Whether ghost nets, lines or bait hooks: large quantities of these get into the sea from fishing ships. Hundreds of fishermen from seven countries were interviewed to determine how much waste was collected. One result: only the longlines lost each year could be wrapped around the earth 17 times.
Nets, lines or hooks – about two percent of the fishing gear used worldwide ends up in the sea every year. Taken together, the lost gillnets alone covered an area of ??almost 3,000 square kilometers, with purse-seine nets even covering 75,000 square kilometers.
In addition, around 740,000 kilometers of longlines and around 14 billion bait hooks are lost every year, Australian researchers report in the journal Science Advances. The lost equipment threatened marine animals and plants, coastal habitats and ultimately food security.
Ghost nets are often mentioned when it comes to equipment that gets into the sea from fishing vessels. Experts speak more precisely of “abandoned, lost or otherwise discarded fishing gear” (ALDFG). These are usually not complete nets that waft around in the sea afterwards, often they are just remnants of nets and lines, ropes or bait hooks. Fish traps and other trapping cages are also included.
How large the amount of these legacies is is not yet known for sure, write the researchers led by Kelsey Richardson from the University of Tasmania (Australia). The figure of 640,000 tons that is often quoted is outdated and imprecise. “It has become accepted wisdom over time, but it may be wrong,” said study leader Chris Wilcox. However, a realistic assessment is important in order to understand how big the problem is – “and whether it is big enough to have a high priority compared to other marine management issues”.
In order to get more detailed information, the researchers asked a total of 451 fishermen from seven countries about their losses. They combined the information with data on the global fishing volume and also took into account the influence of the respective ship size in their calculations.
According to the calculations, a single trawl fishing vessel loses a good 2000 square meters of net per year – an amount that adds up to a total of 218 square kilometers worldwide for all vessels. A gillnet fisherman loses a good 3,100 square meters of net a year, and a good 58,000 square meters of purse seine nets are lost from every single ship. Furthermore, according to the projection, almost 14 billion bait hooks and a good 25 million fishing cages end up in the sea every year.
‘This research shows that even relatively small fractions of gear losses can, in some cases, result in quite large, aggregated gear discharges into the world’s oceans, which often represent very high levels of pollution,’ explains Kelsey. Fishing gear, as a major contributor to global marine plastic pollution, has a disproportionately greater impact on marine life and habitats compared to many other types of plastic pollution.
“The estimates can be used by fishermen, managers, policy makers, non-governmental organizations and researchers and can form the basis of new risk assessments for the use of different fishing materials,” the researchers write.
The fishermen surveyed came from Iceland, Morocco, New Zealand, Belize, Indonesia, the USA and Peru – the latter three are among the ten most important fishing nations in terms of catch volume, according to the Food and Agriculture Organization (FAO). Not among them, however, were fishermen from China, by some distance the largest fishing nation in the world. However, an attempt was made to select a sample that was as representative as possible, and countries with high and low gross domestic product or larger and smaller production volumes were taken into account, explained Wilcox.
With their investigations, the researchers also want to better understand the reasons why material is lost in the first place in order to develop countermeasures on this basis. Wilcox cites overcrowding in the fishing grounds as a possible cause of material loss.
For example, one fisherman’s gear could get tangled up in another’s, for example a gillnet could be severed by a boat and drift away. This is fundamentally different from the loss of material due to bad weather. “The key question is which are the most important drivers and which of them lend themselves to intervention.”
