Events & Media

Jan. 5, 2017

How China Maintains Large Catches Despite Intense Industrial Fishing
… and what it might mean for fishery management elsewhere in Asia

China, the world’s largest seafood producer, has done something extraordinary. For the past twenty years, despite minimal management and some of the most intense industrial fishing in the world, it has maintained large catches of key species in its most productive waters. That same kind of intense, lightly managed industrial fishing has collapsed other fisheries, such as Newfoundland’s cod fishery in the 1990s. China’s ability to maintain its catches has puzzled scientists, some of whom have even questioned the accuracy of China’s catch reports.


Cody Szuwalski
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A new study from the University of California, Santa Barbara, suggests another explanation: by reducing the population of predatory fish, China has increased populations of species they prey on. “If you fish down the large predatory fish, then you can catch more small prey fish, because the prey are no longer being eaten before you get to them,” explained Cody Szuwalski, a fisheries scientist in UCSB’s Sustainable Fisheries Group and the study’s lead author.

Key to the success of this approach is that predators typically need to eat around ten pounds of prey to add one pound to their own weight, so fishing out predators tends to increase prey catches by much more than it reduces predator catches.

This “shortening of the food chain” by removing predators to increase harvests is common on land; in fact, it’s a key feature of modern farming. “If farmers could earn as much from raising venison on a field as they can from growing corn on it, they probably wouldn’t try to keep deer out of their fields,” said Matt Burgess, a postdoctoral researcher and co-author of the study.

Largehead hairtail caught in the East China Sea and landed in Zhoushan, China

But in the oceans, shortening the food chain looks different, because who eats whom among fish is generally based on body size rather than species. Bigger fish eat smaller fish, even when the two are from the same species (cannibalism) or the smaller fish are the juveniles of predator species and the bigger fish are adults of prey species. So while you would not likely see an adult gazelle eat a baby lion, you might see an adult sardine eat a young largehead hairtail, a predatory species that is one of China’s most common catches.

The study was based on a model of the East China Sea ecosystem built to account for this size-based feeding as well as the history of intense trawl fishing in the region. The model was able to roughly re-create reported catches of all major species. It also correctly predicted that under China’s current approach, even catches of such predator species as the largehead hairtail would remain high, although they would consist mainly of one-year-old fish. “This is exactly what you see when you visit Chinese fish markets,” said Szuwalski.

Beyond providing an answer to an important fisheries puzzle, the study also offers important lessons for fishery management in Asia. When used to simulate various possible management strategies in the East China Sea, the model predicted that Western-style, single-species management would decrease catches instead of increasing them, by reversing the changes to the food chain that have so far allowed catches to remain high. The same could be true in many other major fishing countries, especially in East Asia, which have fishing histories similar to China’s.

“The standard refrain is that most countries can catch more by managing their fisheries like we do,” said Christopher Costello, the Sustainable Fisheries Group’s co-principal investigator. “What if we’re giving them the wrong advice?”

Given the negative impacts on biodiversity and potentially reduced ecosystem resilience in the face of climate change, “engineering” ecosystems by removing predators to enable large harvests is not necessarily an advisable long-term fishery management strategy. Still, the study suggests, in places where predator removal has already occurred, managers need to take the food chain into account to avoid unexpected consequences. Indeed, the model predicted that it is possible for such ecosystem-level management to increase catches, revenue, and biomass in China — a win-win-win.