From bycatch mortality and overfishing to habitat destruction, industrial fishing has had severe consequences for our oceans. While overfishing can be managed by reducing catch size and monitoring populations in overfished regions with the cooperation of fishermen, bycatch is a far more complex problem. Gear types like driftnets and longlines, often set to catch swordfish, are killing endangered and vulnerable IUCN Red List species like leatherback sea turtles, shortfin mako sharks, and sperm whales as bycatch. They have also drastically reduced populations of other species like the blue shark, forcing them onto the Near Threatened list as an estimated 20 million of these sharks are caught annually as bycatch.

TIRN wants to make our oceans safer for sealife by replacing deadly swordfish driftnet and longline fisheries with less harmful gear types. In this article, you will learn about the gear types commonly used to catch swordfish, including driftnets and longlines, in addition to a wide variety of other fisheries impacting sealife throughout the world. By more fully understanding how fish are caught, we hope you will be able to make more informed seafood decisions.

The following five gear types are used to catch swordfish. Driftnets and longlines, overwhelmingly used as the major swordfish gear type internationally and domestically, have some of the highest bycatch rates of any gear type. Despite the availability of less harmful gear types, the vast majority of swordfish consumed in America and worldwide is caught by unsustainable fisheries. To learn more about international swordfish fisheries, visit our fact sheet.


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Known as “Curtains of Death”, gillnets stretch under the water for an average of a mile, are nearly invisible to sealife, and catch anything that happens to swim into their path. There are two kinds of gillnet: anchored or drift, and both can remain in the water for days at a time, leading to suffocation of marine mammals, sharks, and turtles. Drift gillnets (or driftnets) in particular have an extremely high bycatch rate, and in the California driftnet fishery, as much as 61% of the catch ends up being thrown overboard, and 21% of the catch consisting of IUCN Red List Species like leatherback sea turtles and mako sharks. Driftnets are also commonly used in small-scale swordfish fisheries internationally, particularly in Latin American and South American regions. This is especially apparent in Ecuador, where 90% of the total small-scale fishery swordfish catch comes from driftnets in some ports. Many countries also have both swordfish driftnet fisheries and larger-scale longline fisheries. In Sri Lanka, there is a combination driftnet-longline fishery for swordfish. Worldwide, underreporting of driftnet bycatch and illegal small-scale fishing are major problems, meaning we cannot know exactly how many other animals are being killed by these nets annually.

Commonly Used To Catch: Swordfish, Tuna, Cod, Salmon



Longlines are the main international large-scale fishery for swordfish. This gear can stretch for up to 60 miles into the open ocean, and are covered in thousands of baited hooks. Like driftnets, longlines are left in the ocean for days at a time, which leads to high bycatch and mortality rates of species like turtles and sharks. In the Australia/New Zealand region, tuna and swordfish longlines have an especially big impact on blue sharks, with this species making up 80% of the total observed bycatch, while vulnerable shortfin mako and thresher sharks make up another 3% each. In Mexico, some driftnet fisheries have been replaced with longline fisheries in an effort to reduce bycatch problems, but longlines are equally destructive, making this an entirely unsustainable solution. This gear also has an especially high risk for seabirds like albatrosses, which tend to gather around longline vessels as seen in the above photo. These birds become hooked, tangled, or severely wounded after trying to take the free bait from the hooks. In Brazil, a major exporter of swordfish, high numbers of seabirds are regularly reported to be caught in longlines. Because of underreporting, exact numbers aren’t known; however, according to the American Bird Conservancy, long line gear in Alaska alone kills an average of 20,000 seabirds a year.

Commonly Used To Catch: Swordfish, Tuna, Mahi-Mahi, Sea Bass



One of the least harmful fishing methods, harpooning is used to catch large species at the ocean’s surface. Unlike other gear types, harpooning has no bycatch rate whatsoever because fishermen can individually target their intended species. The only major concern associated with harpooning is its use in catching Bluefin Tuna, which are facing population decline; however, this method also does not contribute to rapid overfishing because fishermen only catch one fish at a time, and only as many fish as they need, as opposed to mass industrial fishing.

