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10.9.3: Destructive fishing methods

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    When we think about destroying the oceans, most people think of destruction via pollution. Although chemical dumping and plastics have a drastic effect on marine life and ecosystems, it is very important to consider another major issue that is causing detrimental effects on marine systems. This issue is destructive fishing methods. Destructive fishing includes practices that leave marine populations irreversibly damaged and can destroy entire habitats for fish and other organisms.

    According to the World Wildlife Fund (WWF), there will be no more fish left in the oceans by 2048. This is because more than 30 percent of the world’s fisheries have been pushed beyond their biological limits. Therefore, we need stricter regulations and laws to prevent this disaster.

    Destructive fishing is mostly done in underdeveloped countries which don’t have regulations for fishermen to follow. These methods are used because they are effective in getting a large amount of fish in a short period of time saving fishermen time and effort. Some dangerous methods include over-fishing, blast fishing, bottom trawling, and cyanide fishing.


    Over-fishing is when fish are captured before they can reproduce, which can significantly reduce population sizes for the future. This disrupts not only the species that was harvested, but also the other organisms that depend on those species and potentially the whole ecosystem.

    trawlers_overfishing_cod.jpg“Trawlers over fishing cod” by Asc1733 [CC BY SA4.0]

    Facts from the WWF :

    – In just over 40 years there has been a decrease in recorded marine species by 39%.

    – Around 93 million tons of fish were caught world-wide.

    – Entire species, such as the Pacific Blue-fin tuna and swordfish, are highly endangered and are at an all-time low.

    overfished_us_stocks_2010.png“Overfished US stocks 2010” by NOAA [CC BY-SA 3.0]

    – Other marine species, such as whales, dolphins and turtles, are unintentionally killed as a result of over-fishing.


    A major issue is the open access to the ocean and the absent regulations and monitoring of the water. Due to the increased number of fisheries, management has begun to slack. Current rules and regulations are not strict and do not mark a limit of intake. More importantly, there is little to no international fishing regulations. Even if the nations did come together to fight this issue, we still face illegal fishing. To reduce the intake of fish it should be mandatory to report intake and there must be a maximum limit that is determined by biologists and not companies. Also, we need stronger monitoring of the ocean, which may be hard due to the number of fisheries and the huge surface area the ocean covers.


    The WWF states that the populations that are mainly targeted are top predators in the ecosystem such as Billfish, Tuna, Salmon, and sharks. This is because of the economic and social demands of the fishing industry. Decreases in the top predator population can severely disrupt other marine populations. A prime example of this is increases in population sizes of smaller marine animals at the bottom of the food web that are fed on by top predators. This impacts other aspects of the marine ecosystem such as increases in algal overgrowth, which can be dangerous to coral reefs. Algae, although essential for the ecosystem, can have negative effects if there is a large abundance.

    Another issue that is closely related to over-fishing is by-catch. By-catch refers to non-target animals such as turtles or dolphins that are captured or killed in fishing nets. This threat causes the loss of billions of fish and other animals such as sea turtles and cetaceans.

    sea_turtle_entangled_in_a_ghost_net.jpg“Sea Turtle Entangled in Ghost Net” by Doug Helton [CC BY SA]

    Watch this Tedtalk on over fishing here and a video on by-catching here.

    Over-fishing causes a cascade of effects in marine communitiesthat can destroy habitats and result in the loss of biodiversity both in terms of overall abundance and species richness (Coleman, 2002). Not only does over-fishing destroy marine ecosystems, it also impacts food security for people. Humans that live in coastal communities rely largely on fish as a protein resource. Over-fishing decreases food security by threatening the long-term food supply, especially for individuals in developing countries.


    There have been new movements to push fisheries to practice sustainable fishing. The WWF has helped develop and set environmental standards to help set a plan for sustainable fisheries. Approximately 15,000 seafood products hold to the standard of sustainable fishing, which is a great first step. There are other ways to help with over-fishing and one way is by influencing the market for fish. By reducing the need for fish products, less fish will be caught and hopefully it will allow some time for re-population.

    1280px-__.jpgBy Drajay1976 [CC by 3.0]

    Blast Fishing

    Blast fishing or dynamite fishing is a practice outlawed in most of the world, but is still used in southeast Asia. It involves using explosions to stun or kill large schools of fish for easy collection. The explosions often destroy underlying ecosystems from the strength of the blast. Around 70,000 fishermen still use this practice. Researchers believe that destructive fishing practices like blast fishing are one of the biggest threats to coral reef ecosystems. Coral reefs are less likely to grow in places of constant disturbance. The damage done to coral reefs has an immediate negative effect on the fish population in the area. From a single blast, it takes a coral reef about 5-10 years to recover. From constant blast fishing it leaves coral reefs unable to grow leaving an ocean of rubble. To reduce the use of this method, enforcement officials patrol the seas to try to catch and reprimand offenders.

    Trawling_Drawing.jpg“Trawling Drawing via Trawl” by NOAA under Public Domain

    Bottom trawling

    Bottom trawling is a method that uses a large net that scrapes against the ocean floor to collect large groups of fish. Global catch from bottom trawling has been estimated at over 30 million tons per year, an amount larger than any other fishing method. The trawl doors disturb the sea bed, create a cloud of muddy water which hides the oncoming trawl net and generates a noise which attracts fish. The fish begin to swim in front of the net mouth. As the trawl continues along the seabed, fish begin to tire and slip backwards into the net. Finally, the fish become exhausted and drop back, into the “cod end” and are caught. The problem with bottom trawling is that it is un-selective in the fish it catches and severely damages marine ecosystems. Many creatures end up mistakenly caught and thrown overboard dead or dying, including endangered fish and vulnerable deep-sea corals that can live for hundreds of years or more.

    Cyanide fishing

    Cyanide fishing is a fishing technique used to gather fish for aquaria. In this process, a cyanide solution is used to stun fish for easier collection. This method can kill neighboring fish communities and severely harm coral reefs. Recent studies have shown that the combination of cyanide use and stress of post capture handling results in mortality of up to 75% of the organisms within less than 48 hours of capture. With such high mortality numbers, a greater number of fish must be caught in order to supplement post-catch death.

    The information in this chapter in thanks to content contributions from Maddison Ouellette and Bryce Chouinard.

    10.9.3: Destructive fishing methods is shared under a not declared license and was authored, remixed, and/or curated by LibreTexts.

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