The industrial zones set aside by Mayor Michael Bloomberg five years ago are having trouble holding onto their boundaries as hotels, superstores, and other retail businesses move into the areas. A recent New York Industrial Retention Network report says that although residential conversion is prohibited in 16 areas in the outer boroughs, as per the Bloomberg administration’s policy, non-industrial businesses are setting up shop there anyway. The report says 39 sites within the zones are non-industrial, including two bowling alleys, an art gallery, and a number of bars in Williamsburg; and a shopping center in East Greenpoint. The industrial zoning was intended to keep real estate prices low, but industrial rents are up to $18 per square foot, which is double the price in 2000. Industrial advocates say companies are being driven out of the city in the absence of zoning enforcement, while a spokesperson for the city’s Department of Small Business Services said some commercial development can be “healthy” for industrial zones.