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Mapping ghost nets in Danish waters

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

There is currently no overview of how much lost fishing gear there is in the waters around Denmark or where it is located. DTU Aqua’s new survey 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. 

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. 
Learn more about the previous mapping of ghost nets on aqua.dtu.dk

Sonar and underwater camera surveys 

The new project entitled ‘Ghost nets in Danish waters’ will conduct a practical investigation of whether ghost nets actually gather in the areas identified in DTU Aqua’s previous survey. 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-soegelsesgarn-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.

Contact: Senior Consultant Eva Maria Pedersen, DTU Aqua, ph. +45 21 15 43 66, emp@aqua.dtu.dk.

Facts about the project

The project, ‘Ghost nets in Danish waters’, is headed by DTU Aqua, Technical University of Denmark. 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.

The article is written by Communications Officer Karin Stubgaard, DTU Aqua.

Published on cnogear.org 23 August 2019.