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Methods of Overfishing

Bycatch

Every year, about 10 million tons of unintentionally caught fish are discarded in the fishing process. Many of these marine animals become trapped in fishing gear but are not the intended catch. This unwanted catch, referred to as bycatch, usually dies. Sometimes the bycatch are fish too small to sell, other times it consists of animals such as sea turtles, sharks, dolphins, seabirds, and even whales. Bottom trawling for shrimp and longlining produce some of the highest bycatch rates. In some cases, such as bottom trawl shrimp fisheries, bycatch can be 3 to 15 times higher than the target catch. Many fisheries have successfully reduced bycatch by using appropriate gear technologies and fishing practices.

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

Technological advancements are helping to prevent bycatch. The "Turtle Excluder Device," or TED, is one example. It allows turtles like the endangered loggerhead sea turtle to escape from trawl nets through a grid of bars at the top or bottom of the net. In some fisheries, such as the Australian Northern Prawn and Torres Strait Prawn fisheries, TEDs are mandatory. The attachment is a solid grid that directs larger animals such as turtles, sharks, and stingrays out and away from the back of the net. After their introduction in this fishery, turtle bycatch decreased as much as 99 percent. 

bycatch waste being discarded
Bycatch are tossed from a commercial fishing boat,

Birds, too, are susceptible to getting caught in fishing gear. Albatross, large birds with massive wingspans, commonly get caught in longline gear. Enticed by the bait on the long hooks and lines, they can get pulled underwater and drown. 

Now, fishermen are turning to bird scaring lines to help deter the birds from going after their bait. And the solution is simple—as the lines are being set the fishermen attach brightly colored streamers that scare away the birds. One of the most successful implementations of bird scaring lines is in South Africa. Between 2006 and 2014 total bird bycatch in the trawl industry decreased by 90 percent, and by 99 percent for albatross. The success of South Africa is now the source of inspiration for many other countries.

Ghost Gear

Fishing gear serves a purpose to trap fish for the eventual collection by fishermen. But sometimes that gear gets lost at sea, whether due to an accident, abandonment, or a storm that dislodges it from its anchor. When this occurs the fishing gear becomes derelict, sometimes known as “ghost gear.” Ghost gear continues to entrap fish, often killing animals when they are unable to escape. The gear can also ensnare other creatures like whales and turtles and damage the environment. 

ghost nets overfishing
About a 300 foot long gill net found in Hawaii. The net had trapped parrotfish, wrasses, goatfish, surgeonfish, coral crabs, spiny lobsters, slipper lobsters and other fish.

One common type of ghost gear is the crab pot. Roughly 85,000 ghost pots exist in the Florida Keys killing an estimated 630,000 lobsters every year. In Louisiana, about 450,000 pots used to catch blue crab are lost. In the Chesapeake, that number is about 160,000, and an estimated one million crabs die in Virginia’s portion of the bay. Out of the three million lobster traps that are set along the Maine coast, about 10 percent are lost every year. Not only does ghost fishing harm local ecosystems, it negatively impacts the success of fisheries. One study estimates that removing just 10 percent of derelict crab and lobster traps worldwide could increase the value of seafood caught by $831 million dollars a year.

Some traps now have a dissolvable panel that only begins to decay if left in the water for an extended period of time. The Maine lobster fishery devised both an escape route for lobsters too small to be legally sold and a dissolvable hatch called a “ghost panel” that releases trapped lobsters after 6-12 months underwater. And the Virginia Institute of Marine Science has been experimenting with its own dissolvable panel that could be used in the Chesapeake Bay and Gulf of Mexico. 

Seafood Fraud

Mislabeling and substitution in fish markets and behind the seafood counter occurs for several reasons. This seemingly simple action can be a potential health concern as some seafood carries more contaminants, toxins, or allergens than others. Though mislabeling sometimes occurs due to mistaken identity, fish are also mislabeled on purpose to make a profit—a cheap fish is sold under the name of a more expensive fish. It can also allow sellers to falsely meet market demand. Some commonly mislabeled and substituted species in the U.S. include red snapper, which is substituted with Pacific Rockfish or other kinds of snapper, mahi mahi, which is substituted with yellowtail amberjack, and swordfish, which is substituted with mako shark. Some non-profit and advocacy groups are promoting the idea that species be traced throughout the entire supply chain by their species name. The Marine Stewardship Council (MSC), a nonprofit that sets standards for sustainable fishing, uses DNA testing to ensure seafood sold under their label is the species it claims to be.


It is often difficult to determine exactly what species of fish you are purchasing since fish can often be labeled under different terms. 

Overfishing supermarket mystery fish

To help with accurate seafood identification and labeling, the Food and Drug Administration (FDA) maintains a Regulatory Fish Encyclopedia that includes acceptable market names of seafood in the U.S., along with corresponding high-resolution images of the whole fish, fillets and other information. Also, check out the Smithsonian’s role in DNA barcoding below.

