• SharkieSophie

Threats to the fin

Updated: Apr 23

You might imagine that sharks are indestructible; those intimidating teeth, the incredible speed, their ability to survive in the cold, dark, high pressure environment of the deepest oceans. However, in reality, sharks are extremely vulnerable to many anthropogenic threats and are declining globally to a shocking degree.


Image source: www.huffingtonpost.com.

Sharks have been around for over 400 million years, but over the past decades, their populations have declined globally by as much as 70%. Some species of sharks are now threatened with extinction within our lifetimes and more species are added to the red list of “threatened” species every year (IUCN, 2020). To give you some examples, such iconic species as the hammerheads (Sphyrna lewini and Sphyrna mokarran) are now considered “critically endangered”, the beautiful whale (Rhinocodon typus) and basking sharks (Cetorhinus maximus) are both classified as “endangered”, and even the magnificent great white (Carcharodon carcharias) is classified as “vulnerable”(IUCN, 2020).

Image source: Bland et al, 2020.

Sharks are affected by multiple anthropogenic threats, which can be broadly defined into two categories: habitat degradation and overexploitation in fisheries.


Sharks are Extracted Unsustainably in Fisheries

In regards to fisheries, sharks are both the target of fisheries and are also killed as “bycatch” in fisheries targeting other species. Sharks have been targeted since the 1960s for many products, including their meat, skin, teeth, jaws and liver oil, but are predominantly fished for their fins, which are sold for shark fin soup on the lucrative Asian market (Stevens et al, 2000).


Sharks are also commonly caught as “bycatch”, meaning they are accidentally killed by fishing gear which is being used to fish other species. Many species of sharks which are victims of bycatch are not even particularly commercially valuable. Sometimes sharks caught as bycatch are thrown back in the hopes they survive, but they are also often landed anyway, to be sold as cheap meat.


In total, it is estimated that 830,000 tonnes of sharks and rays are landed by fisheries every year (Lucifora et al, 2011).


As if this wasn't bad enough, many sharks are also killed every year by "ghost nets" - discarded fishing gear left to roam the ocean unsupervised (to learn more, see Ghosts in the ocean) and in beach nets, which are implemented to protected ocean users at bathing beaches.


In total it is thought that as many as 100 million individual sharks are killed by humans beings every single year!



Sharks' Habitats are being Seriously Degraded

In regards to habitat degradation, sharks can be impacted by pollution, ocean acidification and deoxygenation, prey depletion, habitat loss and urbanisation. The habitat can also be degraded by the loss of prey species that sharks depend on, which can be caused by overfishing, pollution or habitat loss. These processes are a particular problem for coastal shark species, which are especially exposed by their close proximity to human activity.


There are many forms of pollution which can be detrimental to sharks. Chemical pollution from industries or oil spills are a serious problem. These accidents can be instantly lethal, but can also cause damage to the health of sharks when they are exposed throughout their lives (to learn more, see Not so Slick). However, a more insidious and potentially huge problem comes in the form of littering and plastic pollution, which can cause death by entanglement, but can also ruin a shark's health, and even cause a slow death by suffocation or starvation (to learn more, read The Worst... Beware of the Plastics!).


Habitats can also be damaged by human activities, such as shipping or dredging. Areas of critical habitat can be entirely lost due to urbanisation and development; with construction work damaging vital underwater structures or reclaiming areas for human use. Even the noise from these activities can also be seriously disruptive to sharks (to learn more about "noise pollution" check out Keep the Noise Down).


Image credit Steve de Neef, Source: www.newsdeeply.com.

Habitat degredation also includes extended, ongoing damage from climate change. For example, climate change-associated ocean acidification, can have physiological effects, which damage the shark's health (to learn more, check out Climate Change, What a Pain in the Gut). Whatsmore, acidification can also erode eggs in “oviparous” (egg-laying) species, meaning populations cannot be bolstered by reproduction (To lean more, you can read Pickled Eggs). Similarly, ocean deoxygenation caused by climate change can change the distribution of certain species of sharks and affect their ability to find prey.


Confounding these issues, is the “life history strategy” employed by sharks. Sharks are described as having a “K-selected life-history strategy” (as opposed to “R-selected”), meaning they have very slow growth and late maturity, reach a large size over a long life-span, and require significant investments for reproduction. This means that, when overexploited to the point that populations are severely depleted, recovery can be incredibly slow, or even impossible.


However, there may be some hope… some light at the end of the tunnel… With growing public awareness and increased pressure generated by public opinion, conservation initiatives designed to protect sharks can gain momentum! It is up to each and every one of us who cares about sharks, to ensure our voices are heard, by supporting conservation and management measures, and demanding sustainability.

References

Bland L, Keith D, Miller R, Murray N & Rodríguez J. (2017). Guidelines for the application of IUCN Red List of Ecosystems Categories and Criteria, version 1.1. 10.2305/IUCN.CH.2016.RLE.3.en.


IUCN (2020). The Red List of Threatened Species. Access online.


Lucifora, L.O., García, V.B. & Worm, B. (2011). Global diversity hotspots and conservation priorities for sharks. PLoS One, 6:5, e19356. Access online.


O’Bryhim JR & Parsons ECM. (2015). Increased knowledge about sharks increases public concern about their conservation. Marine Policy, 56, 43–47. Access online.


Stevens JD, Bonfil R, Dulvy NK & Walker PA (2000). The effects of fishing on sharks, rays and chimaeras (chondrichthyans), and the implications for marine ecosystems. ICES Journal of Marine Science, 57, 476-494. Access online.


By Sophie A. Maycock for SharkSpeak.

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