All day Wednesday, customers coming into Ben Budd's bait-and-tackle shop in Cape May County marveled at the thousands of dead menhaden they had seen along the Delaware Bay shoreline.

By late afternoon, the state Department of Environmental Protection had announced that it was investigating what it termed a "major" washup of dead fish.

Officials reported that the swath of dead menhaden - a small bait fish also known as peanut bunker - extended along seven to eight miles of shoreline from Kimbles Beach in Middle Township south to Villas in Lower Township, including an area known as Pierces Point.

Water samples collected by the U.S. Environmental Protection Agency showed no indication of "red tide" or other toxic phytoplankton, the state said.

The DEP is also analyzing oxygen levels in the water.

"Right now, we just don't know" what caused the die-off, said DEP spokesman Larry Hajna. "It's a mystery."

Budd, a commercial crabber and owner of Budd's Bait & Tackle in Villas, said there were millions upon millions of bunker in the bay.

"If you're on my boat when we're working, the bunker are jumping all over. Sometimes the water is wrinkled with them," he said.

Eric Stiles, vice president for conservation and stewardship of New Jersey Audubon, said he had never heard of such a massive die-off of menhaden. They are a "critical fish" in the ecology of the bay, he said, so the fish kill is likely "highly significant."

DEP conservation officers are working with the Cape May County Office of Emergency Management to evaluate the beaches.

The area is marshy and largely inaccessible from land, so the DEP also dispatched an aircraft to better assess the extent of the die-off.

Contact staff writer Sandy Bauers at 215-854-5147 or sbauers@phillynews.com Visit her blog at http://go.philly.com/greenspace.