FIGURE 3 Diel-scale migration timing of female (red) and male (blue)
Sakhalin taimen spawners (a) and post-spawners (b) in 2019 during ascent
at MS1 and descent at MS4, respectively. Grey shading indicates
approximate night-time (1837–0420).
3.3 Biological and behavioral effects on migration
timing
Sex was the only significant fixed effect influencing seasonal migration
timing during MS1, with male spawners arriving at Site L several days
earlier than females in both years (P = 0.000, Table 1, Fig. 2).
Males also arrived earlier than females at tributary sites (MS2,P = 0.000). Arrival timing at this stage also depended on which
tributaries spawners entered first, with those entering T2 and T4 being
the earliest and latest, respectively (P = 0.012, F -test).
Contrary to MS1 and MS2, departure from the tributaries at MS3 appeared
to be earlier for female than male post-spawners (Fig. 2); this was true
only for the daytime migrants and led to a significant interaction
between Sex and DN in the model (P = 0.041). There was a small
but significant shift from daytime to night-time departure at MS3 by
both sexes as the season progressed (P = 0.043). Individuals that
spawned in two tributaries tended to depart later from the last (second)
tributary than those spawning in one tributary (P = 0.043, Fig.
S2). Sex was again the only fixed effect to explain downstream migration
timing at MS4, with the female post-spawners preceding the males
(P = 0.009).
TABLE 1. Best linear mixed-effects models to explain the seasonal
migration timing of Sakhalin taimen during four migration stages (MS).
Sexm and DNn denote Sex = male and DN =
night, respectively. First2, First3, and
First4 are the effects of entering tributaries T2, T3,
and T4 relative to entering T1, respectively.