#CreatureFeature – Selachimorpha (Shark)

Just like orcas and big cats, sharks are apex predators. Sleek, perfectly hydrodynamic and accomplished hunters after 450 million years of evolution, they are majestic and rightly fearsome creatures. Yet underappreciated, and unjustly villianised by mainstream media, a lack of love and overexploitation of sharks has led to over a quarter of shark and ray species becoming imperiled with the vortex of extinction.

Sharks maintain ecological function and balance in the marine world. In the pelagic zone, their predation on fish effectively prevents the depletion of phytoplankton, which are responsible for producing 70% of the world’s oxygen. In the Shark Bay World Heritage Area, which boasts the planet’s most extensive and healthy seagrass meadows, roaming tiger sharks scare dugongs and sea turtles. This keeps the herbivores moving onto different patches, essentially protecting each seagrass bed from overgrazing. When the 2011 marine heat wave killed off 25% of Shark Bay’s meadows – and up to 90% in some smaller areas, it was the sharks that assisted ecosystem restoration. Recently, a study by the Florida International University, the University of Washington, and Deakin University determined that, by moving on dugongs and turtles, the tiger sharks not only encouraged seagrass bed reestablishment, they also prevented degradation that would eventually cause the grazers to starve themselves. This also protects habitat of other creatures living in the seagrass, such as snapper and squid, which are commercially and recreationally valuable to humans too. Without sharks, the ecosystem would lose resilience.

However, we haven’t exactly treated our oceanic guardians with due respect. The International Union on the Conservation of Nature (IUCN) has listed at least 25% of all known sharks and rays as threatened. Here in WA, our very own Grey Nurse Shark (or Sand Tiger) is critically endangered, whilst Scalloped Hammerheads and Whale sharks are endangered. Great White and Dusky sharks are vulnerable, and Tiger sharks are near-threatened. Sharks can take 13-30 years to become sexually mature, meaning that they are slow to recover from population crashes. Some have declined by 99% in the last 30 years alone.

In Australia, the capture of sharks as bycatch in the wild-caught tuna industry is the main threat. However, worldwide illegal/unreported/unregulated fishing activities, shark finning, overfishing, bycatch, pollution, entanglement in marine debris, habitat degradation and climate change are threatening shark populations. Additional pressures are shark-control actions like culling, shark nets and drumlines. Behind this is demand for shark meat (sold as flake in fish and chip shops), shark liver oil for cosmetics, sunscreen and pseudo-vitamin supplements, and fishmeal for feeding to intensively farmed animals and aquaculture fish. Of course, there is also the international demand for shark fin soup.

Sharks have seen through five mass extinctions. This one – the sixth – is caused by humans. We can save sharks, and they in turn can help us look after the natural ecosystems upon which we depend.

Here’s a few things you can do to help look after our sharks:

  • Spread awareness of how awesome they are, what’s threatening them, and why they are worth protecting. You can also join a shark or marine conservation group. Advocate for stronger legal protection of sharks.
  • Are you a diver? Show people footage of your shark encounters so they can see how peaceful they can be.
  • Avoid eating flake, and intensively-farmed animals, including fish. Eat sustainably-sourced seafood caught locally, and species lower in the food web such as anchovies and whiting.  As they are at the top of the food chain, sharks accumulate toxins, microplastics and mercury in their flesh, which can be harmful if eaten.
  • Find alternatives for cosmetics, sunscreens and supplements that contain squalene (shark liver oil).

References

Shark Conservation Australia – https://www.sharkconservation.org.au/

https://www.theguardian.com/environment/2021/mar/22/sharks-critical-restoring-climate-damaged-ecosystems-study

Kahree Garnaut – Biodiversity Project Officer

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