Does this imply that evolution would take place in the blink of an eye?

  • prabirkumarray

    Learning a lot.

  • carlos rodriguez

    Could be nice and useful to know if the ratio has been accelerated in recent years for the overfishing laws currently applied on Asturias (coming from the 40´s of XX century), which allow anglers to kill the biggest and the best individuals of the last Spanish Salmon by hundreds.

  • Jon

    Daggar brings up an interesting point about climate. Bergmann’s Rule states that organisms are larger in cold climates, smaller in warm. This has to do with heat regulation and the square/cube principle. While adverse selection undoubtedly has some impact (everyone wants the biggest fish, which theoretically has the best genetics), as time progresses and average temperatures rise then the smaller fish are the ones that are the most fit and are the most likely to pass on their genes.

  • Charlie

    I find it very difficult to believe that prehistoric fishermen were effective enough in their harvesting of big fish that they could impact the evolution of an entire species. It makes sense that over time they would impact very specific fish populations — but there is too much water on this planet for primitive humans to rape all of it. The other question you need to ask yourselves is — why is this theory applicable to brown trout and atlantic salmon and no other species?? Did they keep the large salmonids but throw back all the big cod and bass??? Doubtful. It makes sense to me that this decline in size has more to do with forage. Somewhere down the line, a few of their favorite foods disappeared from the menu and they gradually grew smaller.

  • Rihards

    Hello, Charlie! I don’t quite understand why people living in a particular region and fishing quite efficiently couldn’t affect the fish size in this region by this simple principle, we see it with modern industrially caught fish like cods and tuna, don’t we? And the effect is basically worldwide in what, 50 years? Though i doubt they just threw away the small fish, they probably didn’t or couldn’t even target them with their basic fishing tools. Also they do mention climate is likely a part of this shrinkage, or who knows what else, but i think this brings us to think about effects of heavy fishing.

  • Chris Harrod

    Two things.

    First, how about a link to the actual paper? The story is great, but a link to the original paper (rather a lazy link to the journal itself) would be so much more useful. http://rsos.royalsocietypublishing.org/content/1/2/140026

    Secondly, similar patterns have been seen elsewhere, e.g. on coral reefs across the Caribbean prior to the arrival of Columbus

    Nice paper here http://link.springer.com/article/10.1007%2Fs003380100142

    I’ll use this new paper in my teaching, so apart from my sniping, thanks for bringing to my attention Nat Geog.

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