Impact

The Issue of Ghost Net – Sharks Get Entangled in Plastic Waste

A video released by the Smithsonian Channel shows a diver trying to release a whale shark that has become trapped in fishing gear. 

Sharks are being threatened by ghost fishing everywhere in the world’s oceans (Colmenero et al. 2017). It has been reported that 16 kinds of sharks are often entangled in fishing gear, and 88% of them are categorized as being either endangered or nearly endangered species (Colmenero et al. 2017).

Fishing nets and fishing lines that have been deliberately or accidentally released into the ocean are called ghost nets and are one of the main sources of marine debris (UNEP & GRID-Arendal 2016).

Around less than 10% of the total marine waste is considered a ghost net (Macfadyen et al. 2009); however, issues that are being created by ghost nets are rapidly increasing, especially in the past few decades. This has happened due to the widespread expansion of fisheries and fishing grounds.

Plastics are inexpensive and lightweight but also durable and strong. Notwithstanding these great advantages, plastics are one of the most dangerous materials for the ocean environment (Laist 1997).

Because these fishing nets and fishing lines are made of plastic they are very strong, and once marine animals get entangled, they cannot easily be freed (Kühn et al. 2015).

Dusky sharks living around coastal areas are the species of shark most frequently entangled in the ghost net (Laist 1997, Colmenero et al. 2017).

It has been reported that a blue shark was entangled in plastic straps in the Mediterranean Sea. These plastic straps were obstructing the shark’s gill slits and probably caused breathing issues (Colmenero et al. 2017). The same kind of issue has also happened in the Atlantic Ocean, where a blue shark was entangled in some plastic packing string for packing, wrapped around its gills (Colmenero et al. 2017).

Sharks tend to be captured by ghost nets when these are floating on the ocean’s surface (Bird 1978) because sharks often try to get closer to figure out what it is when they come across an unknown object. It is in their nature to check out whatever they find floating in the water, but this has led to an increase in the risk of sharks becoming entangled in ghost nets (Colmenero et al. 2017).

If there are small fish dwelling in the ghost net, then predatory animals, such as sharks, are more likely to become tangled there (Cliff et al. 2002, Tschernij & Larsson 2003).

Once sharks are entangled in plastic lines, these lines will deprive their ability to eat and do branchial respiration (Sazima et al. 2002).

Researchers have found that some sharks’ spines have become deformed due to plastic strings being tangled around them for a long time. Sharks are also unable to grow up healthily when the strapping bands have become entangled around their body (Sazima et al. 2002).

Furthermore, when large quantities of periphyton, such as rock barnacles, adhere to the fishing gear, this disturbs the efficiency of the sharks’ swimming, reducing their speed as well as severely affecting their ability to turn (Wegner & Cartamil 2012).

Even though sharks are often badly injured or killed by ghost nets, scientists have still not been able to clearly establish the actual effect of ghost fishing and its influence on the decrease in shark populations (Cliff et al. 2002).

Nevertheless, scientists are concerned that because sharks are a keystone species in the marine environment and are at the top of the food web, if their population is reduced, this may lead to unexpected results that can negatively affect the marine ecosystem (Barría et al. 2015).

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