What will happen to the seabed when bottom trawling comes to an end – a major new project tracks areas before and after closure

During these mild days in May, researchers are collecting the first samples in an unusually long-term research project in Danish waters. Over the next 12 years, a major interdisciplinary research collaboration will document what happens to marine life and seabed habitats as more areas are closed to fishing with bottom contacting gear.

In May, researchers from DTU Aqua, the University of Copenhagen, GEUS and the University of Southern Denmark have begun the preliminary studies for the PReMaH project (Passive Nature Restoration of Marine Habitats), which over the next 12 years will map the effects of closing marine areas to fishing with bottom contacting gear. Photo: DTU Aqua.

Thursday 21 May 2026

Anne Trap-Lind

Right now, in May, researchers have begun the important baseline studies that will form the foundation for assessing the effects of closing areas to fishing with bottom contacting gear in the marine zones selected under the Fisheries Agreement in July last year.

The project is called PReMaH – Passive Nature Restoration of Marine Habitats – and is a collaboration between DTU Aqua, the Geological Survey of Denmark and Greenland (GEUS), the University of Southern Denmark (SDU) and the University of Copenhagen (KU).

PReMaH runs for 12 years, which is unusual in a research context, where many projects typically last 3–5 years:

“A project of such long duration offers a unique opportunity to study effects both immediately after closure and, in particular, over the long term – ecosystem recovery can take a long time. Just because an impact stops one day does not mean things improve the next,” says Helle Torp Christensen, project leader of the PReMaH project at DTU Aqua.

Baseline studies in the Kattegat, off Grenaa and in the southern Belt Sea

The researchers are carrying out the baseline studies aboard DTU Aqua’s research vessel r/v Havfisken from 9 to 28 May 2026. They are sailing to survey stations in the Kattegat between Læsø and Anholt, off Grenaa, and in the southern Belt Sea.

Here they will collect a wide range of samples from the seabed, from organisms living both in and on the seabed, and in connection with the areas that will be closed to the use of bottom contacting gear before the ban comes into force. These samples will form the project’s so-called baseline.

“The different samples are analysed together with climate, environmental and fisheries data, and the results are used to assess the environmental status of marine nature, biodiversity and food webs, as well as changes resulting from the closure to fishing with bottom contacting gear,” explains Principal Investigator Grete Elisabeth Dinesen, DTU Aqua.

Follow the project:  As the project proceeds, results, pictures and updates from the field work will be published at the website.

Sediment samples

Focus on benthic fauna, meiofauna and other species using eDNA, as well as climate and water quality

BENTHIC FAUNA. Using sediment samples and underwater video, the researchers will focus in particular on benthic fauna – the animals that live on and in the seabed – as well as on so-called meiofauna, the very small bottom-dwelling organisms. DTU Aqua is responsible for studies of the larger benthic fauna, while researchers from KU BIO are in charge of analysing the smallest organisms.

OTHER MARINE LIFE. At the same time, water and sediment samples will be collected for environmental DNA analyses, which can reveal which species are present in the area, even if they are not directly observed.

CLIMATE AND WATER QUALITY. Sediment processes that are important for the seabed’s role in climate regulation and water quality will also be investigated.

Before and after – and with control areas

PReMaH is based on a classical experimental design known as BACI – Before, After, Control, Impact. This means that the researchers examine and monitor the same sites:

  • before the closures come into force
  • after the closures – both in the short term and over the longer term
  • in areas that are closed to bottom trawling
  • and in control areas, respectively where bottom trawling continues and where no bottom trawling has taken place in previous year

This approach makes it possible to distinguish between natural variation in the marine environment and changes that can be directly attributed to the ban on fishing with bottom contacting gear.

Throughout the project period, DTU Aqua will revisit the fixed sites in the study areas a number of times. The data collected here will be linked with data gathered under the national monitoring programmes.

