| Introduction | Creek Description| Rotenone Treatment| Procedure | Discussion| Results|

Chinook Salmon

Historically fall-run chinook (or king) salmon were probably common in all local streams, entering the creeks whenever the water was high enough between October and February and spawning immediately. Spring-run chinook were found in mountain streams where they could get far enough upstream to over-summer in deep cold pools. Both adults and smolts of fall-run fish can still be observed in most local creeks, but their abundance is way down. Remnant spring-run populations can be found in Deer, Butte, Mill and Big Chico Creeks. Most juvenile salmon begin moving downstream soon after hatching, but they feed voraciously on their way and may reach sizes of 140 mm before entering the river. Particularly in low water years, some spring-run juveniles may over-summer in their natal stream. This was so uncommon in Big Chico Creek, that only four were collected in the fall samples over a nine-year period.

Rainbow Trout

Big Chico Creek, like most local streams, historically supported two populations of rainbows, a resident population in the headwaters and the anadromous steelhead which migrated in from the ocean, spawned in lower canyons and returned, leaving the eggs to hatch and the young to grow for a year or two in the creek before smolting and returning to the ocean. Anadromous populations have been reduced or lost from many streams but resident populations persist in most. Rainbows spawn in February in this area. Rainbow data

Brown Trout

Brown trout were introduced from Eurasia. In the upper zone of Big Chico Creek they have become the dominant trout species, and have completely replaced the native rainbows in the headwaters. In the middle zone, they were quite rare before the rotenone treatment. Brown trout data


The hardhead is a large (to 500 mm) torpedo-shaped minnow with a bluish tint to the dorsal surface. According to the limited literature, young hardheads eat invertebrates while larger ones feed on filamentous algae and submerged aquatic plants. Our data suggests that, at least in small streams, adults also eat snails and insects and an occasional small fish. Local creeks generally have two subpopulations of hardheads, a resident one, and one which migrates into the creek in spring for spawning during April to May, then typically returns to the river either immediately or with the fall rains. Hardheads grow slowly and typically are not sexually mature until their fourth year. Hardhead data


The Sacramento squawfish is a very large slender minnow with a large mouth. While specimens in the Sacramento River may get to 1250 mm, they would not be expected to exceed 500 mm in smaller streams except in the lower reaches of tributaries where large fish migrate in for spawning in March. According to the literature, juveniles feed on invertebrates while individuals over 250 mm prefer small fish. Personal observations agree with this except that adults in small streams seem to feed as much on insects as fish. Squawfish also do not become sexually mature until their fourth year. Squawfish data

California Roach

The California roach is a small (under 120 mm) minnow which matures at one year and seldom lives two years. It does well in lower elevation permanent parts of local streams including sections which dwindle to seasonal pools, but seems unable to coexist with the introduced smallmouth bass. Roaches are usually the most abundant fish in the middle zones of local creeks. They feed on invertebrates and filamentous algae. Roach data

Sacramento Sucker

The Sacramento sucker is a component of almost all local streams. Foothill streams usually have two subpopulations; a resident one and one which migrates into the creek in spring for spawning, then returns to the river, although some would strand in low-water years. Suckers use their specialized mouths to scrape epilithon and associated aquatic insects from the substratum. Like the hardhead and squawfish, suckers usually don't spawn until four years old. Sucker data

Green Sunfish

The green sunfish, introduced from the Mississippi drainage, has become a common component of California Central Valley streams with intermittent pools, often to the detriment of native fish which it out-competes or eats. Green sunfish will become sexually mature at one year of age. Sunfish data

Smallmouth Bass

Within the Centrarchidae, smallmouths are the best adapted to streams. They have become the dominant predators in most low-gradient segments of tributaries to the Sacramento River. Smallmouths hunt by ambush or slow stalking and will eat any animal that fits into their mouths, including fish nearly as large as themselves. They have eliminated or severely depleted populations of native fish in many local areas. Smallmouths typically mature in their second year. Smallmouth data

Riffle sculpin

Riffle sculpins are lie-in-wait predators of high gradient streams. They wait quietly under rocks for prey to move near enough; grabbing anything that moves and will fit into their ample mouths. Since they are small (under 150 mm) they often get preyed upon themselves, but their cryptic habits provide enough protection for them to co-exist with larger predators like smallmouth bass and rainbow trout. Sculpins spawn under rocks; the male defends a cavity and the female attaches the eggs to the roof overhead. Sculpin data