BAR HARBOR – The popular Island Explorer bus system is a tad less popular so far this year, with ridership slipping by 19 percent through the July Fourth holiday.

Paul Murphy, executive director of Downeast Transportation, which runs the system, said it’s too early to say how the overall season will go.

“My guess is that it’s mostly because of the weather,” Murphy said Wednesday. “Much of Bar Harbor is down, but I just don’t think we have enough of a sample” to draw any firm conclusions.

“If we get to mid-August” and the numbers are still down, “I’ll consider it a trend,” Murphy said.

The dip in Island Explorer riders is apparently a first for the propane-powered buses financed by Acadia National Park, the communities and businesses of Mount Desert Island, and federal and state transportation agencies.

People interviewed over the holiday weekend cited several reasons, besides the weather, that could be affecting the vacation season.

In addition to the more obvious possible reasons, such as high gas prices, William Haefele, president of the Mount Desert Island Regional Chambers of Commerce, noted that there are more hotel rooms this summer in Bar Harbor, which could explain why there are so many hotels with vacancy signs as the peak vacation season begins.

He agreed with others who report that business is down so far this year. He said May was just slightly down, but June was definitely down. The July Fourth weekend also was off, he said.

“Most resorts have a reputation for being full on weekends and perception is reality,” Haefele said Monday. “Our busy days are Monday through Thursday, which goes against the norm for resort areas.”

Haefele said people also can be influenced when they see advertisements for the big hotels, which can cost $200 a night in peak season.

“People see ads for the waterfront hotels and they think all rooms are expensive,” he said. “The perception is if you can find a room you can’t afford it.”

Most people think there is a combination of factors driving down vacation numbers:

. Continued unease over security and terrorism.

. The upcoming presidential election and uncertainty about what the outcome might mean for family incomes and jobs.

. The ongoing conflict in Iraq.

. High gas prices and insecurity about the economy.

. Lousy weather.

Not all businesses in the Mount Desert Island region are recording losses, either. Some places are steady with last year and others have recorded strong sales, according to some business owners.