KYOTO - An international research team that included Kyoto University professor Tetsuro Matsuzawa has said it has observed wild chimpanzees preying on river crabs for the first time.
The finding is contrary to the common belief that anthropoid apes, such as chimpanzees and gorillas, the closest species to humans, do not eat aquatic animals.
A paper on the study was published Wednesday in an online version of the Journal of Human Evolution.
In 2012, the team observed chimpanzees eating river crabs at a water hole in the forests of Guinea, in West Africa.
The team set up camera traps at four water holes between 2012 and 2014 and managed to record chimpanzees eating the crabs 181 times.
“Our study is the first evidence showing that non-human apes regularly catch and eat aquatic fauna,” Kathelijne Koops, researcher at the Department of Anthropology at the University of Zurich, said in the research paper.
The research team discovered that chimpanzees living in the rain forest in the Nimba Mountains of Guinea consumed freshwater crabs year-round.
The chimpanzees searched for crabs in shallow streams in the mountainous rain forest region by scratching and digging up the riverbed with their fingers.
Although the chimpanzees ate the crabs throughout the year, they were seen eating crabs more often when they were not eating ants. According to the team, river crabs and ants have similar nutritional compositions.
“Female chimpanzees and their offspring fished for crabs more often and for longer than adult males, which we had not expected,” Koops said. A possible explanation for this finding may be that crabs provide essential fatty acids, as well as micronutrients such as sodium and calcium, which are crucial for maternal and infant health.
Studies have found that human ancestors ate fish, turtles and other aquatic animals as far back as 2 million years ago, when they left forests to live in the savanna.
Matsuzawa said that humans may have been eating aquatic animals since the earliest humans lived in forests over 4 million years ago.
“The study may give us a clue to find out when and how humans began to eat aquatic animals,” Matsuzawa said.
The team also said there was no correlation between the crab-fishing activity and the amount of monthly rainfall. The rate of crab-fishing remained the same in both the dry and rainy seasons.