1. A rational conservation program for such migratory fishes as the salmon must be based on a knowledge of (a) whether or not the species consists of local, self-perpetuating populations and (b) the nature and extent of the oceanic migrations. 2. The conservation of a species that is broken up into local self-perpetuating populations involves the determination of the causes of mortality at all stages in the life history of each group. 3. Species that are not so broken up may be conserved by measures of more general application. 4. In the case of migrating species the routes traversed by the individuals of each population group must be known in order that the causes of mortality may be determined and that appropriate conservation measures may be applied. 5. In the case of the Pacific salmon, the evidence shows clearly the existence of local, self-perpetuating populations. 6. The evidence also shows clearly that the Pacific salmon return from their life in the sea predominantly to their home streams thus justifying acceptance of what is known as the "home stream theory." 7. It has also been shown that many of the Pacific salmon travel hundreds of miles in the ocean, by the nearest route, from places where they have been captured and tagged, before they enter streams for the purpose of spawning. 8. In the absence of any conflicting evidence it is believed that the "home stream theory" applies to these fish that travel long distances in the ocean as well as to those that may not travel so far and that the basing of practical conservation measures upon an acceptance of the "home stream theory" as of general application is justified.