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Welcome to the first-ever episode of The Whole Tooth! To kick off the podcast, we will be answering a question from Juri, aged 10, about the weird and wonderful world of shark mating and reproduction. With over 1,000 species of shark and ray on the planet, there are many different ways reproduction occurs – and things can get very strange! From eggs that look like corkscrews to baby sharks eating their brothers and sisters while still inside the womb…we cover it all in this episode!
Joining me today are two very special guests with a serious passion for elasmobranchs: Jillian Morris-Brake and Jenny Bortoluzzi. Originally from Maine, Jillian now lives and works in Bimini – AKA a shark scientists paradise – and spends her days in tropical waters, hanging out with and filming the locals (hammerheads, lemon and nurse sharks, to name a few!). She tells us about her amazing career: with a background in marine science, Jillian is an award-winning underwater photographer, SCUBA instructor, educator, filmmaker and author. She has written two books, Norman the Nurse Shark and Shark Super Powers, and founded the non-profit Sharks4Kids, which aims to inspire the next generation of shark advocates through outreach, education and conservation. Jenny is an ambassador and virtual lessons coordinator for Sharks4Kids and mentions in the episode how much she loves connecting with students from all over the world. We also talk about Jenny’s fascinating research on blue sharks and her life exploring the oceans.
We start to answer the question by discussing how hard a question it is to answer! Not only are sharks and rays incredibly diverse, but for many of these species we haven’t actually discovered how they reproduce! Especially for migratory, offshore or deep-sea species, observing and recording these behaviours is very difficult. Jillian mentions that a lot of what we do know is inferred from the habits of just a few species that scientists have been able to reliably study, including nurse sharks (as a side note, we recorded this episode in June so – happy nurse shark mating month!).
Of the species we have been able to study, we know that sharks use internal fertilisation (27.30). The male reproductive organs, claspers, are inserted into the female’s, as opposed to other fish species where the female lays an egg, which is then fertilised by the male externally. We discuss how there is very little romance in the shark world – no fancy courtship rituals or lifelong partners! In fact, Jenny explains that some female sharks will mate with multiple males (31.19), or some have no need for a male at all. In a process called parthenogenesis (31.56), some female sharks have been observed giving birth to young without ever having encountered a male, instead producing a miniature copy of themselves.
We also discuss the three main strategies for shark reproduction (35.06): viviparity (live birth), oviparity (laying eggs) and ovoviviparity, which is a strange mixture of the first two! We also find out that sharks are generally slow to reproduce, and invest lots of energy in raising small numbers of offspring (39.32). This contrasts with other fish species, who typically produce large numbers of young – such as the sunfish, which Jenny tells us can lay millions of eggs at a time! It also makes sharks quite vulnerable to exploitation, as individuals are taken at a faster rate than they can be replaced (45.41).
We cover all of this and so much more in the episode – so make sure to tune in to hear about shark parenting, shark nurseries, and which species of shark Jillian and Jenny would both like to be…
You can find out more about shark mating and reproduction here!
Born and raised in Maine, Jillian’s love for the ocean started at an early age and has continued to play an integral role in her adult life. She has spent thousands of hours in the field working and diving with sharks across the globe. She is a marine biologist, shark conservationist, scuba instructor, educator and founder of Sharks4Kids. She has filmed for numerous television shows and networks, has appeared on Shark Week, is a PADI Ambassadiver, was named Scuba Diving Magazine's July 2016 Sea Hero, was named the 2020 Go Blue Awards Blue Ambassador and was awarded the inaugural Shark Con Shark Hero Award in 2017. She is the author of Norman the Nurse Shark and Shark Super Powers and a member of the prestigious Ocean Artists Society.
Jenny is currently a PhD researcher at Trinity College Dublin, Ireland, where she studies the ecology of large marine predators, specifically blue sharks. She takes a multi-disciplinary approach to understand the diet, movements, physiology and reproduction of blue sharks as well as their importance to the local economy in an aim to ensure sustainable conservation. She is an ambassador and virtual lessons coordinator for Sharks4Kids and is passionate about sharing her love of sharks with kids and adults alike. She is a freediver, a scuba diver, an underwater photographer and a wild swimmer. The top of her bucket list of species to see is the basking shark and the mako shark.