We’re celebrating a decade of the Academic Minute this week with one segment from each year.
This segment from 2012, Sora Kim, postdoctoral researcher in the department of geology and geophysics at the University of Wyoming, shed light on the diet of Great White Sharks.
The best word to describe my path to now is circuitous. I went to college interested in the environment and started as an environmental studies major but found myself drawn to the questions and techniques within earth sciences. My senior thesis introduced me to stable isotope analysis, and I’ve been hooked since. Stable isotope analysis is a tool that allows me to explore a wide range of processes and mechanisms at the intersection of ecology, physiology, geology, and chemistry. Although much of my work these days focuses on sharks, I have ongoing projects on mammals, nutrient cycling, and lake sediments. I feel fortunate to have a creative career where I can meld my intellectual interests in ecogeochemistry with my passions in education and social justice.
Dartmouth College (2002), BA in Environmental Studies and Earth Sciences
Univ. of California, Santa Cruz (2010), PhD in Earth Sciences
Univ. of Wyoming (2010-2013), postdoctoral research associate
Univ. of Chicago (2014-2016), T.C. Chamberlin Fellow
Univ. of Kentucky (2016-2017), Assistant Professor
Diet of Great White Sharks
Jaws made sharks look like vicious killers… But ecologically, it’s more accurate to describe a shark as an apex predator, an animal at the top of its food chain. It is important to understand the role of apex predators because their diet can have strong effects on a food web. Because white sharks are marine species and travel long distances, they are difficult to study and their diets are not well known.
To get a better idea, my colleagues at UC Santa Cruz and I used stable isotopes of carbon and nitrogen from shark vertebrae. These isotopes are natural tracers that offer clues about what the sharks ate. White shark vertebrae have a similar pattern to tree rings and so we could correspond diet to an age and year. White sharks tend to feed higher on the food chain as they get older, but we found that the patterns and shifts differed among the individuals. Some shifted from a fish and squid-dominated diet to more seals and sea lions at approximately 4 years old, but others had no clear pattern.
We also found that not every white shark eats the same thing. Some ate a wide variety of prey, but others are pickier. Most of these selective eaters ate seals or sea lions near shore and fish or squid when offshore, but there was at least one specialist that only ate fish and squid.
Finally, white shark diets also shifted subtly after the mid-1980s. They ate more seals and sea lions, which were more abundant after the Marine Mammal Protection Act was passed in the ‘70s. Our findings were interesting because white sharks tend to migrate to and from the same places, and yet their diets vary widely. It is important to understand these details when establishing conservation and management policies.