Study says large sharks hit hardest by ocean overfishing

By Stephen Beech via SWNS

Large sharks - including great whites - are among the species most threatened by overfishing, warns new research.

The apex predators have an "oversized" influence on their ecosystems - but are also the hardest hit by the fishing industry, say scientists.

They explained that a healthy ocean requires sharks of different shapes and sizes.

But sharks’ diverse contributions are under threat from overfishing, climate change, habitat loss, coastal development and shipping.

Now, an international team of scientists says that shark conservation must go beyond simply protecting shark populations - it must also prioritize protecting the ecological roles that sharks fill.

Their findings, published in the journal Science, shed new light on the role sharks play in healthy oceans, and why size should be a factor in conservation decisions.

The research team explained that the largest individuals of apex species - such as tiger sharks and great whites - help maintain balance through their eating habits.

Sometimes their sheer size is enough to scare away prey that could over-consume seagrass and other plant life needed for healthy oceans.

Study co-author Professor Jennifer Caselle said: “Despite the fact the sharks are well recognized and appreciated in popular media and lore, their importance in maintaining ecosystem health was understudied and underappreciated.

“We show that sharks are critical components to ecosystem function, making their global population declines particularly worrisome."

Caselle, a marine biologist at the University of California, Santa Barbara (UCSB), added: "Conservation measures to protect sharks are urgently needed.”

Besides playing critically important roles within the food web, she said reef sharks feed in offshore waters and bring nutrients back to the reef, while others move around nutrients that are used at the base of the food chain.

The research team showed that sharks can also serve as food for other species and even as scratching posts for fish to remove parasites.

But the problem is that shark abundance, for oceanic species, has plummeted by 71% in the past 50 years.

Populations of the top five reef shark species have declined by 63%.

And, as their numbers nosedive, their important roles in ocean health are also lost, say scientists.

Study lead author Dr. Simon Dedman, a researcher at Florida International University (FIU), said: “It’s time to have a conversation about everything sharks are doing to maintain ocean health so we can better prioritize conservation efforts and have the biggest impact."

The research team built on several datasets and previous studies to estimate global shark population trends.

For instance, former UCSB doctoral student Erin Dillon discovered that she could use fossil shark scales excavated during digs in prehistoric reefs in the Caribbean to estimate the region’s shark populations.

The shape and prevalence of different shark scales allowed her to estimate the type and abundance of sharks going back almost 6,000 years.

By comparing data from multiple sites in the new report, she was able to document that shark abundance in the region declined by around 70% since prehistoric times.

But it's not all bad news for all sharks.

The research team found a few "promising" instances where smart and responsible management appears to be helping sharks — and the jobs they perform in nature — to recover.

Study co-author UCSB Professor Douglas McCauley, who studies white sharks in Santa Barbara using drones and AI, cites their situation as a hopeful example.

As well as laying out a roadmap to see more such shark success stories, the new study also provides advice on how humans can share the oceans with sharks.

McCauley said: “We’ve learned a lot about how to co-exist with ecologically important species that we’ve brought back on land, like bears and wolves, that can help us better share space with these recovering ocean wildlife."

The researchers say shark conservation is becoming more critical as global temperatures increase, leading some species to head into new areas where they can find the temperatures they thrive in.

Lee Crockett, executive director of the Shark Conservation Fund which funded the study, said: “This study verifies what we’ve long suspected – sharks are critical to ocean health.

“This landmark study serves as confirmation that marine conservationists, philanthropists, policymakers and the public alike need to recognize that sharks are keystone species that have a now-proven significant effect on marine environments.”

With the expansion of "blue economy" industries such as aquaculture and tourism, human encounters with sharks are likely to increase.

Finding a balance that protects the sharks most needed for healthy oceans is hitting a critical point, says the research team.

Study co-author Professor Mike Heithaus, an FIU marine ecologist, said: “National and international policy must focus on actions that rebuild populations and restore sharks' functional roles.

“That requires action to increase both spatial measures like marine protected areas and fisheries management measures like catch/size limits and gear limitations."

He added: "If people want healthy oceans, we need healthy shark populations.”