Nick Dulvy

By Sharon J. Proctor

Photography by Perry Zavitz

Imagine you’re scuba diving around a tropical coral reef. Then, suddenly, a giant creature with enormous fins comes toward you, mouth wide open. It’s huge. You brace for the collision. And then…nothing. The visitor has absolutely no interest in you. It just swims around, minding its own business, moving its wings up and down like a bird in air.

Mantas and their close relatives, the devil rays, are among the most mysterious animals on Earth. They look like spacecraft, with their strange-looking flat bodies. Picture two massive wings with a whip tail at the back and vacuum cleaner at the front. The largest can grow to nine metres across and weigh almost one and a half tonnes. And yet these are gentle giants. They would never hurt anyone. Unlike most sharks, mantas feed on plankton, tiny plants, and animals suspended at the water’s surface. Mantas swim with their mouths open, and as water passes through their mouth and out the gill slits, plankton are caught in the sieve-like gills, then swallowed.

Since his university days Dulvy has added manta rays and sharks to his special interests. He worries that overfishing is pushing them toward extinction.

Them and us

“Mantas and their shark relatives are unusual fish,” explains Dulvy, “in that they give birth to live young. This is relatively rare in nature. Mammals do this. So do some reptiles. Birds, insects, and most other species, however, lay eggs. Not only that, many sharks and rays go one step further. They have a placenta for nourishing their developing young, similar to the placenta in mammals. And it gets even more interesting: sharks and rays with a placenta have larger brains as adults than non-placental sharks and rays. So we think there’s a strong link between brain size and how a species nourishes its developing offspring. Smarter newborn sharks, after all, would be better able to avoid predators.”

Why have a placenta? “In mammals,” replies Dulvy, “it transports long-chain fatty acids from mother to developing baby. These fatty acids are essential for proper brain development and function. Perhaps the placenta plays a similar role in sharks and rays.”

Any similarities between sharks and mammals shouldn’t surprise us, as mammals, birds, reptiles, amphibians and fish – and their brains – all have a common evolutionary origin. In fact, the blueprint for our own complex brain was first drawn in ancient sharks and their relatives. That’s right. They were the first backboned animals to evolve a brain that’s divided into a hind-brain, mid-brain, and the maze-like cerebellum.

A worrisome trend

Nick Dulvy’s home base is SFU’s Burnaby campus, where he holds the Canada Research Chair in Marine Biodiversity and Conservation. Born and raised in Northern Ireland, he earned a Bachelor of Science at the University of Birmingham and his PhD at the University of East Anglia (both in the U.K.). How did he become interested in mantas and their shark relatives? Dulvy says, “At Birmingham I studied physiology, as I was fascinated by how animals regulate their bodies internally in order to survive in hot or cold environments. At East Anglia I explored skate biology and migration. This involved studying the effect of commercial fisheries on skates, and understanding the evolution of sharks and rays.”

For his PhD thesis he spent two years in Welsh and English fishing villages, tagging skates to learn their distribution patterns. Skates, like mantas, have flat bodies and are related to sharks. They live on the sea bottom, grow to one and a half metres long, and are caught regularly for food. “I tagged the skates, then waited until fishermen caught them and turned in the tags to a government office. Meanwhile, I became curious about the fishery.”

Any similarities between sharks and mammals shouldn’t surprise us, as mammals, birds, reptiles, amphibians and fish – and their brains – all have a common evolutionary origin.

Government records showed that skate catches were stable year after year. “I knew there were at least six species being caught, and that the government was lumping them in a single category, ‘skates and rays.’ So I plotted the trajectory of each species.” Dulvy discovered that the largest skate species were declining rapidly, while the smaller species were increasing in numbers. In other words, while the total catch stayed the same, the species composition changed. “We had been blind to these worrisome declines because they were masked by poor statistics.”

Since his university days Dulvy has added manta rays and sharks to his special interests. He worries that overfishing is pushing them toward extinction. Shark fins, for instance, are in demand everywhere, even in Canada. They’re used in shark fin soup, which is considered by some to be a show of wealth and status, rather than simply a food. The shark is captured at sea, its fins are cut off, and then it’s thrown back into the water – while it’s still alive.

There’s a huge demand for manta gill rakers, too. These are used in traditional Chinese medicine, nominally to treat chicken pox, cancer, kidney disease, skin problems, infertility, and a host of other ailments. And, of course, sharks and rays are caught for food in many places.

How do we save them?

Saving these animals won’t be easy! First, there’s a healthy market for them. One kilogram of gill rakers from a large manta, for instance, can fetch up to $200 in China. Poor villagers in remote places can transform their lives with the money they can earn by harvesting manta rakers and shark fins.

Second, many people around the world fear or hate sharks, and they don’t care if these fish just vanish. Some people are more closely affected because they know someone who was killed by a shark. For those who think shark extinction would be better than the risk of humans being attacked, Dulvy has a suggestion of how to think about the situation: “Nothing I can say will take away the pain of such a tragedy. Like any other rare chance event, on an emotional level it can be hard to understand a shark attack. On the other hand, the chances of dying from a shark attack are incredibly low. Far more people die each year from drowning, lightning strikes, falling televisions, and dog bites. That said, a world without risk would be boring and unchallenging. It would be a world without life.”

Photo: Richard Pierce

As for manta rays, how do we stop the use of their gill rakers in traditional medicine? “This is a vexing challenge,” admits Dulvy. “There would be no threat of extinction if fishermen would stop killing them. But the Chinese demand for gill rakers is very powerful. I try to work with both sides. Both groups have much to lose if mantas go extinct.

“We human beings depend on healthy ecosystems for our survival – for fuel, clothes, building materials, food, and even the oxygen we breathe. And we know that each plant and animal species plays a role in keeping its ecosystem healthy. How many species can we afford to lose before a tipping point occurs and we’re profoundly affected? We don’t know the answer. Nor do we know which species are vital to ecosystem survival.”

Little is known of the private lives of sharks and their relatives. Consequently the knowledge needed to save them (or any species) can come only from further scientific research. “Unfortunately there’s an increasing disdain for science in North America,” says Dulvy. “So we’re seeing the slow death of evidence-based decisions. And yet our entire modern lifestyle is founded on science and technology. Science is a powerful foundation and impetus for action. To ignore it in making environmental decisions is to fail future generations.”

April 2013