What is ghost fishing?
The term "ghost fishing" is used when derelict nets and fishing gear in general continue to catch marine vertebrates and invertebrates that may become tangled in them. Commonly known as ALDFG (Abandoned, Lost or otherwise Discarded Fishing Gear), and often nearly invisible in dim light, ALDFG may either get snagged on the rocky bottom (as in the tegnùe habitats of the north Adriatic) or drift in the open sea for long periods due to its low biodegradability. ALDFG may be lost due to technical problems during fishing or in adverse weather conditions. As losing fishing gear is a financial loss for operators, they will certainly try to recover it. However, as time and labor spent retrieving gear depend on its value, retrieval may often be impractical, and operators may prefer to carry on fishing rather than take chances and try to recover their lost gear.
Unfortunately, once fishing gear has lost its financial value, it may deliberately be abandoned by careless and irresponsible fishermen who believe dumping it in the sea is a handy way of disposing of it.
What are the effects of ghost fishing?
Abandoned nets stranded on the seabed or drifting at sea may turn into true traps for marine organisms which become trapped and consequently starve. Once trapped, fish, dolphins, sea turtles, seabirds, crabs and other animals that swim free in the water column or creep on the seabed may die for the lacerations and infections caused by struggling to free themselves, or suffocate when unable to breathe. Alterations to the marine environment and its habitat functions, obstacles to navigation and possible damages to vessels, hazards for recreational and / or professional divers are other risks associated with ghost nets. Eventually, abrasive environmental conditions cause fishing nets to break up into progressively smaller fragments. The lighter plastic and polystyrene parts continue to float and may be washed ashore or disintegrate due to the effects of sunlight, leading to the formation of microplastics. These particles, smaller than 5 mm, are absorbed by planktonic and filter-feeding organisms and enter marine food webs. They may also release hazardous chemicals such as phthalates, known to interfere with the reproductive activities of many sea organisms.
It has been estimated that 640,000 tons of ghost nets are scattered in the world oceans, i.e. an incredible 10% of all marine debris (UNEP/FAO, 2009). About 100,000 marine mammals and one million seabirds die each year trapped in fishing nets or by ingesting related debris (UNEP, 2005). Although the loss of marine resources due to ghost fishing is hard to assess, several studies show that it amounts to about 10% of the target population (UNEP, 2005).
In addition, ingesting plastic resin pellets is one of the main threats to seabirds, which mistake them for fish eggs or other types of food (UNEP, 2005). Regrettably, data on the amount of fishing gear lost or abandoned at sea and its effects on biodiversity are either totally absent (Adriatic Sea) or very poor (the Mediterranean in general).