I am a postdoctoral fellow in the fish ecology group (Hobbslab) at the Wildlife, Fish and Conservation Biology Department, UC Davis. Currently I am using isotopic tracing to investigate habitat changes and movement patterns of various California native fish species including Delta and Longfin Smelt and Chinook Salmon. My background is in isotope geochemistry and GIS analysis and I was a PhD student at the Australian National University, Canberra, Australia. There I was involved in the application of stable isotopes to trace prehistoric human and animal mobility in France. 

Email: mwillmes@ucdavis.edu

Delta Science Fellowship 2017-2019

In search of refuge: Investigating the thermal life history of Delta Smelt through in-situ oxygen isotope ratio analysis of otoliths

The Delta Smelt (Hypomesus transpacificus) is a small pelagic fish and rapidly approaching extinction. It is endemic to the Sacramento-San Joaquin Bay-Delta which is an important link in California’s water supply. This estuary is managed for human use as well as for several species of threatened and endangered fish and the Delta Smelt is at the center of conflict between human and environmental uses of the limited water resources.

Here we used strontium (87Sr/86Sr) and oxygen (δ18O) isotope tracers from archived Delta Smelt otoliths to reconstruct life history and thermal resilience at fine temporal scales. 87Sr/86Sr ratios from otoliths can be used to reconstruct salinity habitats, while δ18O reflects the water temperature a fish has experienced.

The combination of these two isotopic tracers will allow us to investigate the relationship between Delta Smelt abundance, freshwater outflow and water temperature. Understanding this relationship can give new insights into resilience and habitat utilization of Delta Smelt in the face of warming water temperatures during prolonged drought periods and long-term climate change.