Biological clocks are powerful drivers of hourly, daily, and even seasonal rhythms throughout life. They are why some of us wake up 2 minutes before the alarm goes off in the morning, for example. 

Brian Prendergast, professor at the University of Chicago, wants to understand how the time of year affects daily (or circadian) rhythms not in humans, but in fish. Predergast typically studies hamsters and mice, but was intrigued when his previous undergraduate advisor, Steve Zottoli, told him about the striped bass that reside in Woods Hole’s Eel Pond during the spring and summer months. 

Zottoli, professor emeritus at Williams College and adjunct senior scientist at MBL, has built an education and outreach program for middle and high school students to work with striped bass, and has tagged and tracked these creatures for the last four years. The project began with just body temperature tracking but, with the help of Scott Bennett, manager of MBL Marine Research Services & Secondary Education, has recently expanded to include depth and location sensing. Compared to more well-studied mammals, little is known about how marine vertebrates form an internal representation of time and how they anticipate cyclic changes in the environment based on the seasons, so Prendergast was excited to hop on board. Prendergast is the inaugural MBL Barbey Fellow and his work is supported by the Edwin Barbey Charitable Trust, which funds resident scientists or visiting investigators to conduct research on biological and ecological questions that relate to striped bass.

This summer, Prendergast’s goal is to analyze the plethora of data collected from these tracking devices and begin to understand how striped bass rhythms change throughout the seasons.

JP Riggle, Brian Prendergast, Scott Bennett and Jharnae Love discuss striped bass outside at the MBL.
Brian Prendergast (center left) and his PhD students, Jharnae Love (right) and recently graduated JP Riggle (left) discuss with Scott Bennett from the Marine Resources Center about body temperature sensing in striped bass. Credit: Nora Bradford

“I think unpacking each one of these behaviors and finding out how each is relevant to their fitness is the next step,” says Prendergast. 

Prendergast and his PhD students, Jharnae Love and recently graduated JP Riggle, have already observed that, like many other animals, striped bass go through periods in which their circadian rhythms have higher or lower “amplitude.” 

“Think of a pendulum. Amplitude would be based on how heavy and long the pendulum is,” says Prendergast. It’s very hard to change the swinging of a huge, heavy pendulum with a large amplitude, like the ones at science centers. Whereas a nickel swinging on a string has a lower amplitude, which means it’s very easy to adjust or stop. 

Generally, animals tend toward having high amplitude rhythms in stable situations, but certain situations call for lower amplitude rhythms. “There might be times of year when you need to change your clock and override your circadian rhythms, so that allows behavioral flexibility.”

From looking at how deep in the water these fish are through the day, the team can see higher or lower amplitude periods of their circadian rhythms. Right after the striped bass arrive in Eel Pond in May, and again right before they leave in October, their rhythms appear to be less robust and more chaotic. In other words, their depth doesn’t depend on the time of day during these transitional periods.

Transmitters on the striped bass show their locations on map.
Transmitters on the striped bass allow Prendergast's team to track the location of individual fish every couple minutes. Here, yellow dots show where the fish was in Eel Pond during the day and blue dots show night location. Credit: Brian Prendergast

“Have you ever gone on a long trip?” asks Prendergast. “You have to take your last trip to the store, pack your bags, get your passport.” These fish have to do a similar thing. They prepare before migration and adjust after arriving at the destination, and it shows up in their daily behavioral patterns. 

The team plans to investigate what other factors, like location and body temperature, might reveal about their circadian rhythms. Their findings will be one of the first explorations of how seasonal changes affect circadian rhythms within marine invertebrates.