Seb Pardo is a biologist currently doing a PhD at Simon Fraser University in Canada. He is broadly interested in the biology, ecology, and conservation of sharks and rays. At present, his research is focused on borrowing tools from evolutionary biology to predict the biology and extinction risk of poorly studied sharks and rays. By using these data-poor methods, he hopes to make the most out of currently available data to inform policy decisions relevant for the sustainable management of sharks and rays. His twitter handle is @sebpardo
Rays rarely get the same amount of attention as sharks do. Perhaps the most notable exception are the manta rays (genus Manta), which are charismatic, filter-feeding rays that inhabit warm waters throughout the world’s oceans. Their closest relatives, the devil rays (genus Mobula), are not nearly as “famous” — even though they are the only other members of the family Mobulidae. There are nine species of devil rays found throughout the world’s tropical and temperate oceans, and while they are smaller than mantas (only reach over 3 metres in width), devil and manta rays are so similar that they are sometimes confused with each other. Because devil rays garner less public interest, the are very few studies on their basic biology and ecology, hindering our ability to assess their status.
Devil and manta rays face similar threats. Both are often caught as bycatch in industrial and artisanal fishing operations, which may result in considerable mortality even after being released. On top of this, there has been an increase in the international demand for their gill plates, which are used a health tonic in Chinese medicine. This has increased targeted fishing and bycatch retention in many places around the world. However, because of the lack of information on devil rays, it is very difficult assess whether this level of catch and trade is sustainable. This is the key question we set out to answer.
“Our unprecedented analysis shows that sharks and their relatives – which make up one of the earth’s oldest and most ecologically diverse groups of animals — are facing an alarmingly elevated risk of extinction,” said Dr. Nick Dulvy, IUCN SSG Co-Chair and Professor at Simon Fraser University in British Columbia.
As of the writing of this paper, the IUCN Shark Specialist Group recognized 1,041 species of chondrichthyans. However, a new species is described, on average, every two or three weeks! Out of these 1,041 species of chondrichthyans, approximately one in four are considered “Threatened” by IUCN Red List criteria; 113 species are Vulnerable, 43 are Endangered, and 25 species are Critically Endangered. 487 species are considered Data Deficient, but the IUCN Shark Specialist Group estimates that 68 of them are likely to be Threatened as well! Most alarmingly, only 23% of known chondrichthyan species are considered Least Concern, the lowest percentage out of any group of vertebrates on land or sea!
A hierarchy of IUCN Red List categories. Note that “Threatened” includes Vulnerable, Endangered, and Critically Endangered
One of the two main factors influencing Threatened status is the size of the animal. Larger bodied species are sensitive to overfishing because they typically have a life history with slow growth, late age at maturity, and relatively few offspring. Additionally, living in coastal habitats (in other words, close to humans) makes a species more likely to be Threatened.
WhySharksMatter found Nemo at Disney's Living Seas Aquarium
Like most marine biology geeks, I’m a huge fan of Disney/Pixar’s “Finding Nemo”. In addition to a heartwarming story of a father trying to bring his son home to their aneme…anemeneme… amenememe… anemone, the film showcases an enormous variety of beautiful real-life coral reef species. According to research published today in Conservation Letters, however, we may soon only be able to see some of these animals in the movies. The paper, titled “Extinction Risk and Bottlenecks in the Conservation of Charismatic Marine Species”, concluded that many of the stars of Finding Nemo are in deep trouble.
Manta rays are true gentle giants; though they can grow more than 20 feet wide from wingtip to wingtip, they eat only plankton. Swimming with these animals is a rare thrill for SCUBA divers, and manta-viewing ecotourism is worth over $100 million each year. Like many species of sharks, manta rays grow slowly and reproduce rarely. According to Dr. Nick Dulvy of the IUCN Shark Specialist Group, ” they give birth to an average of one offspring every two years…they are a long-lived species with little capacity to cope with modern fishing methods.” They also migrate across huge distances, regularly crossing between national boundaries and spending much of their time on the high seas, making management difficult.
Photo credit: David Shiffman (Georgia Aquarium)
Although their biology cannot support a large-scale fishery and their behavior makes any fishery inherently difficult to manage, manta rays are very much in demand. At least part of them is: their gill rakers. According to Lucy Harrison, program officer for the IUCN Shark Specialist group, “Increasing demand for these fishes’ filter-feeding system for traditional Chinese medicinal purposes, especially in Hong Kong, is rapidly driving down their population everywhere.”
By some measures, the global population of manta rays has declined by more than 30% in recent decades, with some local populations facing much larger declines. Earlier this week, an IUCN Shark Specialist Group team led by Andrea Marshall has concluded that both species of manta ray (the giant manta Manta birostrisand the reef manta Manta alfredi) should be declared Vulnerable* to extinction.
The IUCN Shark Specialist Group recommends that several steps be taken to protect mantas from further population declines. These include discussing the value of international conservation treaties, such as CMS and CITES, for both species as well as national-level policy changes in countries that fish for mantas. Some of these proposals may benefit from the support of the online conservation community, so please stay tuned! I’ll continue to report on these suggested policies as they moves forward.
* “Vulnerable” in the context of an IUCN Red List status should be capitalized, as should other IUCN Red List statuses. For more information on what “Vulnerable” means, please visit the Red List website here.
“There are known knowns; there are things we know we know. We also know there are known unknowns, that is to say we know there are some things we do not know. But there are also unknown unknowns – the ones we don’t know we don’t know.” – Former U.S. Secretary of Defense Donald Rumsfeld.
As nature documentary viewers often hear, there is a lot about sharks and rays that scientists don’t know… but what are the most important things that we need to know? A new paper written by Colin Simpfendorfer, Will White, and former Shark Science Monday interview subjects Michelle Heupel and Nick Dulvy attempts to identify these “known unknowns” of shark and ray conservation. “The importance of research and public opinion to conservation management of sharks and rays: a synthesis”, which arose out of the 2010 Sharks International conference, is the most complete record ever created of the research questions that we need to answer in order to better conserve and manage these animals. For young shark researchers eager to work on projects with practical conservation importance, this paper is a great place to start looking for ideas. Additionally, future published work that claims to be important for conservation and management would do well to cite it, and anyone interested in this subject should read it.