Japanese macaques have been directly observed catching and eating fish in a flowing river. It’s the first time a monkey has been seen fishing, and researchers believe the behavior may have evolved in a specific group of macaques to survive the freezing winters of the Japanese Alps.
“Japanese macaques, macaca fuscata, from Kamikochi in the Japanese Alps endure one of the coldest and harshest environments in winter when food scarcity puts them at risk,” the study authors explain. Typically, the monkeys feed on bamboo leaves and other woody plants during the annual freeze, although the Kamikochi area contains many streams fed by volcanic springs, which maintain a year-round temperature. of 6°C (42.8°F) and do not freeze in winter.
Assuming that the aquatic organisms residing in these streams could help maintain the local population of snow monkeys when other food is scarce, the researchers spent three consecutive winters examining the contents of the monkey poop. Sure enough, they found brown trout DNA in about 20% of the fecal samples, indicating that the macaques may have been eating fish.
However, it was unclear whether the monkeys were actively catching live trout or just dead fish. To investigate, the researchers tracked several troops of Japanese macaques along the banks of the Azusa River between January and March 2022.
“We successfully observed the behavior of Japanese macaques capturing active fish and potentially consuming them fourteen times, six times by direct observation and eight times with infrared sensor cameras,” the study authors write. “The camera trap data included six other possible catches, although this could not be reliably confirmed to be fish.”
“In addition to these successful fishing behaviors, we also observed several failed attempts when Japanese macaques reacted to the sound of fish splashing in the water,” they explain.
Describing the crude methods used by monkeys to catch their aquatic prey, the researchers explain how the animals hunted fish in shallow water before holding them with both hands and biting them.
“Having obtained evidence that Japanese macaques in the Kamikochi catch and eat live fish, the next step for us in this research was to investigate how these fish eating behaviors spread within the group of macaques,” explained l. author of the study, Koji Tojo, in a press release. “Is it genetic? Is it a kind of culture that can be transmitted within the group? “.
While the researchers hope their ongoing observations will answer these questions, they speculate the behavior likely evolved in stages as the macaques gradually began to exploit the river for food during the winter. According to their theory, the monkeys probably started by feeding on aquatic plants, which would have led to the inadvertent consumption of aquatic insects living among this vegetation.
Over time, macaques may have begun to deliberately seek out these river bugs, learning to knock over rocks and catch sinking insects. This, in turn, may have provided them with the skills to hunt fish.
“We hypothesize that the acquisition of the behavior to catch sinking aquatic insects may have become a pre-adaptive behavior to catch crankbaits,” the authors write. “In fact, since sinking aquatic insect catching behavior was frequently observed in this study, it is very likely that the fish catching behavior first occurred accidentally.”
The study is published in the journal Scientific Reports.