Trained animals

Chinese man with fishing cormorant.In China and Japan, the practice of cormorant fishing is thought to date back some 1300 years. Fishermen use the natural fish-hunting instincts of the cormorants to catch fish, but a metal ring placed round the bird's neck prevents large, valuable fish being swallowed. The fish are instead collected by the fisherman.[19]

The people of Nauru used trained frigatebirds to fish on reefs.

The practice of tethering a remora, a sucking fish, to a fishing line and using the remora to capture sea turtles probably originated in the Indian Ocean. The earliest surviving records of the practice are Peter Martyr d'Anghera's 1511 accounts of the second voyage of Columbus to the New World (1494).[20] However, these accounts are probably apocryphal, and based on earlier, no longer extant accounts from the Indian Ocean region.

Dating from the 1500s in Portugal, Portuguese Water Dogs were used by fishermen to send messages between boats, to retrieve fish and articles from the water, and to guard the fishing boats. Labrador Retrievers have been used by fishermen to assist in bringing nets to shore; the dog would grab the floating corks on the ends of the nets and pull them to shore.

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Toxins

Main article: Cyanide fishing

Many hunter gatherer cultures use poisonous plants to stun fish so that they become easy to collect by hand. Some of these poisons paralyse the fish, others are thought to work by removing oxygen from the water.[21]

Cyanides are used to capture live fish near coral reefs for the aquarium and seafood market. This illegal fishing occurs mainly in or near the Philippines, Indonesia, and the Caribbean to supply the 2 million marine aquarium owners in the world. Many fish caught in this fashion die either immediately or in shipping. Those that survive often die from shock or from massive digestive damage. The high concentrations of cyanide on reefs harvested in this fashion damages the coral polyps and has also resulted in cases of cyanide poisoning among local fishermen and their families.

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Explosives

Main article: Blast fishing

Dynamite or blast fishing, is done easily and cheaply with dynamite or homemade bombs made from locally available materials. Fish are killed by the shock from the blast and are then skimmed from the surface or collected from the bottom. The explosions indiscriminately kill large numbers of fish and other marine organisms in the vicinity and can damage or destroy the physical environment. Explosions are particularly harmful to coral reefs.[22] Blast fishing is also illegal in many waterways around the world.

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Electrofishing

A relatively new fishing technique is electrofishing, typically used for stream classification surveys and catching brood stock for hatcheries, or making estimates of populations in a body of water. A gated pulse of direct current is used to cause muscular contractions in a fish, called galvanotaxis, causing them to turn towards the source of the electrical current and swim towards it when correct pulse speeds and durations are used, along with correct current.

A low voltage or short pulse with long gaps will cause the fish to swim away from the device, and high voltage or long pulses with short rests can cause galvanonarcosis, or unconsciousness. Techniques for setting pulse length and patterns, current and voltage require great skill to fish effectively without killing or injuring fish if they are to be left unharmed. Dissolved minerals in the water can decrease resistance causing less of the current to pass through the fish, whereas fish recently entering fresh water from the ocean have high salinity and are more prone to electric shock. Also the smaller the fish, and consequently the less surface area in contact with the water, the higher the current required to produce galvanotaxis. Smaller fish also require shorter pulses, closer together, while large fish should have longer pulses at lower power and longer gaps between pulses.

Rigs can be battery powered back-packs or powered by a generator if they are mounted in a boat. They are typically equipped with a "dead-man switch" and a tilt switch to disable the device if the unit is tipped or the operator incapacitated. Protective equipment must be worn to isolate the operator and prevent electrocution.

Electro-fishing is also used to illegally catch Razorfish or Spoots, using a boat based generator. Current is passed into the sediment causing the Razorfish to 'jump' and be harvested by divers. For obvious reasons this method of electro-fishing is banned due to the risk to the divers.

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Modern fishing