MIDDLE TWP., N.J. - In time for the spawning season of the horseshoe crab and the subsequent spring migration of shorebirds like the ruddy turnstone and the red knot, the U.S. Fish and Wildlife Service has completed a $1.65 million restoration project along five Cape May County bay beaches.

It is the first of 31 such "coastal resilience" projects focusing on rebuilding natural areas after Hurricane Sandy, according to Eric Schrading, a field supervisor for the service's New Jersey field office.

The Delaware Bay supports the largest spawning population of horseshoe crabs in the world.

The 1.5-mile expanse of beach that was restored - a relatively undeveloped area on what is known as the inner shoreline of the cape - includes Reeds Beach, Kimbles Beach, Moores Beach, Cooks Beach, and Pierces Point. Other habitat beaches along the coast being restored by the service include a 22-mile stretch of coastline in Brick Township being managed by the Edwin B. Forsythe National Wildlife Refuge.

The work here is part of a first wave of coastal resilience projects being funded by the Department of the Interior through the 2013 Disaster Relief Supplemental Appropriations Act.

Crews began last year to clear 800 tons of debris from the area, including chunks of asphalt, bricks, concrete pipes and slabs, and wooden pilings that had washed up or were exposed along the shoreline after Sandy hit on Oct. 29, 2012.

Beginning in mid-March, it took contractors about a month to bring 45,000 tons of locally mined sand to the five beaches to replace about three feet of sand lost to the hurricane's surge and erosion following the storm.

The storm pulled tons of sand from the beaches and washed it into the bay or surrounding marshes. The beach was so denuded that all that was left was a sod-like layer with the consistency of springy carpet.

In other areas of the Delaware Bay, the storm's devastation uncovered a century of human development, exposing old docks, bulkheads, and pilings that had been long buried.

By the time the storm was over, biologists said, as much as 70 percent of the optimal spawning habitat had been ruined. What remained was an unsuitable landscape along what is considered to be among the most important spawning and migratory habitats in North America.

"We're very happy that this project was completed so quickly," said Schrader. "This is an important restoration project, not just for the horseshoe crab spawning but also for shorebirds foraging."

Schrader said the quick completion - of a project begun the moment funding was in place and all permits were approved by the state Department of Environmental Protection and the Army Corps of Engineers - was a race against time.

Various groups pitched in, partnering with state and federal officials, including the American Littoral Society and the Conserve Wildlife Foundation of New Jersey. Local property owners also gave the OK for crews to access the beachfront via their lands to expedite the process, officials said.

Getting the sand onto the beaches before the highest tide in April - on the 15th - meant that it had time to settle properly, and laid the groundwork for when the crabs would begin making their migration out of winter hibernation beneath the mud and muck of the nearby wetlands, onto the beach to lay their eggs.

The spawning usually happens at night and coincides with high tide during full and new moons.

So far, only a few crabs have made their way to the beaches, thanks to colder-than-usual water for this time of the year - currently hovering in the 50s - said Schrader.

The nutrition-rich lipids contained within the horseshoe crab eggs are the boost that shorebirds need on a stopover as they migrate along one of the Earth's vastest flyways, from South America to the Arctic - a 9,500-mile journey.

But relatively uncontrolled harvesting of the marine arthropod in recent years along the East Coast - for use in fertilizer, or as bait - has led to a significant decline in the number of horseshoe crabs, which have existed for an estimated 450 million years. Although they resemble crustaceans, they are more closely related to arachnids - spiders and scorpions.

Horseshoe crabs are also used in pharmaceuticals, on a catch-and-release basis in which their bluish blood is harvested and they are then returned to the sea. Industry experts say the mortality rate of the crabs used for this purpose is between 3 percent and 15 percent, while species advocates say it is between 10 percent and 30 percent.

A lack of habitat - and the eggs that the crabs spawn upon it - could create a problem for various bird species already in trouble.

Most significant is the red knot, which once numbered as many as 100,000 as the birds migrated twice annually along the Cape May peninsula. Its numbers have dropped to only about 15,000 a year, according to Larry Niles, a New Jersey biologist and executive board member of the Western Hemisphere Shorebird Reserve Network.

Biologists say about half of the red knot worldwide population makes the stopover along the Delaware Bay. The red knot, a cinnamon-breasted short-legged bird, is being considered for inclusion on the federal endangered species list.

Niles contends that restrictions put in place in 2006 for harvesting of horseshoe crabs have helped spawn a rebound for various bird species like the red knot, whose numbers appeared to be on a slight increase last year.

But all could have been lost had the sand replenishment not been finished in time for the crab spawning season, officials said.

To help keep tabs on the crabs and their spawning habits, the wildlife service will host two horseshoe crab tagging events - one on May 15 and the other on May 29, both at 8:30 p.m. - so volunteers can help tag as many as 1,000 of the crabs, officials said.