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Bycatch: The Cost of Catching What You Don’t Want

When people go out fishing, they  often have something specific in mind, but it's very difficult to catch only what you're looking for. Pulling a net through the water or across the sea floor catches all the animals in its path, not just the tasty fish, and can destroy important ecosystems. Baited hooks attract seabirds, sharks and other animals along with the big tuna or swordfish that are being sought. Even if animals are able to survive being caught in a net and are thrown back overboard, many still die. Some nets and traps are “lost” but continue to kill, a phenomenon called ghost fishing.

All the animals that are caught unintentionally are called bycatch, and it's an enormous waste of ocean resources and animal life. Some species are especially vulnerable to being killed accidentally by fishing activities and are threatened with extinction. Around the world, governments are working to develop methods to reduce bycatch.

A pile of bycatch species.
Guitarfish, rays, and other bycatch are tossed from a shrimp boat in La Paz, Mexico in 2006.
An albatross caught on a fishing line.
The Gulf of Mexico shrimp trawl fishery scoops up a lot of unwanted fish along with the shrimp. In the 1990s, for every pound of shrimp caught, more than 4 pounds of other fish species were caught as bycatch and discarded dead.
Using dynamite to stun or kill bigger fish to sell at market leaves behind many dead undesired fish as bycatch.
A net used to trawl the ocean floor scooped up this large specimen of deep-sea coral.
Giant drift nets, placed around the world’s oceans to catch commercial fish species, kill non-commercial animals just as efficiently, often taking far more of the latter for every useable species ensnared.
This is North Atlantic right whale #3333 who was spotted with fishing gear trailing from his mouth during an aerial survey off the coast of Georgia on January 29, 2008.
A Yellow spotted trevally struggles to free itself from a fisherman's discarded net. Discarded nets continue to fish long after they have been lost, devastating the local fish populations and choking the life out of the reef on which it becomes entangled
An abandoned fishing net carrying 17 dead sea turtles was discovered off the coast of Bahia, Brazil days after a storm.
About a 300 foot long gill net found abandoned on a shallow reef in the surf zone on Oahu, Hawaii. The net had trapped parrotfish, wrasses, goatfish, surgeonfish, coral crabs, spiny lobsters, slipper lobsters and other fish that had decayed beyond identifi
Lost nets become entangled on a coral reef in the NW Hawaiian Islands, doing damage for decades. Wave action on the net breaks pieces of coral off until the net breaks, when it is free to catch on new reefs and do more damage.
A thresher shark was killed after becoming stuck in a gillnet.
Sunset over a fishing net.
A Turtle Excluder Device (TED) enables a loggerhead turtle to escape from a net.
A pile of bycatch species.

A Net Full of Bycatch

Credit: Eliott Norse, Marine Conservation Biology Institute/Marine Photobank

Bycatch includes species that are not the target of a fishery, such as sea turtles and seabird, as well as species that are targeted, but are too small or large based on regulations, and must therefore be discarded. The skate shown here is one of many bycatch species caught in this shrimp trawl net, which also contains starfish, crabs and red snapper.

It was once believed that bycatch didn't have a serious impact on animal populations. Now it is known that it can be a leading factor in population declines of a wide range of marine wildlife. In many fisheries, the majority of fish that are discarded as bycatch are juveniles of the target species that never had the chance to breed, and now never will. Continued loss of large parts of the future breeding stock is a direct threat to a population's survival.

Guitarfish, rays, and other bycatch are tossed from a shrimp boat in La Paz, Mexico in 2006.

Bycatch Raining Down From Above

Credit: WWF Deutschland
Guitarfish, rays, and other bycatch are tossed from a shrimp boat in La Paz, Mexico in 2006. Many species caught as bycatch are never recorded, so scientists and wildlife managers don't know what has been lost. The loss of millions of small coastal sharks, such as those shown here, to shrimp trawls and gillnets in the Gulf of Mexico has no doubt altered that environment, as they are food for many bigger animals and prey upon even smaller ones.
An albatross caught on a fishing line.

