Harmful fishing practices

Bottom trawling used to have a more limited effect, as trawlers were unable to operate in areas where their nets would snag and tear, such as reefs. However, since the 1980s, trawl nets have been fitted with rubber tyres or rollers, which allow them to move over rough surfaces and therefore exploit more environments. The two boards on either side of the mouth of some nets, known as otter boards, can be extremely heavy and plough deep furrows through the sea bed. Causing even more damage than otter boards is a method known as a beam trawl, that has chains disturbing sediment twice as deep. The largest trawl nets can have a mouth over 100m wide and can be 0.5km long, something which has developed as boats have become powerful enough to pull them.

Diagram courtesy of Save Our Seas (www.saveourseas.com/threats/overfishing)

Ghost fishing is the term for the damage caused by lost fishing gear, which is often made of non-biodegradable synthetic fibres. Although not actually a fishing practice in itself, it’s the end-result of a variety of different practices. The damage caused by ghost fishing is difficult to measure, but thousands of kilometres of nets are lost every year; often catching seabirds if they remain near the surface. Nets can become snagged on the bottom and fill up with catch, or drift through the water, still trapping marine life. Ghost fishing only stops if the net is destroyed by storms and swells, or it washed ashore. Pots (box shaped traps filled with bait usually used to attract crabs or lobster), are often made of more durable materials than nets and if lost, can continue to operate almost indefinitely as scavengers are attracted to them; continually providing fresh bait in a cycle of consumption and decay.

Hand collection by scuba divers should be the most selective method to a target species, particularly if it takes place on a small scale. But in recent years, divers have been causing significant damage to vulnerable ecosystems by using two techniques: dynamite and cyanide. Fishermen use mining explosives and armaments to create an explosion in deep water, known as blast-fishing. The shockwave created kills most fish in a 50m radius or more, most of which are not even collected by the fishermen. The explosions cause irreversible damage to reefs, as they are reduced to rubble, resulting in a marked reduction in biodiversity. Blast-fishing is most prevalent in Southeast Asia.

Cyanide fishing has also grown markedly over the last 30 years, to satisfy the demand for live fish both for the aquarium trade and human consumption. This is also most common in Southeast Asia to meet the growing demand from Singapore, Hong Kong and more recently, mainland China. The cyanide only stuns the fish, so they can be removed and will recover, at least temporarily, if placed in clean water. Cyanide damages coral and for every fish caught using this method, a square metre of coral is destroyed.

Other methods which have been criticised for being harmful to the marine environment include fish aggregating devices (FADs), which are used to attract large schools of tuna in purse seine fisheries. They also attract a variety of other species, such as turtles and sharks, which are caught in the net as by-catch (non-target species caught accidentally).

Purse seines as a method of fishing is not always a bad thing. This method involves surrounding a large group of fish with an even larger net and ‘pursing’ up the bottom of the net to enclose the fish. Where fish school in tight groups of just one species, such as herring or mackerel, there is nothing necessarily wrong with this method. However, the method is also used to catch species that congregate in large numbers with other, non-target species (made even worse by the use of FAD’s as mentioned above), leading to their capture and unnecessary death. Furthermore, the practice is also used to catch species that are already endangered or overexploited.

One final and common method of fishing is long lining. The process involves throwing out a ‘long line’ with floats along it to keep it on the surface. At set intervals separate lines hang down into the ocean with baited hooks. Depending on the target, these ‘snoods’ may be only a few metres long (pelagic long lines), to catch species such as tuna, or long enough to reach the bottom (demersal long lines), to catch groundfish, such as halibut. Unfortunately, while the snoods may only be a few meters long, the main line of a commercial operation may be several miles long with thousands of baited hooks. These lines catch large numbers of incidental species including sharks, dolphins and turtles. Thousands of long line vessels may operate in relative small areas of ocean and it has been estimated that around 100,000 albatroses are killed every year by long lines.

None of the harmful fishing practices described is sustainable: if the oceans are to be preserved as a food resource, they must be fished more responsibly. Many people, not just fishermen, rely on the seas for their livelihoods. Tourism for example, will suffer if marine life continues to be degraded by our current fishing methods.

If we wish to protect marine life for the sake of us all, the damaging effects of fishing must be addressed to stop the decline in biodiversity.  Overfishing itself causes enough problems to marine ecosystems, but methods that damage them directly, must also be prevented for the long-term health of the seas. With climate change also threatening many fragile marine ecosystems, they must be protected as much as possible and not put under further stress by these harmful fishing methods.

Public support is vital in bringing about changes in fishing practices, and in establishing marine reserves which can prevent the use of harmful techniques. A successful Greenpeace campaign in 2011 persuaded all of the UK’s major tinned-tuna companies to phase out the use of FADs from their supply chains, but this was only achieved after a lot of public pressure.  In Indonesia, cyanide and blast fishing has been reduced by up to 75% in many national parks, showing that with management, damage can be reduced. Marine Stewardship Council (MSC) certification is often used as a marker of sustainability; fish caught using dynamite or cyanide are not certified. While the MSC acknowledges that bottom trawling is viewed as destructive, it does certify trawled fish if it is well-managed and has effective controls and enforcement.

Deep-sea habitats must be protected from bottom trawling and this is only possible by banning the practice in sensitive areas. This has been achieved at depths below 1000m in the Mediterranean Sea and around the Azores, so it could be implemented in other locations as well. Efforts are being made to reduce the impacts of ghost fishing by making nets with biodegradable material, so that they don’t pose a long-term threat. Furthermore, biodegradable escape panels could be fitted to pots making them harmless when abandoned. Financial incentives can also be used to encourage the reporting of lost gear and to bring old and damaged gear into port.