Bycatch: Issues and Animals Affected

August 14, 2021Lu Shegay


Fishing practice is known and practiced in every part of the world. The regular type of fishing is generally done due to various reasons, such as aquaculture, commercial trade, sports fishing, or recreational fishing. While in the fishing industry, certain aquatic animals are targeted, there is another practice called bycatch, in other words, accidental catch of aquatic animals during the exercise of regular fishing. Bycatch can be the wrong species, the wrong sex, undersized or juvenile species of targeted animals. Sometimes bycatch is also regarded as undesirable animals, “rough fish” in the United States and “coarse fish” in the United Kingdom. In 1997, the Organisation for Economic Cooperation and Development identified bycatch as “total fishing mortality, excluding that accounted directly by the retained catch of target species.” While bycatch is usually an unintentional catch, there is the term “deliberate bycatch” that is used in illegal wildlife trade in several countries across the globe.

The issues of bycatch first appeared in the 1960s, when dolphins were unintentionally caught in tuna nets. Bycatch significantly contributes to the decline in aquatic population, although oftentimes not given sufficient attention and consideration. In the United States, for instance, during 1990-1999, the average annual bycatch rate of pinnipeds and cetaceans was around 6215 animals.

"Laysan Albatross Chick in Marine Debris" by NOAA Marine Debris Program is licensed under CC BY 2.0

Issues of Bycatch

While fishing is the major cause of the decline in aquatic population, bycatch comprises the substantial number of aquatic animals that are caught during this practice. Bycatch is an environmental and economic issue for every country. Aquatic animals that are caught accidentally through bycatch are generally discarded and die too, as well as those who are caught deliberately. Thus, these animals are not able to reproduce, which in its turn impacts the entire marine ecosystem. For instance, unintentional catches of whales or sea turtles put these animals at further risk, while catching corals or sponges may lead to damage to protected coral reefs and some important fish habitats. Bycatch also, like regular fishing, affects the entire food chain among aquatic animals, i.e, it can change the availability of prey for some aquatic animals, thus, leads to the reduction of many other species of aquatic animals.

While some groups of aquatic animals die from bycatch due to being caught in fishing nets and are discarded back to the waters afterward, other animals suffer from bycatch due to being entangled in fishing equipment, such as nets, fishing gears, etc. It is estimated that more than 300 000 small species of whales, dolphins, and porpoises die every year because of entanglement in fishing nets, which is the largest cause of mortality for small-sized cetaceans. For instance, the vaquita from the Gulf of California and Maui’s dolphin from New Zealand face extinction, and one of the major causes of their population decline is the bycatch practice. Hundreds of thousands of endangered loggerhead turtles and critically endangered leatherback turtles die every year on longlines that are set for tuna, swordfish, and other fish species.

“Fishing gear is largely non-selective - any species can be caught, including non-target species. Longlines, trawling, and the use of gillnets are the fishing methods that most commonly result in bycatch. Longlining is a commercial fishing method commonly targeting swordfish, tuna, and halibut, where hundreds or thousands of baited hooks hang at intervals along a single fishing line. The hooks (commonly called “J hooks”) cause problems for marine turtles when swallowed, usually resulting in death. Sharks, non-target billfishes, and juvenile tunas are often hooked as well.

With trawling, boats drag large nets along the seabed, catching almost everything in their path. They can damage coral reefs and at shallow depths, catch marine turtles. Gillnets are mesh nets that allow fish to pass their heads and gill coverings through a hole in the mesh and then get stuck when they try to back out. They can be several miles long and up to 100 feet deep. Bycatch occurs because the nets also trap everything larger than the net’s mesh, which includes juvenile fish, sharks, seabirds, marine turtles, and cetaceans (whales, dolphins, porpoises). The nets are very hard to see, blending in perfectly with the water and difficult for cetaceans to detect by echolocation. Gillnets that are lost at sea are rarely recovered and can continue to capture marine animals for many years.”

"fis01504" by NOAA Photo Library is licensed under CC BY 2.0

Animals and Places Affected

The most vulnerable places in the world where bycatch is widely practiced and seriously affects the population include the Arctic, coastal East Africa, the Coral Triangle, the Gulf of California, the Mesoamerican Reef, Southern Chile, the Galapagos, etc. Animals that are mostly impacted by bycatch are the vaquita, the whale shark, the blue whale, the gray whale, the great white shark, the green turtle, Hector’s dolphin, the leatherback turtle, sea lions, penguins, albatrosses, etc.


The highest rate of bycatch of non-targeted species that was recorded was the trawling of tropical shrimp. Generally, trawl nets and shrimp trawls, particularly, have been recognized as sources of mortality for cetaceans and finfish species. In 1997, FAO found that discard rates of shrimp were as high as 20:1 with a world average of 5,7:1. “Alverson et al, for instance, suggest, that in the Northwest Pacific 97% of the shrimp bycatch is discarded producing over 4 million tonnes of waste fish. This, however, is countered by information provided by Zhou and Yimin (1996) who suggest that the Chinese shrimp trawl fleet discards very little of the non-shrimp catch. According to Zhou and Yimin, the shrimp fishery of China catches about 1.8 million tonnes of bycatch all of which is used, much for feeds for the Chinese aquaculture industry. In Southeast Asia, there has also been a growth in recent years in industries that use bycatch from shrimp fisheries for human consumption.

Recent (1997) evidence from the countries of Central America and the Caribbean suggests that the amount of incidental catch that is now utilized in the region is greater than that suggested by Alverson et al. In countries such as Belize, Colombia, Costa Rica, and Nicaragua, for instance, it seems that between 20 and 30% of the once discarded bycatch is now utilized, and in Venezuela, it is probably at least 30%. In Guyana and Brazil, the amount of utilization has increased and probably now accounts for about 10% of the incidental bycatch. In Cuba, where the state operates fishing, marketing, processing, and distribution, it is thought that virtually all edible bycatch is now used which probably accounts for up to 70% of the non-shrimp catch.”

Read more: FAO: A Study of the Options for Utilization of Bycatch and Discards from Marine Capture Fisheries


Cetaceans are also affected by bycatch. It is commonly known that many cetaceans are caught for further sale to entertainment parks, food in some countries, or scientific purposes, however, these animals are victims of bycatch too. For instance, dolphins, turtles, and whales suffer from bycatch through direct capture by hooks, trawl nets, fishing gears. At present, the number of cetacean bycatch is increasing in intensity and frequency. One of the most common examples of cetacean bycatch is dolphins that are caught in tuna nets. Because dolphins are mammals, they die drowning stuck in nets under the water. Also, the Caspian seal bycatch is recognized as one of the biggest entanglements of pinnipeds across the globe.

Read more: Assessment of the Sturgeon Catches and Seal Bycatches in an IUU Fishery in the Caspian Sea


If underwater bycatch might be common, unfortunately, seabirds are also affected by this practice. The IUCN Red List has 21 species, while 19 of them are listed as Threatened, and the other two are classified as Near Threatened. One of the major threats for albatrosses is commercial long-line fishing because these and other seabirds who feed on offal are attracted to the set bait, after which they get hooked on the lines and it makes them drown and die.

Read more: Albatross Mortality and Associated Bait Loss in the Japanese Longline Fishery in the Southern Ocean

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