Is Extinction Inevitable for Delta Smelt and Longfin Smelt? An Opinion and Recommendations for Recovery

Hobbs, James A.; Moyle, Peter B.; Fangue, Nann A.; Connon, Richard E.

doi:10.15447/sfews.2017v15iss2art2

Cited by 66 publications

(74 citation statements)

References 35 publications

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“…; Hobbs et al. ) while linking ecological functions with hydrological and geomorphologic functions (e.g., Florsheim et al. ; Moyle et al.…”

Section: Discussionmentioning

confidence: 99%

“…; Bennett and Moyle ; Hobbs et al. ). As in the case of the upper SFE, global hydrological alteration by humans has ecologically impaired many estuaries and has caused reductions in fisheries production (Gillson ; Arthington ).…”

Section: Discussionmentioning

confidence: 99%

“…The long‐term declines in Delta Smelt and Longfin Smelt since the 1980s support the conclusion that the carrying capacity for these and other threatened and endangered fishes has been substantially reduced (Cloern ; Hobbs et al. ). The results from our study and previously reported declines of fishes in the upper SFE suggest a strong connection between hydrological alteration and multiple synergistic interactions contributing to fish declines.…”

Section: Discussionmentioning

confidence: 99%

“…Limited freshwater inflow and outflow constitute a recurring hydrological pattern affecting fish communities of the upper SFE. Although declines of freshwater and estuarine fishes have been consistently reported during droughts in the upper SFE (e.g., Herrgesell et al 1981;Moyle et al 1992Moyle et al , 2016, water diversions have been implicated in fish population declines and in exacerbating drought conditions within the upper estuary (Arthur et al 1996;Bennett and Moyle 1996;Hobbs et al 2017). As in the case of the upper SFE, global hydrological alteration by humans has ecologically impaired many estuaries and has caused reductions in fisheries production (Gillson 2011;Arthington 2012).…”

Section: Abiotic and Biotic Changesmentioning

confidence: 99%

“…Our study suggests that assessment of community-level responses may complement adaptive field application of flow regime models that account for natural flows and flow augmentation actions to minimize hydrological alteration (e.g., Arthington 2012; Sakaris 2013). Improving the habitat for threatened and endangered native species in the upper SFE requires the removal or management of multiple stressors (e.g., Cloern 2007;Borja et al 2010;Hobbs et al 2017) while linking ecological functions with hydrological and geomorphologic functions (e.g., Florsheim et al 2008;Moyle et al 2010;Bever et al 2016). Management actions that favor the quality, quantity, and variability of abiotic habitat components for native species could minimize the influence of synergistic interactions that limit the carrying capacity of native species.…”

Section: Management Implicationsmentioning

confidence: 99%

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Community Patterns and Environmental Associations for Pelagic Fishes in a Highly Modified Estuary

2018

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Understanding how natural and human‐induced processes interact to influence ecosystem responses is essential for their effective management and conservation. Long‐term environmental degradation of the upper San Francisco Estuary, California, has resulted in numerous species declines. In this study, we used pelagic fish monitoring and hydrodynamic data during winter–spring 2002–2014 to evaluate how natural and human‐induced environmental changes in the upper San Francisco Estuary may have influenced the distribution, abundance, and community structure of the pelagic fishes. Delta outflow and turbidity tended to decline and salinity tended to increase since the early 2000s. Twelve of the 27 pelagic fish species sampled were introduced, most of which were freshwater‐dominant species in highly altered upstream areas. Overall mean relative abundance was similar between native and introduced fishes across all study areas. The upstream distribution of the eight most abundant pelagic fishes was generally associated with their salinity habitat components. Among these species, the Delta Smelt Hypomesus transpacificus and the introduced Threadfin Shad Dorosoma petenense had the highest rates of population decline over the period 2002–2014 and the largest relative increase in salinity predicted in their habitats due to hydrological alteration. Community structure was significantly related to abiotic factors (water temperature, salinity, and turbidity) and spatiotemporal variation (longitude and month), which accounted for 30–33% of the variation. Low to intermediate outflows due to droughts and water diversions since the early 2000s likely interacted synergistically with multiple factors, decreasing the abundance of several pelagic species. Management actions linking ecologic, hydrologic, and geomorphic processes with multiple stressors could help to reverse the long‐term decline of Delta Smelt and other threatened and endangered fishes in the San Francisco Estuary.

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“…; Hobbs et al. ) while linking ecological functions with hydrological and geomorphologic functions (e.g., Florsheim et al. ; Moyle et al.…”

Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Section: Abiotic and Biotic Changesmentioning

confidence: 99%

Section: Management Implicationsmentioning

confidence: 99%

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Community Patterns and Environmental Associations for Pelagic Fishes in a Highly Modified Estuary

2018

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Size, fecundity and condition factor changes in endangered delta smelt Hypomesus transpacificus over 10 generations in captivity

Ellison

Rahman

Finger

et al. 2023

Aquaculture Fish & Fisheries

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The once abundant delta smelt Hypomesus transpacificus is now on the verge of extinction. At the UC Davis Fish Conservation and Culture Laboratory, a refuge population has been maintained since 2008 as a safeguard against extinction and to breed and provide fish for research. Due to artificial aquaculture operations, it is assumed that the fish are impacted by life in captivity leading to questions about differences between cultured and captive wild fish. This study looked at the differences in fork length (FL), body weight (BW), fecundity (F) and condition factor (K) of cultured and wild (captive) delta smelt over the last 10 generations (2009–2018) to determine if there were any changes of life‐history traits between the two, which may indicate domestication. Results revealed that the cultured population had significantly higher FL, BW, F and K than the wild population. The correlation tests found significant positive relationships between all measured traits except FL and K of wild fish. Significant changes in the measured traits of the cultured population over time were found, whereas none was observed in most wild fish year‐classes. This study demonstrated changes of life‐history traits in a well‐managed fish population over 10 generations in captivity and provides critical information to the coming supplementation plan for the species.

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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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Is Extinction Inevitable for Delta Smelt and Longfin Smelt? An Opinion and Recommendations for Recovery

Cited by 66 publications

References 35 publications

Community Patterns and Environmental Associations for Pelagic Fishes in a Highly Modified Estuary

Community Patterns and Environmental Associations for Pelagic Fishes in a Highly Modified Estuary

Size, fecundity and condition factor changes in endangered delta smelt Hypomesus transpacificus over 10 generations in captivity

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

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