The common skate, Dipturus batis, was a familiar fish of northeast Atlantic trawls and one of the first large marine fishes recognised as commercially extinct across much of its range. Work published in 2010 compared morphology and genetics across the range and found two consistently separable species living side by side: a smaller blue skate and a much larger flapper skate.
The consequence was awkward. Every catch record, stock assessment and conservation listing before the split had pooled two animals with different sizes, depths and life histories, so no historical series can be cleanly assigned to either.
Both are slow, late-maturing and lay large egg cases that sit exposed on the seabed for well over a year. Scottish sea lochs, including a protected area in Loch Sunart and the Sound of Jura, hold known egg-laying grounds, and marked individuals there are now followed by divers and researchers.