Impact of Climate Change & Overfishing on Fishstocks in East & South China Sea

By Sophie le Clue 22 November, 2021

Cautionary tale on Asia’s fisheries is told by ADMCF's new report - foundation's new CEO Le Clue expands

As COP26 drew to a close last week, it was hailed as a success, as an abject failure and perhaps more guardedly, as the best we could expect given current geopolitics, economic complexities and political will.

Commentary has since reported optimistically that the negotiations have kept 1.5^oC alive, and pessimistically that the current level of global commitments to stem climate change will tie the world into a catastrophic 2.7^oC rise by the turn of the century.

Whichever outcome we are looking at, we are potentially in for a bumpy ride and one that will likely see vast changes in our ocean and its fisheries.

Research released in the midst of COP26, conducted by the University of British Columbia in collaboration with ADMCF, indicates that two of the most productive fisheries in the world, the East and South China Seas (ECS and SCS), are in a precarious position.

Catches from ECS & SCS fisheries has value of ~US$22.8 bn/yr but both are in a precarious position

Catches from these fisheries had a value of USD 7.4 billion per annum in the ECS and USD 15.4 billion in the SCS as of 2018.

But due to the combined effects of ocean warming and lack of sustainable management regionally, these fisheries have experienced decades of pressure.

ECS experienced rate of warming 10X the global rate

The ECS has experienced a rate of warming ten times the global rate. Although the SCS fares slightly better, minor increases in sea temperatures are significant given the already warm and tropical nature of the ecosystem.

The social and economic consequences of any further degradation and disruption to these marine resources are without doubt concerning.

The research findings presented in the report “Sink or Swim – The Future of Fisheries in the South and East China Seas” – tell a cautionary tale of two climate change options (mild and severe) modelled under four fishing effort scenarios ranging from reduction of effort by 50% through Business as Usual (BAU) to increase in fishing effort by 50%.

Two climate change scenarios:

• Severe – RCP8.5 scenario represents a business-as-usual, high emission scenario, which translates to 1370 ppm concentration of atmospheric CO₂ by 2100.
• Mild – RCP2.6 represents a ‘strong mitigation’ scenario in which greenhouse gas emissions peak mid-century and decrease to a 450 ppm CO₂ concentration by 2100.

Four Fishing Effort scenarios:

Fishing effort, most improvement

• Decreasing fishing effort by 50%, for the first ten years, then keeping that level to 2100
• Decreasing feed-grade fishing (FGF) landings by 50%

Fishing effort, least improvement

• Maintaining current levels of fishing (business-as-usual or BAU)
• Increasing fishing effort by 50% for the first ten years, then keeping that level to 2100

Most extreme scenario results in US$11.4bn loss or 6.4mn tonnes of fish biomass annually in the SCS

The most extreme scenario modelled, a 50% increase in fishing effort combined with severe climate change, predicts that the SCS ecosystem could result in an annual loss of USD 11.4 billion in fisheries revenues or 6.4 million tonnes of fish biomass.

Under the best-case scenario, SCS still could lose US$6.5bn annually

Under the best-case scenarios for both climate change and fishing management (i.e., a low emission scenario with a 50% decrease in fishing effort), the SCS is still projected to lose USD 6.5 billion, or 1.5 million tonnes in biomass across the ten functional groups modelled.

The SCS is not projected to fare well because its fisheries are already under intense fishing pressure and many of the species in its warm tropical waters, are predicted to reach their maximum thermal tolerance as the sea warms. As a result, northward migration to cooler waters is anticipated for many species. The ECS, occupying a more northerly latitude, is in a less precarious position, to an extent being a beneficiary of such migration.

While the ECS fares better, it is still subject to dynamic changes in species composition. Under a severe climate scenario of RCP8.5, warming will lead to lower fish biomass as habitats or oceanographic conditions become unsuitable.

Even in the best-case scenario, biomass & annual revenue of shark can’t recover to present

These falls in biomass mean quite simply that some of the fish species we are used to seeing in local markets, such as croakers and threadfin bream, may become increasingly rare. Large demersal such as sharks could become virtually extinct under the severe scenarios leading to an associated annual revenue loss of over USD 1.4 million. Even in the best-case scenario (i.e., mild climate change and a 50% decrease in fishing effort), biomass and annual revenue of shark fisheries cannot recover to present-day levels in the South China Sea.

Shrimps by contrast are predicted to fare relatively well

But marine ecosystems are dynamic, and shrimps by contrast are predicted to fare relatively well as predators are removed and their relatively higher tolerance to heat takes hold.

Aquaculture now represents 50%+ of seafood produced for human consumption

Seafood lovers may take some solace from the fact that aquaculture is thriving and now represents over 50% of seafood produced for human consumption, and is forecast to grow.  There is however a ‘but’, as with all the best tales. In Asia, we are seeing an increasing trend for large scale fishing for non-target species captured using nets with decreasing mesh sizes, often in contravention of local regulations. This results in the indiscriminate taking of small fish including the juveniles of commercially important species. Ironically, much of this so-called ‘Trash Fish’ or rather Feed Grade Fish – goes into animal feed – including aquaculture.

But large-scale fishing & ‘trash fish’ is leading to the decline of stocks in order to meet the deands of fed aquaculture so aquuaculture could actually exacerbate

The premature removal of juveniles from wild populations before they mature and reproduce contributes to the decline of stocks in order to meet the demands of fed aquaculture. Depending on the species farmed – more fish can go in as feed than is produced for consumption.

As such, aquaculture will not on its own solve our overfishing problem. It could exacerbate it.

Letting juveniles reach maturity could actually increase in revenues

This phenomenon was modelled as a ‘Rebuild” scenario whereby catches were only of mature adults. In contrast to being captured as juveniles, fish that grow to marketable sizes can be sold at a higher per-unit price for direct human consumption. The results indicate a significant increase in revenues by letting juveniles reach maturity, outperforming the Business-as-Usual case.

The above cautionary tale inevitably has different endings. If the optimists are right, and we can hold warming to 1.5^oC and if we work collectively to manage Asia’s fisheries and stem the overexploitation, fishery resources can recover. If the pessimists are right, the tale is no longer cautionary and devastating social, economic, and ecological consequences for Asia’s marine ecosystems and the billions of people who depend on it, are likely to ensue.

Further Reading

• Aquaculture: 8 Fishy Facts – Think because we get fish from water that its “Fish forever more”( 年年有“鱼”)? China Water Risk’s Woody Chan shares 8 must-knows on aquaculture that will make you re-think this
• Something Fishy This Christmas? – Some may opt for fish as a healthier option but not all is well in the oceans. With depleting stocks of some species close to 60%, Sophie le Clue explains why seafood needs to be sustainable. See which to pick & avoid
• 8 Risks You Missed During COVID-19 – Been focused on COVID-19? You are not alone but we can’t get distracted from the climate crisis. Catch-up with CWR’s Chien Tat Low who runs through 8 latest climate & water risks
• Race For Water – Fighting Plastic Pollution In Our Oceans – What does the world’s largest solar-powered catamaran have to do with ocean plastic pollution? The Race for Water Foundations’ Lee explores this sustainable solution for ocean conservation with us

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