Bronte Wells
Sharks are an ancient group of creatures that have existed for over 400 million years, outliving the dinosaurs. Unfortunately, their survival is now threatened by human activities. While overfishing is the primary driver of shark extinction, pollution also plays a significant role. The degradation of coastal, estuarine, and riverine habitats threatens shark populations. Pollution, along with residential and commercial development, mangrove destruction, dam construction, and water control, has put 14% of sharks and rays at risk of extinction. The combination of overfishing, accidental bycatch, habitat loss, and pollution has put one-third of all shark species in danger of extinction.
| Characteristics | Values |
|---|---|
| Sharks that have gone extinct | Lost shark (Carcharhinus obsoletus), Java Stingaree (Urolophus javanicus), and Red Sea Torpedo (Torpedo suessi) |
| Reason for extinction | Overfishing, bycatch, habitat loss, and pollution |
| Sharks at risk of extinction | Hammerhead shark, oceanic whitetip, Great hammerhead (Sphyrna mokarran), Basking shark (Cetorhinus maximus), Sand tiger shark (Carcharias taurus), angel shark, giant manta ray (Mobula birostris) |
| Threats to sharks | Overfishing, habitat degradation, persecution due to fear, marine pollutants (microplastics, agricultural runoff, fishing debris, man-made chemicals), climate change, warming waters |
| Impact of shark extinction | Loss of keystone species, ripple effect on the ecosystem, trophic cascade, loss of tourism revenue |
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What You'll Learn
Overfishing and accidental bycatch
Overfishing is the primary driver of shark extinction, with one in four chondrichthyan species threatened, according to a systematic analysis. Chondrichthyans include sharks, rays, and chimaeras. The analysis reveals that overfishing, whether targeted or accidental, poses a significant risk to these species.
Sharks are particularly vulnerable to overfishing due to their slow growth, late maturity, and low reproductive rates. This makes it challenging for them to recover from population depletion. The 'fin trade' further exacerbates the issue, as the fins of sharks are highly valued in some Asian countries. As a result, more than half of the chondrichthyans involved in the fin trade are under threat.
Accidental bycatch is a significant contributor to shark mortality. Commercial fishing nets often unintentionally trap fast-moving shark species like hammerheads and whitetips, leading to their accidental capture and death. Bycatch kills approximately 100 million sharks annually, highlighting the severity of this issue.
The Lost shark (Carcharhinus obsoletus), last recorded in 1934, and the Ganges shark, once found in Pakistan, Myanmar, and Borneo, have likely become extinct due to heavy fishing pressure. The oceanic whitetip shark, once abundant in the open ocean, is now among the most threatened species due to the failure of regional fisheries management organizations to address its decline.
To address these issues, urgent measures are needed, including improved management of fisheries, science-based limits on fishing, effective marine protected areas, and approaches to reduce or eliminate fishing-related mortality. These steps are crucial to prevent further extinctions and ensure the sustainability of shark populations and the ecosystems they support.
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Habitat loss and degradation
Sharks are keystone species that play a crucial role in maintaining the health of marine ecosystems. They are an important part of our ecosystem, and many of them are seriously endangered. The degradation of coastal, estuarine, and riverine habitats threatens 14% of sharks and rays.
Freshwater sharks and rays suffer multiple threats and have narrow geographic distributions. For example, the Endangered Roughnose stingray (Pastinachus solocirostris) is found only in Malaysian Borneo and parts of Indonesia. The Ganges shark is quite an unusual species as it relies on tropical river and estuarine habitats. Unfortunately, this has made it susceptible to fishing pressure and the modification and degradation of its habitat, and experts now believe it to be locally extinct in Pakistan, Myanmar, and Borneo, with continued declines in other parts of its range in the Indo-West Pacific.
Habitat loss is a significant problem for shark populations, especially those that rely on coastal habitats like mangroves, kelp forests, and reef systems. These habitats are important feeding and nursing grounds for baby sharks and rays, providing safety and shelter from predators. Reef ecosystems are particularly vulnerable right now, as they are under threat from ocean plastic, pollution, and mass tourism. While bycatch, overfishing, and ocean pollutants have the most direct impact, these problems are exacerbated by inactivity and a lack of shark protection policies.
The degradation of coastal habitats also threatens shark populations. This includes residential and commercial development, mangrove destruction for shrimp farming in Southeast Asia, dam construction, and water control. These activities can destroy important feeding and nursing grounds for sharks and rays, as well as alter water flow and quality, making it unsuitable for these species to survive.
Overall, habitat loss and degradation pose a considerable threat to shark populations, especially when combined with other factors such as overfishing, pollution, and climate change. It is important to address these issues through improved management of fisheries, trade, and conservation efforts to ensure the long-term survival of shark species.
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Ocean plastic and pollution
Plastic in the ocean comes from a variety of land and ocean-based sources. Rivers are a significant pathway for plastic to reach the ocean, with coastal cities in middle-income countries being the world's plastic emissions hotspots. During storms and heavy rain events, plastic emissions can increase as trash is washed into waterways. Once in the ocean, plastic accumulates in huge subtropical oceanic areas called gyres, which are massive circular currents that trap floating plastic for decades or even centuries. The Great Pacific Garbage Patch, located between Hawaii and California, is one such gyre and is estimated to be twice the size of Texas.
