Bycatch

Bycatch, also written as by-catch, is a term used in the fishing industry. It refers to fish or other marine animals that are caught by accident when fishermen are trying to catch specific types or sizes of fish. These accidental catches can be the wrong species, the wrong sex, or too small to keep, including young animals known as juveniles.

The problem of bycatch has been recognized for many years. It contributes to the decline of fish populations and is a part of what is called overfishing. One well-known example happened in the 1960s when dolphins were unintentionally caught in nets used to catch tuna.

There are different ways people use the word "bycatch." It can mean fish that are kept and sold but are not the main target, fish that fishermen throw away, any fish not intended to be caught, or even unwanted animals like seabirds, sea turtles, and sharks. Tools exist to help set limits on bycatch so that animal populations do not get hurt too much.

Activities that produce bycatch

Bycatch happens whenever fishing occurs. It isn’t just fish that get caught by accident — dolphins, sea turtles, and seabirds can also become bycatch. The most common fishing methods that cause bycatch are gillnetting, longlines, and bottom trawling. These tools can stretch for many kilometers and catch nearly everything in their path.

Shrimp trawling is especially known for bycatch. In fact, for every kilogram of shrimp caught, there can be almost six kilograms of bycatch. Even with tools designed to reduce bycatch, many animals like fish and crabs are still caught accidentally and often cannot survive. Bycatch isn’t limited to fishing — it can also happen when scientists or pest controllers set traps for insects or animals, sometimes catching unintended creatures instead.

Victims

Sharks and rays

Different fishing tools like longlines, trawls, and purse seine nets have put many shark species in danger. Young sharks are also often caught by accident, which can affect how many new sharks are born. Because of this, many shark and ray populations have dropped by more than 70% since 1970.

Cetacean

Main article: Cetacean bycatch

Animals like dolphins, porpoises, and whales can get caught in fishing nets, lines, or hooks. Sometimes they are kept to be used as food or bait. For example, dolphins can drown when caught in tuna nets because they need to breathe air, unlike fish that can breathe underwater. This problem has led some tuna to be labeled “dolphin friendly,” though this only means the dolphins were not specifically targeted.

Albatross

See also: Longline fishing

Many albatrosses are threatened because they get caught on longline fishing hooks while looking for food. This can happen especially when illegal fishing happens, which makes the problem even worse for these birds.

Sea turtles

Main articles:

Sea turtles are also often caught in shrimp trawl nets. The speed and time these nets are used can affect how many turtles survive. Different kinds of sea turtles are caught more in different places, like Kemp’s ridley turtles in the Gulf of Mexico and loggerhead turtles along the US Atlantic coast.

Mitigation

Concern about bycatch has led fishers and scientists to look for ways to reduce catching unwanted animals. There are two main methods.

One method is to stop fishing in places where too much bycatch happens. These breaks can be permanent, for a season, or just for a short time when a problem occurs. Fishers might need to move to a different area if bycatch becomes an issue.

The other method is to use different fishing tools. A simple way is to use nets with bigger holes so smaller fish can escape. Some tools, like bycatch reduction devices and the Nordmore grate, help fish get out of shrimp nets.

These devices help many fish escape, but they do not work perfectly for every species. New tools, like SharkGuard, show promise in reducing the catch of sharks and rays.

Seabirds can also get caught on longlines. Using bright, flapping lines called streamer lines near longlines scares seabirds away, helping to protect them.

Retention

Some fisheries keep bycatch instead of throwing it back into the ocean.

Bycatch can be sorted and sold as food, especially in Asia, Africa, and Latin America. It may be sold frozen as "assorted seafood" or used to make fish hydrolysate for organic agriculture, fish meal, fish paste, or surimi. In Southeast Asia, bycatch is sometimes used to make fish sauce. It can also be given to fish farms to feed other fish.

Norway has a "no discards" policy, meaning fishermen must keep everything they catch. This policy has helped reduce waste and encouraged research and changes in fishing habits.