Dr. Guy Fournier claims that although female beach goers in France have traditionally bared their breasts without a second thought, the trend has declined due in part to the declining economy.
He reasons, that bare breasts are viewed as totally natural on French beaches, but public morality follows people's confidence and optimism in their wealth. During an economic downturn, women are less inclined to let it all hang out and more likely to cover up.
If true, this would make topless bathing on French beaches a lagging indicator of economic activity.