what is a reason for the sea dogs' raids on spanish shopping?

Answer 1

Very simply to steal the treasure (gold, silver, emeralds, etc.) which the Spanish were stealing from the natives of Mexico and Peru. Some English ships were sponsored by Queen Elizabeth who received a cut of the take. That is one of the reasons the Spanish attempted to invade England in 1588 - the time of the Spanish Armada - thought the Spanish were also interested in returning England to the Catholic Church.