A recent documentary by Joakim Odelberg (in co-operation with Emma Watson and Peter Isaksson), funded by the BalticSea2020, strikingly illustrates the severe but often neglected problem of ghost nets in the Baltic Sea.
โGhost netโ is the expression for nets that have been lost or abandoned, which continue to kill fish and other marine life. In Europe, the problem with ghost nets is especially severe in the gill net fishery for cod in the Baltic Sea and the deep sea fishery outside the British Isles.
The reason why ghost nets constitute such a significant problem in the Baltic Sea is because of its cloudy nature, thus sunlight does not penetrate deeply into the water. This causes algae to grow at a slow rate at depths where gill net fishing for cod normally occurs. Hence, the nets are not rendered visible by algae growth and continue to fish for a long time.
It has been assessed that about 165 km of nets are lost annually by Swedish fishermen alone. Moreover, it is estimated that 200-300 tonnes of cod are caught on an annual basis as the catching efficiency of these nets can be up to 10 %, even after they have been lost for two years. Were these figures to be extrapolated to the whole Baltic fishery for a period of 20 years, the total length of ghost nets makes up a distance of approximately 18 times the north-south length of the sea basin.
Although the documentary describes a dark picture of the situation, there are also suggestions for technical solutions to prevent ghost nets causing so much damage, such as better marking the positions of set nets and using biodegradable material in some parts of the nets. Net retrieval practices could also be improved.