A large swath off the New Jersey coast will be studied beginning in January to assess wildlife density where offshore windmill farms may be built as an alternative energy source, the state Department of Environmental Protection said Friday.

The 18-month survey will focus on the 70 or so miles of coast between Seaside Park in Ocean County and Stone Harbor in Cape May County and extend as far as 20 nautical miles, or 23 miles, offshore.

The survey will compile information on the activity of birds, sea mammals and sea turtles in the zone, as well as evaluate the impact of turbines on natural resources in the area, such as reefs and sand bars, to determine what portions of the area are most suitable to host windmills, said Gary Buchanan, the project manager for DEP. "There is limited data once you move a few nautical miles offshore. These are the large data gaps this study is designed to fill," he said.

Geo-Marine Inc. will conduct the survey after winning the contract to oversee the $4.5 million project. Dan Wilkinson, vice president of environmental resources for Geo-Marine, said vessels and planes will monitor wildlife using radar, thermal imaging and underwater acoustic recordings.

Although the study stems from a recommendation from a May 2006 report from the state's blue ribbon panel on developing wind energy farms in New Jersey, Jeff Tittel, executive director of the New Jersey chapter of the Sierra Club, said the research is unnecessary and just delays the construction.

An interim report about the results will be issued in January 2009, with the final report due in September 2009.