Homing ability and migration success in Pacific salmon: mechanistic insights from biotelemetry, endocrinology, and neurophysiology

摘要

ABSTRACT: Salmon have precise abilities to migrate long distances from the ocean to their natal streams for reproduction. Using chum salmon Oncorhynchus keta in the North Pacific Ocean as well as sockeye salmon O. nerka and masu salmon O. masou in Lake Toya and Lake Shikotsu (Hokkaido, Japan), mechanisms of homing ability and migration success were investigated using 3 different approaches: biotelemetry studies of behavior, endocrinology studies on the brain-pituitary-gonadal (BPG) axis, and neurophysiological studies on olfactory function. Physiological biotelemetry techniques were used to compare homing behavior of adult chum salmon from the Bering Sea to Hokkaido with lacustrine sockeye and masu salmon within Lake Toya, demonstrating that salmon can navigate in open water using different sensory systems. Hormone profiles in the BPG axis were analyzed in both chum salmon and sockeye salmon during their homing migration, and showed that salmon gonadotropin-releasing hormone is an important factor facilitating homing during migration. The olfactory functions of salmon were investigated using electrophysiological, behavioral, and biochemical techniques, suggesting that dissolved free amino acid compositions in natal streams are crucial for olfactory imprinting and homing. These topics are discussed in terms of mechanisms of homing ability in Pacific salmon with special reference to navigation abilities in open water, hormonal controlling mechanisms during homing migration, and olfactory discriminating abilities of natal stream odors—all necessary to successfully reach spawning grounds.