Non‐lethal assessment of reproductive stage for female blue sharks Prionace glauca using sex steroid hormones

Plasma concentrations of progesterone (P4) and 17β‐oestradiol (E2) in juvenile, pre‐ovulatory, early, mid‐ or late pregnancy stages of female blue sharks Prionace glauca were analysed. Concentrations of P4 were significantly higher in pregnant than in non‐pregnant individuals, whereas E2 concentrations increased with embryonic and follicular development. A highly accurate (86.1%) random forest classification model was developed to predict shark pregnancy. It is proposed that hormone concentrations could be used for the subsequent non‐lethal determination of female P. glauca reproductive state.