BOSTON -- Park rangers who patrol the Cape Cod National Seashore around Provincetown and Truro are trying to come up with strategies to discourage increasingly common incidents of illegal public sex on area beaches.

They say complaints about explicit, open public sex on the national park beaches have tripled in the past decade, with activity ranging from flashing to men's public orgies.

The rangers have been trying to crack down by enforcing a federal misdemeanor charge of disorderly conduct, which prohibits obscene acts, the Cape Cod Times reported.

Seashore rangers issued 132 citations for public sex acts last year, compared with about 70 annually from 2003 to 2006, and about 40 citations annually in prior years, Seashore acting chief ranger Craig Thatcher said.

A New Jersey family walking with children in the dunes wrote in a September 2007 letter that they encountered "several couples and then a large group of men having group sex in the nude, including oral and anal sex right out in the open," the park service said.

A whale-watch boat captain carrying a boatload of tourists also reported seeing 20 to 30 nude men "playing around" near Wood End Lighthouse, another letter from August 2007 reported.

Provincetown has a large gay population and attracts large numbers of gay tourists, according to the Times.

Rangers said they are working with Provincetown police and town officials to start a public education campaign aimed at discouraging the behavior.