Long-tailed macaques use stone tools to crack open cockles at low tide.

Long-tailed macaques use stone tools to crack open cockles at low tide. Mark MacEwen/NPL

Ecology

Monkeys threaten seafood stocks — just like human over-fishing

Tool-using macaques drive down the size and number of shellfish in the islands they inhabit.

Macaques that have learned to use stone tools for fishing risk depleting prey populations, work in Thailand has shown.

Lydia Luncz at the University of Oxford, UK, and her colleagues compared local shellfish populations on two adjacent islands in Khao Sam Roi Yot National Park. The team observed that long-tailed macaques (Macaca fascicularis), which inhabit both islands, regularly used stone tools to hunt for shellfish, including rock oysters (Saccostrea cucullata) and tropical periwinkles (Planaxis sulcatus). The primates’ technology seems to affect shellfish size and abundance on both islands, but the effect is more pronounced on Koram Island, which has a much larger macaque population than NomSao Island.

The team also observed that although macaques on Koram Island target the same prey species as their cousins on NomSao Island, they select significantly smaller stone tools. This may indicate that the monkeys have switched to using smaller tools in response to reduced prey size and abundance. The creatures might even reach a point at which they stop using — and eventually lose the ability to use — tools altogether, the scientists say.