Some Charleston area attractions had an unexpected surprise after they tallied up their summer ticket sales: Numbers that had been climbing inexplicably took a dip. 

Attendance over the last last two years was "incredibly good" at Patriots Point Naval & Maritime Museum in Mount Pleasant, said executive director Mac Burdette. 

"We saw no reason why that was going to change," he said. 

The economy was doing well, Charleston was topping lists of must-see travel destinations and summertime visitors were pouring into Charleston International Airport. 

"Things just went flat," Burdette said, "for no apparent reason." 

Patriots Point was short about 6,000 visitors for June and July compared to last year, Burdette said.

And it wasn't alone. 

The South Carolina Aquarium also experienced a decline in ticket sales that was "in line with other attractions in the area," said Bethany Morgan, spokesperson for the aquarium. 

At the Charleston Museum's properties, which include the museum, the Heyward-Washington House and the Joseph Manigault House, attendance was down 2 percent in June and 11 percent in July, director Carl Borick said. 

That may have been due to the fact that 2017 was an exceptionally strong year, he said, making year-over-year gains more difficult to meet. Day-to-day weather conditions contribute to attendance figures, too. 

Still, Borick said, he can't be sure. 

"I have been analyzing museum attendance figures for over 20 years, and sometimes you can just never tell why you have a certain increase or decrease," he said. 

Unlike hotel rooms or airplane flights, the decision to pick one activity or attraction over another is often made spontaneously, said Daniel Guttentag, director of the Office of Tourism Analysis at the College of Charleston. 

That makes predicting attendance numbers — or determining what causes a peak or dip in ticket sales — particularly difficult. 

And it's not just historic houses, museums and other classic Charleston-area attractions competing now for discretionary spending dollars, he said. Those attractions are also up against brewery tours, escape rooms, an ever-growing list of special events and festivals and the city's shopping and restaurant scene. 

"We've seen an increase in visitors, but we've also seen an increase in things to do here," Guttentag said. 

Sign up for our new business newsletter

We're starting a weekly newsletter about the business stories that are shaping Charleston and South Carolina. Get ahead with us - it's free.

Patriots Point and the Charleston Museum also found that, when compared to ticket sales over the last several years, this summer, though slower than last, was on par with average performance. 

It was a signal, Burdette said, that comparing one year to the last is a "false indicator," and that they can benefit by comparing figures to averages rather than expecting growth year after year. 

In early September, the Charleston Area Convention and Visitors Bureau organized a meeting for representatives from about 20 area attractions. Discussion at the meeting focused on increasing promotion for attractions, said CVB chief executive Helen Hill.

Since the bureau doesn't keep track of the ticket sales at area attractions — each are operated independently — the organization couldn't outline specifics about trends in ticket sales, but Hill confirmed that attractions reported a dip in attendance. 

However, the sales slump wasn't experienced across the board. 

Some attractions, like Middleton Place, a historic plantation about 15 miles northwest of Charleston, saw sustained or slightly higher visitation. Don Bussey, spokesperson for the Middleton Place Foundation, said ticket sales at the plantation increased about 4 percent this year compared to June and July last year. 

Historic Charleston Foundation's house museums saw a slight increase, too, which marketing director Holland Williams attributed in part to an increase in advertising spending and a focus on new promotions, such as banner ads at the Charleston International Airport and curated social-media posts on Instagram. 

In November, Hill said the visitors bureau will offer another meeting for Charleston-area attractions where they can reconvene and continue the discussion on marketing their sites to visitors. 

Reach Emily Williams at 843-937-5553. Follow her on Twitter @emilye_williams.

Emily Williams is a business reporter at The Post and Courier, covering tourism and economic development. She is also the author of the weekly Business Headlines newsletter. Before moving to Charleston, her byline appeared in The Boston Globe.