Albino rays, yes - but three species?

Albinism shows up in all the vertebrates from time to time.  What's interesting about these rays - three captured in the North Sea or adjoining English Channel over a three-year period - is that all were from different species.  The first ever record of albinism in skates, and it turned up in three species in two years.  A coincidence, presumably, but certainly an odd one.
Thanks to Chad Arment for the original post of this item.