Severe flooding often leads to downstream displacement of aquatic animals. Despite this, many salmonid populations persist in habitats located upstream of tall barriers, such as artificial check dams and/or natural waterfalls, that completely block fishes from returning to the upstream areas after flooding. The evolution of such populations may be affected by spatial sorting due to differential rates of downstream displacement. This study examined whether a morphological trait (increased body depth) that allows individuals to better maintain their position during flooding has evolved in juvenile amago salmon Oncorhynchus masou ishikawae inhabiting above-barrier habitats in two rivers. In both rivers, juveniles collected at the stations with multiple downstream barriers had deeper bodies than those collected at other stations. Similar differences were found in juveniles reared in a common-garden experiment. Field experiments with natural flooding also indicated that deep bodies help juveniles resist downstream displacement. These results consistently suggest that juveniles in some above-barrier habitats have evolved deep bodies to resist downstream displacement due to flooding. Our study is the first to show the evolutionary outcomes of passive spatial sorting during severe climate events.

Data for Morphological evolution reduces downstream displacement in juvenile landlocked salmon Yamada and Wada, Evolution 2021.

These files contain all data for the field survey, field experiment, and common environment experiment. 
Data for the field survey and common garden experiment are divided into two data files (i.e., Koza River data and Hirai River data).

Explanation for the variables:

 Release day (File for the field experiment):
  Release group for the field experiment ("8-Jun" and "20-Jun"corresponds to the first and second release group, respectively).

 Retention status (File for the field experiment):
  Juveniles were assigned a retention status of 1 if they were recaptured above the first check dam, and a retention status of 0 if they were recaptured further downstream. 

 Ascent status (File for the field experiment):
  Juveniles were assigned an ascent status of 1 if they were recaptured upstream of the uppermost step, and an ascent status of 0 if they were recaptured further downstream.

 Cage ID (Files for the common garden experiment):
  ID of the cage in which the juveniles were raised.

 Habitat group (Files for the field survey and common garden experiment):
  Attributes of each study station regarding barriers.                                           

 Station (Files for the field survey and common garden experiment):
  Name of each study station.

 PC1 (Files for the field survey, field experiment, and common garden experiment):
  PC1 obtained by principal component analysis of the log transformed body depth measurements for all data (i.e., the field survey, field experiment, and common garden experiment).
 
 PC1 residual (Files for the field survey, field experiment, and common garden experiment):
  Residuals calculated from the predicted values of linear regression models and the −PC1 values.
  
 Caudal peduncle depth-1 (Files for the field survey, field experiment, and common garden experiment):
  Measurement values of the caudal peduncle depth at the posterior end of the adipose fin.

 Caudal peduncle depth-2 (Files for the field survey, field experiment, and common garden experiment):
  Measurement values of the caudal peduncle depth from the posterior end of the anal fin to the anterior end of the adipose fin.

 Body depth-1 (Files for the field survey, field experiment, and common garden experiment):
  Measurement values of the body depth from the lateral line to the anterior end of the dorsal fin.

 Body depth-2 (Files for the field survey, field experiment, and common garden experiment):
  Measurement values of the body depth at the anterior end of the anal fin.
 
 Fork length (Files for the field survey, field experiment, and common garden experiment):
  Measurement values of the fork length.