What is bycatch and how does it affect marine life?


Bycatch is a term used in the fishing industry to refer to animals caught unintentionally while anglers target other marine species. Bycatch includes both animals caught and released and animals accidentally killed during fishing operations.

While fish, marine mammals and seabirds can all be caught accidentally, some marine animals are much more likely to end up in fishing nets by mistake. Various regulations are used today to reduce the amount of bycatch caught while fishing, but some marine animals still end up being bycatch at dangerous rates.

How Bycatch Affects Marine Animals

While any marine animal can be taken accidentally as bycatch, certain species are more likely to become bycatch depending on where they live, what they eat, and their ability to escape nets.

Marine mammals

Marine mammal populations are among the most affected by bycatch. In fact, research suggests that bycatch is far more deadly to marine mammals than any other human activity.

As marine mammals need to breathe air at the surface, they are particularly susceptible to drowning in fishing nets. Marine mammals can also become bycatch due to their associations with species targeted by anglers.

For example, some species of dolphins in the eastern tropical Pacific Ocean tend to swim above schools of yellowfin tuna. To increase their chances of catching yellowfin, fishermen will place their nets around the dolphins. Not surprisingly, fishing methods that intentionally seek out marine mammals dramatically increase the number of mammals mistakenly caught as bycatch.

At the population level, marine mammals are also particularly susceptible to bycatch due to the time it takes for populations to recover. Like humans, marine mammals can live a long time but only produce a few young per year. If too many marine mammals are killed by fishing operations, populations may be unable to reproduce fast enough to keep pace with these losses.


Bycatch is considered one of the greatest threats to sea turtle populations worldwide.

Turtles are susceptible to becoming bycatch for many of the same reasons as marine mammals. Like marine mammals, sea turtles must come to the surface to breathe. Unfortunately, the need to breathe air makes sea turtles susceptible to drowning in nets.

While sea turtles are also caught incidentally by longlines, research shows that sea turtles are killed much more often by nets and trawls.

sea ​​birds

Seabirds are also at risk of being inadvertently caught in fishing gear. Many seabirds are attracted to fishing boats by the presence of fish; for them, a fishing boat may seem like a great place to grab an easy meal. Unfortunately, these interactions can be deadly.

Seabirds are particularly at risk of becoming bycatch through the use of longlines. During the process of adding bait to the hooks of a longline, birds get caught on the hooks and then dragged underwater as the line is set, eventually causing the birds to drown. Albatrosses, cormorants, loons, puffins and gulls are all seabirds susceptible to becoming bycatch.

For seabirds, fishing boats look like an opportunity for an easy meal.

Jeff J. Mitchell/Getty Images

Prevention of bycatch

Managing the impacts of bycatch is particularly challenging due to lack of data and high levels of uncertainty.

Most bycatch information comes from fisheries observers. However, the frequency of bycatch captured in observer data inevitably underestimates the true impact of bycatch, as observers can only account for animals caught as bycatch that make it to the surface.

Presumably, other animals are caught by fishing gear but escape before reaching the surface. These escapees are not detected by fisheries observers, but contribute to the toll of bycatch on marine animals.

Fishing equipment

Many fisheries have mandated fishing operations and use specialized fishing gear known to reduce bycatch rates. For example, US regulations require the use of “turtle excluder devices,” or TEDs, by fishermen using trawls to fish for shrimp and summer flounder. Other regulations, such as California’s Drift Gill Net Transition Program, encourage the use of safer equipment.

Fishing spots

Fisheries managers can also reduce the likelihood of fishermen setting nets in areas full of sensitive marine animals by restricting fishing operations to certain locations. Depending on the circumstances, access to certain fishing grounds may be permanent, as for certain marine protected areas, or temporarily established when a certain level of bycatch is reached during a given fishing season.


Fisheries can also be managed to operate only at certain times of the year to avoid times when non-target species are abundant. For example, US fisheries officials have imposed seasonal swordfish fishery closures to reduce sea turtle bycatch.

Similarly, efforts are underway to reduce seabird bycatch by requiring fishermen to set longlines at night, reducing the chance of interaction between seabirds and fishing gear.


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