Fish community ecology in an Altered River delta: Spatial patterns in species composition, life history strategies, and biomass

Nobriga, Matthew L.; Feyrer, Frederick; Baxter, Randall D.; Chotkowski, Michael A.

doi:10.1007/bf02732915

Cited by 76 publications

(108 citation statements)

References 30 publications

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“…Our study and others (Feyrer and Healey 2003;Toft et al 2003;Grimaldo et al 2004;Nobriga et al 2005;Nobriga and Feyrer 2007) show that native and introduced fishes in the Delta use a variety of habitats and that their trophic pathways vary with their body size and prey selection. Others have shown that physical habitat for native fishes can also be defined by water quality conditions or some measure of freshwater inflow (Kimmerer 2002a(Kimmerer , 2002b.…”

Section: Consequences For Restorationsupporting

confidence: 70%

“…The estuary is considered one of the most highly invaded ecosystems in North America (Cohen and Carlton 1998). Of note, the fish community in the Delta is now dominated by introduced species, many of which are associated with introduced species of SAV (Grimaldo et al 2004;Nobriga et al 2005;Brown and Michniuk 2007).…”

Section: Study Areamentioning

confidence: 99%

“…The species composition of fish generally reflected relative abundance in their environment (Feyrer and Healey 2003;Grimaldo et al 2004;Nobriga et al 2005;Brown and Michniuk 2007). The dominant species collected were introduced species (Table 1).…”

Section: Fish Collectionsmentioning

confidence: 99%

“…However, in the San Francisco Estuary, Brazilian waterweed and other introduced species of SAV are considered a nuisance because they impede recreational boat traffic, clog water diversions, and provide little or no economic value (California Department of Boating and Waterways 2000). Biologically, the Brazilian waterweed may be considered an ecosystem engineer (Jones et al 1994) because it has altered the physical environment of the estuary, which in turn has had direct and indirect consequences for native fish populations in the estuary (Brown 2003;Nobriga et al 2005;Brown and Michniuk 2007;Feyrer et al 2007). Here, we show that Brazilian waterweed supports invertebrates that are important energy sources for fishes in the Delta.…”

Section: Consequences For Restorationmentioning

confidence: 99%

“…Finally, there is very little evidence that flooded islands support native pelagic fishes (delta smelt Hypomesus transpacificus and longfin smelt Spirinchus thaleichthys; Grimaldo et al 2004;Nobriga et al 2005). Much of the justification for restoring flooded islands hinged on the premise that such areas would provide beneficial habitat for imperiled smelts, but these species are often found in the tidally dominated open waters and channels of the Delta (Grimaldo et al 2004;Rockriver 2004).…”

Section: Consequences For Restorationmentioning

confidence: 99%

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Dietary Segregation of Pelagic and Littoral Fish Assemblages in a Highly Modified Tidal Freshwater Estuary

2009

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Estuarine food webs are highly variable and complex, making identification of their trophic pathways difficult. Energy for the food web of the San Francisco Estuary is thought to be based largely on in situ phytoplankton production, but little attention has been paid to littoral habitats, where other energy sources may be important. We analyzed the stomach contents of over 960 juvenile fishes and the stable carbon and nitrogen isotope ratios of these fishes and their potential food resources in pelagic and littoral habitats from the tidal freshwater area of the estuary. The mixing model IsoSource was used to examine energy sources important to consumers. Our results show evidence of two predominant food web pathways. Pelagic fishes and some littoral fishes showed strong dependence on a zooplankton–phytoplankton trophic pathway. However, the majority of fishes in littoral habitats had diets and carbon isotope ratios consistent with energy arising from submerged aquatic vegetation and epiphytic macroalgae. IsoSource revealed that the overall majority of nutrition of littoral fishes originated from consumption of grazer amphipods. Examining both stable isotopes and stomach contents allowed us to identify a food web with contributions to resident fishes that had been previously underestimated in the estuary. This study provides insight to how estuarine food webs have changed over the last few decades and highlights why the functions of habitats must be understood for effective restoration planning.

