Common Predator, Rare Prey: Exploring Juvenile Striped Bass Predation on Delta Smelt in California's San Francisco Estuary

We examined a 36-year record of concurrent midwater trawl and water quality sampling conducted during fall to evaluate habitat trends for three declining fish species in the San Francisco Estuary, California, USA: delta smelt (Hypomesus transpacificus), striped bass (Morone saxatilis), and threadfin shad (Dorosoma petenense). Generalized additive modeling revealed that Secchi depth and specific conductance were important predictors of occurrence for delta smelt and striped bass, while specific conductance and water temperature were important for threadfin shad. Habitat suitability derived from model predictions exhibited significant long-term declines for each species; the southeastern and western regions of the estuary exhibited the most dramatic changes. Declines in habitat suitability were associated with anthropogenic modifications to the ecosystem. For delta smelt, an imperiled annual species endemic to the estuary, the combined effects of fall stock abundance and water quality predicted recruit abundance during recent years of chronically low food supply. Our results are consistent with existing evidence of a long-term decline in carrying capacity for delta smelt and striped bass and demonstrate the utility of long-term data sets for evaluating relationships between fish and their habitat.

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Early Life History of Fishes in the San Francisco Estuary and Watershed

Early Life History of Fishes in the San Francisco Estuary and Watershed ◽

10.47886/9781888569599.ch4 ◽

2004 ◽

Keyword(s):

Life History ◽

San Francisco ◽

Striped Bass ◽

Early Life ◽

Early Life History ◽

San Francisco Estuary ◽

Delta Smelt ◽

History Of ◽

Acanthogobius Flavimanus ◽

Longfin Smelt

Abstract.—We analyzed data on spring and summertime larval and juvenile fish distribution and abundance in the upper San Francisco Estuary (SFE), California between 1995 and 2001. The upper SFE includes the tidal freshwater areas of the Sacramento–San Joaquin Delta downstream to the euryhaline environment of San Pablo Bay. The sampling period included years with a variety of outflow conditions. Fifty taxa were collected using a larval tow net. Two common native species, delta smelt Hypomesus transpacificus and longfin smelt Spirinchus thaleichthys, and four common alien taxa, striped bass Morone saxatilis, threadfin shad Dorosoma petenense, gobies of the genus Tridentiger, and yellowfin goby Acanthogobius flavimanus, were selected for detailed analysis. Outflow conditions had a strong influence on the geographic distribution of most of the species, but distribution with respect to the 2 psu isohaline (X2) was not affected. The distribution patterns of delta smelt, longfin smelt, and striped bass were consistent with larvae moving from upstream freshwater spawning areas to downstream estuarine rearing areas. There were no obvious relationships of outflow with annual abundance indices. Our results support the idea of using X2 as an organizing principle in understanding the ecology of larval fishes in the upper SFE. Additional years of sampling will likely lead to additional insights into the early life history of upper SFE fishes.

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Environmental contaminant effects on juvenile striped bass in the San Francisco Estuary, California, USA

Environmental Toxicology and Chemistry ◽

10.1002/etc.386 ◽

2010 ◽

Vol 30 (2) ◽

pp. 393-402 ◽

Cited By ~ 9

Author(s):

Jimmy L. Spearow ◽

Rama S. Kota ◽

David J. Ostrach

Keyword(s):

San Francisco ◽

Striped Bass ◽

San Francisco Estuary ◽

Environmental Contaminant

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Early Life History of Fishes in the San Francisco Estuary and Watershed

Early Life History of Fishes in the San Francisco Estuary and Watershed ◽

10.47886/9781888569599.ch13 ◽

2004 ◽

Keyword(s):

Growth Rate ◽

San Francisco ◽

Striped Bass ◽

Growth Rates ◽

Early Life History ◽

San Francisco Estuary ◽

Annual Growth ◽

Factors Affecting ◽

Juvenile Abundance ◽

History Of

Abstract.—We investigated factors affecting growth of larval striped bass Morone saxatilis in the San Francisco Estuary from 1984 to 1993. We estimated ages and growth rates of larval striped bass from daily otolith increments. Mean annual growth rates of 6–14 mm standard length striped bass varied from 0.13 to 0.27mm/d, the lowest rate occurring in 1989 and the highest in 1992. The 1989 growth rate was significantly lower than all other years, and growth rates for 1992 and 1993 were significantly higher than all other years, but did not differ from one another. Differences in annual growth rates apparently were due mainly to differences in mean annual prey densities because growth rate increased as prey density increased. Compared to both laboratory measured growth rates and growth rates of field-caught Chesapeake Bay larvae, growth rates from the San Francisco Estuary appeared to be high for the food available, indicating that larvae can grow at relatively high rates even at low prey densities. Correlation analyses did not support density-dependent control of growth rates. Growth rate was not significantly related to mean annual conductivity, water temperature, mortality rates, or the juvenile abundance index, but was significantly and positively correlated with densities of 1-mm length-groups of 9–14-mm striped bass.

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