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.”