Fish-hunting and eating behaviors confirmed in Japanese macaques

Recent video evidence shows Japanese macaques engaging in fishing behaviors to sustain themselves throughout the barren, harsh winter months in the Japanese Alps. Recently published results support the original report that was published in November 2021 in the same journal which hypothesized these fish-seeking efforts.

The results were published on November 29th, 2022 in Scientific Reports.

This catching and feeding behavior appears to be an extension of existing, documented behaviors of feeding on vegetation that grows above the surface of the snow as well as aquatic plant matter and by extension, insects found on these plants. The streams containing these aquatic plants are also home to many cold-water salmonids, so it's only natural to think perhaps the macaques may stray from their insect meal to a fish one.

"Video analysis has also shown that during these behaviours, when the fish are nearby, their attention is diverted to the fish. We interpreted this sequence of behaviour as a pre-adaptation to fish-eating, and that fish-eating behaviour may have evolved through these several stages," said Masaki Takenaka and Koji Tojo, corresponding author and Professor of the Department of Biology at Shinshu University.

These "pre-adaptations" are the proposed mechanism for the fish-hunting and eating behaviors observed, though evolutionary pressures due to the unrelenting winter conditions can be contributors to the unique behavior that has been observed in the macaques of this area.

After confirming fishing behaviors in Japanese macaques in the Kamikochi region, the next step is to further understand why, and how, these behaviors developed.

"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 behaviours spread within the macaque group -- Is it genetic? Is it a kind of culture that can be transmitted within the group?" Tojo says. Interestingly, some of these macaques are observed to disregard the fish entirely. Whether this is genetic or something else entirely is yet to be seen.

Now, after identifying 200 individuals across four distinct groups, Tojo and his team seek to identify relationships based on these individuals and their fish-seeking (or fish-avoidance) behavior to see how it may be passed onto other individuals in the group and future generations.

Masaki Takenaka and Koji Tojo of the Department of Biology, Faculty of Science at Shinshu University, Alexander M. Milner of the Institute of Mountain Science at Shinshu University; School of Geography, Earth and Environmental Science at University of Birmingham, Kosuke Hayashi of NHK Enterprises, Inc., Genki Yamada of G-Vision, Inc., Takayuki Ogura and Mone Ito of Kozo Production all contributed to the research for this study.