The Problem of Bycatch and How It Harms Marine Life, Explained

Commercial fishing decimates coral reefs and endangered species alike — but can it be stopped?

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Explainer Climate Oceans

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The problem of bycatch first came to light thanks to a biologist who went undercover as a cook aboard a Panamanian tuna fishing vessel in 1987. During his four-month voyage, the biologist, Sam LaBudde, was able to document how hundreds of dolphins were killed as bycatch in the process of harvesting tuna. LaBudde then shared the graphic footage of these dolphins with journalists and, later, U.S. Congress, sparking so much public outrage that lawmakers ultimately passed a law known as the Dolphin Protection Consumer Information Act. The legislation outlined the first regulations for dolphin-safe tuna, prohibiting the sale of tuna that was harvested in such a way that caused harm to dolphins.

Although this legislation helped bring attention to this problem in commercial fishing, bycatch remains a major issue in the  industry to this day. Beyond the millions of animals caught for food, hundreds of thousands more are caught accidentally — and die in the process — every year. Let’s take a closer look.

What Is Bycatch?

Bycatch are all of the nontarget species of marine life that are scooped up in fishing nets or on hooks in addition to the target fish. Bycatch can include a range of different animals, from fish to seabirds and even whales.

Bycatch causes serious physical harm — and often death — in marine life. When fish and other aquatic animals are brought to the surface by fishing gear, the rapid change in water pressure can cause their internal organs to rupture, which can be lethal. Other times, nontarget species are brought onto the decks of fishing vessels and tossed back into the water as they are either dying or already dead.

What Is the Cause of Bycatch?

Bycatch occurs essentially because commercial fishing prioritizes economic gains over concerns for animal welfare or ecosystem health. Fishing vessels, and the specific gear they utilize, are designed to capture the greatest amount of fish possible, using methods like trawling or longlining. More discerning fishing methods, such as pole and line fishing, in which one fish at a time is hooked, are generally not used by commercial fishing vessels because they are more expensive and time-consuming.

Modifications to net technology are sometimes implemented to reduce bycatch. For example, some fisheries have developed trawling nets that allow turtles to escape. Although these nets can prevent some damage associated with bycatch, more destructive fishing methods are incentivized by the industry. Because there is such high consumer demand for cheap seafood, commercial fisheries aim to produce the greatest volume of fish at the most competitive price.

Which Fishing Methods Cause the Most Bycatch?

Industrial-scale fishing operations produce far greater volumes of bycatch  compared to small-scale subsistence fishing. There are several primary commercial fishing methods, all of which capture sea creatures indiscriminately.

Gillnets are relatively inexpensive for the large amount of fish they capture, a combination that makes them some of the most commonly used fishing methods in the world. The nets hang vertically in the water, and the mesh (sometimes nicknamed “walls of death”) is designed to snag fish by their gills as they swim through, often entangling nontarget species who starve to death. Another method, longline fishing, consists of a series of baited hooks connected by a main line that runs along the surface of the water. Although designed to catch specific species, the bait often attracts other animals who become hooked.

Purse seine nets get their name from the drawstring-like function of the nets. They are drawn closed after encircling a school of fish, usually tuna, sealing off their escape. Purse seines are often used in conjunction with fish aggregating devices (FADs) that attract large groups of fish who are then drawn into the net. Finally, trawl fishing entails massive nets attached to the back of a ship that collect fish either midwater or on the bottom of the ocean. Bottom-trawling nets destroy everything in their path, including endangered coral reef systems, turning the ocean floor into a sparse landscape.

What Is the Most Common Bycatch?

This non-selective fishing gear, used by almost all industrial fishing operations, commonly catches larger animals that prey on and eat fish, including whales, dolphins, seabirds, sharks and sea turtles. Other smaller nontarget species that get caught in fishing gear usually either die from suffocation once they are out of the water, or die later from injuries they sustained before they are thrown back in the ocean.

What Are the Species Most Affected by Bycatch?

Countless species are killed as bycatch, but some species are more heavily impacted than others. The following species are highly migratory with low reproductive rates, meaning it can be difficult for populations to recover after individuals are caught and killed.

Sea Turtles

  • Six species of sea turtles are found in U.S. waters, all of which are endangered, and all of which get caught as bycatch
  • Bycatch is the greatest single threat to sea turtles
  • Lights, which attract turtles, are often used on longlines

Dolphins & Whales

  • Cetaceans are the primary marine animals impacted by tuna fishing operations
  • Some species (whale sharks, dolphins and baleen whales) are used to indicate the location of large schools of tuna
  • Bycatch is a primary contributor to the demise of the endangered vaquita


  • Most seabirds are protected under the Migratory Bird Treaty Act
  • Both fish bait and fish themselves can attract birds to fishing operations
  • Short-tailed albatross are a highly endangered species that often fall victim to bycatch

Sharks & Rays

  • Sharks & rays are more impacted by bycatch than any other taxonomic group
  • Pelagic shark populations have declined over 70 percent  as a result of global fishing operations
  • Though the practice is banned in the U.S., some sharks caught as bycatch have their fins removed by fishermen before they are thrown back into the ocean, alive and mortally injured

Can Fishermen Use or Sell Bycatch?

