Fish Assemblages in Reference and Restored Tidal Freshwater Marshes of the San Francisco Estuary

Lenny Grimaldo,Robert Miller,Chris Peregrin,Zachary Hymanson

doi:10.15447/sfews.2012v10iss1art2

Abstract

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.

Highlights

Estuarine habitats continue to be altered by human encroachment, water diversions, contaminants, and invasive species (Nichols and others 1986; Kennish 1992; Schlacher and Woolridge 1996; Cohen and Carlton 1998; Stewart and others 2004; Moyle and Bennett 2008)
It is widely acknowledged that estuarine restoration should be based on a thorough understanding of the factors that affect aquatic assemblages, rarely are such mechanistic processes understood before such restoration efforts are implemented (Zedler and others 1997; Zedler and Callaway 1999; Kimmerer and others 2005; Zedler 2005)
Along with the loss of habitat, water diversions, increased contaminant loads, and a precipitous drop in lower trophic food web production have all been identified as possible factors responsible for fish declines in the estuary (Sommer and others 2007a)

Summary

Introduction

Estuarine habitats continue to be altered by human encroachment, water diversions, contaminants, and invasive species (Nichols and others 1986; Kennish 1992; Schlacher and Woolridge 1996; Cohen and Carlton 1998; Stewart and others 2004; Moyle and Bennett 2008). In many estuaries, ongoing restoration efforts are underway to bolster the abundances of aquatic organisms, but the benefits of restoration remain largely untested and unknown (Simenstad and Cordell 2000; Kimmerer and others 2005; Zedler 2005). In the San Francisco Estuary, restoration projects are underway to restore estuarine habitats to promote recovery of native fish populations that have hit record low abundances (Kimmerer and others 2005; Sommer and others 2007a). Research should accompany restoration projects to understand how habitats and fish abundances interact at smaller spatial and temporal scales so that they can be linked with patterns of change over larger spatial and temporal scales (Kimmerer and others 2005; Zedler 2005)

Methods

Results

Conclusion