Spawning fraction (SF) by sample day, and spawning interval (SI; days), calculated as the inverse of SF, for Connecticut River American shad in 2015.

SF was initially calculated as the proportion of fish spawning per day from different histological markers, each adjusted to spawning: the next day (day -1; most advanced oocyte stage [MAOS] = NM1), that day (Day 0; MAOS = NM2, NM3, H, or POF0 [fresh postovulatory follicle]), yesterday (Day +1; POF1 [12–24 hour old POF]), or the previous day (Day +2; POF2 [24–24 hour old POF]). Final estimate of SF was a mean of these separate values. See text and Table 1 for additional explanation of histology codes. Sampling sites are Hadley Falls (H), Cabot (C), and Vernon (V). N = number of females sampled for histology by date.