From Tangled to Mangled

Have you ever wondered how most of the fish we eat is caught? I used to think that it was just from rod-and-reel fishing, but now, I am learning that most of the fish on our dinner plates are caught en masse either by long lines, trawling, or by gillnets.


Let’s start with the baddest of the bunch. Bottom trawling is the worst kind of fishing practice there is; it destroys more ocean habitat than any other fishing practice. This method uses large weighted nets to drag the ocean floor, cutting off a huge amount of habitat in their path. The real-life practice of ‘casting a wide net’ might yield the greatest catch, but it is also the most damaging to the ecosystem.

A bottom trawl net has two weighted doors that keep the net open and keep it on the ocean floor. They can weigh up to several tons to keep it grounded on the seafloor. The bottom of the net is a metal cable with heavy balls made out of steel to crush everything as the net goes through the water. The scars left behind from these contraptions can take centuries to heal. In Alaska, there are thousands of coral reefs that are estimated to be 4,200 years old. With one swipe of a bottom trawl, they can be destroyed.

According to the National Academy of Sciences, bottom trawling “reduces the complexity, productivity, and biodiversity of benthic habitats,” the deep bottom of a body of water. The damage is most severe in areas with corals and sponges; 90% of a coral colony and ⅔ of a sponge population can perish when a bottom trawl net comes by. A study done in 2012 believes that the reason for this level of damage is that trawling alters the chemistry and geology of the ecosystem, permanently impacting how the ecosystem functions. Once coral and spine colonies die, commercial fish and other animals depending on them for spawning, nurseries, and food may disappear, too. Many animals also need these colonies for protection from other species. To put the damage in perspective, one trawl can destroy nearly 150 times the amount of forest that is usually cut at once. 

Not only does bottom trawling destroy habitats, it also destroys all marine creatures in its path. Trawls scoop up fish, animals, marine animals, plants, and turtles in the net, but the vessel only keeps the targeted species. They discard the unwanted fish and animals-mostly dead or dying and leave behind a decimated ecosystem that might never recover. 


 Longlines are baited hooks attached to lines extending up to 60 miles long. Pelagic (mid-water) longlines consist of a mainline ranging from hundreds of meters with only approximately 20 hooks in some fisheries (near-shore, deep-sea), to 100 km long with over 1,000 hooks. As seen in the picture below, there is a mainline with buoys attached and there are smaller baited hooks attached to the smaller lines called snoods. Pelagic longlines are not anchored and drift near the surface with a radio attached so the boat can track the catch. This specific type of line is used for catching certain types of pelagic (pelagic longlines) species on the surface, for example, tuna, swordfish, and other pacific billfish. Dr. Michael Laurs, director of the National Marine Fisheries Service Honolulu Laboratory in Hawaii says:

''If it's a pelagic species and is in a white-tablecloth restaurant, it is likely to have been caught on a long line.''  

Demersal lines on the seafloor are similar to pelagic longlines. They have a rope mainline with baited hooks spaced every 2-5 meters on monofilament or braided cord snoods. The mainline is attached at both ends to downlines that have large buoys, which have anchors at the bottom to hold the gear in place. To haul bottom-dwelling fish like cod or halibut up to the surface, the vessels often use hydraulic winches that are attached to the deck of the boat.

Effects of Longlining

While Pelagic longlining is an effective way to catch the targeted species, it often can also attract an array of species that are not targeted, including whales, sharks, and turtles. Discarded marine species due to encounters with fishing vessels and gear become known as Bycatch. Once these animals become hooked, they can be severely injured or dead by the time they are retrieved from the baited hooks. According to Daniel Abel and R. Dean Grubbs, in United States pelagic longline fisheries, only 3-15% of the bycatch is discarded.

Sharks are the dominant bycatch. In the west tropical Pacific, for every two tuna caught, one shark is caught in the bycatch. The common sharks that are in bycatches are blue sharks, silky sharks, and oceanic white tips. Blue sharks are globally the most common shark caught in pelagic longlines. Shark bycatch is lower where fisheries are fishing deeper as opposed to fishing that is done closer to shore for shallow fish because of the baited hooks they are using.

Demersal longline fishing causes little damage to the seafloor and has a limited level of bycatch. Some of the deepest fisheries use demersal longlining. Oftentimes the bycatch is 50% or more of the overall catch. The bycatch is high for Portuguese dogfish, lantern sharks, gulper sharks, and some catsharks. Some are kept and sold for liver and meat but most small sharks are discarded at sea. Mortality is guaranteed often due to broken Jaws by the auto-line retrieval system aboard the fishing vessel.


Another controversial fishing practice is the usage of gillnets. Gillnets are walls of netting that are either drifting or anchored in the water. They can be up to two miles long and anchored hundreds of feet deep or floating at the surface. Fish that try to swim through get stuck around their gills and will often die. For this reason, in 1922, the United Nations and other countries banned the use of gillnets. In 1993, they also banned drift gillnets longer than 2.5 km (1.5 mi). High seas drift gillnets are often criticized for their high rates of mammal and seabird bycatch. Abel and Grubbs wrote that in 1990, around 2 million blue and salmon sharks were caught in a squid drift gillnet fishery in North America (p. 367). These nets are responsible for more marine mammal bycatch deaths than any other type of fishing gear.

I struggled with writing about this topic because I know that so many fishermen depend on this method of fishing to earn a living. It is sad and difficult to realize that for some, this is one of the only ways they can provide for themselves and their families, but it is our oceans and their inhabitants who really pay the price. While I was looking for statistics about bycatch numbers, I struggled to find more current ones. I couldn't understand why, but then I asked a fisherman I know, and he responded that the fishermen don't want to report their numbers because they do not want to be labeled the ‘bad guys.’ This is a side of fishing that people do not really talk about. These fishermen did not invent these harmful fishing practices, but they have to utilize them in order to make a living in a highly-competitive industry; they are not blameless, but they are not innocent, either. Until a more efficient and eco-friendly solution exists, our oceans will continue to be ravaged. 



Cover Photo:

*click on other photos to get the link


Abel, Daniel C., et al. Shark Biology and Conservation: Essentials for Educators, Students, and Enthusiasts. Johns Hopkins University Press, 2020.

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