Common Skates Complex (Flapper and Common Blue)

Identified as two separate species in 2010 (NatureScot, 2023), these skates are listed as priority features by the Scottish Government (Scottish Government, 2011). While the complex was once very common (specifcially the blue skate species), both species are now critically endangered worldwide (IUCN, 2024 a & b) due to historical targeted fishing, and the continued risk of bycatch (Shark Trust, 2020 a & b). Since 2009, it has been illegal to fish for either species, but their benthic nature means bycatch still causes significant damage to population numbers (OSPAR, 2021). 

The two species used to be abundant throughout Scottish waters, however overexploitation reduced their levels to that of today (Scottish Government, 2011). While in certain regions a slight increase in abundance has been observed, overall information is so limited that the real population status is unknown (OSPAR, 2021). 

Dipturus intermedius – Flapper Skate (fig. 2)
The larger of the two species, growing up to 230cm (Shark Trust, 2020a), this puts Flapper Skates at higher risk of bycatch compared to Blue Skates (OSPAR, 2021). Their reproductive cycle is long, taking 10 years to reach sexual maturity, and eggs taking a year to develop once laid (NatureScot, 2023). Of the two species, Flapper Skates historically had a more north easterly range than the Blue Skate (fig. 1)

Dipturus batis – Blue Skate (fig. 4)
Growing up to a maximum length of 150cm, Blue Skates are the smaller of the two species (Shark Trust, 2020b). They demonstrate a slightly different range to the Flapper Skates (figs. 1 and 3), reaching north around Iceland (IUCN, 2024b). Overfishing throughout the 20th century has left them in their critically endangered state of today (IUCN, 2024b). 

Various monitoring studies of skates are ongoing, including tagging operations, the Skatespotter database, and the Shark Trust Great Egg Case Hunt (NatureScot, 2023).