Good Fisheries Management is Good Carbon Management

In this new study, scientists offer a fresh perspective on how managing overfishing is one of the most effective strategies in protecting ocean carbon stores and mitigating the impacts of climate change.

The ocean is a provider. By regulating climate, supplying food and water, and even reducing stress and anxiety, the ocean contributes to bettering human wellbeing and quality of life. Another essential ecosystem service provided by the ocean, is its ability to store atmospheric carbon, through both biological and physical mechanisms. In fact, since 1750, the ocean has absorbed 28% of all human-emitted CO2 and plays an essential role in buffering the impacts of human induced climate change. The ocean’s biological pump works by converting atmospheric CO2 into organic carbon via the help of photosynthetic plankton. These microscopic organisms serve as the foundation of the marine food web and are consumed by zooplankton, fish and other larger marine organisms. As carbon moves up the food chain, it becomes incorporated into the tissues of marine organisms. Ultimately, carbon-rich waste products such as faecal pellets, respired CO2, and the sinking of deceased organisms, transport this carbon to the ocean’s depths where it is stored, or sequestered, indefinitely. It is thought that fish faecal pellets could be responsible for more than 20% of the carbon stored in the deep ocean, whilst whales pull down 33 tons of CO2 on average, when they die.

Fish are being increasingly recognised as “carbon engineers” for their important role in this biological pump. By feeding, breathing, excreting, and eventually dying, fish are estimated to contribute to approximately 16% of organic carbon transferred from the ocean’s surface layers to its depths. It comes as no surprise, therefore, that commercial fisheries may be having a critical influence on the ocean’s ability to store atmospheric CO2. Fishing activities are thought to have halved the number of targeted species in our ocean, including tuna, sharks and mackerels, resulting in a notable reduction in fast-sinking, carbon-rich faecal pellets and deadfalls. Consequently, this alteration disrupts the ocean’s biological pump, leading to a decreased export of carbon from the ocean’s surface to its depths. Overfishing interacts with other human stressors, such as climate change and pollution, worsening their impacts and leading to lower resilience of fisheries and marine ecosystems.

The study highlights how overfishing is disrupting the ocean carbon cycle, causing disturbance and damage to the carbon-rich seabed, and contributing to rising greenhouse gas emissions through increased fossil fuel use. The authors show that by phasing out the use of destructive fishing practices such as bottom-trawling, we can enhance the ability of marine organisms to store atmospheric carbon. Furthermore, ending overfishing would restore marine biodiversity, and strengthen food security, driving the climate resilience of marine ecosystems and the communities that depend on them.

From its contribution to regulating climate and supplying food to its crucial role in storing atmospheric carbon, the ocean plays a pivotal part in maintaining the health of our planet. However, fishing activities, particularly overfishing, pose significant threats to the ocean’s ability to store carbon and maintain ecosystem balance. Scientists advocate for effective fisheries management as a key strategy not only to protect ocean carbon stores but also to mitigate the impacts of climate change, curb greenhouse gas emissions, and promote marine biodiversity, food security, and community resilience. By implementing such measures, we’re able to generate numerous positive outcomes whilst minimising the negative impacts of unsustainable fishing practices on marine ecosystems such as seabed destruction, illegal, unreported, and unregulated (IUU) fishing activities, and bycatch.

Key Findings:

  • Since 1950, fisheries targeting large fish such as tuna, sharks and mackerels have prevented the sequestration of 21.8 million metric tons of carbon
  • Climate change is projected to substantially modify mid-ocean productivity, with predictions suggesting potential losses of up to 22% at low and mid latitudes by the end of the 21st century
  • Organic carbon that reaches the seafloor is stored in marine sediments and can remain locked away for centuries to millennia
  • Bottom trawling destroys the seabed and results in a 30% decline in stored organic carbon and prevents another 70% of carbon rich compounds from being stored.
  • Every year 10.8% of the global fisheries catch is discarded, of which 60% is from bottom trawling fisheries.
  • Overfishing and marine habitat degradation threaten ocean biodiversity and reduce the ability of the ocean to buffer the impacts of climate change.
  • Implementing good fisheries management can reduce or remove many of the impacts associated with overfishing, including fish stock collapse, destruction of seabed habitats, provision of harmful subsidies and accompanying socio-economic impacts.
  • Managing overfishing is one of the most effective strategies in protecting ocean carbon stores and can make an important contribution to climate mitigation and adaptation.