Destructive fishing practices
Published: 13/07/2010Fishing activities also affect the wider marine environment, mainly by accidentally catching other species (bycatch), discards and disturbing the seabottom and its communities.
Contents:
1. Bycatch
Species that are not targeted by the fishery, such as marine mammals, seabirds, turtles and other fish species, as well as juvenile fish may be caught unintentionally in fishing gear. Practically all fisheries have some level of bycatch. On average, at least 25 per cent of the global catch is bycatch. Every year, around 30 million tonnes are thrown overboard again, dead or dying. Fish that are of the target species but are too small to fetch a reasonable price or are below the legal minimum landing size are also discarded at sea. In some fisheries, such as the whithing fishery west of Scotland, the number of discarded fish has often exceeded that landed.
In the North, Celtic and Baltic seas, a yearly bycatch of 7,000 harbour porpoises has been recorded in the gillnet fisheries targeting cod, turbot and other species. Sharks, rays and skates are also caught in large numbers, often in trawls, and many species have shown a dramatic decline over the last decades. The common skate, for example, was once abundant in the North-East Atlantic. It can live for 50 years and matures late, making it vulnerable to overfishing. The skates are now too few to be the target of a fishery, but many are still caught in other fisheries. This has led to the common skate being listed as an endangered species by the IUCN.
Bycatch is mainly a result of the use of non-selective gear, such as trawls and bottom-set nets. It can to a certain extent be avoided by using different bycath reduction devices, such as grids or panels inserted into parts of the trawl nets. These so-called exclusion devices help, for example, turtles or dolphins or unwanted fish to escape from the trawl before it is taken out of the water. Larger mesh sizes or use of square meshes rather than conventional diamond-shaped meshes also greatly reduce bycatch in certain fisheries. For other fishing methods, such as longlines, it may help to set the lines at night. Means to reduce bycatch are increasingly required by law, but much still remains to be done.
Contents:
- Bycatch
- Discards
- Direct effects of gear
2. Discards
Discards constitute one of the main problems with the world’s fisheries today, and are defined as all organic matter of animal origin retained by a fishing gear and thrown back into the sea, dead or with little chance of survival. Discards may be fish of one or several untargeted species, but they may also be crustaceans, molluscs, marine mammals or seabirds.
The lack of regulations in the majority of fishing grounds causes a great part of the catch to be returned to the sea, as their marketing is prohibited or not commercially viable, are of a protected species, or juveniles too small to be landed, or they are under the legal minimum landing size or else the ship has already filled its fishing quota. In some cases, fish that are perfectly marketable are discarded to make room on the vessel for specimens that have a higher sales value, an unethical and wasteful practice known as highgrading.
The volume of discards is related to the quantity of unwanted species caught in fishing gear (see by-catches). The volume of by-catches in turn is influenced by various factors, such as the general state of the stock, if it is overfished a greater number of juveniles and other species will end up in the nets, or the type of fishing gear used, for instance beam trawls drag the seabed and bring in more by-catches than other gear.
Lack of regulations
Each year, depending on the fishery, up to 60% of live fish and other organisms caught in European fishing gear are thrown back into the sea. These discards undermine the effectiveness of measures taken to conserve the resource, particularly in the context of the CFP reform of 2002, since even though these fish are not landed, they nevertheless die and thereby reduce the existing stock and its spawning capacity.
Several of the fisheries with the highest discard rates are concentrated in the North Sea. The European Commission is currently developing two discard regulations. One of them will include a requirement for the fleet to reduce by-catches in flatfish beam trawling in those waters where 70% of the catches are discarded.
The objective to reduce by-catches and discards is thus a key to the Common Fisheries Policy (CFP), as the Commission already highlighted in 2002 in a Communication on this subject. On the basis of experiments conducted in Europe and elsewhere, as well as recent scientific studies, the European Commission presented a new Communication in 2007 with proposals for a policy to reduce the level of unwanted catches and eliminate discards in European fisheries.
3. Direct effects of gear
Fishing, especially trawling, also has a direct impact on the habitat in which it takes place. A trawl beam may weigh a tonne or more. As it is dragged across the seabed, it ploughs up soft bottom substrates and leaves destroyed bottom structures behind.
Soft bottoms host many organisms, such as filter-feeding mussels, brittlestars and polychaete worms recycling decaying organic matter. Many fish live close to the bottom, such as flatfish, rays and skates. Hard, rocky bottoms are also full of life, with hard and soft corals, sponges and algae living attached to the substrate and providing living and hiding space for fish, shellfish, crustaceans and many other organisms.
A single trawl run across a hard or soft bottom may destroy the habitat for many species. As cold-water corals and many other organisms grow very slowly, it may take them many years to recover when disturbed. The Darwin Mounds, an area of cold-water coral reefs off Scotland, show evidence of extensive trawling. Deep scars caused by heavy trawls criss-cross the bottom, lined with crushed corals. In March 2004, the EU passed legislation to prohibit trawling in the area, in order to protect what was left of the coral. But this is the exception; many areas are fished several times a week, and the bottom fauna and flora have no chance to recover.