"Juvenile White Sharks in Monterey Bay: Effects of Thermal Habitat Patchiness on Local Densities of a Range Shifting Predator"
A Thesis Defense by Kelsey Montalto
Live-Stream July 25th, 2025 at 3:00 pm PST
Abstract
Climate change has shifted species’ distributional ranges in many marine and terrestrial systems. For marine species, those shifts in ranges associated with ocean warming are often poleward or into deeper waters. Juvenile white sharks (Carcharodon carcharias) are one such species, having exhibited a 270 km range shift of the cold edge of their thermal range extending northward up to the Monterey Bay. However, little is known about the fine-scale habitat selection of marine organisms at the cold edge of their shifting range and how localized thermal gradients or warm pools may permit persistence in these newly inhabited locations. The Monterey Bay provides a unique study system with high spatial variability of environmental conditions, and a range-shifting endothermic predator, the white shark, that is highly mobile and known to be sensitive to ambient temperatures. This research investigates fine-scale habitat selection by juvenile white sharks in this dynamic system at the submesoscale (1-10 km) using remote sensing, aerial surveys, and acoustic telemetry to link spatial and temporal patterns of site occupancy with environmental conditions. Results indicate that increases in sea surface temperature (SST) and K490 (light attenuation coefficient proxy for turbidity) are significantly positively associated with juvenile white shark abundance from both remote sensing and acoustic telemetry perspectives. As juvenile white sharks extend their range northward, they may be utilizing pockets of warm water, enhanced by increased turbidity, as thermal refuges in regionally cooler areas. Additionally, higher residence times were observed at subsurface sites between the hours of 9:00 PM and 7:00 AM, indicating potential foraging behavior offshore before returning to coastal surface waters to rewarm. Understanding range shifts of predators is important as their presence in novel locations can result in changes in predator-prey interactions and new top-down effects on local ecosystems.
Bio
Kelsey grew up in both Southern and Central California, moving from Hermosa Beach in Los Angeles to Oakhurst in the Foothills of the Sierras with her sister, mom, and dad when she was ten. After graduating from high school, she attended Fresno State as a Presidential Honors Scholar. Initially entering as an Undeclared major, she found herself drawn to the sciences. She eventually declared as a Biology major with a Spanish minor, while maintaining a healthy level of involvement in the music department in her spare time. As she progressed through her program, she was able to travel to Clearwater, Florida, to participate in shark and ray research for two summers, solidifying her desire to pursue marine science. She was able to use these data to conduct her undergraduate thesis on the drivers of elasmobranch biodiversity in this area for Fresno State's Biology Honors Program, graduating in the Spring of 2022.
Looking for a way to expand her skillset, Kelsey decided to pursue a marine-related Master's degree, finding MLML as a program that could bolster her experience with research, course material, and practical skills in the marine sphere. Kelsey joined the Ichthyology Lab at MLML and the Ocean Predator Ecology Lab at CSUMB in the Fall of 2022, co-advised by Drs. Sal Jorgensen and Scott Hamilton. During her time at MLML, her thesis work has investigated how temperature, phytoplankton biomass, and turbidity are associated with juvenile white sharks within Monterey Bay after their novel appearance in 2014. However, she could be found helping others with their various projects, TAing at CSUMB, and working for MLML's California Collaborative Fisheries Research Program (CCFRP) and surf zone MPA monitoring programs in her spare time. She is excited to be making this next step towards her career and to see what new challenges await her on the other side of her Master's.
