Tidal Wetlands and Environmental Drivers in Species Recovery: Suisun Marsh, CA (USA)

Suisun Marsh is the largest tidal wetland on the west coast of North America, existing at the interface of the Sacramento-San Joaquin (SSJ) Delta and the San Francisco Bay in California. This dynamic landscape acts as a model system for observing the impacts of environmental changes; as a result, long-term monitoring efforts have been consistently deemed as a priority to evaluate the efficacy of restoration projects. We analyze the trends in fishes and water quality variables in Suisun Marsh from 1995-2024, specifically honing in on the recovery of an obligate floodplain-spawning fish (Sacramento Splittail) and contextualize what may have influenced its increases in abundance. We use the Normalized Difference Water Index as a proxy for floodplain availability compared to abundance data within Suisun Marsh, collected monthly at 25 sites. We additionally delve into distributions of fishes in Suisun Marsh and where they occur spatially, with respect to environmental conditions. Water quality samples were taken at each of the sites alongside biotic surveys once a month, including salinity, dissolved oxygen, turbidity, depth, and temperature, which were additionally compared to calculations of Delta Outflow (a metric representing the approximate quantity of freshwater entering the system). We hypothesize that the recovery of Sacramento Splittail population was ‘unintended’ as a result of nearby restoration efforts to wetland habitat targeting a different species. Once listed as a threatened species, the increases in floodplain availability then seem to represent a marked growth in abundances of Splittail. Larger implications of this project includes the evaluation of the single-species management approach common in the USA as well as the implications for nonnative species management.