Conservation Physiology of California Native Fishes
California fishes, particularly those inhabiting the San Francisco Bay-Delta (SFBD) region, are negatively impacted by many anthropogenic environmental stressors that degrade water quality. Green sturgeon, Chinook salmon, as well as the Delta and Longfin smelt are among the species listed as endangered or threatened in California. Some of the factors thought to be responsible for native fish declines include loss of adequate stream flows due to water diversions for human use, direct loss of fishes due to entrainment against diversion intake screens, loss of suitable habitat, pollutants, as well as climate change. We are exploring the physiological performance of native fishes exposed to ‘real-world’ challenges to determine whether or not these anthropogenic factors are pushing species beyond their physiological tolerance thresholds. The common goal in all of these experiments is to understand the environmental requirements of native fishes in order to protect, preserve and restore native populations.
Fish entrainment risk: We are studying the impacts of small-scale agricultural water diversions (typically open-ended pipes that pump water directly from the rivers while also drawing in, entraining, fish), and historically this has been considered a minor contributor to fish mortality. However, in California, there are over 3,700 water diversions on the Sacramento and San Joaquin Rivers and their tributaries, and in the Sacramento-San Joaquin Delta and Suisun Marsh. Of these existing diversions, over 95% are unscreened with no physical barrier to prevent fish entrainment. We have shown that juvenile Chinook salmon and green sturgeon are susceptible to entrainment at unscreened water diversions and we are testing the efficacy of behavioral and hydraulic deterrents designed to direct fish past water diversion pipes at distances far enough from the pipe’s zone of hydraulic influence.
Physiological, genomic and climate modeling to understand the impacts of climate change on an endemic SFBD fish, the Delta Smelt:
The delta smelt (Hypomesus transpacificus) is a pelagic, annual fish species endemic to the Sacramento-San Joaquin estuary, whose abundance has dramatically declined since the 1980s, and is listed under the Federal Endangered Species Act (ESA). Considerable efforts are underway to understand the causes of this recent population decline as well as to produce accurate risk assessment and management strategies that consider ongoing changes associated with climate change. Combined, climate change models predict that Bay-Delta aquatic organisms will face not only increased temperature, salinity and altered turbidity regimes, but also increased variability in these parameters. We have several projects focused on delta smelt: (1) assessing physiological tolerances for temperature, salinity, and turbidity change, (2) investigating the underlying physiological mechanisms of tolerance, and (3) integrating tolerance and stress response data into spatio-temporal climate change models in the Bay-Delta to assess future habitat suitability.
Splittail: The Sacramento splittail, Pogonichthys macrolepidotus, is Federally listed as a species of special concern and there is very little information available about natural history and population dynamics in this species. A recent study revealed two genetically-distinct populations of splittail thought to occupy distinct regions of the estuary and suggesting to managers that recovery strategies should account for this variation. Notably, these regions of the estuary differ markedly in local salinity regimes. In this collaborative study, we are working with fish geneticists, biotelemetry experts, and population modelers to address population dynamics in splittail. We are testing whether genetic differences translate into intraspecific variation in physiological traits such as growth, metabolism, and behavioral and physiological responses to altered salinity regimes.
Hardhead: Hardhead (Mylopharodon conocephalus) is a California fish Species of Special Concern, yet environmental limits for its management are largely unknown. Hardhead abundance may be declining throughout much of its range partially due to resource competition from non-native fish species, but also from anthropogenic river alterations including temperature and flow changes due to hydroelectric operations. We are evaluating the physiological responses (resting and active metabolic rate determinations, swimming performance, thermal tolerance, and blood-oxygen equilibria) and behavior (thermal preference) of hardhead across a range of environmentally relevant temperatures. These data are intended to assist in developing thermal targets for future and current Federal Energy Regulatory Commission (FERC) licensing of hydroelectric projects in California.
Sturgeon nutrition and stress tolerance: Food webs in the SFBD are changing rapidly, potentially affecting the food source for many species including wild white (threatened) and green (endangered) sturgeon. Additionally, climate change effects (e.g. temperature and salinity alterations in this case) stand to challenge sturgeon physiology. In this new project, we are manipulating nutritional status in larval, fingerling and juvenile green and white sturgeon and assessing the effects on physiological tolerance to temperature and salinity stressors.