Variation in Spring Nearshore Resident Fish Species Composition and Life Histories in the Lower San Joaquin Watershed and Delta

Larry R Brown,Jason T May

doi:10.15447/sfews.2006v4iss2art1

Abstract

Providing freshwater to human populations while protecting or rehabilitating ecosystem health is a significant challenge to water resource managers and requires accurate knowledge of aquatic resources. Previous studies of fish assemblages in the San Francisco Estuary and watershed have focused on specific habitat types, water bodies, or geographic subregions. In this study, we use seining data from two monitoring programs to provide an integrated view of spring nearshore resident fish species composition and life history characteristics in five regions: the San Joaquin River, the upper Sacramento River, the lower Sacramento River, the northern Sacramento-San Joaquin Delta (North Delta), and the Interior Delta. Data for the period March-May from 1994 to 2002, showed that spring species composition of the San Joaquin River was very different from the other four regions. Total catch in the San Joaquin River was dominated by small, short-lived batch spawning alien species (93%), particularly red shiner Cyprinella lutrensis (>75% of total catch). The upper and lower Sacramento River were very similar in species composition and life history characteristics and less dominated by alien fish (<45% of total catch). Ordination of species percentage abundances by non–metric multidimensional scaling confirmed that the major gradient was from assemblages dominated by native species to assemblages dominated by alien species. Two-way analysis of variance of ordination scores indicated that spatial variability was more important than annual variability in explaining patterns in species composition. The potential benefits of San Joaquin River native fish restoration appear high because there is so much potential for improvement; however, it is unclear how to best manipulate the system to achieve such restoration. Addressing such uncertainties is necessary if society desires the reservation and restoration of native biodiversity as human demands on water resources increase.

Highlights

One of the major challenges facing water resource managers is providing freshwater to human populations while protecting or rehabilitating ecosystem health (Postel 1996; Vitousek et al 1997; Postel 2000; Sala et al 2000)
Before major human modifications in the watershed, the Sacramento and San Joaquin Rivers shared a majority of fish species organized into similar assemblages (Moyle 2002)
Our analyses clearly demonstrate differences in species composition and dominant life history characteristics among the spring nearshore resident fish assemblages of the two rivers

Summary

Introduction

One of the major challenges facing water resource managers is providing freshwater to human populations while protecting or rehabilitating ecosystem health (Postel 1996; Vitousek et al 1997; Postel 2000; Sala et al 2000). Water supply infrastructure and operations often disrupt natural flow regimes in rivers, leading to changes in fish assemblages and other aspects of ecosystem function (Ligon et al 1995; Poff et al 1997; Pringle et al 2000; Brown and Ford 2002). Estuaries are affected by water management and other activities, which affect important aspects of ecosystem function, such as fish recruitment (Bennett and Moyle 1996; Rose 2000). Productivity, water quality, and flow regime have been accompanied by declines in native fishes and invasions of alien species, including many alien fishes (Cohen and Carlton 1998; Jassby et al 2002; Moyle 2002; Brown and Moyle 2005).

Methods

Results

Conclusion