This article was published in Scientific American’s former blog network and reflects the views of the author, not necessarily those of Scientific American
The first worldwide analysis of the extinction threat of all sharks and related species has just been published, and the news is sobering. Of the 1,041 known species of chondrichthyan (cartilaginous) fishes—sharks, rays and deep-sea chimaera (aka ghost sharks)—more than 30 percent are endangered, threatened, vulnerable to extinction or near threatened. Another 46 percent lack the necessary data to fully assess their extinction threat. Less than a quarter of shark and ray species are considered to be safe. This makes chondrichthyans arguably the most at-risk class of major vertebrates on the planet.
The study, the work of more than 300 experts from 64 countries who came together under the aegis of the IUCN Shark Specialist Group (SSG), was published January 21 in the journal eLife.
Numerous earlier studies have attempted to illustrate the threats that sharks and rays face in certain regions of the world, but they failed to show the true global state of these species, according to Nick Dulvy, co-chair of the SSG and Canada Research Chair at Simon Fraser University in British Columbia. "Until now, nobody has done a systematic unbiased study of all the habitats and all the species in the lineage," he says. The SSG was able to, as Dulvy puts it, "stitch together all of these jigsaw pieces to see what the big picture is across the world's oceans."
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The report identifies several of the most worrying trends. Sharks and rays in the Mediterranean Sea and the Coral Triangle (the waters between Indonesia, the Philippines and the Solomon Islands) face the greatest levels of population depletion. The large, shallow-water species—especially those that live part or full time in freshwater, such as the endangered Mekong freshwater stingray (Dasyatis laosensis)—are generally at the greatest risk. And rays, which have typically not received the same amount of attention as sharks, are in bad shape: The SSG found that five out of the seven most threatened families of chondrichthyans are rays. "Rays and the sharklike rays have been entirely overlooked by fisheries management agencies and the media for the last four decades," Dulvy says. These include sawfish, wedgefishes, guitarfishes, sleeper rays and stingrays. "These are all incredibly charismatic animals in their own way," he says. "Sleeper rays, for example, produce electricity and stun their prey. They can give you a 220-volt shock. You don't want to mess with those."
Overfishing has put many of these sharks and rays at risk, either by targeting the fish directly for their fins, meat or gills or killing them as incidental bycatch. Dulvy points at the now critically endangered common angel shark (Squatina squatina) as one species hit hard by trawling, which not only damages the seabed but also relies on the use of nets that the big, slow-moving fish can't avoid. "This species was once prevalent from Norway through north Africa and the Mediterranean," he says. "Today we think it is almost gone, apart from a remnant population in the Canary Islands."
Coastal and freshwater development has also put many species at risk. "It turns out there are about 90 species of shark and ray that spend part or all of their life in freshwater, and they're suffering from coastal land reclamation and development," Dulvy says. "This is particularly problematic in the megadelta cities of the world and the huge rivers of the Mekong and the Amazon."
So what comes next? The study calls for a lot more work on the part of fisheries and world governments to protect sharks and rays. "Despite more than two decades of rising awareness of chondrichthyan population declines and collapses, there is still no global mechanism to ensure financing, implementation and enforcement of chondrichthyan fishery management plans that is likely to rebuild populations to levels where they would no longer be threatened," Dulvy and his co-authors wrote.
The SSG also has a lot of work to do now to assess the extinction threat of all 1,000-plus species (in addition to the new ones being discovered at a rate of about one every two to three weeks) as well as studying to find out if current management practices are doing any good. It won't be a quick or easy task. "In England we'd say it's like painting the Forth Road Bridge, which is one of the biggest bridges in Scotland," Dulvy says. "Once you finish it you've got to start again. That might sound tedious but now we're in a position to start assessing species, and that job has started already. We're reassessing the European sharks now."
Meanwhile, the information learned in this global study can help to fill in some of the blanks on the "data deficient" species. "What we've learned is that species that are a meter long and found in shelf waters have a 50 percent chance of being threatened," Dulvy says. "So you can apply that knowledge statistically to the data-deficient species and come up with a probability that those data-deficient species are threatened."
On top of that, the 300 experts who worked on the study have all gone back to their home countries with the news that sharks and rays are at risk—the stories they shared at SSG meetings. Dulvy says this is where change will begin: "It's those words and those stories embodied by the assessors that actually make the action happen at the national and international level." For sharks and rays and related species, that change may be arriving just in time.
Photo 1: A critically endangered northern river shark (Glyphis garricki), by Grant Johnson. Photo 2: A critically endangered common angel shark (Squatina squatina), by Tony Gilbert. Photo 3: Devil ray (of the genus Mobula) having its gill rakers removed at a fishing port in Sri Lanka, by Sonja Fordham. All photos courtesy of IUCN
Previously in Extinction Countdown:
Whale Sharks in the News: Citizen Science, Migration Revelations and High Fashion
Could Farming Sustainable Tilapia Help Cut the Demand for Shark Fin Soup?