The swallows of San Juan Capistrano return to their California mission home every March 19th, one of the natural world’s cyclic wonders.  Nature, however, may have had something rather less dependable in mind with the annual spring running of shadfish.  Last year we posted about shad roe on March 31st.  This year, we’re only a couple of weeks shy of June.  Shad roe is an ephemeral treat, briefly available on short notice, then vanishing, so when the season arrives you have to stay on you toes, prepared to swing into action at a moment’s notice.  I found three seafood stores had the roe… yesterday.  A single purveyor* had it the day I wanted it, one day before blogging.  So if you’re inclined to make this weeks’s  Tagliatelle with Shad Roe, Pancetta and Peas, finish reading this and immediately pick up the phone.  If your favorite fish vendor doesn’t have the roe today, he may be able to get it for you tomorrow.  Next week you might still get lucky, or not.  That’s the way shad rolls.