Preliminary insight into the reproductive traits of the flapper skate (Dipturus intermedius) using in-field ultrasonography and circulating hormone concentrations

Due to global population declines, there is a pressing need for data on the life history
traits of many elasmobranch species to support the development of species-specific management
plans. A lack of information on the reproductive cycle of the Critically Endangered flapper skate
Dipturus intermedius was recently identified as a hindrance to its conservation. To address this
data gap, we combined non-lethal ultrasound and hormone analysis to investigate the size at
maturity and reproductive cycle of the flapper skate in the Loch Sunart to the Sound of Jura
Marine Protected Area off the west coast of Scotland. In-field ultrasound imagery revealed encapsulated eggs in utero and was used to determine the presence and size of ovarian follicles. Combining these images with levels of plasma testosterone, progesterone and oestradiol provided
valuable insights into the timing of the reproductive cycle and maturity state of the flapper skate.
This preliminary study suggests that male skate start to mature at 165 cm and females at 203 cm
total length. Oestradiol appears to be the primary hormone controlling the female reproductive
cycle and, along with ultrasound images, indicates that females lay pairs of eggs throughout a
winter egg-laying season. Our study further highlights how non-lethal methods can be used to
investigate the life history of oviparous elasmobranchs in the field. This information will support
the identification of important life history groups and their associated habitats and contribute to
the development of management strategies for these species.