The Earth’s deep oceans are the last refuge of biodiversity from the reach of human activities. However, research has found that even at extreme depths, deepwater sharks and rays are extremely sensitive to overexploitation and take a long time to recover. These sharks in the dark require immediate international trade and fishing regulations to prevent irreversible defaunation.
Nick Dulvy is the Simon Fraser University (SFU) Distinguished Professor of Marine Biodiversity & Conservation and was recently elected into the Royal Society of Canada, Canada’s highest academic honour. He is a leading marine ecologist and collaborates with scientists worldwide to address global environmental challenges like the effects of climate change and overfishing on marine biodiversity. His research articles are consistently the within the Altmetric top 10 from SFU, and he has garnered much media attention for his compelling work, particularly on sharks and rays.
For a recent study, Dulvy worked with a team of over 300 experts from around the world to complete an eight-year long analysis of 521 species of sharks, rays and chimaeras (a small group of mainly deepwater species). The study found that one-third of deepwater sharks are targets of the growing international liver oil trade, and half of these are threatened with extinction.
The paper, Fishing for oil and meat drives irreversible defaunation of deepwater sharks & rays, made the cover of Nature when published in spring. (Full article link, more info here). The researchers recommend implementing international laws on deepwater fishing—where currently no regulation exists. Even worldwide prohibition of fishing below 800 metres would provide significant refuge for threatened deep-water sharks and rays.
The slow-moving, deepwater dwelling Greenland shark can live to be hundreds of years old. Its greatest threats are fishing, climate change, and loss of habitat. [Photo by Nick Caloyianis, National Geographic]
We spoke to professor Dulvy about his research.
Can you explain what make deepwater sharks and rays so vulnerable to human exploitation?
Deepwater sharks are the old-growth trees of the oceans. Even at extreme depths, deepwater sharks and rays—species that spend most of their lifespan at depths greater than 200 meters—are among the most sensitive marine vertebrates to overexploitation because of their long lifespans and low reproductive rates. Deepwater sharks have biological characteristics similar to marine mammals, which were formerly exploited for their oils and are now highly protected.
The Greenland shark and the leafscale gulper shark, for example, have population growth rates comparable to the sperm whale and the walrus, respectively. Many deepwater sharks and rays can only withstand very small amounts of fishing pressure. Some species may take 30 years or more to mature, and possibly up to 150 years in the case of the Greenland shark. Some only produce 12 offspring throughout their entire life. Deepwater sharks and rays require immediate trade and fishing regulations to prevent irreversible defaunation and promote recovery of this threatened megafauna group.
Tell us about your research methods. How do you count the numbers of sharks and rays to determine their reach and numbers?
We organized 17 workshops engaging 353 participants from 71 countries over 8 years and trained scientists to use the International Union for the Conservation of Nature Red List assessment methodology. This considers the rate of population reduction, threats and conservation actions and is used to classify species into one of nine categories, ranging from Least Concern to Extinct. The deepwater shark assessment was convened in Vancouver in November 2019.
Your research has earned a lot of attention and has helped shape some protections for marine biodiversity—what more should be done to protect deepwater sharks and other deepwater marine life?
Our results highlight that it is time to regulate the liver oil trade. There has been enormous success in regulating the shark fin trade but there are no current trade or fishing regulations specific to deepwater sharks and rays. We recommend depth and spatial limits to fishing activity implemented alongside catch regulations, bycatch mitigation, and international trade regulation. This could include national protections, regulations on deepwater fisheries, as well as listing species in Appendix II of the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES).
What is special about sharks that make them so interesting? Why do people love sharks?
Kids love dinosaurs and sharks; they are awe-inspiring and iconic examples of the wonder of nature. They appeared on our planet before trees evolved and long before Saturn gained its rings. Now their future is threatened by the rapid expansion of overfishing across the oceans.
For more: watch this video on sharks, view the article web page SharksInTheDark - Marine Biodiversity & Conservation and read the Conversation Canada article Fished for their meat and liver oil, many remarkable deep-water sharks and rays now face extinction by study co-authors Brittany Finnuci and Cassandra Rigby.
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