Pacific salmon migrations and homing: mechanisms and adaptive significance.

Pacific salmon are noted for their lengthy foraging migrations and for their precise homing ability. Extensive sampling has documented the general migratory patterns of the major populations, but many basic aspects of their marine ecology are still poorly understood. Their life history pattern has been interpreted as an adaptation to exploit the higher productivity of the marine environment over that in fresh water. The adaptive significance of homing is implied by the specializations of populations for their natal habitat and the competitive superiority of locally adapted populations over transplants from other rivers. However, the establishment of new populations by strays and the levels of gene flow between natural populations have only recently received much attention. Research on salmon migrations has also focused on the mechanisms that guide homing at sea and in fresh water. While salmon have highly developed sensory systems, the ways in which inputs are integrated to guide migration through diverse and complex habitats are still being investigated.