Chimpanzees in West Africa observed fishing for crabs year-round

Scientists observed a population of chimpanzees living in the Nimba Mountains of Guinea in West Africa fishing for freshwater crabs year-round. The fishing behavior was most common among female chimpanzees and adolescents.

Researchers described the phenomenon this week in the Journal of Human Evolution.

Authors of the new study suggest the addition of seafood to the diets of the earliest human ancestors may have triggered brain changes that fueled human evolution.

"The aquatic fauna our ancestors consumed likely provided essential long-chain polyunsaturated fatty acids, required for optimal brain growth and function," Kathelijne Koops, researcher at the University of Zurich and Kyoto University in Japan, said in a news release. "Further, our findings suggest that aquatic fauna may have been a regular part of hominins' diets and not just a seasonal fallback food."

Scientists closely monitored the fishing behavior of the Nimba Mountains chimps for several years. Researchers also analyzed the nutritional value of crabs compared to other foods in the chimps' diet.

The research showed chimps eat freshwater crabs year-round. Crab consumption patterns proved unrelated to changing seasons or fruit availability. However, scientists did find chimps that eat more crabs and less likely to eat ants. Crab consumption is rare among older males, researchers determined.

"Energy and sodium levels in large crabs are comparative with ants," said 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."

Though researchers haven't previously observed crab consumption among apes, evidence of apes eating aqueous organisms, mainly mollusks, has been reported. However, the behavior was observed among chimpanzees living near bodies of water.

"Previous observations were from monkey species in locations consistent with aquatic faunivory -- lakes, rivers, or coastlines -- and not in closed rainforest," Kyoto researcher Tetsuro Matsuzawa said. "It's exciting to see a behavior like this that allows us to improve our understanding of what drove our ancestors to diversify their diet."