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 10, Issue 1, 2012
Embryonic and larval development of Sacramento splittail (Pogonichthys macrolepidotus) was characterized from zygote to metamorphosis in laboratory conditions. Fertilized eggs were obtained from induced and natural tank spawning of adults caught in the Yolo Bypass of the Sacramento River. Splittail produced transparent adhesive eggs with a moderate perivitelline space. Duration of embryonic development from fertilization to hatching was 100 h at 18 ± 0.5 °C. Newly hatched larvae were 5.2 to 6.0 mm total length with no mouth opening. Yolk-sac larvae were demersal and absorbed the yolk within 10 days post-hatch. Exogenous feeding started at 6 days post-hatch, concomitant with swim bladder inflation and swim-up movement. Fin differentiation began at approximately 10 d post-hatch (ca. 8.3 to 8.85 mm total length) and was completed at 50 d post-hatch (ca. 19.6 to 20.85 mm total length) when larval finfold was fully resorbed and the adult complement of fin rays was present in all fins, but scales were still lacking.
We examined the spatial and temporal distributions of fishes at a reference and three restored marshes between April 1998 and July 1999 in the Sacramento–San Joaquin Delta, California, to determine the factors that influence fish assemblages in space and time. Shallow-water fishes were sampled using beach seines with and without block-net enclosures in open-water shoals and submerged aquatic vegetation (SAV). Purse seining was used to sample fishes in deep water, including offshore, tidal slough, and marsh-edge habitats. Overall, fish assemblages in reference and restored marshes were dominated by introduced species. One-way analysis of similarity (ANOSIM) did not reveal study site differences in fish assemblages in either data set. However, nonmetric multi-dimensional scaling (NMS) and ANOSIM tests of the shallow-water collections revealed differences in fish assemblages using habitats with and without SAV. Introduced fishes, including predatory centrarchid fishes, were abundant in SAV. NMS and ANOSIM tests of the deep-water collections revealed differences in fish assemblages between offshore and nearshore (marsh-edge and tidal slough) habitats. Notably, native fishes were abundant in tidal sloughs. Temporal analyses revealed a suite of species more common in winter and spring, versus another group of introduced species that were more common in summer and fall. Our study findings indicate that newly restored habitats in the Sacramento–San Joaquin Delta will be invaded by introduced fishes. To promote native fish habitat, restoration planning should focus on areas and regions of the Delta where tidal marshes can be restored with little intervention, and where invasive SAV is less likely to colonize.
Individual-level and Population-level Historical Prey Demand of San Francisco Estuary Striped Bass Using a Bioenergetics Model
Striped bass are both a major predator of native fishes and support a recreational fishery in the San Francisco Estuary (the estuary). Quantifying their demands on their prey is important for understanding long-term trends of fish in the estuary. In this study, we: (i) applied a bioenergetics model of sub-adult (age 1 and age 2) and adult (age 3+) striped bass (Morone saxatilis) to quantify long-term consumption patterns from 1969 through 2004 in the estuary; (ii) developed a method to estimate the abundances of sub-adult striped bass; (iii) evaluated how consumption varied by age and gender; and (iv) identified factors that affect the resulting consumption estimates. On a ‘per capita’ basis, modeled individual prey fish consumption increased after 1990, and individual total and prey fish consumption by age-2 striped bass increased after 1994. Conversely, individual total and prey fish consumption by adult striped bass decreased over the period analyzed. This decline in individual consumption over the study period was related to a decline in mean length at age of adults. As expected, long-term trends in population consumption (total and prey fish) by all ages of striped bass (ages 1 through 6) closely followed their respective population- abundance trends. Population total consumption and prey fish-specific consumption by sub-adult striped bass was found to be similar to the population consumption by adult striped bass, largely because of the high abundance of sub-adults. Unlike adult striped bass that may emigrate and forage in the Pacific Ocean, the majority of sub-adult striped bass reside within the estuary; hence, consumption by the relatively abundant sub-adult population may have significant effects upon their estuarine prey species.
Contemporaneous Subsidence and Levee Overtopping Potential, Sacramento-San Joaquin Delta, California
The levee system in California’s Sacramento-San Joaquin Delta helps protect freshwater quality in a critical estuarine ecosystem that hosts substantial agricultural infrastructure and a large human population. We use space-based synthetic aperture radar interferometry (InSAR) to provide synoptic vertical land motion measurements of the Delta and levee system from 1995 to 2000. We find that Delta ground motion reflects seasonal hydrologic signals superimposed on average subsidence trends of 3-20 mm/yr. Because the measurements are insensitive to subsidence associated with peat thickness variations over Delta-island length scales, it is most likely that InSAR rates reflect underlying Quaternary sedimentary column compaction. We combine InSAR rates with sea-level rise scenarios to quantify 21st century levee overtopping potential. If left unmitigated, it is likely that 50 to 100 years from now much of the levee system will subside below design thresholds.
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