Industrial fishing practices harm ocean ecosystems in four major ways: overfishing depletes species like Atlantic cod beyond recovery, destructive gear damages seafloor habitats and coral reefs, ghost fishing gear continues killing animals for years, and bycatch traps millions of sea turtles, marine mammals, and seabirds annually. These impacts create cascading effects throughout ocean food webs, though new technologies and fishing restrictions are helping some species recover.
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For centuries, the ocean seemed limitless. Fishermen in the 17th century said cod was so plentiful off Newfoundland that you could walk across the water on their backs. That abundance is gone. Today's industrial fishing fleets can remove fish faster than populations can recover, with radar and sonar turning what was once a hunt into a harvest factory.
The environmental toll goes far beyond empty nets. We're fundamentally reshaping ocean ecosystems in ways scientists are only beginning to understand. New technologies have enabled humans to harvest fish on a massive scale to feed Earth's growing population, but there are serious consequences. Overfishing has been identified as a primary cause of ecosystem collapse in many aquatic systems.
Overfishing
One of the most significant consequences of industrial fishing is that some species have been overfished to the point of near extinction. The Atlantic cod provides perhaps the best-known example. In the 17th century, cod fishing formed the foundation of the New England economy, and many people relied on it for their livelihood.
Here's what changed: In the 1960s, new technologies like radar and sonar enabled fishermen to fish much deeper for cod and catch them much more rapidly. Landings of cod began to skyrocket over the next few decades, but the fishery collapsed dramatically in the 1990s. The area off Newfoundland, formerly the world's largest cod fishery, experienced estimated declines in cod biomass of over 90% in some areas. Six additional stocks off the coast of Canada had declined in biomass by at least 75%.
The number of fish became so few that Canada enacted a moratorium on cod fishing to allow stocks to recover. The United States has also imposed severe restrictions on the industry, cutting the time people can fish and reducing the total amount of cod that can be caught.
Shutting down the industry in Canada had consequences that reverberated throughout coastal regions. Many people saw their livelihoods vanish, and unemployment became widespread. Coastal communities dwindled as people moved to other areas in search of employment.
The ocean was also significantly altered by the removal of cod, a major predator. With their major predators gone, animals that had been the prey of cod-such as shrimp and snow crab-were released from predatory controls and proliferated. This fundamentally altered the food web and the ecosystem's functioning.
This phenomenon, in which the removal of large predators causes population explosions in their prey, is called a trophic cascade. It's a common consequence of overfishing. Exploitation of sharks has increased dramatically over the past several decades, driven in part by rising demand for shark fins and meat.
In the southeastern United States, some large shark populations have declined by over 90%, though figures vary by species and region. Cownose rays are a significant component of the diet for many of these sharks, and as the shark population declines, these rays have virtually no predators in the ocean.
As a result, the increased cownose ray population has preyed heavily on bay scallops, one of their preferred prey items. The bay scallop fishery was once profitable along the Eastern seaboard, but cownose ray predation has contributed to bay scallop declines in some areas. The waters of many places along the coast are now closed to fishing in hopes of a recovery of the bay scallop.
These examples illustrate how overfishing impacts more than just a single species of fish. Their removal can have consequences for the entire ecosystem.
Habitat Destruction
In addition to removing an increasing number of fish from the ocean, many industrial fishing practices also destroy aquatic habitats. Dredging is a standard method for harvesting clams, using a large metal scoop that drags along the seafloor to collect them. The process also churns up sediments along the seafloor, causing them to become suspended in the water column and degrade water quality.
The practice can also dig up burrowing worms from the sediments. These animals are essential because their burrows increase contact between sediments and the water. This returns nutrients to the water, where microorganisms use them in nutrient cycling. Without these burrowing animals, waters along the seafloor can become depleted of oxygen and uninhabitable.
Seafloor trawling, in which equipment is pulled across the seafloor to catch bottom-dwelling fish, decreases the biomass and production of benthic species. The practice also destroys corals, oysters, and sponges that form productive marine habitats. Understanding these habitat relationships requires expertise from oceanographers who study seafloor ecosystems.
The impacts of this destruction can be far-reaching. Oyster reefs, for example, have been decimated in many places by trawling. Without these essential filter feeders, coastal waters can suffer from eutrophication, in which nutrients are present in excess. This, in turn, triggers harmful algal blooms that can lead to widespread die-offs of marine life.
In tropical regions, especially in Southeast Asia and Africa, people sometimes employ blast fishing. In this method, fishermen light sticks of dynamite and toss them into the water. The explosion stuns nearby fish and can make their swim bladders rupture, causing them to float to the surface for easy capture.
With up to $2,000 worth of fish caught from a single blast, the practice can be lucrative for fishermen, but it also destroys coral reef habitat. Like oyster beds, coral reefs are productive habitats that serve as nurseries for many fish. With these essential developmental habitats gone, stocks of many fish species can rapidly decline.
