San Joaquin River - Ecology and Environment

Ecology and Environment

Hundreds of years ago, the San Joaquin flowed freely through a grass and marsh-dominated region variously known as the "California prairie", "California annual grassland", or "Central Valley grasslands". It is widely believed that the dominant grass species throughout the San Joaquin River valley and Tulare Basin, as well as the Sacramento Valley, the Sierra foothills and Coast Ranges, was Nassella pulchra, a type of bunchgrass more commonly known as purple needlegrass. Today, this vegetation community exists only in isolated pockets because of development of the valley for agriculture, and in much of the remnant open areas where it once thrived, now grows introduced flora such as annual rye and wild oat. The vegetation communities created by the introduced grasses are sometimes referred to as "valley grassland", which is highly seasonal but is spread throughout the Central Valley from near Redding to south of Bakersfield. These grasses all thrive in the Mediterranean climate that dominates much of the San Joaquin Valley.

The San Joaquin River and its marshes and wetlands provide a critical resting and breeding stop for migratory birds along the Pacific Flyway. Once, the seasonal bird populations in the San Joaquin basin were immense, especially in the now-dry Tulare Lake region: "It took something different, though, to capture the sound of the blue sky as it turned dark and deafening from the wings and cries of millions of native and migratory birds – Canadian geese, mallards, swans, pelicans, cranes, teal, and curlews. How to mimic the sudden flight of flocks so immense they extinguished the sun? One of the first white men to camp along the lake could think of only one noise, the roar of a freight train, that compared with the takeoff of the birds." Historically, the grasslands and the fringes of the great marshes and lakes provided habitat for large grazing animals including pronghorn, mule deer and the endemic tule elk, which in turn had various predators such as the San Joaquin Kit Fox; all of these species have seen dramatic population declines as their native habitat has fallen under the plow.

Human activities have replaced or altered over 95 percent of the historic wetlands as well as the California oak woodland habitat, which originally occurred along stream and river corridors in the foothills, and the tule grass that once thrived in huge stands on the edges of marshes and lakes. Some of the richest remaining marsh habitats are in the Sacramento-San Joaquin Delta, which despite significant agricultural and infrastructure development, has retained many of its original swamps and backwaters. Before the 19th century, the delta was a region of numerous islands of nutrient-rich peat, alluvial deposits, winding channels and waterways. Since then, most of the Delta islands have been cultivated, and consistent use of the land has resulted in subsidence, in some cases up to 25 ft (7.6 m). Water diversions from the rivers feeding it have increased salinity, which has in turn caused declines in fish populations that once thrived in the region.

As defined by the World Wildlife Fund, the San Joaquin River watershed is part of the Sacramento-San Joaquin freshwater ecoregion, which supports almost 40 species of freshwater fish. These include several types of lampreys, sturgeons, sunfish, perch and various anadromous fish species such as salmon and steelhead. Some of these fish are believed to have descended from fishes of the Columbia Basin in geologically ancient times, when the upper reaches of the Sacramento River watershed were connected with that of the Snake River. Up to 75 percent of the historic species were endemic to the Sacramento-San Joaquin basin. Most native fish stocks have suffered because of predation by introduced species and dam construction. In a study from 1993 to 1995, it was found that the main stem of the San Joaquin River was mainly populated by fathead minnow, red shiner, threadfin shad and inland silverside, all of which were introduced. Downstream portions of the river's main tributaries were populated mainly by largemouth and smallmouth bass, redear sunfish and white catfish, while native species have survived relatively well in the upper reaches of the river and its tributaries, which also play host to introduced brown trout.