SFEWS: Volume 19, Issue 3
In our September issue new research and commentary provide insights on several topics: how to integrate zooplankton science to inform estuary management; how simulated fishing can avoid missed fish and detect gear bias in the water; why juvenile Chinook Salmon length-at-date criteria don't match genetic run assignments; whether declines in breeding waterfowl population relate to wetland habitat and salinity; and what kinds of food web support can be achieved by use of a managed flow pulse.
Photo: Forster’s Terns at Crown Beach, public domain. Attribution: © Ingrid Taylar, Creative Commons 2.0 Generic license.
Catch as Catch Can
"Catchability" refers to the relationship between catch rate and the true population. Ecological monitoring programs use catch per unit of effort (CPUE) to standardize catch and monitor changes in fish populations; however, CPUE is proportional to the portion of the population that is vulnerable to the type of gear used in sampling, which is not necessarily the entire population. Tobais' simulation combines a module for sampling conditions with a module for individual fish behavior to estimate the proportion of available fish that would escape from the sample. The method is applied to the case study of the well monitored fish species Delta Smelt (Hypomesus transpacificus) in the San Francisco Estuary, where it has been hypothesized that changing water clarity may affect catchability for long-term monitoring studies.
Waterfowl Reproductive Success Depends on High Water, Low Salt
Availability of wetlands with low salinities during the breeding season can influence waterfowl reproductive success and population recruitment. Salinities as low as 2 ppt (3.6 mS/cm) can impair duckling growth and influence behavior, with mortality occurring above 9 ppt (14.8 mS/cm). Schacter et al. used satellite imagery to quantify the amount of available water, and sampled surface water salinity at Grizzly Island, in the brackish Suisun Marsh, at three time-periods during waterfowl breeding (April, May, July) over 4 years (2016–2019). Among their findings was during peak duckling production in May, 81%–95% of available water had salinity above 2 ppt, and 5%–21% was above 9 ppt. Local waterfowl populations would benefit from management practices that provide fresher water during peak duckling production in May and retain more water through July.
Deep Dives Among Waterbird Populations in South SF Bay
In south San Francisco Bay, former salt ponds now managed as wildlife habitat support large populations of breeding waterbirds. In 2006, the South Bay Salt Pond Restoration Project began the process of converting 50% to 90% of these managed pond habitats into tidal marsh. Hartman et al. compared waterbird populations in south San Francisco Bay before (2001) and after (2019) approximately 1,300 ha of managed ponds were breached to tidal action to begin tidal marsh restoration. Study results showed average annual nest abundance declined during 2017–2019 by 53%, 71%, and 36%, for American Avocets, Back-necked Stilts, and Forster’s Terns, respectively. All three species established nesting colonies on newly constructed islands within remaining managed ponds; however, these new colonies did not make up for the steep declines observed at other historical nesting sites. For future wetland restoration, retaining more managed ponds that contain islands suitable for nesting may help to limit further declines in breeding waterbird populations.
Managed Pulse Flows as Food Web Support
While freshwater inflow has been a major focus of resource management in estuaries, including the upper San Francisco Estuary, there is a growing interest in using focused flow actions to maximize benefits for specific regions, habitats, and species. To test this concept, in summer 2016, Frantzich et al. used a managed flow pulse to target an ecologically important region: a freshwater tidal slough called the Cache Slough Complex. Their goal was to improve estuarine habitat by increasing net flows through CSC to enhance downstream transport of lower trophic-level resources, an important driver for fishes such as the endangered Delta Smelt. Simulations using a 3-D hydrodynamic model (UnTRIM) indicated that the managed flow pulse had a large effect on the net flow of water through Yolo Bypass, and between the CSC and further downstream. The managed flow pulse resulted in increased densities of zooplankton (copepods, cladocerans) demonstrating potential advection from upper floodplain channels into the target CSC and Sacramento River regions. Though conducted during a single year, this study may provide an instructive example of how a relatively modest change in net flows can generate measurable changes in ecologically relevant metrics, and how an adaptive management action can help inform resource management.
Length-at-Date Criteria and Genetic Run Assignments
Four distinct runs of Central Valley Chinook Salmon are named after their primary adult return times: fall, late-fall, winter, and spring run. Estimating the run-specific composition of juveniles entering and leaving the Sacramento–San Joaquin Delta is crucial for assessing population status and processes that affect juvenile survival through the Delta. Historically, the run of juvenile Chinook Salmon captured in the field has been determined using a length-at-date criteria (LDC); however, LDC run assignments may be inaccurate if there is high overlap in the run-specific timing and size of juveniles entering and leaving the Delta. In this study, Brandes et al. use genetic run assignments to assess the accuracy of LDC at two trawl locations in the Sacramento River (Delta entry) and at Chipps Island (Delta exit).Across years, there was extensive overlap among the distributions of run-specific fork lengths of genetically identified juveniles, indicating that run compositions based on LDC assignments would tend to underestimate fall-run and especially late-fall-run compositions at both trawl locations, and greatly overestimate spring-run compositions (both locations) and winter-run compositions (Chipps Island). We therefore strongly support ongoing efforts to include tissue sampling and genetic run identification of juvenile Chinook Salmon at key monitoring locations in the Sacramento–San Joaquin River system.