Commonly Used To Catch: Swordfish, Tuna

Deep-Set Buoy


A relatively new fishing method, deep-set buoys are designed to catch swordfish without the bycatch problems of driftnets and longlines. Deep-set buoys allow fishermen to reach swordfish in deeper regions, and respond rapidly to a catch, meaning that any other species that happens to be caught can be re-released alive. While driftnets yield only 12% swordfish per catch, deep-set buoy fishermen report a 94% marketable catch rate. This new gear will make a huge difference in the fishery. In California, where the driftnet fishery has one of the highest reported bycatch rates in the world, TIRN is encouraging fishermen to switch from nets to deep-set buoys.

Commonly Used To Catch: Swordfish

Pole and Line


Pole and line fishing is similar to traditional recreational fishing, using a fishing pole and bait to catch individual fish. Like the deep-set buoy, this method has a low bycatch rate because fishermen can immediately release other species. This method also does not contribute as rapidly to overfishing because of its individual approach, much like the harpoon.

Commonly Used To Catch: Tuna, Mahi-Mahi, Swordfish (occasionally)

While the following gear types are not used to catch swordfish, it is important to understand the impacts of other major fisheries on the ocean and its ecosystems. Many of these other gear types are also high in bycatch, while others cause extreme and irreparable  damage to ocean environments.

Bottom-Trawl Nets


Bottom-trawl nets are large, enclosed nets with a wide mouth similar to a bag. When dragged along the bottom of the seafloor, trawl nets catch anything swimming in their immediate path, as well as anything on the seafloor itself. This gear has a very high bycatch and mortality rate, and as demonstrated by this photo, is also extremely destructive to the seafloor. The heavy metal gear causes irreparable damage to deep-sea coral and plantlife, leaving a barren environment in its wake.

Commonly Used To Catch: Haddock, Cod, Rockfish, Halibut, Orange Roughy, Squid



Similar to trawls, dredges are large, heavy metal baskets which are dragged along the seafloor. Also similarly to trawls, the metal gear causes significant destruction to seafloor habitats, coral, and plantlife, and results in high bycatch and mortality rates.

Commonly Used To Catch: Clams, Scallops, Oysters

Midwater Trawl Nets


These nets are the same basic structure as bottom-trawls, but are usually dragged in open water in the pelagic zones. These enormous nets are used to target whole schools of fish at once, and while they don’t cause habitat destruction along the seafloor, they can easily contribute to overfishing problems because of the size of a single catch. They also have a lower bycatch rate than bottom-trawls or driftnets because they tend to specifically target schools, but marine mammals and sharks are still common bycatch species.

Commonly Used To Catch: Mackerel, Herring, Tuna, Anchovies, Shrimp

Surrounding Nets (Purse Seining)


Similar to midwater trawls, these large nets target whole schools of fish. Forming a wall around the fish, the nets are then pulled together like a purse, fully enclosing the school and any other species within its circumference. In the past, purse seining was infamous for its high dolphin mortality rates, and tuna fishermen even intentionally followed dolphins to schools of tuna. Though the U.S. ended this practice, purse seining still poses a high risk to marine mammals. Like midwater trawl nets, purse seining can also lead to rapid overfishing.

Commonly Used To Catch: Tuna, Sardine, Mackerel, Anchovies, Herring

Pots and Traps


Like bottom-trawling and dredging, pots and traps are used to target bottom-dwelling species. Fish and shellfish are lured into cages on the seafloor with bait, where they remain alive until fishermen come back to gather the gear. Unlike trawls and dredges, pots and traps do not cause significant damage to the seafloor or environment, and bycatch levels are very low.

Commonly Used To Catch: Lobsters, Crabs, Shrimp, Pacific Cod



Similar to the pole and line method, trolling uses hooks and lines dragged behind a fishing boat to attract fish with moving bait. This method also has a low bycatch mortality rate because fishermen can immediately release other species, just like in pole and line fishing.


Commonly Used To Catch: Mahi Mahi, Mackerel, Tuna, Salmon