Plastic pollution has a direct and deadly impact on marine life. Marine animals, such as sea turtles, seabirds, seals, and other mammals, can ingest plastic or become entangled in it, leading to injury or death. For example, sea turtles can mistake floating plastic for food, choke on it, or experience internal injuries. Additionally, plastic can absorb harmful pollutants like pesticides, dyes, and flame retardants, further endangering marine life that ingests it.
Sharks are particularly vulnerable to the effects of ocean pollution, including plastic pollution. While overfishing and habitat degradation are the primary drivers of shark extinction risk, pollution exacerbates these problems. The Lost Shark (Carcharhinus obsoletus), Java Stingaree (Urolophus javanicus), and Red Sea Torpedo (Torpedo suessi) are believed to have gone extinct, with overfishing and pollution playing a significant role in their decline. The Ganges shark, which relies on tropical river and estuarine habitats, has also suffered from fishing pressure and habitat modification, leading to its local extinction in Pakistan, Myanmar, and Borneo.
To address the issue of ocean plastic and pollution, urgent action is needed. The Center for Biological Diversity has petitioned the U.S. Environmental Protection Agency to regulate plastics as pollutants under the Clean Water Act. Reducing plastic consumption, improving waste management practices, and participating in local clean-up efforts are also crucial steps in mitigating the impact of plastic pollution on our oceans and the vulnerable species that inhabit them.
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Warming waters and climate change
While overfishing, bycatch, and habitat loss are the most frequently cited causes of shark extinction, climate change and warming waters also play a significant role in the decline of shark populations.
Waters around the world are warming due to climate change, and this has several detrimental effects on shark populations. Firstly, warmer waters can lead to changes in the salinity and acidity of the oceans, which can impact all sea life. Many fish cannot tolerate fresh water, so a decrease in ocean salinity can disrupt their delicate physiology. Similarly, a change in acidity can hinder the formation and growth of marine organisms, affecting marine habitats and the food chain. Sharks may be left searching for a dwindling food supply, and without them as apex predators, the entire ocean ecosystem could become imbalanced.
Secondly, warming waters can cause sharks and other marine species to migrate to find suitable habitats, altering their distribution and potentially leading to competition with other species. For example, the waters around Britain are now warm enough for hammerheads, great whites, and blacktips to travel farther north than ever before.
According to the International Union for Conservation of Nature (IUCN), climate change is a threat to 10.2% of shark species. While this is not the primary cause of shark extinctions, it is a contributing factor that interacts with other threats such as overfishing and pollution.
Sharks have evolved over millennia to live in nearly every part of our oceans and have become an invaluable part of the ocean ecosystem. Their loss would have far-reaching consequences. As keystone species, they play a crucial role in maintaining the health of marine environments. Their extinction would result in irreversible changes to our planet and our oceans.
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Lack of protection policies
While overfishing, bycatch, and habitat degradation are the most significant contributors to the extinction of shark species, the lack of protective policies exacerbates the problem.
Sharks are keystone species, meaning they play a crucial role in maintaining the health of marine ecosystems. They help control the populations of the species below them in the food chain and maintain seagrass and coral reef habitats. The disappearance of sharks would create a ripple effect, impacting the entire ecosystem and potentially leading to mass extinctions.
Despite regulations such as the 2010 Shark Conservation Act, which prohibits finning, and the establishment of 'shark sanctuaries' in certain areas, shark mortality rates remain high. Regional Fisheries Management Organizations (RFMOs) have failed to adequately address the decline in shark populations. The lack of effective management and enforcement of existing regulations has contributed to the ongoing threat to shark species.
The complex interplay of various threats, including overfishing, habitat degradation, and pollution, calls for comprehensive protection policies. However, the inactivity and lack of specific shark protection policies have left shark populations vulnerable.
To effectively protect sharks, governments and organizations must implement a combination of well-enforced catch limits, prohibitions on catching threatened species, and critical habitat protection. Science-based limits on fishing, effective marine protected areas, and approaches to reduce or eliminate fishing mortality are urgently needed. Additionally, addressing the root causes of pollution and climate change is essential to mitigate their impacts on shark populations.
While some species have recovered due to successful conservation efforts, such as the Barndoor skate (Dipturus laevis), the lack of comprehensive and enforced protection policies for sharks continues to threaten their existence.
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Frequently asked questions
The main causes of shark extinctions are overfishing, habitat degradation, and ocean pollution. Overfishing is the universal threat affecting all threatened shark species.
Pollution chokes the oceans and affects all sea life. A marine biologist in South Carolina found a sandbar shark entangled in plastic twine. There have been over a thousand cases of sharks and rays becoming tangled in plastic debris.
The Lost shark (Carcharhinus obsoletus), Java Stingaree (Urolophus javanicus), and Red Sea Torpedo (Torpedo suessi) have not been recorded for over 80 years and are believed to be extinct due to overfishing. However, it is difficult to attribute their extinction solely to pollution.