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Section: Consequences For Restorationsupporting

confidence: 70%

Section: Study Areamentioning

confidence: 99%

Section: Fish Collectionsmentioning

confidence: 99%

Section: Consequences For Restorationmentioning

confidence: 99%

Section: Consequences For Restorationmentioning

confidence: 99%

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Dietary Segregation of Pelagic and Littoral Fish Assemblages in a Highly Modified Tidal Freshwater Estuary

2009

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Resistance and resilience of pelagic and littoral fishes to drought in the San Francisco Estuary

Mahardja

Tobias

Khanna

et al. 2021

Ecological Applications

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Many estuarine ecosystems and the fish communities that inhabit them have undergone substantial changes in the past several decades, largely due to multiple interacting stressors that are often of anthropogenic origin. Few are more impactful than droughts, which are predicted to increase in both frequency and severity with climate change. In this study, we examined over five decades of fish monitoring data from the San Francisco Estuary, California, U.S.A, to evaluate the resistance and resilience of fish communities to disturbance from prolonged drought events. High resistance was defined by the lack of decline in species occurrence from a wet to a subsequent drought period, while high resilience was defined by the increase in species occurrence from a drought to a subsequent wet period. We found some unifying themes connecting the multiple drought events over the fifty-year period. Pelagic fishes consistently declined during droughts (low resistance), but exhibit a considerable amount of resiliency and often rebound in the subsequent wet years. However, full recovery does not occur in all wet years following droughts, leading to permanently lower baseline numbers for some pelagic fishes over time. In contrast, littoral fishes seem to be more resistant to drought and may even increase in occurrence during dry years. Based on the consistent detrimental effects of drought on pelagic fishes within the San Francisco Estuary and the inability of these fish populations to recover in some years, we conclude that freshwater flow remains a crucial but not sufficient management tool for the conservation of estuarine biodiversity.

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Fish predation on a landscape scale

et al. 2020

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Predator–prey dynamics can have landscape‐level impacts on ecosystems, and yet, spatial patterns and environmental predictors of predator–prey dynamics are often investigated at discrete locations, limiting our understanding of the broader impacts. At these broader scales, landscapes often contain multiple complex and heterogeneous habitats, requiring a spatially representative sampling design. This challenge is especially pronounced in California’s Sacramento–San Joaquin River Delta, where managers require information on the landscape‐scale impacts of non‐native fish predators on multiple imperiled native prey fish populations. We quantified relative predation risk in the southern half of the Delta (South Delta) in 2017 using floating baited tethers that record the exact time and location of predation events. We selected 20 study sites using a generalized random tessellation stratified survey design, which allowed us to infer relationships between key environmental covariates and predation across a broader spatial scale than previous studies. Covariates included distance‐to‐nearest predators, water temperature, turbidity, depth, bottom slope, bottom roughness, water velocity, and distance‐to‐nearest riverbank and nearest aquatic vegetation bed. Model selection determined the covariates that best predicted relative predation risk: water temperature, time of day, mean predator distance, and river bottom roughness. Using this model, we estimated predation risk for the South Delta landscape at a 1‐day and 1‐km resolution. This effort identified hot spots of predation risk and allowed us to generate predicted survival for migrating fish transiting the South Delta. This methodology can be applied to other systems to evaluate spatio‐temporal dynamics in predation risk, and their biotic and abiotic predictors.

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Fish community ecology in an Altered River delta: Spatial patterns in species composition, life history strategies, and biomass

Cited by 76 publications

References 30 publications

Dietary Segregation of Pelagic and Littoral Fish Assemblages in a Highly Modified Tidal Freshwater Estuary

Dietary Segregation of Pelagic and Littoral Fish Assemblages in a Highly Modified Tidal Freshwater Estuary

Resistance and resilience of pelagic and littoral fishes to drought in the San Francisco Estuary

Fish predation on a landscape scale

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