Ghost net. Photo: DTU Aqua.

Mapping ghost nets in Danish waters

Friday 23 Aug 19

Contact

Eva Maria Pedersen
Senior Consultant
DTU Aqua
+45 35 88 34 32

Facts about the project

The project, ‘Ghost nets in Danish waters’, is headed by DTU Aqua. Also participating in the project are Danish Fishermen PO, the Geological Survey of Denmark and Greenland (GEUS), and diving company P-Dyk.  

The project has received DKK 3 million in funding from the European Maritime and Fisheries Fund and the Danish Fisheries Agency and will run until the end of 2020. 

 

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How much derelict fishing gear is there in the sea around Denmark, and how can it be removed? DTU Aqua will now investigate this.

There is currently no overview of how much lost fishing gear—also called ghost nets—there is in the waters around Denmark or where it is located. DTU Aqua’s new study for the Danish Fisheries Agency aims to remedy that. The Agency wants information about how many ghost nets there are and where they are located as well as suggestions for how they can be removed and how to prevent more of them from ending up in the ocean. The survey is the result of a tender won by DTU Aqua. 

Lost fishing gear has a destructive impact, because for months or years it continues to catch fish and crustaceans to no use, and because marine mammals and diving birds can become entangled in it and drown. Furthermore, fishing nets are a source of pollution, as they eventually break down into microplastics. 

Both commercial and recreational fishermen may lose fishing gear, e.g. if it gets stuck on rocks or wrecks, rips due to stormy weather, is carried away by a strong current, or is destroyed by ships sailing into them. 

Sonar and underwater camera surveys 

DTU Aqua has previously identified areas in the Danish waters where you—in theory—can expect a particularly large quantity of derelict fishing gear. These are areas with fishing activities close to plane and ship wrecks, rocks and reefs, and marine traffic.
Read more about the previous mapping of ghost nets on aqua.dtu.dk

The new project will conduct a practical investigation of whether ghost nets actually gather in these particular areas. In addition, the project aims to quantify the amount and type of ghost nets as well as the animals getting caught in them. 

"We will examine the frequency of ghost nets in selected areas by means of high-frequency sonar and underwater robots equipped with cameras and by sending divers down. Furthermore, we will incorporate data on marine litter from DTU Aqua’s standard expeditions in the Baltic and North Seas as well as from the reports by commercial fishermen. We will also conduct interviews with fishermen, divers, and NGOs to include their knowledge in the project," says Project Manager Eva Maria Pedersen, DTU Aqua.

The four sea areas and five wrecks to be examined according to the contract are yet to be determined.

Sonar og video af spøgelsesnet. Foto: DTU Aqua.
Left: Ghost net identified with Edgetech 4125-sidescansonar, 600 kHz during a cruise with the DTU research vessel Havfisken in June 2018. Centre and right: Photos from video recordings with BlueROV during the same cruise verifying that the identified object is a ghost net. The photo in the centre shows a floatline. On the photo to the right you can see netting on top of macro algea and a fish caught in the net.

Testing methods for net removal

The main purpose of the project is to investigate and quantify the incidence of ghost nets in Danish waters. However, the project will also look into methods for removing the ghost nets from the sea in a low-impact and cost-effective way. For this purpose, DTU Aqua will collect knowledge from other countries and conduct field tests, where the methods are put into practice. 

"We will mainly be testing and adjusting two different methods for removing the ghost nets from the sea. In areas where the seabed is smooth and has few rocks, we will use an anchor-like tool that hooks into the masks of the net to try to drag them out of the water. Around wrecks and reefs, professional divers will go down and try to remove the nets. But first we must assess whether it’s possible to remove a net without doing more harm than good, for example if it’s stuck on a carbonate mound," says Eva Maria Pedersen. 

The retrieved nets will be sent to recycling, where possible. 

 

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