Imprinting of Hatchery-Reared Salmon to Targeted Spawning Locations: A New Embryonic Imprinting Paradigm for Hatchery Programs

Abstract

Straying by hatchery-reared salmon is a major concern for conservation and recovery of many salmon populations. Fisheries managers have attempted to minimize negative ecological and genetic interactions between hatchery and wild fish by using parr-smolt acclimation facilities to ensure successful olfactory imprinting and homing fidelity. However, the effectiveness of offsite acclimation for returning adults to targeted locations has been mixed. Since laboratory and field studies indicate that the period of hatching and emergence from the natal gravel is a sensitive period for olfactory imprinting, we propose an alternative imprinting approach wherein salmon are exposed as embryos to targeted waters transferred to their rearing hatchery. To test the feasibility of this approach, we conducted a series of electrophysiological and behavioral experiments to determine whether water can be successfully transferred, stored, and treated for pathogens without jeopardizing its chemical integrity. Stream water could be frozen or stored for one week at 4° or 10° C without affecting the olfactory signature. Ultraviolet light treatment altered the responses of the olfactory epithelium to stream water; however, behavioral studies suggested that this treatment did not alter the attractiveness of this water. Finally, we describe several alternative approaches to embryonic imprinting using artificial odors.

La fuga de salmones cultivados es un asunto considerable para la conservación y recuperación de muchas poblaciones naturales de salmón. Los manejadores de pesquerías han intentado minimizar las interacciones negativas de orden ecológico y genético entre los peces cultivados y los silvestres mediante el uso de instalaciones en las que se asegure una impronta olfatoria y una filopatría exitosas. Sin embargo, la efectividad de la aclimatación remota para que los adultos regresen a los sitios de desove, no ha sido contundente. En virtud de que los estudios de laboratorio y de campo indican que el periodo de cultivo y emergencia en el sitio de nacimiento es un lapso sensible para que se establezca la impronta olfatoria, en este trabajo se propone un enfoque alternativo de impronta en el que el salmón, siendo embrión, es expuesto a sitios seleccionados a los que se les traslada desde las áreas de cultivo. Con el fin de probar la efectividad de este enfoque, se realizaron una serie de experimentos electrofisiológicos y etológicos para determinar si el agua puede ser exitosamente transferida, almacenada y tratada contra patógenos sin comprometer su integridad química. El agua de río puede ser congelada y almacenada por una semana a 4° C o 10° C sin afectar su firma olfatoria. El tratamiento con rayos UV alteró las respuestas del epitelio olfatorio al agua de río; sin embargo, los estudios etológicos sugieren que este tratamiento no altera la atracción hacia este tipo de agua. Finalmente, se describen diversos enfoques alternativos a la impronta embrionaria utilizando olores artificiales.

ACKNOWLEDGMENTS

We thank Christian Torgersen for helping to facilitate this study. We are grateful to Joseph O'Neil and Coulter Dittman for assistance with behavioral trials and Abby Tillotson for providing experimental fish for EOG studies. We are also grateful to Thomas Quinn, Steve Schroder, and Christian Torgersen for their thoughtful and helpful reviews of earlier versions of this article. The ideas for this article were inspired by many fruitful discussions and collaborations with Tom Quinn.

FUNDING

We thank Grant County Public Utility District, the Oregon Hatchery Research Center, and NOAA Fisheries for funding support.