Field Notes: A Change of Scene

Science takes place in all sorts of circumstances, and for me, those circumstances are usually inside of a lab. They are also often spread across multiple facilities and at very odd hours of the day (or night), and those are entire research stories of their own. Nonetheless, one of my favorite things about research is the inherent capacity for change. The saying that no two days look the same is impressively true when it comes to carrying out various research projects.  I am a graduate student who studies the influence of variation on both the physiology and behavior of native California salmonids. It might be said that I have a bit of “a thing” for change. As luck or the fickle will of research would have it, this year’s changes brought about a new opportunity entirely: the field.

Environmental Variation: Not Just for Study Systems

Whether it is the average PhD student shifting between lab and field, or a fish swimming along in the Sacramento River, animals frequently encounter environmental variation. Ability to predict and respond to changes in the environment is critical for those animals to thrive. Animals do this by using flexible physiological and behavioral mechanisms. For example, the construction of cellular membranes can change to maintain function in higher or lower temperatures [1]. Alternately, fish can mediate interactions with their environment through changes in behavior, such as altered swimming and migratory behaviors [2]. How animals cope with environmental changes (like temperature and resource abundance) is ecologically insightful for understanding their needs and functions, and it is also extremely important in the context of human-induced climate change. Our world is rapidly changing, and models suggest that long-term climate trends will shift along with an increase in short-term, day-to-day variation [3]. Around this time of year, most of us are intimately familiar with sudden heat spikes as the weather goes from cold to hot. Unlike us, however, wild fish do not have climate-controlled homes or other technology to combat these changes. Instead, they must rely on a combination of biological strategies to navigate their complex world. As part of my work, I am attempting to address the influence of environmental variation on juvenile Chinook salmon in the context of these shifting temperature regimes. This year, I took all those questions, interests, and several dozen cages of fish with us to the field.

A native California PhD student, sited in the field setting up cages to study Chinook salmon in a natural-type wetland conservation easement.

Into the (Almost) Wild

The field is an interesting place from which all manner of insight can be gleaned. However, it also presents several challenges to collecting data. In order to rear juvenile Chinook salmon out in the field, we deployed the fish in a series of tethered mesh cages. This would expose the fish to the same environmental conditions that their wild counterparts would encounter, all while allowing us to keep track of them and have easy access to collect observations. These cages were deployed to four different sites, with the goal of mimicking a range of naturally-encountered feed resources. Those sites included an agricultural rice field, two river-like tow drains outside of the rice field, and a well-ditch leading into the fields. The cages were constructed using welded metal frames, wrapped in mesh that would allow food and water in while keeping predators out. It stands to reason that these types of cages are built to contain things like our study fish—to hold them inside a single location. While ours did that with great success, I was utterly baffled by the number of other things that we would find on the sides or within. I remember sitting in on a physiological ecology course several years ago, where the class was discussing the usage of pitfall traps. Pitfall traps are a method of animal capture, where wild individuals are passively caught in open-topped enclosures, placed within the ground. The concept of these incredibly simple and yet highly effective tools certainly captivated the interest of budding-researcher me. After this field season, I find myself just as intrigued but all the more understanding of their efficacy. It turns out that science is like a cage full of fish—you never know what else you’re going to find. Crayfish, invertebrate larvae, aquatic snails, and even a pikeminnow at one point all made an unexpected appearance in and around our cages. Nonetheless, we successfully deployed over forty cages full of juvenile Chinook salmon to our field sites, and we were able to rear and regularly observe them for several weeks under natural conditions.

Agricultural rice fields are incredibly rich in zooplankton—a tasty treat for any growing juvenile salmon. Researchers have deployed cages with fish in order to understand the influence of this nutrient-rich rearing environment on the development and outmigration of Chinook salmon.
A view of the tow drain, where runoff from the rice fields is let out. Cages were placed here to simulate natural river environments that wild salmon might encounter during outmigration. We would access the cages by paddling around on our jon boat, fondly referred to as The Warmouth for the extent of our small field season.

