First dedicated application of the Daily Egg Production Method (DEPM) to jack mackerel (Trachurus declivis).

Large numbers of eggs and adults collected from key spawning area off eastern Australia during what has been identified as the main spawning period.

Adult sampling method appears to provide unbiased estimates of spawning fraction and may be applicable to other species.

Spawning biomass of jack mackerel off eastern Australia during January 2014 estimated to be approximately 157,805 t (95% CI = 59,570–358,731).

Sensitivity analyses indicate this estimate is robust to likely uncertainty in estimates of key parameters.