More than the seabed

Although the effects on seabed fauna – the animal life – are central to the fieldwork carried out with Havfisken in May, the PReMaH project will also map seabed habitats.

GEUS is responsible for mapping the habitats, and these results will be linked both to the benthic fauna studies and to investigations of sediment processes, for which SDU is responsible.

With regard to how fish fauna are affected, data will be collected in connection with DTU Aqua’s ongoing monitoring of fish stocks in Danish waters.

As for large marine mammals such as harbour porpoises, changes in their distribution will be investigated using acoustic listening devices and environmental DNA, in a collaboration between SDU and DTU Aqua.

The preliminary studies for PReMaH are being carried out on board DTU Aqua’s research vessel Havfisken.
Researchers carrying out the preliminary studies for PReMaH in May 2026 on board Havfisken.
Preliminary studies for the PReMah project.
Sediment samples.
Sediment samples.
Sediment samples.

Ecosystems in a broad sense

Finally, all components of the ecosystem will be integrated into data models, enabling assessment of environmental impacts and future trade-offs in management measures in areas that have been closed to bottom trawling, for example the effect on harbour porpoises when fishing activity changes.

Changes in the marine environment will also be considered in relation to changes in, and the valuation of, ecosystem services, i.e. the benefits we derive from nature. This work is led by KU-IFRO.

Overall, the PReMaH project will contribute to future ecosystem-based assessments of fisheries management measures.

“We take a broad view of ecosystems and the ecological functions and societal services they provide. It is precisely this holistic understanding that is lacking in Danish waters when new nature and fisheries management measures are assessed,” says Helle Torp Christensen.

Knowledge base for new fisheries management

PReMaH is closely linked to the Fisheries Agreement A New Direction for Danish Fisheries, which was concluded on 2 July 2025, and in particular to the initiative on zones where bottom contacting fishing gear is prohibited.

Experience from, among other places, Sweden indicates that marine nature and biodiversity improve in areas that are closed to bottom trawling. PReMaH will now investigate whether similar effects can be documented in Danish waters under the natural environmental conditions of these areas.

PReMaH is an interdisciplinary collaborative project between DTU Aqua, GEUS, SDU, KU-BIO and KU-IFRO, and is funded with just over DKK 24 million through the Research Reserve under the Green Programme for the Transition of Fisheries and Aquaculture (GPOFA-24-0010).

FACTS about the PReMaH project

PReMaH – Passive Nature restoration of Marine Habitats is a long-term research project investigating how ecosystems change when areas are closed to fishing with  bottom contacting gear.

  • Project period: 2025–2036
  • Study areas: Kattegat, the southern Belt Sea and off Grenaa
  • Experimental design: BACI (Before, After, Control, Impact)
  • Focus: The seabed’s physical and biological conditions, biodiversity, food webs, ecosystem services and management scenarios
  • Reporting: Every three years


    The project aims to provide robust scientific documentation of the effects of new fisheries management measures.

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Collaboration and funding

PReMaH is a broad interdisciplinary collaborative project in which multiple research communities contribute their respective expertise.

Project leader: DTU Aqua

Partners:

  • Technical University of Denmark (DTU Aqua)
  • Geological Survey of Denmark and Greenland (GEUS)
  • University of Southern Denmark (SDU)
  • University of Copenhagen – BIO
  • University of Copenhagen – IFRO

Funding:
The project is funded with just over DKK 24 million through the Research Reserve under the Green Programme for the Transition of Fisheries and Aquaculture (GROFA-24-0010), and supports the initiative on zones where  bottom contacting gear is prohibited under the Fisheries Agreement “A New Direction for Danish Fisheries” of 2 July 2025.

Contact

Helle Torp Christensen

Helle Torp Christensen Senior Executive Officer National Institute of Aquatic Resources Mobile: +45 20814828

Grete Elisabeth Dinesen

Grete Elisabeth Dinesen Senior Consultant National Institute of Aquatic Resources Phone: +45 35883359 Mobile: +45 21315137