The Role of Resources

Pacific salmonids (Oncorhynchus spp.) are largely considered cold-water species that face ever-increasing population decline as temperatures continue to rise [4,5]. California contains 21 at-risk Pacific Salmonids, of which several federally listed species are projected to be extinct within 50 years under current trends [6,7,8]. Among those species, Chinook salmon (O. tshawytscha) is of particular conservation, economic, cultural, and recreational importance. Ongoing research seeks to broaden our understanding of how this species responds to changes in their environment. By doing so, researchers hope to highlight challenges to conservation and identify actions that can be taken to assuage future losses. My research interests hone in on the role of temperature and food abundance specifically.

Wild populations of Chinook salmon may have limited access to food resources and optimal rearing temperatures, compared to fish which are reared in hatcheries or laboratory settings. All biological processes require energy, and limitations on energy input could constrain biological output. Therefore, limitation in food availability could result in energetic tradeoffs between performance and growth for developing Chinook salmon. Past research on other salmonids has demonstrated that fish with abundant food resources can thrive in warmer water temperatures [9]. Understanding this phenomenon may open up new management opportunities such as food supplementation via floodplain restoration to protect juvenile Chinook salmon. Our research has significant potential toward informing practical-use management interventions for key California salmonid resources, particularly during crucial periods of early development. Of course, our work on understanding these trends is still in progress now as I write this. Stay tuned for our findings, and hopefully it won’t be long before we get to share our exciting work over in the Ethogram’s News Room!

A released juvenile chinook salmon, breaching the surface of the water to catch insect prey.

Cassidy is a PhD student in the Animal Behavior Graduate Group at UC Davis in the Fangue Lab. Her research focuses on how variable environments drive physiology and social interactions in Chinook salmon. When she’s not keeping company with fish, she’s off on adventures with her dog, horses, and other various vertebrate friends.

Photo Credit: All photos were taken and provided by Cassidy Cooper.


[1] Hazel, J. R. (1984). Effects of temperature on the structure and metabolism of cell membranes in fish. American Journal of Physiology-Regulatory, Integrative and Comparative Physiology, 246(4), R460-R470.

[2] Holleman, R. C., Gross, E. S., Thomas, M. J., Rypel, A. L., & Fangue, N. A. (2022). Swimming behavior of emigrating Chinook Salmon smolts. PLoS ONE, 17(3), e0263972.

[3] Thornton, P. K., Ericksen, P. J., Herrero, M., & Challinor, A. J. (2014). Climate variability and vulnerability to climate change: A review. Global Change Biology, 20(11), 3313–3328.

[4] Crossin, G. T., Hinch, S. G., Cooke, S. J., Welch, D. W., Patterson, D. A., Jones, S. R. M., Lotto, A. G., Leggatt, R. A., Mathes, M. T., Shrimpton, J. M., Van Der Kraak, G., & Farrell, A. P. (2008). Exposure to high temperature influences the behaviour, physiology, and survival of sockeye salmon during spawning migration. Canadian Journal of Zoology, 86(2), 127–140.

[5] Moyle, P., Lusardi, R., Samuel, P., & Katz, J. (2017). State of the Salmonids: Status of California’s Emblematic Fishes 2017.

[6] Katz, J., Moyle, P. B., Quiñones, R. M., Israel, J., & Purdy, S. (2013). Impending extinction of salmon, steelhead, and trout (Salmonidae) in California. Environmental Biology of Fishes, 96(10), 1169–1186.

[7] Kope, R., & Wainwright, T. (1998). Trends in the status of Pacific salmon populations in Washington, Oregon, California, and Idaho. North Pacific Anadromous Fish Commission Bulletin, 1, 1–12.

[8] Moyle, P. B., Kiernan, J. D., Crain, P. K., & Quiñones, R. M. (2013). Climate Change Vulnerability of Native and Alien Freshwater Fishes of California: A Systematic Assessment Approach. PLoS ONE, 8(5), e63883.

[9] Lusardi, R. A., Hammock, B. G., Jeffres, C. A., Dahlgren, R. A., & Kiernan, J. D. (2020). Oversummer growth and survival of juvenile coho salmon (Oncorhynchus kisutch) across a natural gradient of stream water temperature and prey availability: an in situ enclosure experiment. Canadian Journal of Fisheries and Aquatic Sciences77(2), 413-424

[Edited by Josie Hubbard and Maggie Creamer]

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