Accidental Catch

Credit: Projeto Tamar Brazil/Marine Photobank

A fishing line with bait on the hook intended for tuna and other big fish is also a tasty snack for other animals such as this albatross, which drowned after being accidentally caught on a longline near Brazil. A 2003 study found that 300,000 birds are killed each year as bycatch, of which 100,000 are albatrosses. Fishermen are working with scientists to figure out ways to reduce these losses, such as new kinds of fishing lines and hooks that are less likely to catch albatrosses, and setting lines at night when the birds are less active.

The Gulf of Mexico shrimp trawl fishery scoops up a lot of unwanted fish along with the shrimp. In the 1990s, for every pound of shrimp caught, more than 4 pounds of other fish species were caught as bycatch and discarded dead.

Shrimp Trawls Catch More Than Shrimp

Credit: S.McGowan/AMC 2008/Marine Photobank

The Gulf of Mexico shrimp trawl fishery scoops up a lot of unwanted fish along with the shrimp they are seeking. For every pound of shrimp caught, more than four pounds of other fish species are caught as bycatch and discarded dead. This can do major damage to the other species and the ecosystem. For example, approximately 30 million juvenile red snapper were dying in shrimp trawls each year before 1998, ultimately sending the species into a severe decline. But in May 1998, regulations went into effect requiring shrimp trawlers to install escape hatches to reduce bycatch.

Using dynamite to stun or kill bigger fish to sell at market leaves behind many dead undesired fish as bycatch.

Fishing with Dynamite

Credit: (c) 2004 Berkley White/Marine Photobank
Blast fishing, when dynamite or other explosives are used to stun or kill fish, is a practice used in many parts of the world where poor fishers are desperate to feed their families. Hundreds of fish can be seen strewn across the reef afterwards, left as bycatch, such as these fish in Thailand. Fishers target larger, valuable species such as grouper, which command a hefty price at the market—yet all the reef species pay the price. The practice is unsustainable since the entire community is disrupted by the blasts, including the corals that the fish use for shelter. Reefs can take decades to recover from blast fishing.
A net used to trawl the ocean floor scooped up this large specimen of deep-sea coral.

Coral Trapped in Trawler Net

Credit: ©Greenpeace/Malcolm Pullman/Marine Photobank

While bottom trawling—a fishing method that drags a large net with heavy weights across the seafloor—fishermen often catch more than their target fish. Here, they've scooped up a large deep-sea coral, which is likely centuries old. While this method is good at catching lots of fish, it also does a lot of damage along the way because it captures everything in its path, even digging into the seafloor. The trawl can destroy large areas of seafloor habitats that give marine species food and shelter, and has been compared to strip mining on land. Increasingly, vulnerable habitats such as seamounts are being put off-limits to trawling.

Giant drift nets, placed around the world’s oceans to catch commercial fish species, kill non-commercial animals just as efficiently, often taking far more of the latter for every useable species ensnared.

Sea Lion Drowned in Drift Net

Credit: (c) Save Our Seas Ltd./ Tom Campbell/Marine Photobank
This sea lion has been caught and killed in a giant drift net, or a “curtain of death,” as photographer Tom Woodward calls them. These giant drift nets, placed around the world’s oceans by commercial fishing vessels, kill non-commercial animals just as efficiently, often taking far more of the latter for every useable species ensnared. Billions of tons of dead creatures, like this sea lion, are dumped overboard, wasted and removed from their place in the ecosystem. The fishermen aren't trying to kill sea lions and other animals, but by placing their nets where they are likely to catch target fish, they capture other creatures as well.
This is North Atlantic right whale #3333 who was spotted with fishing gear trailing from his mouth during an aerial survey off the coast of Georgia on January 29, 2008.

Whale Entanglement

Credit: New England Aquarium/K. Mahoney

This is North Atlantic right whale #3333 who was spotted with fishing gear trailing from his mouth during an aerial survey off the coast of Georgia on January 29, 2008. Entanglement is one of the most serious threats facing North Atlantic right whales. Fortunately this individual was seen without the fishing gear the following August in Canada’s Bay of Fundy.

A Yellow spotted trevally struggles to free itself from a fisherman's discarded net. Discarded nets continue to fish long after they have been lost, devastating the local fish populations and choking the life out of the reef on which it becomes entangled

Trevally Dying in Ghost Net, Oman

Credit: Sijmon de Waal/Marine Photobank

A yellow spotted trevally struggles to free itself from a fisherman's discarded net. Discarded nets continue to fish long after they have been lost, devastating the local fish populations and choking the life out of the reef on which it becomes entangled. New programs are being developed in which villagers are paid for discarded nets, which are then turned into carpets and other products.

