Japanese chum salmon reproductive traits

Geographic clines in life-history traits are often recognized as adaptations to the associated transitional environments. As life-history traits evolve in response to anthropogenic processes, these geographic clines can change over time. The geographic and temporal trends of reproductive traits in Japanese chum salmon Oncorhynchus keta were analyzed. Data were collected from 23 rivers located between 36° and 45° north latitude and 136° and 146° east longitude from 1994 to 2010. We confirmed the geographic clines of reproductive traits: relative gonad weight increased in more northeasterly locations, and females had fewer, but larger, eggs in more northeasterly locations after standardization by body size. The geographic clines changed over the years. The northeastward geographic trend of increasing gonad weight became more pronounced over time. Temporal trends toward smaller but more numerous eggs were evident, especially in northeasterly locations. Under natural and sexual ...