FIGURE 5 The critical time windows of water temperature and water level for female Sakhalin taimen (horizontal bars), and their average travel time (i.e. departure timing) from the river mouth to the spawning ground (vertical dashed line) with the 95% confidence interval (grey shading).

3.5 Social interactions during ascent and descent by migrants

There were 19 comigrating pairs of female Sakhalin taimen ascending through Site L during MS1, of which only two pairs entered the same tributaries for spawning. This was less than half the number (4.9) expected by chance, but the difference was not significant (P = 0.157, Table 2). Similarly, only three female pairs departed from the same tributaries, out of 22 comigrating pairs descending through Site L during MS4, which was half the expected number but also not significant (P = 0.204). The numbers of male pairs of comigrating spawners and post-spawners entering or departing from the same tributaries, respectively, were not less than or greater than those expected by chance (P > 0.05).
TABLE 2. Randomization test results of the social interaction hypothesis, showing the observed numbers of comigrating pairs, and of observed and simulated (mean ± SD) pairs that entered or departed from the same tributaries.