An abandoned fishing net carrying 17 dead sea turtles was discovered off the coast of Bahia, Brazil days after a storm.

Turtles Caught in Abandoned Net

Credit: Projeto Tamar Brazil/Marine Photobank
This abandoned fishing net carrying 17 dead sea turtles was discovered off the coast of Bahia, Brazil days after a storm. Trapped in a net, the turtles were dragged through the water with no access to the surface to breathe, causing them to drown. It's estimated that some 4,600 sea turtles are accidentally killed by fishing nets and hooks every year in U.S. waters.
About a 300 foot long gill net found abandoned on a shallow reef in the surf zone on Oahu, Hawaii. The net had trapped parrotfish, wrasses, goatfish, surgeonfish, coral crabs, spiny lobsters, slipper lobsters and other fish that had decayed beyond identifi

Discarded Gillnet Traps Fish

Credit: Frank Baensch

This roughly 300 foot long gill net was found abandoned on a shallow reef in the surf zone on Oahu, Hawaii. The net had trapped parrotfish, wrasses, goatfish, surgeonfish, coral crabs, spiny lobsters, slipper lobsters and other fish that had decayed too much to be identified.

Lost nets become entangled on a coral reef in the NW Hawaiian Islands, doing damage for decades. Wave action on the net breaks pieces of coral off until the net breaks, when it is free to catch on new reefs and do more damage.

Lost Nets Hurt Coral Reefs

Credit: NOAA/NMFS
Lost fishing gear can harm coral reefs and their ecosystems, like this one shown in the Northwest Hawaiian Islands. When they get caught on coral, waves pulling on the ensnared nets and lines break off coral heads—reef structures that took decades or centuries to grow. If the nets are freed, the cycle continues, with them continuing to snag and damage other coral. The process continues until the derelict gear is removed, becomes weighted down with enough coral to sink, or it is fully incorporated into the reef structure.
A thresher shark was killed after becoming stuck in a gillnet.

Thresher Shark Killed by a Gillnet

Credit: Brian Skerry
"Tens of millions of sharks are killed each year, often only for their fins. I have wrestled with how to take pictures of dead sharks that resonate with readers. One morning, I jumped into the sea in Mexico and swam along a gillnet, where I found a thresher shark that had recently died in the net. As I composed the frame, the scene struck me as a crucifixion. Finally I had an image that would create empathy for these animals and give voice to the problem." — Photographer Brian Skerry
Sunset over a fishing net.

Technology and Sea Turtles

Credit: John Wang, Joint Institute for Marine and Atmospheric Research

Sea turtles may have survived the planetary changes that killed the dinosaurs, but now they are threatened by fisheries. It's estimated that some 4,600 sea turtles are killed by fishing nets and hooks every year in U.S. waters. But off the coast of Mexico, one community is trying something different: hanging lights on their nets so turtles can avoid them. They've found a 50% reduction in turtle catch at night, while the fish catch has actually gone up! Learn more about the project in this video and this New York Times blog post.

A Turtle Excluder Device (TED) enables a loggerhead turtle to escape from a net.

Loggerhead Escapes from Fishing Net

Credit: NOAA

One of the biggest threats to sea turtles, such as the loggerhead turtle (Caretta caretta) pictured here, is being accidentally caught and killed in fishing nets. Trapped in a net, the turtles are dragged through the water with no access to the surface to breathe, causing them to drown.

To address this problem, NOAA Fisheries worked with the shrimp trawling industry to install escape hatches into their nets called Turtle Excluder Devices, or TEDs. A crosshatch of bars in the middle of the net create a grid large enough for small shrimp to pass through, but not turtles and other large animals. When they hit the grid, they can then swim out through a hole in the net and escape.

Before TEDs were installed, an estimated 70 to 80 percent of turtle strandings on beaches were caused by shrimp nets. But since they were installed by U.S. shrimpers in the Gulf of Mexico in the late 1980s, strandings caused by shrimp nets are estimated to be down by at least 44 percent.

Tags: Bycatch