5 research outputs found
Evaluating entrainment vulnerability to agricultural irrigation diversions: a comparison among open-water fishes. Pages 281–295
Abstract.-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 Hypomesus transpacificus and alien threadfin shad Dorosoma petenense, inland silverside Menidia beryllina, and striped bass Morone saxatilis; 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. * Correspondin
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Fish Assemblages in Reference and Restored Tidal Freshwater Marshes of the San Francisco Estuary
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.
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Using Conceptual Models in Ecosystem Restoration Decision Making: An Example from the Sacramento-San Joaquin River Delta, California
The Sacramento–San Joaquin Delta (the Delta) is located on the western edge of California’s Central Valley and is of critical ecological and economic importance. However, ecosystem alterations for human uses changed many of the Delta’s natural processes, and it is now considered in need of restoration. An approach was developed to evaluate and rank restoration actions in the Delta under the Ecosystem Restoration Program’s Delta Regional Ecosystem Restoration Implementation Plan (DRERIP). The DRERIP approach provides an explicit framework for evaluating restoration actions, using linked conceptual models, an action evaluation procedure, and a decision-support tool. Conceptual models allow scientists and managers to synthesize scientific information and make qualitative predictions about ecosystem function and restoration outcomes to guide and focus restoration efforts. The action evaluation procedure is a structured assessment of restoration actions. The procedure clearly describes actions to be evaluated, assesses the magnitude (importance and scale) and certainty of anticipated ecological outcomes, estimates degrees of worth (achieving intended outcomes) and risk (causing adverse consequences), evaluates the reversibility of the action, and identifies opportunities for learning. The values for worthiness, risk, reversibility, and learning opportunity are used in the decision- support tool to determine the fate of a proposed action. The decision-support tool is a structured decision tree that determines the disposition of an action: whether a restoration project should be discarded, revised with a different approach and re-evaluated, or implemented; and, if implemented, at what scale (targeted research, pilot project, or full implementation). The DRERIP approach provides managers with a valuable tool for restoration planning, and a foundation for integration with quantitative methods for a comprehensive ecosystem restoration plan