UC Davis

Fishes are highly important recreational, commercial, cultural, and food resources throughout the world. Of all fishes, estuarine fishes are perhaps the most accessible to humans and highly impacted by development and exploitation due to their proximity to major ports and centers of development. As a result, many populations of estuarine fishes have experienced drastic declines in abundance and shifts in distribution. This is especially true for the fishes of the San Francisco Estuary (SFE), which have had to contend with stressors in the form of waterway channelization, floodplain and marshplain “reclamation”, aquatic toxicants, overexploitation, major shifts in hydrologic regimes, and the export of large quantities of freshwater from both riparian and appropriative water users. In response, numerous agency and university long-term monitoring programs have been established to monitor and inform the management of estuarine fishes in this system.

These monitoring programs have documented the precipitous decline of several fish species in the SFE. Of these species, striped bass are unique and contentious. Introduced to the SFE in 1879, striped bass soon colonized several other Pacific Coast estuaries, including the Umpqua Estuary in southern Oregon. In the century following their introduction, striped bass were heralded as a locally important recreational and commercial species, with much management focused on the persistence of their fisheries. In more recent history, they have been less highly regarded by management agencies, owing to their trophic positioning as a piscivore and their perceived impact on native fishes. Regardless of their perception as a predator, striped bass still represent productive recreational fisheries and play an important role as an indicator of estuarine “health.”

My dissertation investigates the changes in abundance and distribution of juvenile striped bass and several other estuarine species, including Delta smelt, longfin smelt, and American shad. In addition, I investigate the current distribution of subadult and adult striped bass in the Umpqua Estuary. The analysis of estuarine fishes in the SFE starts with the integration of 14 long-term monitoring datasets and a cursory analysis of abundance in Chapter 1. This is then followed by a spatiotemporal analysis of abundance and distribution trends of striped bass and other estuarine fishes using generalized linear mixed models in Chapter 2. Finally, the investigation of subadult and adult striped bass distributional patterns is conducted using laser- ablation plasma mass spectrometry of striped bass otoliths to determine movement in relation to water isotopic signatures in Chapter 3.

Through my analyses I demonstrate the utility of integrated datasets and produce a dataset and web application for other researchers to utilize. I also show a decline in abundance and a change in the distribution of striped bass as well as several other estuarine fishes in the SFE. The distribution of these fishes has constricted considerably, with the Central and South Delta largely devoid of iconic estuarine fishes once common throughout the SFE. Finally, I show that striped bass are both present and actively reproducing in the Umpqua River Estuary, with no evidence of immigration from the SFE.