Above: Blacktip reef shark.
The ocean is salty from the tears of misunderstood sharks.
Ever since the film Jaws came out in 1975, sharks have had a bad reputation; this mega-hit film series invoked a sense of fear in beach-goers and caused a shark-horror tend in Hollywood. The irony of this fear is that we as a human race do far more damage to shark populations across the globe than they could ever do to us.
The shark fishing industry is still rife, particularly in Asia where the cartilage in shark fins is shredded and made into shark fin soup, a delicacy thought to represent good fortune and high status. The demand for this luxury item has increased since the late 1980’s, and has led to sharks being targeted heavily by fisheries in recent decades.
Obtaining shark fins involves cutting them off often while the animal is still alive. Since there is no value of shark meat to the fishermen, the rest of the shark’s body is discarded at sea. This cruel practice offers short-term economic gain for fishermen, but most earn very little compared to fin traders higher up the chain. Hence, this practice is not only ecologically but also economically unsustainable.
Shockingly, around 100 million sharks are killed every year for their fins and most sharks are expected to become extinct in the next few decades thanks to over-fishing. Arguably, this industry represents the biggest threat to shark populations worldwide.
Science is helping to understand the fin trade in more detail. Molecular genetic tools are being used to ID shark species from their fins alone. Tissue samples are taken, DNA extracted and sequenced and analysis performed. These ID studies have proven to be vital in understanding how the fishing industry is contributing to the decline of different shark species.
For example, a 2006 study that analysed species composition in the Hong Kong shark fin marked found that up to 45% of the Hong Kong trade is composed of only 14 shark species. They also found that blue sharks formed a particularly large component of the market; this species is listed as near threatened on the IUCN red list, so such a finding has strong conservation implications.
Above: Blue shark. Image source: http://www.iucnredlist.org/details/39381/0
But what are the ecological impacts of shark decline? The short answer: nobody knows for sure. However, there are some strong theories.
Sharks and other elasmobranchs are top predators in the food chain, meaning they control the populations of their prey. This ‘top-down’ control maintains the balance of the ecosystem; sharks have been shown to control species composition in many ecologically important habitats, including coral reefs.
Image source: https://www.infographicsarchive.com/environment/sharks-count-why-its-important-to-save-sharks/
Hence, the loss of sharks is likely to be far-reaching. Loss of predation has shown to cause ‘trophic cascades’; reduced predation by sharks reduces mortality rates in prey species, causing changes in the abundance, distribution, and even the behaviour of small elasmobranchs, marine mammals, and sea turtles that have few other predators. These trophic cascades cause a ‘downgrading’ of the ecosystem, as overall biodiversity decreases.
Not all doom and gloom?
Thanks to increased public awareness and scientific data, there have been heavier regulations placed on the shark fin trade in recent years. In 2013, EU regulations were strengthened such that a shark could only be landed with its fins attached. Other countries, such as the Bahamas, Egypt, French Polynesia, Israel, Fiji, Maldives, Tokelau, Palau and many more have banned shark fishing altogether.
There is, however, still a long way to go. This industry still continues and, coupled with habitat degradation, sharks are now more threatened than any other vertebrate group.
Please, if you are offered shark fin soup- DON’T EAT IT!
S. C. Clarke et al., 2006. Identification of Shark Species Composition and Proportion in the Hong Kong Shark Fin Market Based on Molecular Genetics and Trade Records. Conservation Biology. 20(1).
F. Ferretti et al., 2010. Patterns and ecosystem consequences of shark declines in the ocean. Ecology letters. 13: 1055-1071
Heupel et al., 2014. Sizing up the ecological role of sharks as predators. Marine Ecology Progress Series. DOI: https://doi.org/10.3354/meps10597
Shark Savers. http://www.sharksavers.org/en/our-programs/shark-sanctuaries/learn-more/laws-protecting-sharks [accessed 16/05/18].