Lost or intentionally discarded: Lost fishing gear is a deadly hazard to marine life. Now a new survey shows that around two percent of all hooks, longlines and nets used in commercial fishing worldwide end up in the ocean. Every year there are around 14 billion longline hooks, 25 million pots and traps and almost 740,000 kilometers of suspension lines - the latter is enough to span the globe 18 times.
Fishing makes an important contribution to the food supply and creates jobs in many countries. But overfishing and the resulting declining fish stocks cast a shadow on fishing. In addition, large bottom trawls, which aim to maximize yields, destroy the seabed and thus the habitat of the fish. Another problem that has only recently been recognized is that gear such as nets and lines are often left behind, lost or otherwise discarded at sea during fishing trips and other fishing trips, thereby adding to ocean pollution.
On the trail of "ghost nets".
While government efforts are already underway to limit the loss or disposal of equipment at sea, there is not enough data on the scale of the problem to make regulations and bans appropriate and effective. "As global fisheries have increased and fishing techniques have improved over the past half decade, updated global estimates are needed that reflect the current state of global fisheries and allow for targeted solutions," say Kelsey Richardson of the University of Tasmania and her colleagues.
The scientists have therefore made it their task to fill this gap. For their study, they interviewed 451 fishermen from around the world regarding their gear and losses. The fishermen, who came from the USA, Indonesia and Morocco, among others, answered questions about which nets, pots and other gear they use, how much and how often they are used and how often the various pieces of gear are lost. Based on this data, the size of the ship and other data, the research team then extrapolated what this means for the total annual losses in global fisheries.
18 times around the world
According to the calculations, almost two percent of the global equipment used in commercial fisheries is lost at sea every year. "We found that 14 billion longline hooks, 25 million pots and traps and nearly 450,000 miles of longline end up in our oceans each year from global commercial fishing," said co-author Britta Hardesty of the Commonwealth Scientific and Industrial Research Organization in Australia (CSIRO). The lost longlines, knotted together, would go around the world 18 times.
The results also showed that bottom trawl nets lost the largest annual loss at 3.94 percent and that these fishing boats lost significantly more gear than, for example, fishermen who cast their trawls in higher water layers. "The higher gear losses observed here for bottom trawls compared to midwater trawls are consistent with results from previous analyzes of greater losses for bottom-contact gear," Richardson and her colleagues report.
Small boats lose more
Even if large fishing vessels usually have more equipment on board, the researchers' results indicated that small boats have a significantly higher loss rate than large trawlers. According to Richardson and her colleagues, this is due to the mostly higher quality fishing gear, navigation and technology on board that are commonly used on larger fishing vessels.
According to the scientists, this improved equipment, which has been increasingly used in recent years, is probably also the reason why they were able to demonstrate less loss of equipment with their current data than previous studies. But that's not a reason to breathe a sigh of relief, because the survey was far from complete and only covered commercial fishing: "However, there are still major knowledge gaps regarding gear losses due to artisanal and recreational fishing activities as well as illegal and unregulated fishing," say Richardson and her team .
Source: University of Tasmania/CSIRO, Article: Science Advances; doi: 10.1126/sciadv.abq0135