The arrests were made yesterday and the fishermen were brought to provincial capital Karachi.
Pakistan Maritime Security Agency (PSMA) spokesman Lt Commander Wajid Nawaz said that all the fishermen were arrested when they were in Pakistani waters.
"We arrested 70 fishermen yesterday," Nawaz told PTI.
He said the fishermen will be handed over to police in Karachi to register cases against them.
Nawaz said that 10 boats were also confiscated.
Earlier reports had said that Pakistan arrested 100 fishermen.