That steep decline comes after a Nov. 1 report in Chinese state media about AIS stations in coastal Guangdong province that warned “the intelligence extracted from this data endangers China’s economic security and the harm cannot be ignored.”

China’s decision to curtail the flow of information out of its ports coincided with the Personal Information Protection Law, which took effect on Nov. 1. That legislation is meant to regulate the flow of Chinese data overseas and ensure the gathering of such data is minimized, according to state-run media.

Shipping companies have already reported a diminished ability to accurately track activity in Chinese ports without the data, Charlotte Cook, head trade analyst at VesselsValue, told the newspaper. AIS signals previously allowed companies and governments to assess activity levels in Chinese ports, which have been congested by supply chain snarls and pandemic controls in recent months.

Earlier this month, China punished an unnamed non-governmental organization for collecting “sensitive” maritime data and sharing it abroad. The NGO set up coastal monitoring stations near military sites to track offshore debris, threatening China’s national security, the Communist Party’s highest law enforcement body, the Central Political and Legal Affairs Commission, said on its website.