We propose protective regulations under section 4(d) of the Endangered Species Act (ESA) for the conservation of the giant manta ray (Mobula birostris). The prohibitions listed under section 9(a)(1) of the ESA automatically apply when a species is listed as endangered. In the case of a species listed as threatened, the first sentence of section 4(d) provides that the Secretary of Commerce (Secretary) shall issue such regulations as deemed necessary and advisable to provide for the conservation of the species. The second sentence of section 4(d) states that the Secretary may by regulation prohibit with respect to any threatened species any or all acts prohibited under section 9(a)(1). The final rule to list the giant manta ray as a threatened species under the ESA was published on January 22, 2018, and became effective February 21, 2018 (83 FR 2916). Protective regulations for the species were not adopted at that time. Since the publication of the final rule, new information has revealed that giant manta ray bycatch occurs in many U.S. fisheries, including likely high levels of at-vessel and post-release mortality. While the most significant threat to the giant manta ray is overutilization primarily by artisanal fisheries operating in areas outside of U.S. jurisdiction, we are proposing to apply the section 9 prohibitions to the species to reduce and mitigate fisheries-related mortality resulting from bycatch in U.S. fisheries. We are proposing limited exceptions to the prohibitions for scientific research and emergency response and salvage activities.