Merced River - Ecology

Ecology

According to a study in 2006, there were 37 species of fish, 127 bird species, and 140 insect and invertebrate species found in the Merced River watershed. Most of these species are divided between the upper and lower watershed, which is usually defined by Lake McClure, formed by New Exchequer Dam.

Of the fish, there were 26 species found in the lower Central Valley portion of the river, including Sacramento sucker, smallmouth bass, largemouth bass and carp, all but three of which are resident species, and some of which were intentionally introduced by humans. The three anadromous fish species that still use the lower Merced are the chinook salmon, Pacific lamprey and striped bass. The upper section of the river, defined as the stretch from Lake McClure to the headwaters, had 11 species of fish. Historically, the range of anadromous fish extended to the head of Yosemite Valley, but by the 1950s and 1960s, except in the wettest years, not enough water flowed down the Merced and San Joaquin Rivers at all to allow them to spawn in significant numbers. New water use requirements have allowed many anadromous species to revitalize, from a low of 500 chinook salmon in the mid-20th century to a high of 30,000 fish in 1984. After the 1970s, the annual run was about 5,300 fish.

Of the one hundred and twenty-seven bird species found along the Merced River, only 35 occur along the entire length of the river. Many of these birds are migratory and only pass the area a few times every year, while 109 species of birds are found only in the breeding season. However, despite the more extensive modifications to the lower part of the river, there are more species of birds found in the lower watershed, due to the slow-flowing nature of the river that forms marshes and riparian zones. Common species of bird throughout the basin include ruby-crowned kinglet, cedar waxwing, American robin, yellow-rumped warbler, tree swallow and European starling, and several endangered species, including white-tailed kite and Swainson's hawk. Birds that occur commonly in the middle and upper sections of the Merced River include mourning dove, Cassin's finch, California quail, dark-eyed junco, woodpecker, dipper, great blue heron, scrub jay, red-winged blackbird, red-tailed hawk, turkey vulture, cliff swallow, canyon wren, merganser, and rarely, bald eagle. Of the 140 insect and invertebrate species, which include mayflies, stoneflies and caddisflies, there are also three major exotic species: Asiatic clam, Chinese mitten crab, and New Zealand mud snail.

Many species of plants are found throughout the middle and upper basin, including California poppy, white alder, Oregon ash, oak, poison oak, bigleaf maple, Indian rhubarb, buttonbush, willow, whiteleaf manzanita, and historically, sugar pine, before logging began in the late 19th century. Squirrels, raccoon, jackrabbits, bats, skunks, beavers, mule deer, coyote, bobcat and black bear are among the mammal species found in the middle and upper watershed.

One species of interest is the limestone salamander, an extremely rare amphibian whose only habitat is in the Merced Canyon downstream of Yosemite Valley. The limestone salamander depends on the granite walls of the Merced Canyon to survive. To protect the species, a 20-mile (32 km) segment of the canyon covering 1,600 acres (6.5 km2) was designated in 1986 an "Area of Critical Environmental Concern".