Feeding a fear: new research on the decline of sharks
400 million years old. Over 1000 species. A crucial keystone animal of the marine world. When I say shark, this is rarely what we associate. Rather, we hear a heart-thumping, two-noted cello tune and palms go clammy as we imagine a razor-toothed, mechanical monster. The 1975 film ‘Jaws’ continues to perpetuate a fear of sharks which shackles folks to the shore but, with new research showing a decline in shark populations, it’s time for us to get our cossies on and learn about our role in protecting them from extinction.
Despite their battered image, sharks are recognised amongst biologists as essential apex predators and up until recently, the majority of our data on sharks was sourced from commercial fisheries, informing of a limited range of species and offshore ecosystems. From this, researchers gathered that shark populations were declining. We just didn’t realise how severely.
Shark fishing has fluctuated throughout history with demand for products such as squalene, a common addition to cosmetics, and shark fin soup, a luxury dish popularised in Imperial China. Despite public exposure of the cruel, wasteful harvesting of fins, current shark fishing remains at 100 million sharks per year (270,000 sharks per day). In addition to fishing pressures, research has shown that sharks are also highly vulnerable to changes in climate including ocean warming and acidification resulting in stunted growth and impaired behaviour, including hunting and food identification. Decline in shark numbers and a reduced ability to hunt have substantial flow-on effects within the food chain. Without apex predators such as sharks, prey experience a population boom which increases demand on smaller fish and vegetation. This is already being observed in the North Atlantic with declines in 11 major shark species, including the scalloped hammerhead. Abundance of cownose rays (an important shark prey species) has swollen so that increased demand on their prey has crashed the 100-year-old North Carolina scallop fishing industry.
So how long until this happens elsewhere? Only recently have coordinated efforts been made to conduct global research specifically to determine the conservation status of sharks. Global Finprint is a marine conservation organisation, funded by Microsoft founder Paul Allen, conducting surveys of marine ecosystems in the Atlantic, Indian Ocean, Western Pacific and Central Pacific. Using baited remote underwater video systems, called BRUVS, they observe marine life for an hour at each location to determine the abundance of sharks (see the mesmerising footage by one of these BRUVS below). Since 2015 they have recorded over 20,000 hours of footage and surveyed 400 reefs in 58 countries. An impressive effort.
The research article Global Finprint released to Nature states that of their 15,000 recordings, 63% did not include sharks. This is particularly concerning since it coincides with 19% of surveyed reefs having no shark sightings, and 59% have a shark abundance lower than expectations. Areas in close proximity to low-socioeconomic human communities were particularly quiet on the shark-front, presumably due to high-intensity fishing and environmental degradation.
This is a sobering realisation for many as we grapple with how vulnerable the ocean’s top dog really is. Current solutions include interventions in shark-fishing communities to switch to shark tourism, creating catch limits for commercial fishing and the development of shark sanctuaries like that in the Bahamas. Ultimately, protecting sharks requires multi-level efforts applying policy, conservation science, NGO’s and community behaviours to prevent overexploitation.
Like many conservation stories, this isn’t going to be easy. But, humans have officially snatched the title of biggest fish in the sea, and that means we must now care for our shark elders.
To support the research that Global Finprint is doing, click here.
References:
Macneil, M., Chapman, D., Heupel, M., Simpfendorfer, C., Heithaus, M., Meekan, M., Harvey, E., Goetze, J., Kiszka, J., Bond, M., Currey-Randall, L., Speed, C., Sherman, C., Rees, M., Udyawer, V., Flowers, K., Clementi, G., Valentin-Albanese, J., Gorham, T., … Angulo-Valdés, J. (2020). Global status and conservation potential of reef sharks. Nature, 583(7818), 801–806. https://doi.org/10.1038/s41586-020-2519-y
Roff, G., Brown, C.J., Priest, M.A.et al. (2018). Decline of coastal apex shark populations over the past half century.Communications Biology 1,223. https://doi-org.ezproxy1.library.usyd.edu.au/10.1038/s42003-018-0233-1
Rosa R, Rummer JL, Munday PL. (2017). Biological responses of sharks to ocean acidification. Biology Letters,13(3):20160796. doi:10.1098/rsbl.2016.0796
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