Thousands of pogies turned up dead Saturday in Portland Harbor and Casco Bay, apparently the result of predation by bluefish and stripers.

Kevin Battle, Portland’s acting harbormaster, said the predator fish chase the pogies into shallow water, where some are eaten and others die when the sudden influx of fish exhausts the oxygen in the water.

Battle said the fish die-offs were reported around Great Diamond, Little Diamond, Peaks, Cushing and Long islands. He said he began getting calls early Saturday morning, although there were reports of a lot of fish jumping near the islands Friday night, a sign that they are being chased by predators.

Battle said he investigated to make sure the die-off wasn’t the result of pollution.

“Every indication is this is a natural event,” he said. “No foul play.”

Battle said the last major fish die-off of this nature in the bay and near Portland Harbor was about seven or eight years ago, although it’s happened more recently elsewhere along the Maine coast. He also said there’s no way of knowing whether the die-off is over or will continue for a few days.