The theme for this year’s International Day of Forests (21 March) is ‘forests and health’. It provides an opportunity to reflect on the important role that forests play in our lives and whether our national environmental laws, which are currently under review, are doing enough to ensure that future generations...
A new study, published last week in Nature, has revealed that oceanic shark and ray populations have declined by over 70% in the last 50 years. Sobering, but honestly, not all that surprising.
Industrial fishing fleets have decimated ocean life in an insatiable quest for protein and profits in a manner that truly epitomises the ‘tragedy of the commons’ – when users of a public resource act independently according to their own self-interest and end up destroying it. This attitude, coupled with the long-held presumption that the ocean’s resources are inexhaustible, has inevitably led us to this point.
Sharks are some of the most important and vulnerable marine animals. As top predators in marine food webs, sharks keep all the other levels of the chain in balance. They regulate disease by removing the weak and sick, they clean the oceans by removing the dead, and they maintain the balance by not allowing any one group to become too abundant. But they are vulnerable. A shark’s slow growth and low reproductive rate causes them to be acutely impacted by fishing pressure, by being unable to grow and reproduce quickly enough to replace their numbers lost to nets and hooks.
The 70% decline in the last half-century is owed to the fact that there has been an 18-fold increase in fishing pressure, and now three-quarters of sharks and ray species are threatened with extinction. As stated earlier, it’s not at all surprising when one remembers that catches of sharks reached an estimated peak of 63-273 million individuals in the early 2000s before declining due to overfishing.
If we breakdown the decline by ocean basin, the paper finds the following results:
- Atlantic Ocean, after a long period of decline since 1970, abundances began to stabilise at low levels after 2000 with an overall decline of 46.1%.
- Pacific Ocean, abundances decreased steeply before 1990, then declined at a slower rate with an overall decline of 67%.
- Indian Ocean, shark abundances have declined steeply since 1970 with an overall decline of 84.7%.
It was further noted that tropical sharks declined more steeply than more temperate species with declines of 87.8% for tropical species and 40.9% for temperate species.
The decline affected different species at different times in a pattern easily recognisable in fisheries management. Serial depletion begins with the largest species (being the most valuable and slowest to reproduce), followed by declines in medium-sized species, and eventually relatively small species.
Despite this precipitous decline, there are ways to end the unsustainable exploitation and begin to recover these populations. The implementation of fisheries management and trade regulations has been outpaced by fishing effort but it can catch up. Additionally, there’s been great improvements in conservation commitments by nations and international treaties in recent decades, but still, relatively few countries impose catch limits specific to oceanic sharks, and fewer still can demonstrate population rebuilding or sustainable fisheries for these species. We must prohibit retention and restrict international trade of threatened sharks and rays. Regional fisheries organisations must heed scientific advice and begin using more ecosystem-based management to maintain the system rather than a single species.
Finally, Endangered and Critically Endangered species must not be allowed to be caught, retained, traded or sold, and strict measures to prohibit landings and minimise bycatch mortality by avoiding hotspots, modifying gear and improving release practices are urgently needed to halt declines and rebuild populations.
Action is urgently needed to stall and prevent shark population collapses and the frightening host of negative consequences that would follow. Governments must adopt, implement, and enforce catch limits for oceanic sharks that are capable of supporting sustainable fisheries, and retention prohibitions and bycatch mitigation, for those threatened species that cannot.
At HSI we have built a community to address the issues facing our sharks and rays. Join Shark Champions to help these imperilled and important animals keep their place in our oceans.
A marine ecologist specialising in conservation, research and outreach, Lawrence has spent years working with wildlife, the ocean and the public to engender sustainable relationships between them. He has worked as a field biologist, environmental consultant, naturalist and project coordinator with a BA from the University of San Diego, and an MSc from James Cook University. Lawrence’s work at HSI is currently focused on shark welfare and protection, specifically in regards to culling and control programs, overexploitation, and international protection.