Any protected and regulated species cannot be legally sold in the U.S. Though many fish are lawfully harvested, they are ultimately discarded because they would have low market value; nontarget species must reach market weight in order to be sold. Fishermen must also abide by regulatory quotes and relevant legislation, meaning they are often required to discard many different individuals and species.

Additionally, their bodies must be relatively intact, which is uncommon, since  capture methods are generally violent and involve crushing animals together. More delicate species like octopuses are often torn apart during this process and can no longer be sold.

Why Is Bycatch a Problem?

Bycatch is a global problem. Fishing activities that take place in one area often create problems in adjacent marine ecosystems. Sometimes, they even affect terrestrial systems. Beyond the environmental implications, there are also ethical questions about welfare. Below is a brief discussion on why bycatch is a problem.

The Effects of Bycatch

Apex predators play a significant role in a healthy ecosystem, and these species are frequently victims of bycatch. Sharks and dolphins often sit at the top of their respective food chains, helping maintain the balance of marine ecosystems. That balance is upset when predators are removed at high rates. The disturbances caused by apex predator bycatch often cause reverberations throughout the food web and can even bleed into surrounding ecosystems.

Removing smaller fish and organisms lower down on the food chain also carries repercussions. Large amounts of bycatch can affect the availability of food for larger species, causing further imbalances, and affecting the reproduction rates of predator populations.

Bycatch Statistics

Bycatch statistics aren’t always reliable;  monitoring fishing vessels is notoriously difficult. However, some conservative estimates help give us an ideaof bycatch rates at fisheries around the world. Some sources say over 300,000 whales, dolphins and porpoises die each year from entanglement in fishing nets. Up to 250,000 loggerhead and leatherback sea turtles, and another 300,000 seabirds, drown every year when they are caught on longlines. Bycatch accounts for about 40 percent of total fish caught worldwide, which amounts to almost 40 tonnes of carcasses. Another report estimates that around 20 percent of fish caught on U.S. fishing expeditions was discarded before returning to shore.

Is Bycatch Sustainable?

Whether bycatch is considered sustainable depends on a specific stakeholder’s point of view.

Seafood labeling organizations, such as the Marine Stewardship Council (MSC), admit that in some cases bycatch is unavoidable, but go on to say that fisheries can still be considered sustainable as long as they minimize bycatch as much as possible. Because MSC’s funding comes, in part, from seafood companies who pay to use the organization’s sustainable label on their products, what MSC considers sustainable might be different from an organization that advocates for plant-based diets. Some argue that there is no such thing as sustainable seafood, given the environmental impact of fishing and the increasing demand for seafood products worldwide.

The only thing that seems clear is that, as long as commercial fisheries exist, so will bycatch.

How To Prevent Bycatch

The most effective way to prevent bycatch is to reduce seafood consumption. By eliminating seafood from your diet, there is a decreased demand, which means the fishing industry has less incentive for large scale operations that inevitably result in bycatch.

How Is Bycatch Being Stopped?

Besides reducing the demand for seafood, there are several ways to prevent bycatch with varying degrees of success. In the U.S., the National Oceanic and Atmospheric Administration (NOAA)  published a framework for reducing bycatch. The agency points to its bycatch provisions in three pieces of legislation — the Endangered Species Act, Marine Mammal Protection Act and the Magnuson-Stevens Act — all of which aim to curb bycatch levels. NOAA also urges academics, environmental organizations, and fisheries to monitor and more accurately report and reduce the nation’s bycatch numbers.

What Techniques Are Used To Reduce Bycatch?

Despite these efforts, preventing bycatch remains a stubborn and complex problem. New fishing technologies and methods that reduce bycatch are beginning to be employed for a future fishing industry that produces much less bycatch. Some basic suggestions include fishing with a pole and line to catch fish individually, while other methods are more species-specific to deter seabirds and sea turtles from going after bait. Ultimately, the most effective solution is for commercial fleets to stop fishing altogether.

The Bottom Line

Bycatch occurs because the commercial fishing industry prioritizes profit over both animal welfare and environmental health. Driven largely by consumer demand, the amount of bycatch remains high around the world, regardless of target species and fishing method. In order to combat excessive bycatch, consumers can opt for a diet free of seafood. On a larger scale, strategies to minimize or eliminate bycatch should be the focus of sustainability organizations, consumers and regulatory agencies worldwide.

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