When it comes to meals, chimps have a lot of secrets up their sleeves that we’re only beginning to discover. First, we learned that their taste runs to tortoises, which they bash and smash open to get to the meat inside. Now, we’ve discovered they’re also partial to a spot of freshwater crab, and regularly fish for them even when there’s plenty of fruit lying around.
They’re not quite whipping up their own chowder or devilled crab recipes, but we didn’t know that they regularly fished for crab until now.
Researchers from Kyoto University discovered that wild chimps in the rainforest of the Nimba Mountains in Guinea habitually catch and eat crabs, not just opportunistically or when other food sources are low, the first time this has been observed in non-human apes. Reporting in the Journal of Human Evolution, they suggest this may help us understand how and when our hominin ancestors started dipping into an aquatic diet, a change that would ultimately lead to us.
Millions of years ago, early humans' diets would have looked a lot like chimps’ today – lots of fruit, seeds, plants, and nuts. Around 2.6 million years ago they started eating meat, but there is evidence it was the introduction of aquatic animals into their diet, such as turtles, crocodiles, and fish, around 1.95 million years ago that provided critical brain-growth compounds that played an important part in the evolution of larger brains.
"The aquatic fauna our ancestors consumed likely provided essential long-chain polyunsaturated fatty acids, required for optimal brain growth and function," said first author Kathelijne Koops in a statement.
They first observed the chimps fishing for crabs in the waterways of the rainforest in 2012. They observed the behavior of the chimps for two years, documenting how the mainly female chimps would lift rocks and dig in the mud with their fingers to hunt out the tasty crustaceans, and how often this would be their go-to meal. They also compared the nutritional value of crabs to other readily available foods.
Females teach the juveniles how to look for tasty crustaceans. Kyoto University/Kathelijne Koops
They found that not only did crabbing take place all year round, regardless of season or abundance of other food, but the chimps tended to eat fewer ants, a staple in their diet, suggesting the crabs filled a similar or even better role in their diet.
"Energy and sodium levels in large crabs are comparative with ants," explained Koops, "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."
It isn't the first time primates have been observed catching crabs, but it is the first time an ape that isn't human has been. Notably, the monkeys were observed by lakes, rivers, and coastlines, whereas this took place in a closed forest.
The researchers believe this behavior sheds light on how and why our human ancestors first turned to aquatic animals in two ways. First, by revealing that fishing is not as restricted by habitats as previously thought so humans that lived in forests could have had an aquatic diet. And second, that aquatic animals could have been a staple diet of those humans, and not a supplementary source to fall back on when others were scarce.
We already know that chimpanzees have entered the Stone Age, and they've learned to cross roads. Perhaps a brain boost from an aquatic diet will push them to follow in their ape cousins' footsteps?
