About sarah

Dr. Sarah Friedman is a research scientist who works for the National Oceanic and Atmospheric Administration's (NOAA) Alaska Fisheries Science Center in Seattle. Previously, she worked as a researcher at Yale University and before that, got her PhD at the University of California, Davis. Growing up near Sacramento, CA, Sarah was in love with everything having to do with the ocean, and had an insatiable curiosity about the natural world. She has always known she wanted to be a marine biologist, and loved going to the beach and aquarium. When she's not studying fish, she likes spending time outside hiking, kayaking, and rock-climbing.

In her words: Overcoming obstacles

"I have been rejected from so many professional opportunities I've applied for -- from colleges to grant opportunities to papers I have submitted for publication. Rejection is a normal part of life. The key is to not let it get you down or to take it too personally. That tenacity, I think, is what ultimately makes for a successful scientist."

In 2020, Sarah published the results of a study investigating how the body shape of marine fish species change with the depth of water they live in. There are three main depth zones in the ocean--the pelagic zone (open water), the demersal zone (near the bottom), and the benthic zone (on the bottom). Living at different depths can have big implications for locomotion (moving around) and feeding-- for example, pelagic fish are surrounded by water on all sides, while benthic fish can rest on the bottom so they tend to move around in different ways and their body shapes reflect these differences in locomotion. Similarly, pelagic fish may have to seek out and hunt food, while benthic fish have the option of laying still on the bottom to ambush prey. 

Other studies like Sarah's have been done in the past, but mostly focusing on single species or families of fish. These studies have found predictable changes in body shape as fish move between three major zones of the ocean over an evolutionary timescale (a whole population of fish over a long period of time, rather than one individual fish over the course of its lifetime). Sarah and her collaborators wanted to know if these trends help up across a much wider range of fish families. To do this, they studied the bodies of fish belonging to 3,344 species! Their study set represents nearly 20% of all marine fish species, so it gives a much more comprehensive view of how body shape changes on a benthic to pelagic axis than previous studies did.

Sarah and her team took measurements 8 different body shape characteristics (see figure below) from preserved specimens that the National Museum of Natural History shared with them. They found average measurements for each species, and then used a computer program to organize the data based on the habitat (benthic, demersal, pelagic) of each species. With multiple individuals from each of the 3,344 species studied, they ended up with a lot of data, and needed powerful tools to analyze it.

Sarah and her team found that, as groups of fish evolved to live in new habitats, their bodies changed in ways that were consistent with what previous studies found. In general, benthic fishes that rest on the bottom tend to have much wider bodies, and pelagic fishes that swim around in open water tend to have longer, skinnier bodies. One reason for this is that benthic fish have fewer constraints placed on them by water resistance so they can get away with shapes that aren't as hydrodynamic, while pelagic (and to a certain extent demersal fish) face more challenges related to locomotion and buoyancy. 

While they found some general trends moving between habitats along the benthic-pelagic axis, they also found that there was a lot of diversity within habitats. Body shapes in benthic fishes were found to be the most diverse of fish from the three habitats. So, while they tended to be wider bodied, there were also a lot of benthic fishes with long, skinny bodies, and also all sorts of very unique shapes. Sarah and her team think that this is because being able to rest on the substrate (bottom material like sand, rocks, coral, etc) introduces a wide range of habitats within the benthic zone that fish can become specialized for, while fish that swim through open water experience a pretty uniform habitat. Benthic fish were the most diverse, but they also evolved the most slowly, so this diversity developed over a very long period of time. Even pelagic fish had a wide variety of body shapes. This tells Sarah and her team that, while habitat depth influences body shape, there is more to the story than that! More research is needed to fully understand how the diversity of fish shapes and sizes came to be.