Imprinting Salmon and Steelhead Trout for Homing, 1978 Annual Report of Research.

During 1978, the National Marine Fisheries Service (NMFS), under contract with the Bonneville Power Administration (BPA), initiated research on imprinting salmon and steelhead trout for homing. The primary objectives of the homing research are as follows: (1) determine whether a single imprint or a series of stimuli (sequential imprinting) are necessary to assure homing for various stocks of salmonids; (2) determine a triggering mechanism to activate the homing imprint in salmonids; (3) determine the relationship between the physiological condition of fish (gill ATPase activity, etc.) and their ability to imprint. The ability to activate the imprint mechanism at the proper time should assure a suitable homing cue that, coupled with transportation, will result in high smolt survival and insure adequate return to the homing site or hatchery. For the purposes of this study, imprinting is accepted to mean a rapid and irreversible learning experience that provides fish with the ability to return to natal streams or a selected site. In our tests, we used single imprints and sequential imprints. Single imprinting means cueing fish to a unique, single water supply prior to release. Various mechanical stimuli may be used in combination with the unique water source to achieve a single imprint. Sequential imprinting means cueing fish to two or more water sources in a step-by-step process which will established a signpost for learning the route ''home''