Many of these species are also commercially valuable, so although the short-term payoff is significant, the practice can actually be harmful to fishermen in the long run. Furthermore, people lose valuable ecosystem services provided by coral reefs, such as coastal protection and tourism revenue.
Derelict Fishing Gear
Some kinds of fishing gear can be even more destructive when they become lost or forgotten in the water because they continue to catch animals, a phenomenon known as "ghost fishing." This is particularly wasteful and destructive because the gear can ensnare tons of animals that aren't being harvested or otherwise used.
Fishing piers can be sites of ghost fishing, as lures and lines become wrapped around pilings, trapping animals swimming by. Fish aren't the only victims, however. Birds that dive into the water for prey can also get caught in the lines when they enter the water.
Diamondback terrapins provide a case study of how ghost fishing can impact animal populations. These turtles inhabit salt marshes along the East Coast,t where people also fish for blue crabs. Blue crabs are caught using a crab pot, a metal cage that's dropped to the floor of the marsh and tied to a buoy that floats along the surface.
If the buoy becomes detached, fishermen may not be able to find the gear, and it becomes a "ghost pot." Crab pots have tiny openings that allow crabs to enter but are designed to make it difficult for them to get back out. Terrapins also swim into the pots, attracted by the bait in the middle.
Because they're social animals, when several turtles are in a pot, it often attracts more turtles, leading the ghost pot to catch more and more turtles over time. A single ghost pot was discovered in Georgia that contained more than 130 deceased turtles. This fishing gear is thought to pose a significant threat to many populations of diamondback terrapin.
In addition to direct mortality, ghost pots can also alter population demographics. This is because female terrapins are larger than males, and females often can't fit into the openings in crab pots. As a result, the pots trap males and younger turtles at higher rates, shifting the population toward older turtles and females. This biased sex ratio, along with the removal of many individuals before they reach sexual maturity, can further worsen declines already faced by these populations.
Bycatch
While many fishing practices can be extremely good at harvesting fish, they also often incidentally catch non-target species, known as bycatch. Longline fishing is a major contributor to bycatch. This practice is usually employed in the open ocean and consists of miles of lines, on which thousands of baited hooks are attached. A single long line can have more than 2,500 hooks.
Sea turtles are especially prone to being caught in longlines because they must reach the ocean surface to breathe. When they take the bait on the lines, the hooks lodge in their mouths, and they drown because they can't reach the surface. Even when they're not attracted to the bait, some turtles are so large that the lines can wrap around their flippers as they swim through them.
Marine mammals often become trapped in the lines as well. The bait attracts birds like albatross that fly over the open seas as the lines are put into the water. Once hooked on the line, they're ensnared in the gear and soon drown.
Other fishing practices can also incur significant amounts of bycatch. Trawling can drown turtles that get caught in nets. Gillnets are staked to the ocean floor and unintentionally entrap many animals. The collective toll from these practices is staggering.
Over the past twenty years, an estimated 85,000 sea turtles have been killed as bycatch. Additionally, an estimated 300,000 marine mammals, 160,000 albatross, and 3 million sharks are lost to bycatch from fishing practices each year. This high mortality rate isn't sustainable for these animal populations.
Animals like albatrosses and sea turtles, which are long-lived and slow to reach maturity, are particularly affected by these threats, and many populations have declined precipitously over the past few decades. Fishery managers now implement strict regulations requiring the use of bycatch reduction devices in many commercial fisheries.
As with other impacts of fishing, the consequences of bycatch are often far-reaching, as species become functionally extinct in many areas. For example, leatherback turtles help control jellyfish populations by consuming hundreds of them daily. With their major predators gone, there have been jellyfish population booms in some parts of the ocean.
This has made the waters dangerous for swimmers in some places that rely on tourism for revenue and can also prevent the recovery of depleted fish stocks. Green sea turtles and manatees, which are commonly caught in bycatch, also illustrate the ecological complexities that can result from the removal of key functional species.
These animals are herbivores that graze in seagrass beds. In these habitats, they're essential because their constant grazing keeps the grass at a healthy level, supports nutrient cycling, and prevents disease outbreaks from spreading through the grass beds. Without these grazers, many seagrass ecosystems have suffered from large seagrass die-offs. When this happens, biodiversity declines as these habitats can no longer support a wide range of marine life.
Solutions
Here's where it gets hopeful: In recent years, the consequences of fishing have become a growing focus of research. Much of this has been prompted by the collapse of commercially valuable fisheries and the threat of extinction to many animals. Marine and fisheries biologists have developed several innovative approaches to reduce the environmental impact of fishing.
For some species, such as bluefish and flounder in the mid-Atlantic, implementing catch limits has been successful in restoring depleted stocks. For other species, such as the Atlantic cod, however, such regulations haven't resulted in a rebound in the population. In these instances, factors such as rising water temperature may inhibit recovery.
Research has also focused on new fishing methods that are less destructive. For example, studies on diver harvesting of oysters showed that the technique was less damaging to reef structure than traditional methods such as dredging. Whereas the latter method indiscriminately harvests all oysters, including those that are dead on the reef, diver harvesting is more selective and collects only those that are commercially valuable. The practice was also shown to increase the number of oysters harvested per unit of fishing time.
