FIGURE 2 Seasonal migration timing of Sakhalin taimen during four
migration stages (MS) in 2018 and 2019. Circles indicate the observed
migration timings of females (red) and males (blue) with lines
connecting the same individuals across the years. Spearman’s rank
correlation and its significance (*P < 0.05, **P< 0.01, ***P < 0.001) are shown for
females (ρF) and
males (ρM).
Between-year correlations of the seasonal migration timings were
significantly high for female Sakhalin taimen at all MSs (P< 0.05) but were significant only at MS4 (P <
0.05) for males. For the females, within-season correlation between MS1
and MS4 timings was also significant (ρ = 0.628, P <
0.001), but it was extremely low and not significant for the males (ρ =
0.002, P > 0.05). The reason that there are fewer
lines for MS4 in Fig. 2 is because we terminated PIT detection before
all post-spawners had migrated downstream past Site L in 2018. Only in
the females during MS3 was there a significant between-year correlation
on the diel-scale as well (i.e. female individuals departed from
tributaries at similar times of day in both years) (ρ = 0.497, P= 0.001).
Neither ascent (MS1) nor descent (MS4) by Sakhalin taimen through Site L
was uniformly distributed throughout the day (Fig. 3, Rayleigh test,P < 0.001 for females, and P < 0.01
for males). Both female and male spawners ascended the river mostly
during daytime, peaking before sunset. Descent by post-spawners peaked
early in the afternoon in males, but it peaked
during night-time in females.
Consequently, the diel migration timing of female Sakhalin taimen
differed significantly between ascent and descent (P = 0.000,
Watson–Wheeler test), and the timing of descent differed between the
sexes (P = 0.003).