Homeowners streamed across the Route 72 causeway to check on the damage from Hurricane Sandy on Monday. But of the more than 19,000 housing units on Long Beach Island, only 19 percent are occupied year-round.

The six municipalities that make up the island range from tiny, barely square-mile-sized towns such as Barnegat Light to transportation and business centers such as Ship Bottom to the five-part, segmented Long Beach Township. But each town is similar in terms of its makeup: a small year-round population that lives in less than one in five of the homes on the 18-mile-long island, with the rest mostly second homes or vacation homes.

Just 3,690 units were listed as “occupied” as of April 1, 2010, the day on which the population was officially counted by the census.

The majority of housing units being summer or part-time residences meant that the population of the island at the time of evacuation for Sandy was smaller than if the storm had hit during the summer. But now, the hard work of recovery begins.

The year-round population of 7,493 is mostly made up of middle-aged and senior citizens, with more than 60 percent of the population 50 and older and more than a third 65 and older. In Barnegat Light and Long Beach Township, more than 40 percent of the population was 65 and older.

Just 11 percent of the year-round population are children — in Surf City and Barnegat Light, the under-18 population is less than 10 percent — which has in turn led to a severe drop in school enrollment on the island during the past decade. The Long Beach Island Consolidated School District dropped from 349 students in 2001-02 to 238 in 2011-12, a decline of 32 percent, while the Beach Haven district dropped from 80 students to 62, a decline of 23 percent.

The decline mirrored a drop in the year-round population overall. The combined population of all island towns dropped from 8,556 in 2000 to 7,493 in 2010, a decline of about 12 percent.

Barnegat Light, at the northern tip of the island, saw its population drop 25 percent, from 764 to 574. Surf City’s and Ship Bottom’s populations both dropped by 16 percent, while Long Beach Township’s population dropped by 8 percent.

The township’s 83 percent vacancy rate, though, is second on LBI only to the much smaller Harvey Cedars, which had an 86 percent rate. Ship Bottom, with a 73 percent vacancy rate, was the island town with the largest percentage of units occupied by year-round residents.

Contact Steven Lemongello:

609-272-7275

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