As climate change brings warmer, more acidic waters to China, its offshore fish stocks are coming under pressure.
A number of fish populations – including the large yellow croaker, sea bream and sandlance – are at risk, according to a study by researchers based in the US and China, and published in the Proceedings of the National Academy of Sciences (PNAS).
Ocean warming has been more pronounced in China’s offshore waters than almost anywhere else. Winter surface temperatures in the Bohai, Yellow and East China seas, off the country’s eastern seaboard, rose by nearly 2C from 1958 to 2014 – well above the global average. And with concentrations of atmospheric CO2 rising, more of the gas is absorbed into the ocean, resulting in acidification of surface water. The trend is particularly evident in the coastal waters of southern Jiangsu, the Yangtze estuary and Hangzhou Bay.
Rapid changes in the marine environment are already threatening species most sensitive to such changes.
The impact of climate change on China’s fisheries is alarming scientists, who say that plenty of research gaps on the issue still need addressing. Aside from the need for a high-level programme to meet the challenge at a national level, coastal regions will have to come up with corresponding management approaches that suit their circumstances.
Limited impact for now
As the world’s largest fishing country, China’s marine catch for 2020 stood at 11.8 million tonnes, with 2.3 million coming from distant waters, according to a 2022 report by the UN Food and Agriculture Organisation. However, the same year, its inland fisheries yield slipped to second in the world – behind India – due to the Yangtze fishing ban, the report stated.
The marine catch was significantly lower than the yearly average of 13.24 million tonnes during the 2010s, the report found. The underlying reason for this was the stress on coastal marine animal stocks caused by decades of overfishing.
In an effort to save the industry from collapse, the government has introduced a series of restrictions in recent years, including fishing moratoriums. However, the effects of climate change, notably warmer and more acidic seas, are piling yet more pressure on the marine ecosystem and fisheries sector.
By analysing the impact of climate-induced seawater changes on 67 species of marine animals, the PNAS study identified some key characteristics of climate-vulnerable species. These include: sensitivity to ocean acidification; subjection to overfishing; tolerance of a narrower range of temperatures; and limited migratory capacity as juveniles.
The 67 animals were split into 28 categories on various taxonomic levels (order, family, genus). Positively, the results showed that populations from only six of these categories are currently exposed to a high level of climatic risk, and that recovery potential is medium or high for those in 21 of the categories. It seems the overall impact of climate change on China’s fisheries at this stage is still fairly limited.
Impact varies according to animal type
The study also found that, interestingly, species most able to withstand stress from overfishing are also the most adaptable to climate change. They generally have a high tolerance for temperature change, a broad diet, strong reproductivity and a positive capacity for migration, making them more resilient and able to recover from population decline.
By the same token, less adaptable species are more vulnerable. The large yellow croaker, for example, is especially sensitive to ocean acidification, has a very low tolerance for environmental change, and reproduces relatively slowly.
Overexploitation of the species, which was once distributed throughout the coastal seas of eastern China, has caused wild populations to decline significantly. For Professor Tian Yongjun from the Ocean University of China’s College of Fisheries, the real impact of climate change on large yellow croaker may be even more complex, and is possibly amplifying the effects of overfishing.
As Tian tells China Dialogue Ocean: “A certain level of sea-water temperature rise would actually favour the large yellow croaker, but we haven’t seen any significant increase in wild populations of the fish in recent years. We have studied this, but have yet to come up with a definitive explanation.”
It’s a rather different story for the small yellow croaker, however. Most fish in the temperate waters of eastern China are classified as warm water species (meaning they can live in waters 10C and over), and this includes both the small and large yellow croaker.
Stocks of small yellow croaker have surged in response to warming waters, Tian notes. One possible factor is that the large yellow croaker “has relatively few spawning grounds, unlike the small yellow croaker, and population recovery could suffer once a spawning ground has been wrecked,” he says.
Another factor, he suggests, is that because the large yellow croaker has a relatively long lifespan, “overfishing in the past may have altered the population’s age composition and reproductivity, making recovery difficult.” What’s clear from comparing the situation of large and small yellow croakers is that the effects of climate change on fish populations are complex and involve a great deal of uncertainty.
Nevertheless, China needs to be alert to the risks that climate change brings, especially in how it significantly alters the patterns of fisheries in Chinese waters. A 2022 study by Tian’s team suggests that for 20% of fishery species in China’s seas, a quarter of their habitats are no longer suitable due to rising sea temperatures. Moreover, the situation is projected to worsen in future scenarios, with a quarter of habitats becoming unsuitable for nearly 50% of the species by the 2050s.
Measures tailored to local conditions
China’s policymakers are, to an extent, already aware of the challenges that climate change brings to the fishing industry. The National Climate Change Adaptation Strategy 2035 acknowledges the need to strengthen the conservation and restoration of coastal ecosystems. It calls explicitly for maintaining a stable and strictly enforced system of summer fishing moratoriums, a cap for total marine catch, and promoting the sustainable use of such fishery resources.
The PNAS study highlights that the climatic challenges for China’s fisheries differ between regions, and local conditions demand different adaptation policies.
Around the Bohai and Yellow seas, for example, where catching some types of fish presents high risks to the local marine ecosystem, and where the adaptation capability of the local fishing sector is weak, the study found that resilience would be boosted by diversifying into other seafood products. Increased investment in climate-related research and forecasting would also help, along with greater stakeholder involvement in decision-making within both fisheries and other sectors, the authors stated.
In the East China Sea area, overreliance on fisheries can mean local communities are more susceptible to climate change impacts, despite the sector’s relatively robust capacity to adapt. The key, they noted, is to create opportunities for alternative employment.
The study also highlights how crucial it has proven in other countries to enable fishers and other stakeholders to have a role in governance, and to develop information-sharing mechanisms for the climate-adapted management of fisheries. Such approaches, which have yet to be factored in for fishery and marine-related policy at the regional level in China, need to form part of the next phase of the adaptation effort for Chinese fisheries, the authors wrote.
Tian believes that, before a specific action plan can be developed, gaps in the basic research on China’s fisheries – such as the traits and behaviour of different species – need to be addressed first, and that broadly, fisheries management needs to be backed by scientific research.
“Even with the fishing moratorium system and proposed restrictions on catches, there is the basic problem that we’re still not certain where the spawning grounds of the ‘big four’ families of fish are,” he says, referring to the large and small yellow croakers, hairtail and cuttlefish.
“The life cycle characteristics and concomitant changes for many of the fish are not clear either,” he adds. “That being the case, how do you ascertain the impact of climate change on them?”
