Pacific Salmons are capable of determining the location of their home river due to certain chemical signals; however how they navigate themselves back to the spawning location still remains unclear. Putnam et al. proposes that salmon are able to navigate to their home river because Pacific salmon can imprint on the magnetic fields. Putnam et al. analyzed a 56 year old fisheries data set from the International Pacific Salmon Fisheries Commission to recognize the routes the salmon use to return to their spawning location. The two routes used are the northern entrance, Queen Charlotte Strait, and the southern entrance, Strait of Juan de Fuca. With this information, the researchers compared it to the intensity of the magnetic field and temperatures.
Pacific Salmon's routes were predicted by the geomagnetic fields, where they take the route depending on the intensity of the magnetic fields the salmon recognize before leaving the spawn location. For instance, if the Queen Charlotte Strait consists of similar magnetic intensity as the Fraser River Mouth, then more salmons will take this path, thus further increasing the diversion rate since more salmon will take this route than the other. However, geomagnetic fields alter by a little each year and that is the reason why salmons take different routes. Also, the researchers also find that it is not only one of the factors. Another factor is temperature as more fish enter the northern entrance during the year where the northern seas were warmer, therefore being constrained to northern latitudes.