I am a stable isotope ecologist studying how humans are altering food web dynamics for sharks in the middle of the food web. Stable isotope ecology follows the age old saying, “You are what you eat.” When animals consume their prey, the chemistry (i.e., stable isotope composition) gets incorporated into the predator’s tissues. Chronological shark tissues like teeth, vertebrae, and eye lenses record stable isotope compositions through time, allowing us to infer movement and trophic interactions across seasons and even the entire lifetime of an individual. This is particularly important in California because one of the state’s largest Leopard Shark (Triakis semifasciata) populations resides in the San Francisco Estuary (SFE) and is subject to wastewater effluent discharge from 38 wastewater treatment facilities, which have heavily altered nutrient loads within the SFE. Previous studies have attributed a change in nitrate/ammonium levels in the SFE to this wastewater discharge. While these changes in nutrient levels have been correlated with the collapse of pelagic fish communities within the SFE, the causation of this collapse is still up for debate and more than likley attributed to freshwater flow reduction. With the Leopard Shark experiencing extreme declines in the SFE, this study aims to investigate whether these high levels of wastewater effluent pollution are affecting Leopard Shark dietary and migratory behaviors. We also hope to characterize the species’ life history diversity within California’s northern population by leveraging stable isotope analysis (SIA) and compound specific SIA of amino acids (CSIA-AA). Continuing to develop this approach, I hope to further add to the field of shark conservation.

Long-term monitoring is an extremely useful scientific tool to understand how species' populations are changing through space and time. Using trawling data collected from 1980 to present, I am modeling Leopard Shark population decline in the critically important nursery habitat of the San Francisco Estuary. In addition to population variation through time, I am also modeling how the species is responding to climate change and the corresponding changes to abiotic conditions along a macro estuarine gradient. This project is still ongoing.

The Longfin Smelt (pictured left) primarily follows a 2-year life cycle, is anadromous (i.e., migrating up rivers to spawn), and is a euryhaline (i.e., able to tolerate wide range of salinities) fish. Depending on the water year type and corresponding freshwater outflow in the San Francisco Estuary, individuals will migrate out to higher salinity waters (i.e., ocean) as they mature through their first year and subsequently return anually to fresher water until ready to spawn. However, it is still not understood whether the majority of indivduals follow the same and/or different life history patterns or if there is variation in migratory behaviour between different year classes. To help answer this question, I have been working with a collaborative team at the Universty of California Davis' Otolith Geochemistry and Fish Ecology Laboratory (OGFL). Our work focusses on using otoliths (i.e., ray finned fish ear stones), which grow daily layers similar to tree rings, in combination with a Laser Ablation Inductively Coupled Plasma Mass Spectrometer (LA-ICPMS) to track strontium stable isotope ratios from birth to death. These strontium stable isotope ratios can then be correlated to the salinity experienced throughout the fish's life. This project is ongoing.