An Ecosystem Inverted
For centuries, the Zhoushan Fishing Ground was called the "Chinese fish storehouse." Fed by the nutrient-rich discharge of the Yangtze River, its waters supported a massive ecosystem. The fishery's primary targets were four species: the large yellow croaker (Larimichthys crocea), the small yellow croaker (Larimichthys polyactis), the largehead hairtail (Trichiurus lepturus), and cuttlefish. In the mid-1970s, the annual catch of the large yellow croaker alone peaked at around 200,000 tons. The entire fishery was central to the regional economy, supporting a population of nearly one million people, including over 300,000 fishers.
The collapse began after the 1950s and accelerated dramatically. The introduction of motorized trawlers, bottom-trawling nets that scraped the seabed, and a massive increase in the size of the fishing fleet created unsustainable pressure. By the 1980s, the once-abundant large yellow croaker was nearly gone from the sea, its population having plummeted by over 90 percent. Today, wild-caught large yellow croakers are commercially rare, and the fishery now targets smaller, lower-value species. This process, known as "fishing down the food web," removed the top predators from the ecosystem, led to for a radical transformation.
The Gelatinous Successors
With the large predatory fish gone, their prey—plankton and small organisms—flourished. This created a perfect opening for a new dominant species: the jellyfish. Blooms of the giant Nomura's jellyfish (Nemopilema nomurai) became increasingly common. These organisms are enormous, capable of growing up to 2 meters in diameter and weighing 200 kilograms. They grow incredibly fast, reaching this massive size from the size of a grain of rice in under a year.
The ecosystem shift was reinforced by other human activities. Agricultural runoff and pollution from coastal development created low-oxygen "dead zones." While fatal to many fish species, jellyfish can tolerate these harsh conditions. The proliferation of artificial structures like oil rigs and aquaculture frames also provided ideal surfaces for jellyfish polyps to attach and reproduce. The result is an ecosystem flipped on its head. Where massive schools of croaker once swam, huge swarms of jellyfish now drift, clogging fishing nets and fundamentally altering the marine environment. The Chinese government implemented annual summer fishing moratoriums starting in 1995 to help stocks recover, but the ecosystem remains significantly changed.