There has likewise been much investigation into techniques that reduce fisheries bycatch. For example, studies on longline hooks have shown that specific hooks don't get stuck in sea turtles' mouths, reducing their risk of capture. Acoustic pingers on fishing vessels have been shown to deter marine mammals and reduce their bycatch rates in the California drift gill net fishery.
Swordfish longline fisheries employ lights to attract fish, but they also attract leatherback turtles. Research on turtle light perception has shown that specific light frequencies aren't visible to turtles, but are still attractive to swordfish. This offers a mechanism to reduce bycatch without affecting the catch of target species.
For crab pots, bycatch reduction devices are tiny plastic rings that are attached to the openings. These make the openings smaller, allowing blue crabs to get in while keeping terrapins out.
One of the largest success stories in bycatch reduction has been the use of turtle excluder devices (TEDs) on shrimp trawlers. In the Gulf of Mexico, bycatch of Kemp's ridley turtles by shrimp trawlers was cited as a significant factor in the species' decline. The TED is a large grate that's attached to the inside of the net, and an opening in the net is placed next to it.
Shrimp can easily pass through the grate, but turtles can't. When they come into contact with the grate, the opening in the net provides an escape route, and the turtle can leave the net unscathed. Studies show TEDs have reduced sea turtle bycatch by up to 97% in some cases, contributing to the recovery of Kemp's ridley in the Gulf of Mexico. These avenues of research offer solutions that can mitigate the harmful environmental consequences of fishing and enable more environmentally friendly fishing practices in the future.
Frequently Asked Questions
What is the most significant environmental problem with commercial fishing?
Overfishing represents the most immediate threat, with industrial fishing removing fish faster than populations can naturally replenish. The Atlantic cod collapse demonstrates how quickly abundant species can be decimated-populations declined over 90% in some areas within decades once new technology enabled deeper, faster fishing. This doesn't just reduce fish numbers. It triggers trophic cascades that fundamentally alter ocean food webs.
How does bycatch affect ocean ecosystems?
Bycatch kills an estimated 85,000 sea turtles, 300,000 marine mammals, and 3 million sharks annually as unintended fishing casualties. Since many of these species are long-lived and reproduce slowly, bycatch rates exceed what populations can sustain. When removed from ecosystems, these animals can no longer perform their ecological roles-leatherback turtles stop controlling jellyfish populations, and green sea turtles can't graze seagrass beds, leading to further ecosystem degradation.
What is ghost fishing?
Ghost fishing occurs when lost or abandoned fishing gear continues capturing and killing marine animals indefinitely. Crab pots, nets, and fishing lines trap animals that can't escape, even when no fishermen are present. A single ghost crab pot found in Georgia contained more than 130 dead diamondback terrapins, illustrating how destructive derelict gear can become over time. This represents pure waste since trapped animals serve no purpose.
Can fishing ever be sustainable?
Yes, with proper management and technology. Catch limits successfully restored bluefish and flounder populations in the mid-Atlantic. Turtle excluder devices (TEDs) in shrimp trawlers reduced sea turtle bycatch by up to 97% in some studies, contributing to Kemp's ridley recovery in the Gulf of Mexico. Specialized hooks, acoustic deterrents, and selective lighting can dramatically reduce bycatch while maintaining commercial catches. The key is implementing these solutions consistently across all fisheries.
How do fishing practices destroy ocean habitats?
Bottom trawling and dredging physically damage seafloor ecosystems by churning sediments, removing burrowing organisms, and destroying structural habitats such as oyster reefs and coral reefs. Blast fishing in tropical regions, especially in Southeast Asia and Africa, uses dynamite to stun fish but also obliterates coral reef habitat-the very nurseries that support future fish populations. Without these productive habitats, many commercially valuable species can't reproduce successfully, creating a self-destructive cycle.
Key Takeaways
- Overfishing drives extinctions: Atlantic cod populations crashed by more than 90% in some areas after new fishing technology enabled unprecedented harvest rates, fundamentally altering North Atlantic food webs.
- Habitat destruction reaches beyond target species: Bottom trawling and dredging damage seafloor ecosystems that support countless marine species, including crucial oyster reefs and coral nurseries.
- Ghost gear kills long after abandonment: Lost fishing equipment continues trapping and killing marine animals for years, with single ghost crab pots documented containing over 130 deceased turtles.
- Bycatch threatens vulnerable species: An estimated 85,000 sea turtles, 300,000 marine mammals, and 3 million sharks are killed annually as unintended fishing casualties, impacting slow-breeding populations most severely.
- Solutions exist and work: Turtle excluder devices reduced sea turtle bycatch by up to 97% in some studies, demonstrating that technology and regulation can enable sustainable fishing while protecting ocean ecosystems.
Want to explore careers protecting ocean ecosystems? Marine biologists, fisheries managers, and conservation scientists work on solutions to these fishing challenges every day.
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