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B.C. scientist helps build 'risk of extinction' tool for biggest fish

A shark expert from B.C.'s Simon Fraser University has helped create a tool to measure the biodiversity of the ocean's biggest predatory fish, and conversely, their risk of extinction.
Blue shark off Pico Island in the Azores, Portugal. Blue sharks are among several species that can get caught up as collateral damage in tuna fishing operations.

A group of biologists have found a way to calculate the risk of extinction for some of the world’s biggest predatory fish, and in doing so have helped answer the question: is ocean conservation actually working? 

In a new study recently published in the journal Science, a team of researchers from Spain, the United States and British Columbia’s Simon Fraser University (SFU) analyzed fisheries data for 52 different populations of tuna, sharks and billfish — a group of fish with pointy beaks that include swordfish, Marlin and sailfish.

“We have a really good idea of what's happening to biodiversity on land,” said co-author and SFU biologist Nicholas Dulvy. “But it's very hard for anybody to see what's happening to the life under the ocean.” 

The more valuable the species, however, the more likely fishery scientists have been tracking how many are caught and killed every year.

Predatory fish species like tuna, marlin and swordfish have historically been among the most valuable and, therefore, most tracked. Over the last several decades, they offer some of the best long-term stock data of any species of fish.

It took Dulvy, his former PhD student lead author Maria José Juan-Jordá, and their other colleagues roughly six years to work through all the bugs. Eventually, the research team ran 70 years worth of data through their tool, spitting out a biodiversity index that would make sense to both fishery scientists and policymakers. 

“We basically developed an index that policymakers are used to seeing for mammals, birds, amphibians, reptiles and some plants — and applied it to fish,” Dulvy said.

A mixed story of success

The group’s analysis revealed populations of the planet’s biggest predatory fish are facing mixed prospects of survival.

Between 1950 and the late 2000s, the study found the global extinction risk of oceanic predatory fishes continuously worsened due to overfishing. But in recent years, conservation measures to reduce fishing mortality allowed for the recovery of tunas and billfishes. 

On the one hand, fisheries management programs were found to have the potential to help recover even the most heavily fished species, like tuna and billfish.

“That's the story of hope here. It doesn't have to be a story of fisheries collapses, like the Atlantic cod,” said Dulvy. 

On the other hand, a number of shark species appear to be slipping through the cracks. 

A marine equalizer

Sharks are vitally important for the health of entire ocean ecosystems. 

When tiger sharks show up off Australia’s north coast, they can scare away turtles and dugongs — two species that would otherwise mow down beds of seagrass.

“Tiger sharks are basically propping up seagrass meadows in the same way that otters are promoting kelp forests around our coast,” said Dulvy.

But in the last half century, shark populations have dropped 70 per cent, Dulvy and his colleagues found last year in another study. That's threatening the predator's role as an ecosystem equalizer.

Part of that decline has been been framed as collateral damage from the fishing industry. Mako, porbeagle, hammerhead and blue sharks can be especially vulnerable, as they swim alongside tuna and billfish at sea. In some cases, long-lining boats can pull in more sharks at a time than the species they’re actually targeting, says Dulvy.

Then there’s the shark fin trade and a growing demand for their flesh in some coastal communities.

In 2019, an estimated 63 million sharks were killed in fisheries across the world.

That same year, Canada banned the import and export of shark fins, as well as the practice of shark finning itself. That's the practice where fishermen cut fins from sharks, often while the shark is still alive, and then leave the shark to die at sea.

Many other countries still don’t have laws on the books banning shark finning. Even where laws exist, some don’t have the capacity to properly enforce existing regulations. 

Not just a commodity

Sharks have been around for over 400 million years, making them older than both trees and Saturn’s rings. They are among the first explosion of vertebrate life to develop jaws and a brain we can recognize today. 

And while they have survived several mass extinctions, 100 years of industrial fishing has raised the current extinction rate of sharks and rays 19 to 26 times higher than at any time in the fossil record.

Dulvy says part of that comes down to misguided perceptions. 

“Fish aren't just a commodity. They are wildlife just like rhinos, elephants and cheetahs,” he said.

Take tuna, suggests the biologist. You have likely come face to face with stubby cylinders of its canned flesh. But have you ever seen a yellowfin or skipjack plying tropical waters? 

Or contemplate the overfished Pacific bluefin tuna, whose warmblooded physiology allows it to swim off the coast of Vancouver Island in the summer, and grow up to three metres long and weigh up to 450 kilograms. 

“If you go to the supermarket, the fish counter is full. Go to the aquarium, the aquarium's full. Everyday we see fishing boats come back to Steveston. It's got fish on it,” said Dulvy. 

“[For] all intents and purposes, we have a very biased view of the ocean.”

And while conservation measures have turned around many tuna populations — largely due to its immense popularity as food for humans — protection for sharks has lagged behind.  

A chance to regulate the shark trade

That could change this week as 184 country delegates attend the Convention on International Trade in Endangered Species (CITES) currently being held in Panama. CITES is the group that lists a species’s threatened or endangered status, and regulates the trade of ivory, rhino horn, bear skins or the parts of enumerable other endangered plants and animals. 

About 100 sharks and rays are up for consideration this year in the legally binding treaty. If they get listed, Dulvy says it will regulate about 90 per cent of the world’s fin trade. 

Trading the body parts of any listed species would require three certificates, one indicating their source of origin, another showing they were harvested sustainably, and a third that proves they have been legally sourced.  

“That instantly closes down opportunity for illegal fisheries,” said Dulvy. 

The treaty does not shut down fishing of the listed species. It also doesn’t solve the problem of collateral damage. 

Dulvy said that will require new hooks, different kinds of bait to dissuade sharks, or simply avoiding places where fishing boats accidentally take the most sharks.