From Associated Press:
Monkeys that go fishing discovered
What prompted behavior in primates remains a mystery
June 10, 2008
Now, researchers say they have discovered groups of the silver-haired primates in Indonesia that fish.
Groups of long-tailed macaques were observed four times over the past eight years scooping up small fish with their hands and eating them along rivers in Indonesia’s East Kalimantan and North Sumatra provinces, according to researchers from The Nature Conservancy and the Great Ape Trust.
The species had been known to eat fruit and forage for crabs and insects, but never before fish from rivers.
Other research on monkeys in Indonesia: here.