Growth rate characteristics of juvenile chum salmon Oncorhynchus keta originating from the Pacific coast of Japan and reaching Konbumori, eastern Hokkaido

Juvenile chum salmon Oncorhynchus keta originating from rivers along the Pacific coast of Japan migrate northwards to the Sea of Okhotsk, typically passing off Konbumori, near the easternmost part of Hokkaido Island. We used daily-increment analysis of otoliths to back-calculate the growth rates [mean daily growth rate in fork length (FL)] of 369 juveniles (56–146 mm FL) originating from various rivers southwest of Konbumori, and sampled at Konbumori between 2005 and 2014. We examined differences in growth rate in terms of differences in distance from the source of juveniles, their river or region of origin, to Konbumori, and FL at time of collection. The results show that juvenile chum salmon originating from distant sources tended to grow faster than those from more proximal sources, likely contributing to larger FLs in the former. Growth rates of larger fish (≥ 90 mm FL) differed little (medians: 0.64–0.68 mm/day) among regions of origin, whereas those of smaller fish tended to be low among fish originating from more proximal regions (20–126 km from Konbumori). These results suggest that fish migrating from more distant rivers were better able to survive and to reach Konbumori by achieving or exceeding a certain growth rate.