The main purpose of this legislative text is to amend an existing law called the Magnuson-Stevens Fishery Conservation and Management Act. The objective is to clarify how fishing is regulated in marine national monuments, which are protected areas in the ocean. The key provisions of this amendment include two main points. First, it states that fishing in marine national monuments cannot be prohibited or regulated by a presidential proclamation under a specific law known as the Antiquities Act of 1906.