Distinguishing local growth from immigration-based size shifts for juvenile chum salmon communities in coastal Hokkaido, northern Japan.

The body size of juvenile fish is often used as an index of growth rate, which in turn is influenced by local habitat conditions. We evaluated the size and origin of juvenile Chum salmon Oncorhynchus keta in the coastal areas of three regions (Atsuta, Shari, and Konbumori) of Hokkaido, northern Japan. The origin of the individuals in these communities differed between Konbumori and the other two regions. The former contained juveniles that originated from both the nearest stocked river and other rivers that were outside the area of interest. Conversely, the communities in Atsuta and Shari consisted exclusively of fish from the nearest stocked river. Moreover, the juveniles in Konbumori were larger than those in Atsuta and Shari. The results of our otolith analysis suggest that the larger size of the fish in Konbumori was due to the immigration of large individuals from natal rivers at distant locations. Thus, immigrants were likely to enlarge their body size composition in the area of interest. In summary, if the distance from a natal river is adjusted and daily growth is taken into account, body size can be used as an indicator of growth performance in coastal juvenile chum salmon. [ABSTRACT FROM AUTHOR]