Plastic threat to sea life 'exaggerated' -- That's the headline on a news story from The Australian, a Sydney, Australia, newspaper. That was enough to get my attention.

The thrust of the story is that Colin Limpus, introduced as "Australia's leading authority on sea turtles," believes that environmentalists who are lobbying to ban plastic shopping bags are exaggerating their impact on marine life.

"This has been picked up by the conservation community, but these bags would only account for a small proportion of plastic-related injuries," said Limpus, a scientist with the Queensland Environmental Protection Agency.

The bigger threats, according to Limpus: careless boaters and fishing nets.

As he helped release into Moreton Bay 13 sea turtles that had recuperated after being taken sick or injured to Sea World on the Gold Coast, Dr Limpus identified boat strikes as the biggest threat to turtle populations in coastal waters.

About 100 large turtles are killed each year by boats in southeast Queensland compared with an average of 20 boat-related deaths in the late-1980s.

"These animals are mainly adults which take 30 years to reach breeding age, so the losses are substantial," Dr Limpus said.

Conservationists have used sea turtle and other marine animal deaths as a key argument in their campaign to eliminate plastic shopping bags.

The campaign has often cited a Canadian study to demonstrate that 100,000 animals are killed annually by the bags, although the study identified discarded fishing nets as the cause.

If the government really is serious about protecting turtles, it should regulate the speed of boats in areas frequented by turtles, dugongs and other vulnerable marine animals, Limpus said.

"The problem is that the boats are moving so fast that the animals don't have time to get out of the way and below the propeller," he said.

The newspaper also talked to Clean Up Australia chief executive Kerrie-Ann Johnson, who insisted that the impact of plastic bags on marine life had not been exaggerated. She cited a study by the Australian Marine Conservation Society -- although that group's spokesman denied that it had conducted such a study.

It looks like Limpus is using the raging plastic bag ban in Australia to try to focus attention on what he considers a more serious problem. Good for him.

Still, I don't think this is a signal that the marine debris issue isn't real. It's not going away -- especially in California and Hawaii.