Each fall, king salmon, Oncorhynchus tshawytscha, bound for the Sacramento and San Joaquin River systems, pass through the Sacramento-San Joaquin Delta. Starting in 1961, salmon runs of the San Joaquin, but not of the Sacramento, suffered a disastrous collapse, probably due to water conditions in the San Joaquin part of the Delta. A partial recovery started in 1964. An annually recurring oxygen block caused by pollution in the south-eastern part of the Delta, plus reversal of direction of flow in all three major north-south channels of the San Joaquin (southern) part of the Delta, were believed responsible for the collapse. In the eastern channel, flow reversal which lasts into the salmon migration period occurs only in exceptionally dry falls such as 1961; in the other channels it occurs annually. Reversal is caused by operation of a 4,600 cfs capacity pumping plant which pulls Sacramento River water south through channels that normally carry San Joaquin water north. From 1964 through 1967, salmon tagged with sonic tags were released in the central part of the Delta to determine their reaction to low oxygen levels and reversed flows. Electronic equipment enabled us to follow tags by boat and to record their movement past fixed points. Salmon avoided water with less than 5 ppm dissolved oxygen by staying farther downstream until the oxygen block cleared. Temperatures over 66° F. had a similar but less sharply defined effect. In 1964, pumped water and partial closure of one major west-flowing channel were used to force extra water through the polluted area and break up the oxygen block. At present pumping rates, this method is practical in dry years, but is not needed in normal or wet years. Relatively few fish used either of two western channels which had reversed flows but would have led them to their destination. The pattern of salmon movement is complicated by a large flow of Sacramento River water which diverts through the Delta Cross Channel and Georgiana Slough and flows successively through the Mokelumne and San Joaquin Rivers and back into the Sacramento. Some Sacramento salmon go upstream by this route. A second large pumping plant (10,000 cfs capacity) has recently been completed, and will greatly increase flow reversal problems until a closed canal system (such as the proposed Peripheral Canal) is used to conduct Sacramento River water to the two large pumping plants.

During the past fifteen years the Sacramento River has become one of the most popular fishing streams in California for steelhead rainbow trout, Salmo gairdnerii gairdnerii Richardson. Each fall, fishermen in ever increasing numbers travel from all parts of California, as well as from neighboring states, to participate in the harvest of this prized western game fish.

The increase in the numbers of anglers has been brought about by an accumulation of events, foremost of which has been an explosive growth in California's population and in the numbers of people seeking outdoor recreation. Construction of Shasta Dam, with its stabilizing and cooling effect upon the upper Sacramento, has produced an environment better suited for steelhead. The Sacramento is also a favorite steelhead stream of many anglers because the best fishing is enjoyed during balmy days in the fall, rather than during the cold periods so typical of most winter-run steelhead fishing areas.

This expanding popularity made it essential that the Sacramento River steelhead management program be evaluated to determine whether or not it is adequate to insure continued good fishing in the face of these mounting demands upon the resource.

Provision of good steelhead fishing despite the inroads by man is a problem which faces conservation agencies along the Pacific Coast. The State of Washington has attempted to offset this increase in fishing pressure principally by a long-range management program consisting of releases of migrant-sized steelhead (yearling fish averaging 6 to 8 inches in length) to supplement depleted and heavily fished runs, coupled with protective regulations and installation of fishways and fish screens to protect the runs. The stocking of migrant-sized steelhead during their normal period of seaward migration has definitely built up the runs of sea-run fish in Washington streams.

In California it had been the policy for many years prior to 1940 to stock coastal streams with fingerling steelhead in the summer months. The results of this program shed considerable doubt on the effectiveness of this type of artificial stocking. An experimental program at California's Waddell and Scott creeks from 1932 through 1942 revealed that only extremely small returns of sea-run fish may be expected from releases of fingerling steelhead, but that on the average approximately 2 to 5 percent may be expected to return as adults when allowed to descend to sea as yearlings at their normal migration time.

Until the start in 1952 of the study described herein, the management program for Sacramento River steelhead had consisted primarily of protective regulations and installation of fish protective devices such as fish screens and fish ways. There had been no artificial stocking of steelhead. The only previous significant investigation of Sacramento River steelhead was included in a study of the sport fishery, which was made between 1947 and 1949. Prior to 1952 considerable knowledge had been gained through the years about steelhead in the smaller coastal streams of California, but relatively little was known concerning the life history of Sacramento steelhead or the merits of planting migrant-sized steelhead in the Sacramento River. Therefore, it was decided to examine this important resource more thoroughly and to find out if artificial stocking of large numbers of migrant-sized steelhead in the Sacramento was a feasible method of maintaining or improving fishing for adult steelhead. In 1952 the California Department of Fish and Game's Bureau of Fish Conservation (now Inland Fisheries Branch) initiated a project to determine the effectiveness and economics of supplementing natural steelhead production in the Sacramento River with yearling, hatchery-reared fish. Secondary objectives were to study the fishery and the life history of Sacramento steelhead. It was originally planned to have the field work continue until 1960 but was found possible to complete it by 1958.

The study was carried out as a cooperative program between the California Department of Fish and Game and several other organizations which recognized the need for an evaluation of steelhead stocking in the Sacramento River. Two sportsmen's organizations, California Kamloops, Inc. and Steelhead Unlimited, volunteered to pay for the food fed to the fish at the hatchery and awarded one thousand dollars over a five-year period to fishermen who returned tags to the Department of Fish and Game. Three thousand dollars in merchandise rewards for tag returns were donated by several sporting goods stores and fishing resorts along the Sacramento River between Redding and Meridian. The United States Fish and Wildlife Service trapped and spawned adult steelhead in Battle Creek and reared the resulting young to yearling size at Coleman National Fish Hatchery on the same stream. The Department of Fish and Game paid a small part of the food costs for rearing the fish, marked the yearlings, released them, and evaluated the returns.