Abstract
Abstract Migrations affect the population dynamics, life history, evolution, and connections of animals to natural ecosystems and humans. Many species and populations display partial migration (some individuals migrate and some do not), and differential migration (migration distance varies). Partial migration is widely distributed in fishes but the term differential migration is much less commonly applied, despite the occurrence of this phenomenon. This paper briefly reviews the extent of differential migration in Pacific salmon and trout (genus Oncorhynchus), a very extensively studied group. Three hypotheses are presented to explain the patterns among species: 1) phylogenetic relationships, 2) the prevalence of partial migration (i.e., variation in anadromy), and 3) life history patterns (iteroparous or semelparous, and duration spent feeding at sea prior to maturation). Each hypothesis has some support but none is consistent with all patterns. The prevalence of differential migration, ranging from essentially non-existent to common within a species, reflects phylogeny and life history, interacting with the geographic features of the region where juvenile salmon enter the ocean. Notwithstanding the uncertain evolution of this behavior, it has very clear implications for salmon conservation, as it strongly affects exposure to predators, patterns of fishery exploitation and also uptake of toxic contaminants.
Highlights
Migrations affect the population dynamics, life history, evolution, and connections of animals to natural ecosystems and humans
The first purpose of this paper is to briefly review the prevalence and patterns of differential migration in anadromous Pacific salmon species
The consequences of differential migration can include exposure to higher rates of fishing pressure in coastal waters than offshore for Chinook salmon [76], higher concentrations of chemical contaminants for those feeding in Puget Sound compared to the ocean coast [84], and different growth rates
Summary
Abstract: Migrations affect the population dynamics, life history, evolution, and connections of animals to natural ecosystems and humans. Differential timing of migration is most dramatic among distinct breeding populations but within-population variation occurs, with males and older salmon typically migrating earlier than females and younger salmon These patterns and hypotheses were recently reviewed [47], and will not be detailed here. Depending on the species and point of entry, individuals from one population may migrate north along the coast, both north and south, or mainly south In many cases they feed out in the open North Pacific Ocean, more or less continuously moving, until they approach sexual maturity. The broad distributions of salmon during their feeding migrations at sea complicate determination of whether there are differential patterns or not; variation in distance travelled is so common as to be unimportant, especially in species that vary in the number of years spent feeding at sea prior to homeward migration. Having reviewed the patterns and evaluated the support for these hypothesized factors as influencing differential migration, I discuss the evidence for the influences of genetic, internal (sex, size, physiological condition), and external (environmental) factors in differential migration, and end with an explanation for why these patterns are so important in these fishes, as with so many other migratory animals
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
