WELLINGTON, New Zealand—New Zealand plans to create an ocean sanctuary almost the size of Texas, becoming the latest island nation in the Pacific to put ecological protection and tourism ahead of fishing and mining industries.

At a time when global stocks of many fish species are declining, protected marine areas have been created across thousands of miles of the Pacific Ocean. A big concern of governments is that foreign trawler fleets have been moving in on the region after fish stocks, particularly popular species like...