They are thought to be responsible for a February shipwreck in which four migrants drowned and are accused of trafficking migrants in rickety boats, each carrying between seven and 10 people, between North Africa and Spain.
Their victims, mostly underage Moroccans, were approached in Ceuta, police said in a statement.
They then travelled the few kilometres to the Iberian peninsula, paying an average of 2,500 euros ($3,000) apiece.
In the bust, some 150 police officers backed by Europol agents seized three boats, five firearms, ammunition, and cash.
Death by drowning is frequent in the western Mediterranean where 330 died last year, according to the International Organization for Migration (OIM).
In the first three months of this year, 4,377 migrants arrived in Spain by sea, of whom more than half reached the Canary Islands, where arrivals have increased steadily since late 2019