Differential migration in Pacific salmon and trout: Patterns and hypotheses

Abstract Migrations affect the population dynamics, life history, evolution, and connections of animals to natural ecosystems humans. Many species populations display partial migration (some individuals migrate some do not), differential (migration distance varies). Partial is widely distributed in fishes but term much less commonly applied, despite occurrence this phenomenon. This paper briefly reviews extent Pacific salmon trout (genus Oncorhynchus ), a very extensively studied group. Three hypotheses are presented explain patterns among species: 1) phylogenetic relationships, 2) prevalence (i.e., variation anadromy), 3) history (iteroparous or semelparous, duration spent feeding at sea prior maturation). Each hypothesis has support none consistent with all patterns. The migration, ranging from essentially non-existent common within species, reflects phylogeny interacting geographic features region where juvenile enter ocean. Notwithstanding uncertain evolution behavior, it clear implications for conservation, as strongly affects exposure predators, fishery exploitation also uptake toxic contaminants.