Take a look at a ghost shark and you might say, “What’s with that strange looking fish?”
In recent decades, scientists have learned that these cartilaginous fish, also known as ratfish or Chimaeras, have been around for hundreds of millions of years, and that they have poisonous spines covering their dorsal fins and ‘fly’ their pectoral fins through the water. In fact, they found that most male ghost sharks have a retractable genitalia on their foreheads that resembles a medieval club.
However, there is still much to learn about these strange creatures. Basic biological information, such as how long they live and how often they reproduce, is lacking for most of the 52 known species. The lack of this important information makes it difficult for scientists to manage and track ghost shark populations, even as there is growing evidence that some species are in danger of extinction.
Scientists at the Shark Specialist Group, a division of the International Union for Conservation of Nature, recently assessed the extinction risk of all confirmed ghost shark species and found that 16 percent are “threatened” or “near threatened.” The review, published this month in the journal Fish and Fisheries, also found that 15 percent of ghost shark species are so underexposed that their extinction risk cannot be determined. Now, experts are concerned that certain species of ghost sharks could go extinct before scientists have a chance to study them.
Ghost sharks are found in all of the world’s oceans except the Arctic and South Pole. Most inhabit the deep sea, although a handful of species inhabit shallow coastal waters. Despite their name, ghost sharks are not true sharks, although they are closely related. Unlike their cousins, ghost sharks have long, thin tails and large, continuously growing tooth plates that give them a rat-like appearance. Some have long, lean snouts, while others have a plow-shaped rung that they use to investigate seafloor sediment in search of food.
“They have a face that only a mother or a researcher could love,” said David Ebert, director of the Pacific Shark Research Center at Moss Landing Marine Laboratories in California and co-author of the review.
Almost half of the species known to science have only been discovered in the past two decades. “We are only now starting to figure out that there are a lot more of these things than we realized before,” said Dr. Ebert, whose lab discovered 11 of the 52 known ghost shark species.
Dr. Ebert is one of the few scientists currently studying ghost sharks. It has long been a challenge for scientists to find funding to study them.
“Chimeras don’t have much commercial value, so there’s not much interest in getting more information about them,” said Brit Finucci, fisheries scientist at the National Institute of Water and Atmospheric Research in New Zealand and lead author of the review. “They’re also pretty cryptic, so they’re hard to find and hard to study.” Several ghost shark species are known from just one specimen, including the Bahamas ghost shark.
Ghost sharks are mainly caught as bycatch. While their meat is edible, most of their commercial value comes from their liver, which contains an oil known as squalene that is used in a wide variety of cosmetic and pharmaceutical products.
Although harvested and sold all over the world, 90 percent of ghost shark species are unmanaged, according to the IUCN assessment. This means that those who catch these species are not restricted and not required to share data about their catch.
As fishing fleets venture further into the deep sea, experts fear some species of ghost sharks could disappear before scientists even notice they are in trouble.
“How can we wrap our heads around them to keep them from going extinct if we don’t know about them?” said Dominique Didier, an ichthyologist at Millersville University in Pennsylvania.
To prevent ghost shark extinction from occurring unnoticed, the authors argue, more scientists need to study ghost sharks and marine authorities need to monitor and manage the fisheries for ghost sharks around the world.
“We don’t have to wait,” said Dr. Finucci. “Although these animals are being rated with a lower risk of extinction, we should not wait until they are actually endangered before studying them.”