Adapting Hokkaido Hatchery Strategies to Regional Ocean Conditions Can Improve Chum Salmon Survival and Reduce Variability

Abstract

Returns of chum salmon in Hokkaido, Japan, have increased remarkably since the 1970s, but there have been signifi cant regional variations in survival. We surveyed chum salmon dynamics in several regions to test the hypothesis that variations in survival were related to the nearshore ocean environment, especially sea surface temperatures (SSTs). Time series analyses of return rate data for chum salmon from 14 regions around Hokkaido revealed 4 geographical groups (Japan Sea, Okhotsk Sea, Nemuro Strait, and Pacifi c Ocean) that had distinct survival patterns. In the Okhotsk Sea, Nemuro Strait, and Eastern Pacifi c Ocean, survival patterns were associated with SST patterns in the nearshore environment at the times and places occupied by young chum salmon. In the Okhotsk Sea, SSTs below 8°C appeared to restrict the off shore movement of juvenile chum salmon, while SSTs over 13°C accelerated their off shore movement, apparently resulting in salmon moving prematurely. We recommend that SSTs of 7–11°C are most appropriate for the release of chum salmon. As SSTs are expected to warm but also become increasingly variable as a result of climate change, we encourage an adaptive approach whereby the nearshore environment is monitored in order to align juvenile chum salmon releases with optimal conditions.