SFEWS Vol. 20, Issue 1 | March 2021
#CentralValley #ChinookSalmon #otolithchemistry #Steelhead #monitoring #surveys #catchability #detectionefficiency #DeltaSmelt #supplementation #Ich #pathogens #organiccarbon #stablecarbon #nitrogen #inputs #YubaRiver #watersheds
Variation in Juvenile Salmon Growth Opportunities Across a Shifting Habitat Mosaic
Coleman et al. found that juvenile Chinook Salmon grew faster in the Delta in some years (2016), but slower in the Delta during drought conditions (2014 to 2015). Habitat that featured faster growth rates varied within and among years, suggesting the importance of maintaining a habitat mosaic for juvenile salmonids, particularly in a dynamic environment such as the California Central Valley.
Counting the Parts to Understand the Whole: Rethinking Monitoring of Steelhead in California’s Central Valley
Eschenroeder et al. argue that a reallocation of monitoring resources to better understand the interaction between resident and anadromous Steelhead would provide better data to estimate the vital rates needed to evaluate the effects of recovery actions.
Relative Bias in Catch Among Long-Term Fish Monitoring Surveys Within the San Francisco Estuary
Huntsman et al. assessed relative catchability differences among four long-term fish monitoring surveys from the San Francisco Estuary. Their results demonstrate that catchability is a source of bias among monitoring efforts within the San Francisco Estuary, and assuming equal catchability among surveys, species, and size classes could result in significant bias when describing spatio-temporal patterns in catch if ignored.
Investigation of Molecular Pathogen Screening Assays for Use in Delta Smelt
Gille et al. conducted a pilot study that applied molecular assays originally developed in salmonids to assess the presence of a wide variety of pathogens in the gill tissue of cultured and wild Delta Smelt—as well as cultured fish—deployed in enclosures in the estuary. Although disease is not an overt cause of population decline of Delta Smelt in the San Francisco Estuary, comprehensive pathogen presence and prevalence data are lacking, and unintended transmission of pathogens can have devastating effects on populations already at-risk or on the natural ecosystem at large. Their results corroborate previous work that cultured Delta Smelt do not appear to present a high risk for pathogen transmission during population supplementation or reintroduction.
Multi-Biomarker Analysis for Identifying Organic Matter Sources in Small Mountainous River Watersheds: A Case Study of the Yuba River Watershed
Pondell and Canuel's study focused on identifying the composition of watershed-derived organic matter (OM). To better understand inputs to inland waters and improve distinguish between terrigenous and aquatic sources in downstream systems, such as estuaries and coasts, they surveyed OM sources from the Yuba River watershed in northern California to identify specific biomarkers that represent aquatic and terrigenous OM sources. Results demonstrate the utility of multi-biomarker studies for distinguishing between OM from different sources and land uses, offering new insights for biogeochemical studies in aquatic systems.
Volume 15, Issue 4, 2017
The goal of this paper is to analyze storage projects constructed and planned in California since 1980, in contrast with storage constructed before that date. As a result of California’s highly variable climate, storage is an essential tool for agricultural and urban water users. Today, the state regulates approximately 1,250 reservoirs, with a combined storage of 42 million acre-feet. Federal agencies regulate approximately 200 additional reservoirs. The vast majority of this surface storage was constructed before 1978, when New Melones Dam, the last large on-stream water supply reservoir in California, was completed. The role of storage in meeting future needs remains a high-profile issue in the California water debate. For example, funding for new storage was the largest item in Proposition 1, the most recent water bond voters approved. This analysis included a review of existing literature, such as the California Department of Water Resources Division of Dam Safety database, California Water Commission documents about new storage proposals, water agency documents, and interviews with water agency staff and others. Water managers face dramatically different conditions today, in comparison to conditions before 1980. These conditions have led to new approaches to water storage that represent a dramatic departure from past storage projects. During the past 37 years, a wide range of new water storage strategies have been planned and implemented. These facilities have created a combined new storage capacity greater than that of Lake Shasta, California’s largest reservoir. These new storage strategies suggest the need to revisit the fundamental definition of water storage. With limited potential for new storage drawing from the state’s rivers, California must choose storage projects wisely. By learning from successful strategies in recent decades, decision-makers can make better storage investment decisions to help reverse declines in ecosystem health and improve water supply reliability.
- 2 supplemental PDFs
Simulation of Subsidence Mitigation Effects on Island Drain Flow, Seepage, and Organic Carbon Loads on Subsided Islands Sacramento–San Joaquin Delta
In light of desired implementation of subsidence mitigation practices on Delta islands and the need for evaluation tools, we developed groundwater-flow and solute-transport models and attempted to answer the following questions.
1. How do the groundwater-flow and drainage systems interact to influence island drainage volumes and drain dissolved organic carbon (DOC) concentrations and loads?
2. How will future subsidence affect drainage volumes, DOC loads, and seepage onto islands?
3. How will land-use changes to mitigate subsidence affect seepage, drain flow, and DOC loads?
4. How can seepage and water-quality effects from drainage, restoration, and rice cultivation on Delta islands be minimized?
We used hydrologic and geochemical data and modeling to answer these questions. Subsurface processes dominate subsided Delta island hydrology. Seepage and siphoned irrigation water recharge groundwater, which flows to drains. Drainage water that contains DOC derived from oxidation of organic soils is discharged to adjacent channels. We analyzed the effects of subsidence mitigation by simulating mosaics of rice and palustrine wetlands with varying hydrologic management on a representative subsided island (Twitchell Island). These alternative land uses reduce seepage onto islands and thus contribute to increased levee stability. However, most scenarios resulted in increased drain flow and DOC loads. Reducing drain flow is essential to reducing DOC loads relative to the business-as-usual scenario and can be accomplished through hydrologic controls that reduce drain flow on the islands.
- 3 supplemental PDFs
A Covered Cod-End and Tow-Path Evaluation of Midwater Trawl Gear Efficiency for Catching Delta Smelt (Hypomesus transpacificus)
For nearly 50 years, the California Department of Fish and Wildlife has used a midwater trawl to intensively monitor fish populations in the San Francisco Estuary during the fall, sampling over 100 locations each month. The data collected have been useful for calculating indices of fish abundance and for detecting and documenting the decline of the endangered fish species delta smelt (Hypomesus transpacificus). However, efforts to calculate estimates of absolute abundance have been hampered by the lack of information on gear efficiency, in particular questions about contact selectivity and the effect of tow method on catches. To answer these questions we conducted a study that used a covered cod end on a net towed either near the surface, referred to as a surface tow, or throughout the water column, referred to as an oblique tow. A contact selectivity model was fit to estimate the probability that a delta smelt that has come into contact with the net is retained in the cod end of the net conditional on its body length. Full retention of delta smelt was found to occur around 60 mm fork length. Delta smelt catch densities for the surface tows were an order of magnitude greater than densities in the oblique tows, suggesting a surface orientation at the sub-adult life stage. These results represent an important step in being able to calculate absolute abundance estimates of the delta smelt population size using decades’ worth of monitoring data.
- 2 supplemental PDFs