The extent of mislabeling varies by location and species and can include an inaccurate species name or even country of origin. To date, a comprehensive, large-scale study on frequency and extent of mislabeling and substitution has not been completed. Fraud statistics vary depending on location and sample size. For example, one study concluded that 16 percent of sampled seafood was mislabeled in select U.S. cities, another showed 20 to 25 percent mislabeling across New York, New Jersey, and Connecticut, and a third study in Los Angeles County found 74 percent of restaurants and markets sampled had mislabeled seafood. The nonprofit Oceana conducted a small nationwide study and found that 33 percent of samples are mislabeled nationwide. The discrepancy between studies may be because some cities are better at ensuring fish are correctly labeled. Some areas are more likely to have consumers who demand a greater level of transparency when it comes to knowing what fish land on their plates. 

Inconsistent labeling requirements throughout the supply chain may also cause confusion. For example, a single fish can be sold under various names from the boat, to the distributer, and to the restaurant or market. This stems from a system that allows many different species of fish to be legally sold under one name Ordering sole? You could be ordering blackback flounder, yellowtail flounder, bigmouth flounder, or witch flounder. Or perhaps rockfish? According to the FDA, Pacific Ocean perch, chilipepper fish, cowcod, and treefish can all be legally sold under that name.

In the U.S., NOAA acts as the seafood fraud and illegal fishing “police.” NOAA law enforcement teams inspect fishing vessels and processing plants and also conduct investigations on illegal activity punishable by large fines, and even incarceration. For example, in March 2015, a wholesale seafood business owner was found guilty of illegally trafficking oysters, creating false health and safety records, and conspiracy. He was ordered to pay multiple fines, including $140,000 to New Jersey for oyster restoration efforts in Delaware Bay, sentenced to 26 months in prison, 

Fishing Methods

Many of the most popular fishing methods today are structured to catch the most fish with the least amount of effort. Some of the most common fishing gear used today include:

Demersal Or Bottom Trawl

bottomtrawl bycatch

Bottom trawling is a type of fishing in which a large net is dragged along the bottom of the ocean. Weights keep the net at the bottom of the seafloor while a set of floats on the top keep it open. This type of fishing targets bottom-dwelling species like flounder and crabs. Both sea turtles and marine mammals are at risk of becoming entangled in this type of gear, though turtle excluder devices (or TEDS) are required on nets in the United States in the shrimp and summer flounder fisheries. Bottom trawls are some of the worst fishing gear when it comes to bycatch—as of 2019, about 46 percent of all bycatch comes from bottom trawls.

Pelagic Or Midwater Trawl

A ship pulls a trawl.

Midwater trawling is similar to bottom trawling except the net is towed in the middle of the water column. This fishing mechanism targets schooling fish like sardines, shrimp, and squid. Like bottom trawls, turtles and whales can become entangled in the net. TEDS are required in the pelagic shrimp fishery. In the United States, pilot whales, white-sided dolphins, and bottlenose dolphins are particularly susceptible to entanglement in midwater trawling gear because they swim in this part of the water column.
 

Gillnets

a boat sets a gillnet

Gillnets are large walls of netting that are set at the bottom of the ocean. When fish swim into the net webbing their heads become stuck—if they try to move forward the gap is too small to fit their full body, and if they try to move backward their gills get caught on the webbing. This type of net is usually used to catch salmon, ground fish, and tuna (among other fish). Large marine animals like seals are particularly susceptible to becoming caught in this type of fishing gear.

Longlines

A ship sets a longline

Longline fishing, whether it is deep on the seafloor or at the ocean’s surface, includes hundreds of baited hooks hanging from a main fishing line. This type of fishing is used to catch large fish like swordfish and groundfish. Many fish, turtles, and seabirds are also attracted to the baited hooks, however, and often these animals are hooked on the lines and injured.

Purse Seine

purse seine is a huge wall of netting bycatch

A purse seine is a huge wall of netting that is set in a circle around a school of fish. Once the net is set around the school, a line is pulled and the net closes at the bottom. Purse seining cannot select for a certain type of fish—whatever is encircled by the net is captured. Unwanted fish, turtles, or marine mammals may also be caught. In general, however, fishers try to avoid unwanted species by refraining from setting nets when they are visible from the boat deck. A low percentage of fish caught using a purse seine are bycatch.

Pole And Line

Pole and line fishing is another name for fishing with a rod. Fishermen usually chum the water and spray the surface to make it appear as though there is a large school of fish at the surface. This type of fishing is used to catch larger fish like tuna and is a more sustainable option because an unwanted catch can be released immediately and only one fish is caught at a time, rather than a massive number in one haul.

Pots And Traps

pot traps bycatch killing

Pots and traps are submerged cages that are baited. They are used to catch crab and lobster or even some fish, like eels. Sometimes traps can capture unwanted species. The lines that indicate their location via a surface buoy can also ensnare larger marine animals like whales.

Dredges

bycatch dredging

Dredging is a type of fishing in which a large, metal cage is dragged through the seafloor by a boat. This type of fishing targets shellfish like oysters and clams and is particularly destructive to the environment because the cage destroys anything growing on or just under the seafloor.

Harpooning

A harpoon is a spear with some type of mechanism for propulsion. This type of fishing targets one specific fish, making it a highly sustainable fishing method. There is nearly zero bycatch, and since it takes skill and precision to hit a fish, only a small number are harvested at once.