In my camp, starting tomorrow is our Shark Week! Dun, dun, dun! All day, every day, each grade will learn about all things sharks (and a little about rays, their close relatives. Because why not? Rays deserve love too!). We are all really excited – kids and adults. This week filled up the quickest, months and moths ago, no surprise, because sharks are fascinating. And for good reason! They are ubiquitous (found in every ocean), they are hugely diverse, many are top predators, they are some of the most efficient hunters on earth, and many are still shrouded in relative mystery. Whether you’re scared of them, or love them, you want to learn more about them! You just do. And with all of the ecological and anthropogenic challenges they face these days, the more people who learn about them the better!
I’ve written a bit about sharks a couple of times in my earlier posts, Fiercely Threatened and Shark Super Powers, and I’ve got a planned upcoming post about shark anatomy. But how do we know anything about sharks? From the life works’ of hundreds of researchers obviously. As such, today, I’d like to try something new for this blog. For this post, I’d like to write about one of my favorite shark researchers – Eugenie Clark, usually referred to as The Shark Lady. A lot of what we know about shark behavior and how to take care of them in aquariums we owe to her. Yet I’m willing to bet you’ve never heard about her before. Well, settle in (seriously, I hope you’re comfy because this is longish post but SO WORTH IT) and let me educate you!
In all of my college classes, I never actually learned or even heard about Eugenie Clark, even when the lectures covered marine animals’ ecology and anatomy. The majority of my classes focused on the scientific facts and processes, not how they were discovered or who discovered them. I didn’t realize it at the time, but looking back at my undergraduate education, there was a real lack of instruction on the history and nature of science. When I did eventually learn about the life and work of Clark (online when researching something else as it so happens), it was almost relieving. Finally! A women who pushed past stereotypes and barriers to pursue her passion for marine science! I was so excited by this discovery that I went on to read as much as I could about her. Throughout her career, she made several groundbreaking scientific discoveries about shark’s anatomy and behavior. Her carefully obtained and documented evidence overturned multiple very long held beliefs regarding sharks. Additionally, to make these discoveries, she had to overcome prejudice towards her gender and background to pursue the study of marine science and zoology (she was a half-Japanese women studying marine science during and immediately after WWII).
Since discovering her, I have written a biographical research paper about her for one of my graduate classes, I recently bought a beautiful children’s book about her to share with the little women in my life, and just generally try to tell everyone I know how amazing she was. She is a personal hero of mine, so in honor of my camp’s shark week, I thought I’d write a little homage to the two biggest scientific contributions of her career.
1. She discovered and proved sharks are intelligent, thinking, beings that can be successfully trained.
During her time as the director of the marine research facility that became the Mote Marine Laboratory in Florida, Clark made several huge discoveries and advances in shark training and behavior. Most notable was her work in trained behaviors. She was the first person to ever target train sharks. She experimented with operant conditioning of two lemon sharks and three nurse sharks. Through slow and repetitive positive reinforcement, she taught the sharks to associate a target and underwater bell with food. These training methods, now extremely common in aquariums (I personally used her methods daily during my time taking care of sharks in an aquarium, pictured above), was extremely notable at the time. Previous to her work, scientists and the public alike had always thought sharks were dumb, untrainable monsters (Jaws anyone?). Her study shook up many in marine science. No previous studies had ever been conducted on their trainability due to the prejudice against them having any measurable intelligence. She smashed through that myth, and it only took her a few days of training to do so!
2. She was the first scientist to witness and report that fusiform (football shaped) sharks could breathe while motionless on the seafloor.
Eugenie Clark did not just study sharks in human care, she also embarked on multiple trips around the world over several decades to study sharks in the wild. Her most startling discovery took place in an underwater cave on the coast of Isla Mujeres, part of the Mexican Yucatan Peninsula. Scientists had long known that a few specialized sharks like the nurse shark, wobbegong and angelsharks were able to sit motionless along the seabed. They are able to do so because they have specialized gills that can pump water, like most bony fish. The average, fusiform (torpedo) shaped shark however does not have these specialized gills, their muscles there are very weak. For hundreds of years, they had always been assumed to be obligate ram ventilators (they must continually swim non-stop their entire lives with mouths open to force water over their gills).
Yet, in 1969, a local fisherman named Ramon Bravo reported seeing sharks immobile, appearing to be asleep. In 1972 and 1973, Clark led a group of scientists to the area to see for themselves the sharks in Bravo’s reports. She and the others scuba dived directly into the cave to witness first-hand the phenomena. What they saw was remarkable! Thanks to Ramon, for the first time in history, fusiform sharks (Caribbean reef sharks) had been seen and scientifically documented motionless on the seafloor, slowing pumping small amounts of water over their gills with their weak muscles. While nicknamed ‘sleeping sharks,’ Clark reported that their eyes would track the divers intently, even if their bodies were motionless, so were unlikely to have been actually asleep.
Wanting to understand why they were able to behave so unusually, Clark took water samples from the cave to see if anything about the chemistry was different. What she discovered was the cave contained above normal dissolved oxygen levels, and lower than normal salinity, due to the strong upwelling currents in the area. She and her team continued to observe the sharks, diving into the cave repeatedly. What they found was many of the sharks would spend hours on end in the cave, and many of the returned for repeated visits. At the time, she hypothesized that the extra oxygenated water made it easier for them to breath, even with their weak unspecialized muscles, and also might produce a slightly narcotic effect that the sharks found pleasurable. To date, scientists have still not fully identified the mechanisms behind this behavior.
Since Clark’s study, more species have been observed in the caves all over the world. So far, the Caribbean reef shark, tiger shark, lemon shark, blue shark, houndsharks, whitetip reef shark, grey reef sharks, blackfin sharks, and possibly the bull shark have all been seen acting in such a way.
See why I love her? And this is only the tiniest snippet of her work! Truly, she revolutionized the field of shark study. Previously, research on sharks were mostly centered on their anatomy. Since her pioneer studies, hundreds of behavior, anatomy, and ecology studies have followed. Now, scientists all over the world have also dedicated their lives to studying sharks, gathering evidence to support sharks are trainable, intelligent, complex, vital to their ecosystems, and not at all mindless, vicious killers. During her life, she led expeditions to the Red Sea, Gulf of Aqaba, Caribbean, Mexico, Japan, Palau, Papua New Guinea, the Solomon Islands, Thailand, Indonesia, and Borneo. These far flung studies led to over 175 published articles, ranging from shark anatomy and behavior, to artificial insemination of viviparous fish, to reef fish ecology. She was a Rockstar in marine science, and yet most people have never heard of her. Which is an absolute crime! So I hope you read to the end of this post, so that now you too can love her. And maybe be inspired to learn more about female researchers and sharks. Because both topics are well worth your time!
Who are your favorite scientists, male or female? What was their biggest scientific contribution?
Clark, E. (1959, July 24). Instrumental Conditioning of Lemon Sharks. Science, 217-218.
Clark, E. (1975, April). Into the Lairs of ‘Sleeping’ Sharks. National Geographic, pp. 570-585.