- A high-profile study published in Nature found a 70% decline in shark and ray populations over the last half century.
- Like many other taxonomic groups, shark and ray declines are driven by human actions — in this case, overfishing by commercial fisheries.
- Experts are calling for a retention ban by the EU to prevent the collapse of threatened shark populations.
A near-sharkless open ocean could soon be a reality, according to Nathan Pacoureau, a postdoctoral researcher in the Earth to Ocean Research Group at Simon Fraser University in Canada. Pacoureau and an international research team recently detected a 70% decline in shark and ray populations over the last 50 years. This study, published in Nature, underscores the need for international follow-through on shark and ray conservation policy, experts say.
While sharks may often get bad press, they and their ray cousins support the health of oceans and coastal communities, according to researchers. Losing these apex predators disrupts marine food webs and threatens the sustainability of global fisheries.
Catastrophic population declines are not unique to sharks and rays; many taxonomic groups are experiencing major losses. Insect populations appear to be decreasing by 1-2% per year, according to some research. An estimated 75% of primates are experiencing population declines, while amphibians are undergoing their own catastrophe. Many scientists say these losses may be a symptom of a larger problem: a disconnect between our acknowledgement of global biodiversity decline and our willingness to take the necessary actions to stop it.
“It is undeniable that the current rate of biodiversity loss is several orders of magnitude higher than the background historic extinction rate, leading to a biodiversity crisis,” Pacoureau told Mongabay. “And, while many people now know that we have a decade to stop climate change, far fewer realize we also only have a decade to reverse biodiversity loss.”
Overfishing drives shark decline, raises extinction risk
Assessing the status of high-seas species, like sharks and rays, is not easy. To estimate these populations, the team used multiple lines of evidence. Turning to long-term data sets from scientific literature, Pacoureau and colleagues were able to model trends in relative abundance for 18 species. They also compiled records of fishing offtakes, availability of species in fish markets, and expert opinions as proxies for extinction risk.
Overfishing is most responsible for shark and ray populations decreases over the past half century, according to the data.
Many coastal communities have harvested sharks and rays for hundreds or even thousands of years for their meat, fins, gill plates, and liver oil. But with commercial fisheries employing deadlier fishing technologies, the pressure on ocean species has ramped up. In the past 50 years, the use of longlines and seine nets has more than doubled, bringing in sharks and rays at unsustainable rates, both as target species and as bycatch.
Trends in shark and ray populations show classic symptoms of overharvesting, the study found. The larger, slower-reproducing species declined first, followed by smaller species. In other words, fishers were catching the animals faster than their populations could replenish. When those largely vanished, fishers moved on to less-favorable species.
“Such steep [shark and ray] declines are shocking even to experts, especially when compared to land animal statistics,” Pacoureau said. “Three-quarters of these iconic species now qualify as threatened with extinction under the [IUCN Red List].”
The fossil record tells the story of five mass extinctions in Earth’s history. Two factors, however, make today’s extinction crisis unique: the role that humans are playing in species declines, and the number of people who depend on natural resources for their livelihoods.
With a global biodiversity crisis underway, many governments have joined together to attempt to save species. The U.N. named the 2010s the “Decade of Biodiversity,” pledging to stop biodiversity loss and protect ecosystems by 2020. All member states agreed to 20 targets, dubbed the Aichi Biodiversity Targets, laid out by the Convention on Biological Diversity. By late 2020, however, the U.N. announced that, while many countries had reported progress toward their goals, not a single Aichi target had been fully met.
“International goals and targets require signatories to follow through on their commitments — whether this is in mitigating climate change or conserving biodiversity,” said Derek Tittensor, an associate professor of biology at Dalhousie University in Canada, who was not involved in the shark study. “Without nations stepping up and delivering the actions and policies needed to move towards sustainability, this won’t happen.”
Bridging policy gap for sharks and rays
A 70% decline in shark and ray populations is just one clear sign that the Aichi Biodiversity Targets were not met by 2020. These species are now in a precarious position. But to give up on saving them would be the biggest mistake of all, Pacoureau said.
“It is important to note that many beneficial safeguards are already mandated through global wildlife treaties,” he said. “A relatively simple initial step is for member countries to live up to those commitments through national regulations.”
Global agreements like the Aichi targets point scientists, conservationists and policymakers in the right direction, but lack the follow-through needed to solve the problem.
For example, shortfin mako sharks (Isurus oxyrinchus) may be one of the most studied, and therefore best understood, shark species. But this attention has not led to their protection. Based on current mako population trends, the species’ conservation status was raised to endangered on the IUCN Red List in 2019, form the previous lower-risk category of vulnerable. At the same time, the EU refuses to set satisfactory limits on mako offtake, writes Sonja Fordham, president of Shark Advocates International and a co-author of the study, in a brief for Shark League.
For sharks and rays, enforcing existing fishing regulations and setting new limits on landings could go a long way to help them rebound. In fact, it has been done before.
The white shark (Carcharodon carcharias) is, according to Fordham, “one of the best success stories for U.S. shark conservation.” In response to dramatic declines in the 1990s, a retention ban was placed on the species, allowing populations to slowly recover.
In July 2021, the International Commission for Conservation of Atlantic Tunas (ICCAT) will vote on a shortfin mako retention ban, which Fordham says has the potential to change the future for this overexploited, endangered shark.
The road to effective policy change may seem daunting. But both Pacoureau and Fordham note that meaningful steps can start at the individual level.
“By voicing concern,” Fordham said, “through letters to lawmakers and news editors, as well as social media and art, or as a tourist, everyone can help. Vocal, sustained support for shark conservation from the public is not only truly meaningful; it’s essential for creating a brighter future for these extraordinary animals.”
Citation:
Pacoureau, N., Rigby, C. L., Kyne, P. M., Sherley, R. B., Winker, H., Carlson, J. K., … Dulvy, N. K. (2021). Half a century of global decline in oceanic sharks and rays. Nature, 589(7843), 567-571. doi:10.1038/s41586-020-03173-9
Banner image of a critically endangered oceanic whitetip shark (Carcharhinus longimanus), courtesy of Andy Mann and Trevor Bacon.
