A year after Oahu’s single-use plastic bag ban took effect July 1, 2015, prices have increased, and shoplifting is on the rise as thieves find more ways to walk out of stores without paying for their goods.

“People walk in with their bags, and they put their things in their bags and it’s very difficult for people to tell whether the product was purchased,” said Lauren Zirbel, executive director of the Hawaii Food Industry Association. “Sometimes people will just go in and put products directly in bags, and sometimes loss prevention personnel can’t get everybody. It’s really difficult because you can’t chase people down. It’s a pretty big issue.”

Tamura Enterprises Inc. has experienced a 15 to 20 percent increase in theft over the past year since the prohibition on plastic bags began, said Mike Mita, director of operations. Tamura’s has nine stores, including one that opened Thursday in Kihei, Maui.

“There’s a lot of times that there are those that get away, and it’s hard for us to discriminate or to discern,” he said. “Age doesn’t matter; it’s not only the young and the middle-aged. Anybody can steal. How do you discern one from the next? You cannot just stop people from coming into your store. You cannot watch everybody. It makes for an uncomfortable shopping experience when somebody’s watching you. You don’t want people to feel uncomfortable shopping in your store.”

The company, which has more than 200 workers, is considering hiring more employees to curb the problem.

“For us the deterrent is pretty much having all our employees on the floor, but it’s expensive to keep people on the floor,” Mita added. “It increases the cost to the consumer.”

KTA Super Stores has also seen more incidents of theft at its six Big Island markets since Hawaii County’s plastic bag ban went into effect in 2014, said President and Chief Operating Officer Toby Taniguchi.

“It’s certainly has increased the incidents of those things happening where individuals kind of just walk out,” he said. “We like to … treat everybody with respect and nicely and with good service. While 99 percent of the customers are honest and forthright, unfortunately there’s a very small percentage that do choose to shoplift.”

Foodland executive Andy Kawano said he didn’t have enough information to say whether there’s been an upswing in thievery.

“There’s homelessness; people are under the influence of drugs, poverty,” he said. “To single out the plastic bag ban, I don’t have enough information to take a stand on that.”

Aside from theft, retailers have seen a dramatic increase in their bag expenses, a cost that is passed on to consumers, Zirbel said. Retailers using paper bags are paying as much as 28 cents per bag, substantially more than the 1 to 3 cents for plastic bags.

Tamura’s said about 50 percent of customers bring in reusable bags.

“It’s a direct tax on groceries because bag increases are being passed onto foods — they have to be,” Zirbel said. “The paper bags cost 10 times more than plastic bags did. The increase of reusable bags was not a large enough increase to offset the cost of the paper, so it was a pretty significant increase in their overall cost of providing bags. One of the large supermarkets saw a 92 percent increase in bag expense because customers are choosing to take paper bags.”

Oahu’s plastic bag ordinance was signed by then-Mayor Peter Carlisle in 2012. While retailers can no longer give customers single-use plastic bags, the law allows for a number of exceptions, including distributing thicker, reusable plastic bags.

Retailers and restaurateurs can still use plastic bags to package plate lunches, poke bowls and other prepared food, as well as fresh fruits and vegetables, meat and fish, frozen food and other loose items including nuts, coffee, candy, flowers or plants, medications, newspapers, laundry and pet items.

Hawaii is the first state where single-use plastic grocery bags are banned in all counties, which environmental groups say has resulted in dramatically reducing litter statewide.

“Plastic bags are literally one of the most littered items on the planet. We use them on average for less than 15 minutes, and yet they endure in the environment and the oceans for decades and decades to come,” said Stuart Coleman, Hawaii manager for the Surfrider Foundation, an environmental nonprofit dedicated to protecting coastal areas. “The benefits of banning single-use plastic bags far outweigh any temporary convenience they might serve.”