Pelagic fish in the San Francisco Estuary are harder to catch in recent decades. Over the past thirty years, Delta Smelt catch in the Fall Midwater Trawl Survey has declined by 99%, Longfin Smelt catch has declined by over 95%, and even the notoriously hardy Striped Bass have declined by over 75%. To manage the system and reverse these declines, we need a better understanding of the “bottom-up” processes that exert control on these populations—we need to study fish food. In other words, in addition to studying fish directly, we need to increase our understanding of what pelagic fish eat: zooplankton. In this essay, Hartman et al. break down not only what fish eat (zooplankton) and why they are important drivers of species abundance in higher trophic areas of the food web, but also how scientists and natural resources managers can communicate better to understand which zooplankton data can inform and develop management-relevant questions.
Volume 17, Issue 4, 2019
Sixteen years ago, in October 2003, San Francisco Estuary and Watershed Science (SFEWS) published its first article. An anniversary like this is a good time to remind ourselves of our history, and to ask if the journal is living up to the goals we set in 2003. And if so, are those goals consistent with today’s needs? In 2004, CDL’s eScholarship Publishing Group counted an average of 254 requests per month for SFEWS online articles. In 2010, that increased to 1,232 requests per month, and in 2014 to 1,764 per month. In the first 10 months of 2019, 4,420 articles were requested per month. Downloads have been consistently 35% to 40% of requests. Taking data from 2014 through 2017, the search engine Scopus’ CiteScore for SFEWS increased from 0.32 to 1.64; its rank is 82nd of 203 journals in the Water Science and Technology category for 2018, a remarkable climb from being ranked 120 of 179 in 2014. SFEWS is ranked fifth among 53 open access journals in the aquatic sciences, according to the Science Journal Ranking index; and in the top 25% among all 218 aquatic science journals ranked by that index. Thus, SFEWS has grown from an outlet designed to expand access to regional science to a well-respected scientific journal in its own right. Our look back shows that SFEWS has probably grown beyond our original expectations in size, influence, and stature.
Policy and Program Analysis
Review of and Recommendations for Monitoring Contaminants and their Effects in the San Francisco Bay−Delta
Legacy and current-use contaminants enter into and accumulate throughout the San Francisco Bay−Delta (Bay−Delta), and are present at concentrations with known effects on species important to this diverse watershed. There remains major uncertainty and a lack of focused research able to address and provide understanding of effects across multiple biological scales, despite previous and ongoing emphasis on the need for it. These needs are challenging specifically because of the established regulatory programs that often monitor on a chemical-by-chemical basis, or in which decisions are grounded in lethality-based endpoints. To best address issues of contaminants in the Bay−Delta, monitoring efforts should consider effects of environmentally relevant mixtures and sub-lethal impacts that can affect ecosystem health. These efforts need to consider the complex environment in the Bay−Delta including variable abiotic (e.g., temperature, salinity) and biotic (e.g., pathogens) factors. This calls for controlled and focused research, and the development of a multi-disciplinary contaminant monitoring and assessment program that provides information across biological scales. Information gained in this manner will contribute toward evaluating parameters that could alleviate ecologically detrimental outcomes. This review is a result of a Special Symposium convened at the University of California−Davis (UCD) on January 31, 2017 to address critical information needed on how contaminants affect the Bay−Delta. The UCD Symposium focused on new tools and approaches for assessing multiple stressor effects to freshwater and estuarine systems. Our approach is similar to the recently proposed framework laid out by the U.S. Environmental Protection Agency (USEPA) that uses weight of evidence to scale toxicological responses to chemical contaminants in a laboratory, and to guide the conservation of priority species and habitats. As such, we also aimed to recommend multiple endpoints that could be used to promote a multi-disciplinary understanding of contaminant risks in Bay−Delta while supporting management needs.
The Sacramento–San Joaquin Delta has been invaded by several species of non-native predatory fish that are presumed to be impeding native fish population recovery efforts. Since eradication of predators is unlikely, there is substantial interest in removing or altering manmade structures in the Delta that may exacerbate predation on native fish (contact points). It is presumed that these physical structures influence predator-prey dynamics, but how habitat features influence species interactions is poorly understood, and physical structures in the Delta that could be remediated to benefit native fish have not been inventoried completely. To inform future research efforts, we reviewed literature that focused on determining the effects of predator-prey interactions between fish, based on contact points that are commonly found in the Delta. We also performed a geospatial analysis to determine the extent of potential contact points in the Delta. We found that the effects of submerged aquatic vegetation (SAV) and artificial illumination are well studied and documented to influence predation in other freshwater systems worldwide. Conversely, other common structures in the Delta—such as docks, pilings, woody debris, revetment, and water diversions—did not have the same breadth of research. In the Delta, the spatial extent of the different types of contact points differed considerably. For example, 22% of the Delta water surface area is occupied by SAV, whereas docks only cover 0.44%. Our conclusion, based on both the literature review and spatial analysis, is that the effects of SAV and artificial illumination on predation warrant the most immediate future investigation in the Delta.
A Bayesian hierarchical model that integrated information about state and observation processes was used to estimate the number of adult Delta Smelt entrained into the southern Sacramento−San Joaquin Delta during water export operations by the California State Water Project and the Central Valley Project. The model hierarchy accounted for dynamic processes of transport, survival, sampling efficiency, and observation. Water export, mark−recapture, and fish facility count data informed each process. Model diagnostics and simulation testing indicated a good fit of the model, and that parameters were jointly estimable in the Bayesian hierarchical model framework. The model was limited, however, by sparse data to estimate survival and State Water Project sampling efficiency. Total December to March entrainment of adult Delta Smelt ranged from an estimated 142,488 fish in 2000 to 53 fish in 2014, and the efficiency of louvers used to divert entrained fish to fish facilities appeared to decline at high and low primary intake channel velocities. Though applied to Delta Smelt, the hierarchical modeling framework was sufficiently flexible to estimate the entrainment of other pelagic species.
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