It seems "pilchard" is the common name given to the 6 species of sardine - more scientifically known as the 5 x "Sardinops" species in the Indian & Pacific oceans, and 1 x "Sardinia pilchardus" species in the Atlantic & Med.
Just to be absolutely correct however, 1998 research suggests that there are actually only 2 distinct species since all the Sardinops are probably the same. Sortof like the same basic sardines but speaking in a regional accent if you like.