Cod caught in ghostnet. Photo: Emil Vesterager

First step towards mapping ghost nets in Danish waters

Wednesday 13 Dec 17


Finn Larsen
Senior Researcher
DTU Aqua
+45 35 88 34 96

New report presents the first collection of knowledge about derelict fishing gear in Denmark

Most fishermen will at some point experience losing fishing gear at sea. The gear might be hooked on wrecks or reefs, or active fishing gear may collide with passive gear. Passive gear can also be lost when marine traffic collides with the gear and drag away the buoys or the whole gear. The fishermen have an economic incentive to retrieve their lost gear, but that is not always possible—and the gear then turns into a so-called ghost net.

Ghost nets can continue to trap and kill crustaceans, fish, seabirds and marine mammals, in a process referred to as ghost fishing. Furthermore, as most fishing gears are made of plastic, they will gradually break down to micro plastic. From other countries we know that ghost nets can be a big problem, but we don’t know the size of the problem in Denmark.

Now the first step has been taken to get more knowledge about ghost nets in Danish waters. The Danish Environmental Protection Agency has asked DTU Aqua to conduct a pilot project to collect knowledge about lost fishing gear in Danish marine areas. A report has now been issued.

Identification of risk areas

The report "Ghost nets—A pilot project on derelict fishing gear" maps the places in Danish waters with the greatest risk of losing fishing gear, and where you can expect to find many ghost nets—at least theoretically. The areas pointed out by the report as special risk areas are the sea off the west coast of Jutland, Jammerbugten, Tannisbugten and the area around the northern tip of Jutland, the western Baltic Sea, the Langeland Belt southwest of Funen, the Sound and the southwest of Bornholm.

The risk areas have been identified by combining existing data from systems that collect information about fishing vessels and other ships' positions and activities (VMS and AIS). The authors have mapped places where there is an overlap between fishing with active gear, e.g., trawls and seines, and passive gear, e.g. gillnets and traps, and therefore an increased risk of gears colliding.

In addition, the researchers have identified places where fishing is being carried out on reefs or shipwrecks where the gear might get hooked. And they have mapped areas where fishing and heavy ship traffic overlap and causes an increased risk of losing fishing gear.

Eksample of map from the report
Example of map from the report. The map shows where there is an overlap between passive and active gear in the fishing area around northern Jutland (in the second quarter of the year).

Interviews with fishermen and sports divers

Among the risk areas identified by the survey, the researchers selected three focus areas: Jammerbugten/ Tannisbugten/the area around the tip of Jutland, Langelandsbæltet and the area southwest of Bornholm. In these three areas, 10 fishermen and 32 sports divers were interviewed on how they experience the problem of ghost nets.

The interviews show that fishermen generally do not see derelict fishing gear as a major issue in present days for fishing or for the marine environment, and they rarely lose gear themselves. Most of the interviewed fishermen indicate that the problem was much bigger earlier, when it was common to dump old fishing gear at sea.

Almost all of the interviewed sports divers have encountered derelict fishing gear during diving. Most of them see ghost nets as a safety hazard for divers and they consider ghost fishing as a major problem that needs to be solved.

Download the report

The report “Ghost nets—A pilot project on derelict fishing gear” is written by Special Consultant Josefine Egekvist, Postdoc Lars O. Mortensen and Senior Researcher Finn Larsen, DTU Aqua. The report has been commissioned by the Danish Environmental Protection Agency.
Download the report

Recommendations from the report "Ghostnet—A pilot project on derelict fishing gear"

The authors of the report suggest the following activities to gather more knowledge about lost fishing gear in Danish marine areas: 

  • Conduct side-scan sonar surveys to verify whether the identified zones of interactions are actual sources of derelict fishing gear.
  • Use data from trawl surveys to estimate the relative abundance of derelict fishing gear in Danish waters.
  • Investigate whether derelict fishing gear is a significant source of micro plastic.
  • Carry out pilot trials of derelict fishing gear retrieval.
  • Initiate an information campaign aimed at fishermen to increase awareness of the obligation to report loss of fishing gear.
  • Assess the usefulness of preventative and mitigative measures, e.g.:
    • spatial management (zoning).
    • voluntary agreements on access to fishing areas.
    • deposits for fishing gear as an incentive to return them.
    • technical solutions to avoid lost nets becoming derelict fishing gear.
    • biodegradable nets, corrodible links etc.