WATCH: Chimpanzees Catch Crabs

Researchers observe chimps crab-fishing in West African rainforest, with females and offspring fishing for longer periods than adult males

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Chimps combing streambed and turning over rocks for crabs
Chimps combing streambed and turning over rocks for crabsCredit: Kyoto University/Kathelijne Koops (Youtube)

Chimpanzees can crab, say Japanese researchers who observed the wild apes in Guinea rooting about in a mountain stream. They realized what they were observing was them fishing. For crabs.

Their observation and some speculation about how this appetite for arthropod arose was published Wednesday in the Journal of Human Evolution.

Just how close chimpanzees and humans are depends on who you ask. But the 98 or 99 percent figure touted by ape aficionados is not exact. It could be 80 or 90 percent, depending on criteria.

In any case, it seems that our common ancestor was a fructivore. Our Homo genus and their Pan genus seem to have split between 6 to 7 million years ago, and we have all come a long way since then.

Vegetarianism continued among the earliest species of Homo, scientists say, based on studies of teeth. But later, the two species — chimp and human — eventually converged in omnivorousness. Chimpanzees, like us, will eat practically anything — including, it turns out, freshwater crabs. And they don’t care how much fruit is hanging from the trees or if they’re getting rained on: they’re going to grab that crab.

Mother chimps also teach the kids the art of crabbing, the evidence shows.

Humans have been eating meat for at least 2.5 million years and have definitely eaten water creatures for about 2 million years, going by fish bones found at prehistoric sites — including Olduvai in Tanzania and Turkana in Kenya. They also ate crocodiles, by the way.

“The aquatic fauna our ancestors consumed likely provided essential long-chain polyunsaturated fatty acids, required for optimal brain growth and function,” suggests first author Kathelijne Koops from the University of Zurich and Kyoto University’s Primate Research Institute.

The Nimba Mountains in Guinea where chimpanzees crab.Credit: Kyoto University/Kathelijne Koop

There is no suggestion that hominins millions of years ago were making fishhooks or bravely sailing the briny to catch fish; they were possibly opportunistic grabbers of slow-moving seafood in shallow waters.

Crabbing fits exactly that profile, and the team from Kyoto and the United States says the chimps living along the streams in the rainforest of the Nimba Mountains in Guinea, West Africa, do it habitually.

Koops says that is like early humans: They ate fish regularly, when they could, not just resorting to them as a seasonal fallback food — for instance, when big game migrates elsewhere.

Observation from 2012 showed that the Guinean chimps’ crustacean consumption correlated negatively with their appetite for ants, another diet favorite. And it’s quite the female appetite: Males were the least likely to consume aquatic fauna.

Koops explains how all that makes sense. “Energy and sodium levels in large crabs are comparative with ants,” she says, “leading us to hypothesize that crabs may be an important year-round source of protein and salts for females — especially when pregnant or nursing — and for growing juveniles.”

Enjoy those crabs, chimpanzees. Different crab species seem likely to react differently to climate change — regarding both temperature, which can change salinity, and carbon dioxide levels in the water. Freshwater crabs may be spared ocean acidification, but how they respond to changing salinity depends on species and remains to be seen.