Fishermen are paying the price as Asia's superpowers vie for control of the resource-rich waters and islands of the East China Sea.

The stock of almost all seafood in the area was becoming increasingly scarce as China and Japan asserted sovereignty over a group of eight uninhabited islands—known as Senkaku in Japanese and Diaoyu in Chinese—and their oil riches, fishermen told CNBC.

Zhang Yuxiang from the oil town of Dongying on the mainland's northern coast has been working the East China Sea for the past three decades.

"The water quality doesn't even compare to 30 years ago," he said. "Back then, you would fill your hold with big, fresh crabs in one night. But now those crabs have disappeared."

The waters were less fertile because the fishing grounds overlapped with key oil sites, he explained. "We are at the nexus point where the Yellow River meets the innermost bay of the East China Sea. The government has been investing heavily in the oil platforms throughout these waters. This is the biggest offshore drilling operation in China."

In an April report, the U.S.-China Economic and Security Review Commission explained how increased maritime activity could damage local fisheries, using as an example the neighboring South China Sea, home to some of the world's busiest shipping lanes.

"The sand and silt plumes created by dredging sand and gravel and depositing it on the coral reefs either would have killed fish or expelled them from the reefs," the report said. "Most of the small expelled fish would have been eaten by open-water species as they left the protection of the reef and became exposed to predators."