By Paul Gabrielsen

An employee gathering carts from a sunny parking lot of a Santa Cruz Safeway said shoppers are warming up to the city's new ban on single-use plastic bags. But some still miss the bags' convenience.

"Wrong thing to do," said a middle-aged man of the ban.

"But they're killing the innocent turtles," his wife said, adding that in Europe, reusable bags are a way of life.

The couple's disagreement is typical of the strong feelings evoked by plastic bag bans, which seem to delight environmentalists but aggravate many retailers and consumers. While there is some evidence that the bans have reduced litter on city streets and beaches, ambiguities in the data seem certain to fuel further heated debate.

San Francisco led California's war on plastic, banning bags at large grocery stores and chain drugstores in 2007. But litter surveys in the city, covering the first two years after the ban went into effect, painted a foggy picture.

Surveyors assessed more than 100 randomly selected sites in the city each year, counting every piece of litter in an area half the length of a city block. In 2007, before the ban was introduced, plastic bags amounted to 0.5 percent of large litter. By 2009, the percentage climbed to about 1.5 percent. And during the same period, the average amount of litter stayed about the same.

The city hasn't collected any litter data since the 2009 survey, said Guillermo Rodriguez, a spokesman for the city's environment department.

The ban was expanded to all retailers in July 2012 and will continue to expand to all restaurants this year. San Francisco plans to do another litter survey to see whether the new scope of the ban makes a measurable impact.

San Jose has already seen that impact. The city's 2012 bag ban immediately covered all retailers. Last December, San Jose presented results of litter surveys in city creeks, streets and storm drains. Surveys after the bag ban in 2012 found 89 percent fewer bags in storm drains, 60 percent fewer in creeks and 59 percent fewer on city streets, compared with surveys before the bag ban. Plastic bags made up 8 percent of total creek litter in 2011 and 4 percent in 2012.

A 2012 survey of Bay Area storm drains found that "other plastics," not including plastic bags, made up about 50 percent of storm drain trash. Paper, Styrofoam and drink containers together made up another 30 percent.

Litter on beaches

But the bags also show up in marine litter, making up about 15 percent of trash in the deep reaches of Monterey Bay. The Monterey Bay Aquarium Research Institute reported finding plastic bags in water nearly 2½ miles deep, according to a paper published online in May in the journal Deep Sea Research.

Closer to the ocean surface, concern for the bags' impact on marine life stems from the fact that ocean-borne plastic bags look similar to jellyfish, which sea turtles love to eat.

Whether the bans are preventing bags from reaching the ocean is hard to measure, but surveys of litter on Monterey Bay beaches provide the best available picture.

Santa Cruz-based Save Our Shores promotes weekly cleanups around Santa Cruz and Monterey counties and collects trash data from many of these events. On average, volunteers pick up only six bags at each event, down from a high of 65 in 2008.

The number of bags collected per cleanup has dropped in the past two years because of four bans that took effect in 2012, said Save Our Shores executive director Laura Kasa. The four bans covered unincorporated Santa Cruz County and the cities of Watsonville, Monterey and San Jose.

The latter ban matters because of the volume of tourist traffic coming "over the hill" to Santa Cruz beaches, said Kasa, who also credits the shift in public perception toward plastic bags in the region. "In Santa Cruz it's become the trend to be green and to bring your own reusable bags and not use plastic bags," she said.

Save Our Shores program manager Brad Hunt pointed out that Monterey County has not yet implemented a bag ban, which affects Save Our Shores' average cleanup numbers. "It could go down to one bag per cleanup after Monterey County implements theirs," Hunt said, "but we won't know that until a year or two down the road."

An opposing voice

Opponents of plastic bag bans point out that bags make up a small fraction of litter. "You're talking about such a small amount to begin with that you wouldn't notice any change," said Stephen Joseph of the Save the Plastic Bag Coalition, whose members include plastic-bag manufacturers and retailers.

Joseph said political leaders have exaggerated the problem. He disputes claims by Oakland-based Save the Bay that a million plastic bags enter San Francisco Bay each year. In 16 years of living in the city, Joseph said, he never saw one bag in the bay.

"It's a hoax," he said, adding:

"There's obviously plastic bag litter. Anyone who's never seen a plastic bag flying around is blind. But that does not justify all the exaggeration."