Unseen impacts of fishing: Trawling fuels climate change

Trawling is a major part of the fishing industry, which provides us with fresh seafood. Have you ever wondered what happens on the ocean floor when we go about our quest to catch fish? Does deep sea fishing affect our environment?

A recent study has revealed that trawling disrupts the carbon balance in our oceans, which ultimately impacts our climate.

Deep sea and its carbon secrets

The deep-sea abyss is more than a home for marine life. It acts as a critical carbon sink, holding onto more carbon than it releases.

Animal activity on the seafloor consumes and shifts this carbon into deeper soil layers, safely tucking it away for thousands of years. But when fishing trawls stir up these sediments, it disrupts this natural, delicate balance.

Trawling’s impact on climate

Research carried out at Helmholtz-Zentrum Hereon – in collaboration with the Alfred Wegener Institute, GEOMAR Helmholtz Center for Ocean Research Kiel, and the German Federation for the Environment and Nature Conservation (BUND) – has cast a spotlight on this lesser-known consequence of fishing.

The study has provided significant data on how bottom trawling impacts carbon storage, particularly in the North Sea. The scientists examined over 2,300 sediment samples from the North Sea.

“We found that sediment samples collected in intensely trawled areas contained lower amounts of organic carbon than samples collected in areas with less fishing. We were able to attribute this effect to bottom trawling with high confidence,” said Dr. Wenyan Zhang, the study’s lead author.

According to Dr. Zhang, the methodology used for this research reduces uncertainty in assessing the regional to global impact of trawling compared to previous estimates.

Carbon release due to trawling

The experts uncovered a worrisome trend. Computer simulations demonstrated a steady decline in seabed carbon concentration across the past few decades, and this decline was attributed to intensive trawling activities.

Vulnerable areas were soft, muddy bottoms where damage was most significant. When trawling takes place, it disturbs the sediment, releasing carbon from a low-oxygen environment into the water column filled with oxygen.

Here, microorganisms transform the carbon into carbon dioxide, or CO2, which can escape into the atmosphere. This heat-trapping greenhouse gas is a major contributor to climate change.

Dr. Zhang’s team estimated that North Sea trawling alone releases about 1 million tons of CO2 from sediments annually. The global estimate stands at 30 million tons – which is about 10% less than previous global estimates.

Calling for enhanced seabed protection

The study’s findings highlight the need to protect our ocean floors more effectively, explicitly targeting muddy habitats in marginal seas like the North Sea.

Marine protection measures have traditionally been focused on areas with hard, sandy bottoms and reefs. These areas, despite their ecological diversity, store less carbon.

“Our methods and results might be used in optimizing marine spatial planning policies to gauge the potential carbon benefits of limiting or ending bottom trawling within protected areas,” noted Dr. Zhang.

Rethinking marine protection strategies

The findings on trawling’s climate impact are pushing scientists and conservationists to reconsider current marine protection strategies.

Traditional conservation efforts have focused on areas with high biodiversity, such as coral reefs and sandy seabeds, often overlooking soft, muddy habitats where trawling causes the most carbon disruption.

By shifting attention to these vulnerable carbon-rich areas, policymakers could develop more effective regulations that not only protect marine life but also contribute to climate mitigation.

This renewed focus could involve establishing no-trawling zones in sediment-heavy regions – enhancing carbon storage while safeguarding diverse ocean ecosystems.

While these strategies offer a pathway forward, it’s essential to understand the long-term effects that seabed disturbance has on our oceans’ capacity to store carbon.

Long-term impacts of seabed disturbance

The disruption of seabed sediments through trawling has consequences that extend beyond immediate carbon release.

Once disturbed, these sediments take years or even decades to stabilize and rebuild their carbon-storing capabilities.

This prolonged recovery period means that frequent trawling in the same areas could prevent the seafloor from ever fully regaining its role as a carbon sink.

Trawling and climate change

Over time, this ongoing disturbance diminishes the ocean’s natural ability to capture and store carbon, amplifying the challenge of addressing climate change.

Researchers warn that without intervention, these cumulative effects could lead to long-term losses in carbon storage capacity, highlighting the importance of sustainable fishing practices and regulated trawling efforts.

The study is published in the journal Nature Geoscience.

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