It’s no doubt that one of the greatest threats facing marine biodiversity is overfishing, but why can overfishing lead to ecosystem collapse?
The term “overfishing” refers to catching more fish from a population than nature can replenish.
When the number of fish being taken out of the ocean begins to exceed their natural reproduction rates, the delicate balance in the ocean’s food web will begin to break down. This can result in a loss of marine life that depends on other animal species for survival, including vulnerable reptiles and reef-building corals.
A Broad Definition of an Ecosystem
Ecosystems are habitats where many living and nonliving things interact with one another.
For example, plants, fish, animals, the environment, and weather interact to form an autonomous community in an ocean.
All the organisms in an ecosystem depend on one another, either directly or indirectly. The various members of an ecosystem are interconnected in many ways.
For example, a drastic change in fish population may affect what animals can survive there and the plants that will grow there.
Types Ecosystems Affected by Overfishing
After defining overfishing and ecosystems, it’s important to know which types of ecosystems are affected the most by overfishing.
The effects of overfishing are vast and can be divided into various ecosystems as follows:
Marine Food Webs
Overfishing has already done considerable damage to oceans, with dire consequences for marine life and restructuring major food chains.
Commercial, industrial and recreational fisheries take too many large individuals of higher trophic levels and high-value fish out of the ecosystem at any given time.
As a result, the marine ecosystem services (such as the provision of food and materials to coastal communities) are affected.
The results of overfishing can include:
- The depletion of a population.
- A decrease in the number of species that can be caught.
- The loss of the species itself.
- A decrease in the overall biomass in an area.
Note: Some species distribution and abundance changes may cause local extinctions, redistributing marine composition and its biodiversity.
Marine Habitat Degradation
Overfishing has led to the degradation of important habitats for certain species, including bottom trawling’s destruction of coral reefs and runoff pollution from fish farms.
Large-scale trawling also dumps pollutants such as oil and plastic in various oceanic ecosystems.
Furthermore, consuming seafood that was caught using destructive fishing gear or that has been marred by pollution may affect the environment.
If habitat loss continues at its current rate, marine life will be affected. But this will also mean the decline of coral reefs, and the oceans’ ability to sequester carbon will be reduced.
Increased Carbon Emissions by the Fishing Sector
Currently, the seas and oceans are awash with fishing vessels. The Food and Agriculture Organization estimates that there are currently 4.6 million fishing vessels of various sizes.
Researchers estimate that the capacity and effort being used to catch fish today is between 40 and 60 percent above what is needed to do so sustainably.
Fishing vessels are responsible for more than 1% of carbon dioxide globally, which affects us all.
Fewer fishing vessels chasing fish in the ocean can mean that the fishing sector could cut its emissions by more than half, mitigating climate change.
Fact: If fishing trawlers are standardized for sustainability, it could mitigate their fossil fuel emissions.
Reduced Carbon Dioxide Sequestration by Marine Life
The oceans play an important role in maintaining the balance of carbon by capturing carbon dioxide from the atmosphere and storing it as carbonates and bicarbonates.
Overfishing drastically disrupts this process.
A Solution to Climate Change
Therefore, when figuring out why can overfishing lead to ecosystem collapse, it’s crucial to understand that the tragic effects go well beyond the oceans and seas.
An increase in fish populations within the oceans can help fight ecological problems like global warming, coastal erosion, and other detrimental effects of climate change.
Fact: Approximately 38,000 Gigatons of carbon is trapped by the earth’s oceans, with an additional 6,000 Gigatons in marine sediments.
Ghost Fishing And Gear Loss
“Ghost fishing” refers to lost or discarded nets, traps, and lines that continue to fish without human intervention.
Such gear can continue to fish for months or even years, harming marine life and potentially causing damage to equipment and other fixed structures.
Gear discarded in the ocean can cause harm to multiple species, including some previously-unaffected groups such as sea birds, marine mammals, and turtles.
For example, the number of northern right whales entangled in fishing lines increased significantly after 1980, when ghost fishing began affecting their feeding grounds.
Note: It is unclear exactly how much ghost fishing has on marine ecosystems, but some studies indicate that it is not insignificant.
Bycatch, Discards, and Poor Selectivity
When analyzing what problems does overfishing cause, perhaps the most impactful one is overfishing creates bycatch and discards.
It is unlikely that fishing activity will ever be sufficiently selective to remove only the targeted fish from the ocean.
Unintentional catch of other oceanic species, including endangered ones, results in a bycatch. In most cases, some bycatch can be gutted or discarded together with offal from processing needed fish at sea.
The result is increased food availability for scavenging species such as sea birds. Over time, this can cause oxygen levels in the seabed to decrease and anoxia to set in.
Effects on Dependent Species
The Law of the Sea includes provisions for conserving the fish in a particular fishery and the marine habitat in which it lives and any dependent or related species.
When primary consumers (such as zooplankton) in the lower levels of an ecosystem (the chain) are removed, they take the animals that feed on them and remove important food sources for larger animals further up the food chain.
Take the case of endangered sharks and batoid fishes due to overfishing. They are predators located at or near the top of marine food webs.
Their depletion can significantly impact the intricate trophic interactions that occur in their ecosystems.
Other Effects of Overfishing on Ecosystems
Growth of Algae
Algae are vital for marine life; green algae help fish thrive and grow in controlled amounts.
If it is allowed to grow out of control, it can cause problems for marine life, causing reefs to deteriorate and making fish sick and even die.
When practicing aquaculture, it is essential to have both the proper instruments and the knowledge necessary to establish a proper ecological balance in the water bodies.
For example, the lack of information about eel life cycles and interactions with other organisms has led to aquaculture procedures that upset the balance in the oceans.
Solutions to Overfishing
Helping Developing Countries
In many poor, developing nations, fishing is an important economic activity.
Conservation efforts should focus on developed nations but also be helping these areas develop sustainable practices for the long term.
Conservationists should start working with retailers to provide them with information on the sustainability of their seafood suppliers.
The aim is to pressure fisheries to comply with the standards by building support for the cause.
Farming fish can be carried out sustainably and beneficially to the environment.
Researchers have successfully created sustainable fisheries by practicing catch-and-release with frequently overfished species, such as arctic char and bass.
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Overfishing can be attributed to four main causes besides illegal and unregulated fishing: economic needs, fisheries management, and sustainable fishing.
Therefore, just as it’s crucial to know why can overfishing lead to ecosystem collapse, it’s also equally important to tackle the causes of overfishing.
There are several international conservation groups working to standardize sustainable fishing techniques, thus ensuring the future viability of capture fisheries.
It’s, however, necessary to tackle overfishing from a policy standpoint through the relevant legislative and government channels for lasting solutions.