scholarly journals Estuarine-terrestrial habitat gradients enhance nursery function for resident and transient fishes in the San Francisco Estuary

2020 ◽  
Vol 637 ◽  
pp. 141-157 ◽  
Author(s):  
DD Colombano ◽  
AD Manfree ◽  
TA O’Rear ◽  
JR Durand ◽  
PB Moyle

Nursery functions of US West Coast drowned river valley estuaries are not well understood. Using long-term fish-monitoring data (1995-2017) in Suisun Marsh, San Francisco Estuary, California, USA, we examined spatial and temporal trends in abundance and apparent growth of fishes with diverse life-history types. Focal species were Sacramento splittail Pogonichthys macrolepidotus, striped bass Morone saxatilis, tule perch Hysterocarpus traski, and starry flounder Platichthys stellatus, which collectively represented 55% of total catch (n = 140092). We identified keystone habitat patches that functioned as nursery hotspots during the peak young-of-the-year recruitment window. Deep, flow-through sloughs close to the open estuary were important nursery habitats for the marine transient starry flounder. In contrast, splittail and striped bass mostly migrated through such corridors to rear in shallow, dead-end sloughs bisecting tidal marsh plains, managed tidal ponds, and uplands. Tule perch were concentrated in shallow, interior sloughs, reflecting their resident life-history type and adaptations to variable conditions in a small home range. Interactions among freshwater flows and stationary habitat features (e.g. channel depth, land-to-open-water ratio) were related to fish abundance; however, species and age classes differed in their relationships to these interactions, suggesting a mechanism for habitat partitioning in space and time. Overall, we inferred that habitat connectivity—longitudinal, lateral, and vertical—along the estuarine-terrestrial gradient was a driver of fish species diversity and productivity. Consideration of seascape-landscape dynamics across multiple spatial and temporal scales in estuaries should help maintain or increase fish populations and ecological resilience in the face of rising sea levels and other environmental stressors.

<em>Abstract.</em>—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 <em>Hypomesus transpacificus </em>and longfin smelt <em>Spirinchus thaleichthys</em>, and four common alien taxa, striped bass <em>Morone saxatilis</em>, threadfin shad <em>Dorosoma petenense</em>, gobies of the genus <em>Tridentiger</em>, and yellowfin goby <em>Acanthogobius flavimanus</em>, 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.


<em>Abstract.</em>—We examined assemblage patterns of early life stages of fishes for two major tributaries of the upper San Francisco Estuary: (1) Sacramento River channel, and (2) Yolo Bypass, the river’s seasonal floodplain. Over four hydrologically diverse years (1999–2002), we collected 15 species in Yolo Bypass egg and larval samples, 18 species in Yolo Bypass rotary screw trap samples, and 10 species in Sacramento River egg and larval samples. Fishes captured included federally listed species (delta smelt <em>Hypomesus transpacificus </em>and splittail <em>Pogonichthys macrolepidotus</em>) and several game species (American shad <em>Alosa sapidissima</em>, striped bass <em>Morone saxatilis</em>, crappie <em>Pomoxis </em>spp., and Chinook salmon <em>Oncorhynchus tshawytscha</em>). As in other regions of the estuary, alien fish comprised a large portion of the individuals collected in Yolo Bypass (40–93% for egg and larval net samples; 84–98% for rotary screw trap samples) and Sacramento River (80–99% for egg and larval net samples). Overall ranks of species abundances were significantly correlated for Yolo Bypass and Sacramento River, suggesting that each assemblage was controlled by similar major environmental factors. However, species diversity and richness were higher in Yolo Bypass, likely because of a wider variety of habitat types and greater hydrologic variation in the floodplain. In both landscapes, we found evidence that timing of occurrence of native fishes was earlier than aliens, consistent with their life history and our data on adult migration patterns. We hypothesize that Yolo Bypass favors native fishes because the inundation of seasonal floodplain typically occurs early in the calendar year, providing access to vast areas of spawning and rearing habitat with an enhanced food web. Conclusions from this analysis have implications for the management of aquatic biodiversity of tributaries to the San Francisco Estuary and perhaps to other lowland rivers.


<em>Abstract.</em>—We investigated factors affecting growth of larval striped bass <em>Morone saxatilis </em>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.


<em>Abstract.</em>—In July 2000 and 2001, we sampled adjacent screened and unscreened agricultural irrigation diversions in the Sacramento River, California to (1) evaluate the effectiveness of a custom fish screen for excluding four open-water fishes: native delta smelt <em>Hypomesus transpacificus </em>and alien threadfin shad <em>Dorosoma petenense</em>, inland silverside <em>Menidia beryllina</em>, and striped bass <em>Morone saxatilis</em>; and (2) examine factors affecting entrainment of each species. We also compiled trawl and beach seine data from contemporaneous monitoring programs to make inferences about microhabitat use by these fishes and its implications for entrainment vulnerability. The fish screen reduced entrainment of each species by 99% or more and excluded many fish less than 25 mm, the approximate minimum length it was designed to exclude. Tidal and diel influences on entrainment through the unscreened diversion were observed, but diel cycles appeared to be more important, as most entrainment occurred at night or during crepuscular periods. Except for delta smelt, our results suggested that open-water fishes may undergo ontogenetic changes in vulnerability to unscreened irrigation diversions. Fishes entrained during daylight (threadfin shad and striped bass) averaged only 15–16 mm in length. At night, average lengths of entrained threadfin shad and inland silverside were 22–25 mm, even though larvae continued to be entrained. Similarly, a diel influence on striped bass entrainment was observed only in 2000, when individuals larger than 20 mm were consistently collected. No striped bass were collected at sizes greater than 35 mm, even though larger individuals occupied the study area. We found no evidence of size-related changes in delta smelt vulnerability to entrainment, but the monitoring data indicated that delta smelt were abundant offshore, whereas the other three species were most abundant nearshore. We think that low and inconsistent entrainment of delta smelt reflected (1) predominantly offshore habitat use by delta smelt, and (2) the relatively small hydrodynamic influence of the diversion.


2005 ◽  
Vol 7 (2) ◽  
pp. 333-350 ◽  
Author(s):  
Deborah Rudnick ◽  
Tanya Veldhuizen ◽  
Richard Tullis ◽  
Carolyn Culver ◽  
Kathryn Hieb ◽  
...  

2008 ◽  
Vol 105 (49) ◽  
pp. 19354-19359 ◽  
Author(s):  
D. J. Ostrach ◽  
J. M. Low-Marchelli ◽  
K. J. Eder ◽  
S. J. Whiteman ◽  
J. G. Zinkl

Author(s):  
Oliver Patton ◽  
Veronica Larwood ◽  
Matthew Young

White Sturgeon (Acipenser transmontanus), a species of concern in the San Francisco Estuary, is in relatively low abundance due to a variety of factors. Patton et al. sought identify the estuarine habitat used by White Sturgeon to aid in the conservation and management of the species locally and across its range. By seasonally sampled sub-adult and adult White Sturgeon in the central estuary using setlines across a habitat gradient representative of three primary structural elements, the authors found that the shallow open-water shoal and deep open-water channel habitats were consistently occupied by White Sturgeon in spring, summer, and fall across highly variable water quality conditions, whereas the shallow wetland channel habitat was essentially unoccupied. In summary, sub-adult and adult White Sturgeon inhabit estuaries in at least spring, summer, and fall and small, shallow wetland channels are relatively unoccupied.


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